IMR Press / FBL / Volume 25 / Issue 5 / DOI: 10.2741/4840
Open Access Review
Alpha-fetoprotein is an autoantigen in hepatocellular carcinoma and juvenile Batten disease
Show Less
1 Department of Clinical Sciences and Translational Medicine, University of Rome “Tor Vergata”, Rome 00133, Italy
2 Division of Translational Medicine, Molecular Diagnostics, Wadsworth Center, New York State Department of Health, P.O. Box 509, Empire State Plaza, Albany, New York 12201-0509
Front. Biosci. (Landmark Ed) 2020, 25(5), 912–929; https://doi.org/10.2741/4840
Published: 1 January 2020
Abstract

Failure of immune tolerance leads to production of autoantibodies to self-antigens. The repertoire of autoantibodies detected in cancer patients can indicate the presence of autoimmune disease. Alpha-fetoprotein (AFP) autoantibodies have been found in patients with hepatocellular carcinoma (HCC) and in juvenile Batten disease (BD), a neurodegenerative condition involving autoimmunity. Variant conformational forms of AFP together with exposed occult antigenic determinant sites on the AFP polypeptide resemble the features of a disordered protein which can impair central immune tolerance. These aberrant structural protein forms can lead to the persistence of autoantibody production by immune sensitized B-lymphocytes. Thus, it is not surprising that AFP, a self-antigen, can induce autoimmune responses in humans. Herein, we discuss the molecular and antigenic properties of AFP which make it a disordered protein, and its ability to induce autoantibody production to AFP cryptic epitopes in both HHC and BD patients. Such insights might aid in the future design of AFP-based vaccines and to discovery of novel pathogenic mechanisms of autoimmune diseases which demonstrate the presence of denatured intermediate forms of AFP.

Keywords
Alpha-fetoprotein
Autoimmunity
Antigens
Epitopes
Disordered Protein
Autoimmune Disorders
Batten Disease
Review
2. INTRODUCTION

Antigens are foreign substances targeted and bound either by antibodies in the circulation (humoral type) or by T-cell lymphocyte cell surface receptors (cell-mediated type) (1). In comparison, an autoantigen is a self antigen within a host organism that evokes an immune response (either humoral, cell-mediated, or both) against itself (2). Thus, an autoantigen, despite being an apparent internal “normal” component of the organism, could become a target of the humoral and/or cell-mediated immune response. In like fashion, an autoimmune disease (autoimmunity) is a disorder of an organism that has manifested an immune response against its own molecular components of cells and/or tissues (3).

3. AUTOANTIGENS AND AUTOIMMUNITY

The production of autoantibodies to self antigens is dependent on the failure of immune tolerance (4-8). Autoantibodies to self antigens are found both in sera from patients with systemic autoimmune diseases and with cancer (7-8). The repertoire of autoantibodies detected in cancer patients to some extent encompasses that of patients with autoimmune diseases (7-8). Among these autoantoantibodies, AFP autoantibodies have been found in patients with hepatocellular carcinomas and juvenile Batten Disease (BD) a neurodegenerative condition in which autoimmunity is established as an involved component (9-10). Human autoimmune diseases comprise a large number of illnesses that include: Addison’s disease, Hashimoto’s thyroiditis, systemic lupus erythematosus, and many others. However, protein misfolding diseases are non-immune in origin (Table-1). In comparison, Tregs dysfunction has been observed in patients with paraneoplastic syndromes and/or with autoimmune diseases (11-13).

Antigens are molecular entities that are comprised of multiple subcomponents called antigenic determinants (ADs) sites or epitopes (14). An AD can constitute at least one or more specific part of an antigen that is recognized by the immune system as a foreign substance by antibodies, B-cells, and/or T-cell lymphocytes. Antibodies secreted by B-cell lymphocytes can bind to a specific epitope on the overall antigen, such as a protein. A “linear” antigenic epitope on a protein consists of a continuous amino acid (AA) sequence stretch on a polypeptide chain (15). Whereas, a “conformational” induced epitope consists of discontinuous segments of AA sequence stretches on a polypeptide chain. An antigenic determinant on a protein can interact with antigen-presenting cells bound to a Major Histocompatibility Complex (MHC); these can contain 8-11 AAs (MHC class I) or 13-17 AAs (MHC class II). A major antigenic site on a protein can consist of a molecular weight up to 10,000 Daltons each; thus, a full length protein of 60,000 Daltons, such as Albumin, would consist of a total of 6 major antigens (16).

4. DISORDERED SELF-PROTEINS AND AUTOIMMUNITY

Self-antigens’ structural and immunological properties are driving forces for the selection of the autoantibody repertoire (17-18). Long stretches or clusters of charged residues, and multivalent charges on autoantigens occur in several self-antigens targeted by humoral immune responses. According to the Carl and et al model, the structurally disordered proteins are poorly immunogenic because: (a) they might be hidden to the immune recognition due to their binding to other proteins; (b) their flexibility in conformational form might make it difficult for development of conformation-specific-antibodies; (c) their proteolytic instability might interfere with a strong binding to MHC II and thus hamper the induction of a T cell response amidst immune tolerance. Thus, autoreactive immune cells that bind with low affinity to disordered proteins and to their MHC-complexed peptides loaded on antigen presenting cells, respectively, are not removed during central tolerance development mechanisms and can remain as immunological constituents of the immune repertoire of healthy individuals (18).

In contrast to exposed epitopes, cryptic epitopes are concealed in molecular clefts or crevices of a tertiary-folded protein (19). Cryptic epitopes can be revealed by laboratory procedures, or in nature, by a denaturing and subsequent unfolding of the protein. Cryptic epitopes are capable of triggering inappropriate immune cell signaling events which can lead to inappropriate production of autoantibodies against self-antigens, most commonly proteins. Examples of human autoimmune diseases caused by antibodies against self-antigens include: 1) antibodies against 17-alpha-hydroxylase in Addison’s disease; 2) antibodies directed against thyroglobulin in thyroiditis (Hashomoto’s disease); 3) anti-wheat proteins (gliadin, gluten) in Celiac disease and many others (see list in Table-1, A, B) (14). In addition, there exists many non-immune associated unfolding, improper assembly, and misfolding of proteins in human diseases such as Cystic fibrosis, and Marfan’s Disease (see list displayed in Table 1, C).

Table 1 Selected human autoimmune diseases and their autoantigenic inducing substances and comparison with various nonimmune misfolded protein disorders
Autoimmune Disease Autoantigenic Substance and/or Tissues/Cells
Celiac Disease Tissue Transglutaminase, Gliadin, Gluten
Diabetes mellitus type-1 Pancreatic B-cell surface proteins
Sarcoidosis Granulomatous tissues/cells
Eosinophilic granulomatosis (polyangiitis) Small and medium-sized blood vessels; vasculitis, eosinophil influx
Hashimoto’s Thyroiditis Thyroglobulin protein
Grave’s Disease Toxic diffuse Goiter; thyroid stimulating immunoglobulin
Idiopathic thrombocytopenic purpura Platelet cell surface proteins
Addison’s Disease 17-alpha-hydroxylase enzyme
Systemic Lupus Erythematosus Nuclear proteins; Ribonuclear proteins
Sjogren’s syndrome Salivary gland proteins
Rheumatoid arthritis IgG-Fc Fragment
Ankylosing spondylitis Joints of the spine (pelvis area, and shoulders)
Polymyositis Skeletal muscle cells
Multiple Sclerosis Myelin sheath coating on nerve cells
Primary sclerosis cholangitis Cells of liver and gall bladder (scarring effect), bile ducts
Crohn’s Disease Inflammatory Bowel disease, Intestinal cells
Non-Immune Protein Misfolding Disorders/diseases (Misfolded Protein)1
Cystic Fibrosis (transmembrane conductance receptor TCR)
Tay-Sachs disease (Hexosaminidase)
Sickle cell disease (Hemoglobin)
Marfan Syndrome (Fibrillin Protein)
Alzheimer’s Disease (Beta-Amyloid, tau)
Lou Gehrig’s Disease (superoxide-dismutase)
Eye Cataracts (Crystallin Proteins)
Protein-C deficiency (Protein-C)
Von Willebrand Disease (Von Willebrand Factor)
Creutzfedt-Jacob Disease (Prion Proteins)
Retinitis Pigmentosa (Rhodopsin Protein)
Familial amyloidosis (transthyretin)
Alpha-antitrypsin deficiency (alpha-antitrypsin)
Familial hypercholesterolemia (LDL Receptor)
Glanzmann’s thrombasthenia (GPIIb Integrin)
Scurvy disease (Collagen proteins)
Note: Misfolded proteins do not induce an immune response, 1Misfolded protein is shown in parenthesis, LDL: low density lipoprotein
5. IS AFP A DISORDERED PROTEIN?

The human Alpha-fetoprotein is made by a single polypeptide chain with a molecular mass of 69 kD containing 3-5% carbohydrate content; it is largely alpha-helical comprising three domains of nearly 200 amino acids each (20). The triplicate domain structure of AFP is due to the intramolecular loops dictated by 32 disulfide bridges, resulting in a V- or U-shaped configuration (21, 22). Accordingly, AFP has been classified as a member of a three domain, cysteine-rich translated protein of the albuminoid gene family which currently consists of five members; albumin, vitamin D binding (Gc) protein, alpha-albumin, and the AFP-related gene (ARG) protein (23-25). Serum AFP binds and transports a variety of ligands such as bilirubin, fatty acids, retinoids, steroids, heavy metals, dyes, flavonoids, phytoestrogens, dioxin, and various drugs (26-27). Other ligands for AFP (rodent and human) are biological stains, L-tryptophan, warfarin, triazine dyes, phenylbutazone, streptomycin, phenytoin, anilinonaphthaline sulfate, heavy metals, low carbon chain alcohols, and polyunsaturated fatty acids (28). AFP has been demonstrated to induce immunosuppression in both B- and T-cells lectin stimulation, although AFP can also enhance immune cell activation under particular circumstances (29, 30). AFP has been reported to functionally impair dendritic cells thus leading to immune dysfunction and apoptosis of antigen processing cells (APCs) (30). In addition, molecular variants of AFP have been described. A cationic form of AFP has been demonstrated to complex with immunoglobulin M. Aberrant forms of AFP have been found in the reproductive and urinary tracts as well as in the sera of patients with breast cancer, reproductive organ and genital tract diseases (25-26, 31-33). Truncated forms of AFP have been detected in cell cultures comprising hepatomas, testicular embryonal carcinomas, and breast tumors (26, 31, 32). The denaturation of recombinant-derived AFP was found to be a reversible process independent of its starting source, fatty acid relationship, and glycosylated state (34-35). Accordingly, there are molecular variants of AFP that can be divided into multiple different classes: genetic variants, soluble-free or bound forms, pH Isoforms, carbohydrate heterogenic forms, enzymatic fragments, denatured intermediates. In accordance with the AFP structure and immunological properties, some forms of AFP appear to resemble the features of a disordered protein; thus, it is not surprising that AFP can induce immune response in humans.

6. SPONTANEOUS IMMUNE RESPONSE TO AFP IN HEPATOCELLULAR CANCER (HCC) PATIENTS

Autoantibodies and T cell immune responses to AFP have been reported to occur in patients with hepatocellular carcinoma or with liver diseases (36-53) (Table 2). The low immunogenicity of disordered self-antigens appears to be inconsistent with their capability to induce spontaneous immune response. However, intramolecular and intermolecular epitope spreading mechanisms may contribute to the development of immune responses targeting AFP (18, 54-56). In addition, the abnormal expression of AFP resulting from overexpression, conformational changes or post-translational modifications could have overwhelmed self-tolerance and induced autoreactive immune responses (57-59). The inflammatory status and the enhancement of lysosomal cathepsin B and L blood levels in liver diseases patients might have exposed hidden epitopes, thus inducing ex novo immune responses to conformationally modified forms of AFP (7-8). Indeed, to determine hepatocellular patients immunoglobulin reactivity with linear and/or conformational AFP epitopes, Bei et al. performed western blotting and immunoprecipitation analyses using denaturated and nondenaturated AFP (36). Io order to determine whether the anti-denatured-AFP antibodies recognized protein or carbohydrate epitopes, AFP was deglycosylated with PNGase F to remove N-linked carbohydrate moieties. The authors analyzed patients with various liver disorders that demonstrated the breakdown of immune tolerance to AFP self-antigen. The analysis included 60 hepatocellular carcinoma patients; 15 liver cirrhotic patients; 15 chronic hepatitis patients; and 40 normal non-liver disease patients. Results indicated that anti-AFP antibodies were found in 14 of 60 (23%) hepatocellular carcinoma patients; 3 of 15 (20%) cirrhotic patients (CP); 1 of 15 (6.6%) chronic hepatitis patients (CHP); and 0 of 40 (0%) normal non-liver disease patients. The patient antibodies recognized cryptic epitopes in the denatured and deglycosylated forms of AFP. In patients with pathological conditions of liver disease and cancer, immune tolerance to AFP had been broken and/or circumvented. HCC patients were found to have higher AFP serum levels than CP or CHP (36). Thus, spontaneous immune responses to self-AFP antigens were significantly associated with hepatocellular carcinomas.

Table 2 Evidence of immune responses to AFP in hepatocellular carcinoma (HCC) patients
Immune response Target and stimulators Positive Individuals1 Reference
Autoantibodies Native AFP 14/60 HCC, 3/15 LC, 1/15 CH, 0/40 HD (36)
Autoantibodies-IgM (IC)2 Native AFP 30/50 HCC (38)
Autoantibodies-IgM (IC) Native AFP 48/74 HCC (39)
Autoantibodies-IgM (IC) Native AFP 77/118 HCC, 14/60 LC, 9/63 CH (40)
Autoantibodies-IgM (IC) Native AFP 28 HCC (Kazakh population) and 85 HCC (Han population) (41)
T cells (CD8+) AFP542–550 (immunodominant peptide) HD, HLA-A2.1 (42)
T cells (CD8+) AFP137–145, AFP158–166, AFP325–334 (immunodominant peptides) HD, HLA-A*0201 (43)
T cells (CD8+) AFP137–145, AFP158–166, AFP325–334 (immunodominant peptides) AFP1, AFP492, AFP547, AFP555 (sub dominant peptides) HD, HLA-A*0201 HCC, HLA-A*0201 (44)
T cells (CD8+) AFP357, AFP403, AFP414, AFP424, AFP434 2-8/38 HCC, 0/11 HD, HLA-A*2402 (45)
T cells (CD8+) AFP137, AFP158, AFP325 (immunodominant peptides) 1/18 HCC for AFP158 and AFP325, 3/13 LC for AFP158 (46)
T cells (CD8+) Overlapping peptides spanning the complete AFP sequence 19/40 HCC, 5/14 CH, 4/10 HD (47)
T cells (CD4+) AFP364-373 11/41 HCC (48)
T cells (CD4+) Panel of 60 AFP-derived peptides (10 pools of 6 peptides) and AFP364–373 15/20 HCC (49)
T cells (CD4+) AFP46–55 15/15 HCC, 10/10 HD (higher frequency in HCC than HD) (50)
T cells (CD4+) Soluble AFP Protein-fed DC Adenovirus AFP-engineered DC 0/6 HCC, 8/26 HD 3/6 HCC, 15/26 HD (51)
T cells (CD4+) T cells (CD8+) AFP derived-peptide pools 8/18 HCC, Child–Pugh A, 2 /13 HCC, Child–Pugh B or C, 3/18 HCC, Child–Pugh A, 6 /13 HCC, Child–Pugh B or C (52)
T cells (CD8+) AFP158-166 HD, HLA-A*0201 (53)
1HCC = hepatocellular carcinoma, 2IC=immune complexes. LC = liver cirrhosis and CH = chronic hepatitis patients, HD = healthy individuals. *allelic group. When available, the number of positive subjects/total subjects is reported.

The presence of AFP bound to IgM (AFP-IgM) as an immune complex (IC) has also been analyzed. In 1976, Norgaard-Petersen provided electrophoretic evidence that circulating human AFP was complexed to an immunoglobulin thought to be IgM; this was suggestive of an autoimmune response to AFP (37). Subsequent reports in 2004 and thereafter confirmed that IgM complexed to circulating AFP was present in the sera of liver disease patients detected using ELISA methodology (38). In this latter study, the mean serum concentration of AFP-IgM IC was significantly higher in HCC patients than in cirrhotic patients and in patients with chronic hepatitis. HCC patients had AFP-IgM IC values above the cutoff in 60% of cases (30/50) (38). Jingting et al. found a significant difference between AFP-IgM serum levels of primary HCC patients and healthy subjects. They found that AFP-IgM was better than free AFP in the diagnosis of early primary HCC, although there was false positive reaction of AFP-IgM in patients suffering from cirrhosis and chronic hepatitis (39). Sheng et al. developed a novel time-resolved immunofluorometric assay. AFP-IgM and AFP were increased above the cutoffs in 65.25 and 45.76% of HCC, respectively (40). Wu et al. reported that serum AFP-IgM levels of hepatocellular carcinoma patients in the Han population and HCC patients in the Kazakh population were statistically higher than those of controls (41).

Numerous HLA I-restricted, CD8+ AFP epitopes have been identified and evaluated for their immunogenicity in HCC patients. Several AFP peptides were classified as “immunodominant” due to their robust binding to MHC I and in vitro high level IFN-γ production and cytotoxic T lymphocyte (CTL) induction from stimulated healthy individual T cells. It was reported that T-cell repertoire could recognize AFP in the context of HLA-A2.1. Dendritic cells (DCs) transduced with an adenovirus (AdV) producing AFP recognized the AFP542–550 (GVALQTMKQ) peptide (42). Three additional HLAA*0201-restricted immunodominant epitopes [i.e AFP137–145 (PLFQVPEPV), AFP158–166 (FMNKFIYEI) and AFP325–334 (GLSPNLNRFL)] and 10 hypothetically subdominant epitopes were then identified (43). It was reported that healthy individuals exhibited high-avidity T cell precursors with AFP1 (MKWVESIFL), AFP492 (PVNPGVGQC), AFP547 (TMKQEFLINL), AFP555 (NLVKQKPQI) subdominant epitopes (44). Subdominant -specific T cells recognized AFP-expressing tumor cells (44). Mizukoshi et al. reported that AFP403 (KYIQESQAL), AFP424 (EYYLQNAFL), AFP434 (AYTKKAPQL), AFP357 (EYSRRHPQL) and AFP414 (RSCGLFQKL) peptides were able to stimulate CTLs to release IFN- γ and destroy AFP-producing hepatoma cells in culture (45).

A quantitative analysis was performed on the occurrence of T cells recognizing 3 MHC class I immunodominant AFP epitopes (i.e. AFP137, AFP158 and AFP325) in the naive repertoire of peripheral blood mononuclear cells (PBMCs) from 37 cirrhotic and 54 HCC patients (46). The frequency of the naive T cells recognizing these peptides was minimal (46). Thimme R et al. identified 46 epitope regions targeted by AFP-specific CD8+ T cells in the background of diverse HLA types (47). Alisa et al. reported that the AFP364-373 (QLAVSVILRV) epitope was recognized by peptide specific CD4+ T cells from HCC patients in the context of a HLA-DR site (48). Specific CD4+ T cells to AFP137–145 (PLFQVPEPV) and AFP249–258 (KVNFTEIQKL) as well as to AFP364-373 epitope were detected in HCC patients as opposed to patients with chronic liver diseases or healthy donors (49). On the other hand a subset of CD4+ T cells recognizing the AFP46-55 epitope and releasing TGF-β with inhibitory effects on T cell proliferation in vitro were identified; their frequency was significantly higher in HCC patients than in healthy donors (50). It was then reported that the modality of antigen presentation had an important outcome on the detection of AFP T cell responses (51). Behboudi et al. detected an anti-AFP CD8+ T cell response in controls versus HCC patients, wherein an anti-AFP CD4+ T cell response was restricted only to HCC patients (52). Sun et al. reported efficient activation and expansion of AFP158-166-specific CTLs by APCs (53). Accordingly, the human T cell repertoire is efficient for identifying AFP in the context of MHC Class-I immune responses, even in an environment of low to moderate circulating AFP levels, in both HCC and cirrhotic patients (60). Immune response to AFP occurring in HCC patients might induce biological and pathogenic effects that can modulate tumor growth and survival. Anti-AFP autoantibodies administered to cancer patients could possibly interfere with the growth of AFP expressing tumor cells. Furthermore, Wang et al. reported that the enhanced proliferation of cancer cells by AFP was inhibited by the treatment with anti-AFP antibodies (61).

However, the sensitization of T cells against AFP might induce hepatic cell damage. Geissler M et al, after immunizing mice with DNA encoding mouse AFP, described a significant hepatocyte disruption in regenerating liver that correlated with the number of AFP-specific CD8(+) T cells, the activation of liver regeneration, and levels of AFP synthesis. Autoimmune liver damage was mediated by CD4(+) T cell-dependent CD8(+) cytotoxic T lymphocytes (62).

7. BATTEN DISEASE AND AFP AUTOANTIBODIES

Batten Disease (BD) is one of a cluster of names for a family of human diseases known as “neuronal ceroid lipofuscinoses” (NCL) (63). BD is a neurodegenerative disorder resulting from excessive accumulation and storage of lipopigments (lipofuscin) in body cells including nerve cells. The lipopigments are composed of fat and protein complexes. Ceroids themselves are wax-like golden yellow-brown fatty pigments abundantly found in fibrotic tissue such as liver cirrhosis. Such conditions lead to accumulations of lipopigments in cytoplasmic lysosomes, which in nervous tissue results in neuroinflammation, neurodegeneration, and subsequent nerve cell death (64).

The lipofuscin associated BD, first described in 1903, is a lethal disorder of the nervous system beginning largely in childhood, and occurring in 5 to 10 years old (child) patients (65). Its population incidence is 1 in 250,000 people. NCL is basically a lysosomal storage disease linked to a mutation in the human CLN3 gene on chromosome-16. The onset of BD, although most common in childhood, can occur at four life stages, namely; infantile, late infantile, juvenile, and more rarely, in adults.

The major cytoplasmic component of the NCL disease is reported to affect the “C” subunit of the mitochondrial enzyme ATPase, present in both man and mice (66). Mutated genes in BD have further been localized in lysosomes of neurons at the junctional synapses of both cerebral and cerebellar cortex cells. Associated reports of altered arginine metabolism in BD have also been described in conjunction with the neuronal lysosome alterations (67). Many patients display defects in their GABAergic interneuron pathways. Finally, subtle changes in the urea cycle and the citrulline-nitric oxide cycle pathway often accompany the above cell biochemical alterations (68). The latter pathways are capable of influencing both mitochondrial oxidation and energy generation in various cells of BD patients.

The early signs of onset of BD in infancy involves largely vision problems, seizures, and personality changes (69). Such changes include slow learning, repetitive speech, clumsiness, stumbling, and slowed head-size growth. These characteristics are accompanied by poor blood circulation in the appendages, decreased body fat, and reduced muscle mass. BD progression can further induce curvature spine changes, holding one’s breath, teeth grinding, hyperventilation, constipation, worsening seizures, and reduction in speech and mental skills (70).

Although the precise cause of BD onset is still unknown, mutation of the CLN3 gene is intimately involved (71, 72). The mutation causes production of two truncated variants of the CN3 protein. The normal, non-mutated protein contains a total of 438 amino acids, while the mutated truncated CLN3 protein displays 181 amino acids (73, 74). The non-mutated CLN3 gene encodes for a hydrophobic transmembrane protein normally present on the cytoplasmic lysosome membrane. The CLN3 protein has further been localized in membranes of the endoplasmic reticulum and the Golgi apparatus. While vision loss is the most common diagnostic sign, the exact function of the CLN3 protein has yet to be ascertained (75).

A null mutant mouse model of BD has been developed with the pathologic characteristics mimicking the human BD phenotype (76-77). Similar to man, the null CLN3 mice have alterations in their GABAergic interneuron cell pathways and display circulating autoantibodies against AFP and glutamic acid decarboxylate (GAD65) among other proteins (78). The injection of serum from BD patients into the mouse models is capable of inhibiting the catalytic activity of GAD65 that converts glutamic acid to the neurotransmitter GABA (78, 79). However, autoantibody interference to nerve degeneration and cell death has yet to be explained as is the precise function of the CLN3 transmembrane protein in both man and rodents (80).

The most common onset of BD occurs shortly after birth in infants (81). Unfortunately, no therapeutic strategy intervention procedures are yet available (63). As mentioned above, visual failures accompanied by seizures occur first; followed by progressive declines in cognitive motor skills and performances, eventually leading to premature death of the child (69). The cause of death is largely reported as deficiencies in soluble lysosomal enzymes. However, behind the scenes, multiple mutation genes and their resultant foreign proteins are generated which can induce autoantibodies against several brain protein antigens (see below) (82). Such autoantibodies are deposited in the cerebral spinal fluids of the central nervous system, causing inflammation leading to a breach in the blood brain barrier. This allows a vast insurgence of normally-restricted compounds into the brain (83).

Using 2-dimensional gel electrophoresis, immuno-blotting, and mass spectroscopy, investigators have detected multiple brain occult antigens using BD patient serum-containing autoantibodies. These investigators have detected autoantibodies that recognized denatured epitopes of AFP (10). Of the 13 male Batten disease patients analyzed, 12 (92%) tested positive for the presence of anti-AFP antibodies, whereas 8 out of 18 (44%) of females were positive for the presence of anti-AFP antibodies. Overall, of 31 Batten disease patients tested, 19 (61%) were positive for the presence of autoantibodies against AFP (10). During human fetal development, AFP has been reported to localize in the cytoplasm of neurons; however, it has been shown that AFP is not synthesized and/or produced in nerve and glial-associated brain cells (84, 85). The data from BD patients demonstrated that immune tolerance to human AFP had been circumvented in the neuronal degenerative disorder in both human BD and its mouse models. Following mass spectroscopy analysis in samples of serum from BD patients, 61% of patient further involved at least 4 additional human non-AFP proteins including; 1) dynactin-2; 2) Hsp 70 (heat shock protein-70); 3) GRP58; and 4) peptidase-D (see Table-2). Furthermore, the serum reactivity for each AFP-antibody positive patient was completely inhibited by inclusion of denatured AFP in the mixed test solution. Thus, adding purified denatured AFP to the reactant samples was effective in neutralizing the serum reaction mixture against human AFP (10). In the mutant mouse model, total brain and liver homogenates (extracts) displayed higher levels of circulating serum AFP in age-matched mutant mice compared to wild-type mice suggestive of increased AFP presence (86).

8. CONCLUSION

AFP has been reported to be a significant contributor to normal human brain development (87, 88). This oncofetal protein has been detected in the cytoplasm of developing brain neurons being abundant in nerve cells specific to both symmetrical halves of the brain. However, AFP was not found in limbic, preoptic, and hypothalamic brain regions; in addition, no coding of mRNA was present, and no syntheses of AFP occurred in the brain cells (89, 90). The fetal protein detected in brain cells was engulfed and internalized into the cytoplasm by non-energy procedures of macropinocytotic and endocytotic pathways which transport and deliver essential nutrients (lipids, estrogens) to the developing brain. Moreover, AFP has been found crucial for normal feminization of the female brain and defeminization of the male brain in rodents. In previous reports, it has been confirmed that AFP plays a significant role being involved in regulating the hypothalamic-pituitary reproductive axis (89). In studies of knock-out AFP models in mice, AFP has been demonstrated to not be required for full-term pregnancies; however, second generation female mice were found to be infertile. It is germane to this discussion that hyperandrogenization has also been reported in human female BD patients (10).

In summation, elevated AFP levels are known to be associated with prenatal nervous system pathologies involving birth defects such as neural tube defects and anencephaly. On the other hand, AFP represents one of the most useful markers for hepatocarcinomas and teratocarcinomas and for the monitoring of the patient response to therapy (27). In addition, postnatal and juvenile neurodegenerative disorders such as ataxia telangiectasia and autosomal recessive ataxia-ocular apraxia (brain/eye) disorders have been reported (91). Serum from patients with autoimmune disorders in pregnancy are known to display high circulating levels of both fetal and maternal serum (MS) AFP levels (92). In fact, during pregnancy, MS-AFP screening programs are in routine clinical use for the above mentioned fetal disorders. In keeping with such screening, abnormal serum AFP levels obtained from newborns, infantile, and juvenile patients with BD have been reported: these observation were also observed in BD mouse models (10). It is now apparent that AFP among other proteins, can serve as targets of autoimmune responses to exposed, hidden epitopes exposed on unfolded proteins in the brain of BD patients. Similarly, autoantibodies to AFP-hidden epitopes were detected in hepatocarcinoma patients. Cryptic epitopes may become exposed to the immune system secondary to events, such as trauma and necrosis, which may act by causing conformational change modifications of the protein and/or in the processing machinery (19). Human and rodent AFP are immunogenic in xenogenic animals, while they do not induce immune responses in the species of origin (93, 94). In summary, the unveiling of hidden epitope(s) on AFP may result in an induction of autoantibodies, indicating the activation of B and T lymphocyte clones which were not eliminated during the immune tolerance development (95). Since denatured intermediate forms derived from tertiary-folded AFP resemble those of a disordered protein (Figure 1), it is logical to predict that AFP could indeed induce immune responses in various human diseases.

Figure 1

AFP intermediate forms and immune response. Given that denatured intermediate forms derived from tertiary-folded AFP resemble those of a disordered protein, AFP might induce immune responses in various human diseases including hepatocellular carcinoma and Batten disease.

9. ACKNOWLEDGEMENT

This work was supported by a grant from the University of Rome “Tor Vergata” (Mission Sustainability, Codice Unico di Progetto (CUP): E81I18000330005), Italy.

References
[1]
Abbas K Lichtman P Pitlai S Cellular and molecular. Immunology, Ninth Edition Philadelphia, Elsevier, 2018 97 107
[2]
Parham P The Immune System, 3rd Edition, Garland Science, Taylor & Frances group, Philadelphia, 2009 11
[3]
Rose N. R The Autoimmune diseases, Chapter 2, Academic Press, New York 2013
[4]
WardemannHNussenzweigM. CB-cell self-tolerance in humans. Adv Immunol,20079583110DOI: 10.1016/S0065-2776(07)95003-8
[5]
KyewskiBKleinLA central role for central tolerance. Annu Rev Immunol200624571606DOI: 10.1146/annurev.immunol.23.021704.115601
[6]
GoodnowC. CSprentJStB. Fazekas deGroth, C. G. Vinuesa: Cellular and genetic mechanisms of self tolerance and autoimmunity. Nature200543559097DOI: 10.1038/nature03724
[7]
BeiRMasuelliLPalumboCModestiMModestiAA common repertoire of autoantibodies is shared by cancer and autoimmune disease patients: Inflammation in their induction and impact on tumor growth. Cancer Lett2009281823DOI: 10.1016/j.canlet.2008.11.009
[8]
BenvenutoMMatteraRMasuelliLTresoldiIGigantiM. GFrajeseG. VManzariVModestiABeiRThe crossroads between cancer immunity and autoimmunity: antibodies to self antigens. Front Biosci (Landmark Ed)20172212891329DOI: 10.2741/4545
[9]
BeiRMizejewskiG. JAlpha fetoprotein is more than a hepatocellular cancer biomarker: from spontaneous immune response in cancer patients to the development of an AFP-based cancer vaccine. Curr Mol Med20111156481DOI: 10.2174/156652411800615162
[10]
CastanedaJ. APearceD. AIdentification of alpha-fetoprotein as an autoantigen in juvenile Batten disease. Neurobiology of Disease20082992102DOI: 10.1016/j.nbd.2007.08.007
[11]
GuoJZhouXRegulatory T cells turn pathogenic. Cell Mol Immunol20151252532DOI: 10.1038/cmi.2015.12
[12]
TaniTTanakaKIdezukaJNishizawaMRegulatory T cells in paraneoplastic neurological syndromes. J Neuroimmunol200819616669DOI: 10.1016/j.jneuroim.2008.03.002
[13]
CoolesF. AIsaacsJ. DAndersonA. ETreg cells in rheumatoid arthritis: an update. Curr Rheumatol Rep201315352DOI: 10.1007/s11926-013-0352-0
[14]
PoletaevA. BChurilovL. PStoevY. LImmunophysiologyM. AgapovImmunopathology: natural autoimmunity in human health and disease. Pathophysiology,20121922131DOI: 10.1016/j.pathophys.2012.07.003
[15]
HuangJCEDW. HondaA conformational epitope database. BMC Immunology2006779DOI: 10.1186/1471-2172-7-7
[16]
Alberts C Molecular Biology of the Cell. Garland Science, New York, 2002 1401 405
[17]
PlotzP. HThe autoantibody repertoire: searching for order, Nat Rev Immunol200337378DOI: 10.1038/nri976
[18]
CarlP. LTempleB. RCohenP. LMost nuclear systemic autoantigens are extremely disordered proteins: implications for the etiology of systemic autoimmunity. Arthritis Res Ther20057R13601374DOI: 10.1186/ar1832
[19]
LanzavecchiaAHow can cryptic epitopes trigger autoimmunity. J Exp Med 1811995194548DOI: 10.1084/jem.181.6.1945
[20]
MizejewskiG. JAlpha-fetoprotein as a biologic response modifier: relevance to domain and subdomain structure. Proc Soc Exp Biol Med199721533362DOI: 10.3181/00379727-215-44143
[21]
LuftA. JLorscheiderF. LStructural analysis of human and bovine alpha-fetoprotein by electron microscopy, image processing, and circular dichroism. Biochemistry 22:1983597881DOI: 10.1021/bi00294a043
[22]
MizejewskiGSmithGButtersteinGReview and proposed action of alpha-fetoprotein growth inhibitory peptides as estrogen and cytoskeleton-associated factors. Cell Biol Int20042891333DOI: 10.1016/j.cellbi.2004.09.005
[23]
MizejewskiG. JThe phylogeny of alpha-fetoprotein in vertebrates: survey of biochemical and physiological data. Crit Rev Eukaryot Gene Expr19955281316DOI: 10.1615/CritRevEukarGeneExpr.v5.i3-4.40
[24]
NaiduSPetersonM. LSpearB. TAlpha-fetoprotein related gene (ARG): a new member of the albumin gene family that is no longer functional in primates. Gene201044995102DOI: 10.1016/j.gene.2009.08.014
[25]
MizejewskiG. JPhysiology of alpha-fetoprotein as a biomarker for perinatal distress: relevance to adverse pregnancy outcome. Exp Biol Med (Maywood)20072329931004DOI: 10.3181/0612-MR-291
[26]
Mizejewski G. J New insights into AFP structure and function: potential biomedical applications. In: Mizejewski GJ. Porter IH, Eds. Alpha-Fetoprotein and Congenital Disorders. Orlando: Academic Press; 1985 5 34
[27]
DeutschH. FChemistry and biology of alpha-fetoprotein. Adv Cancer Res199156253312DOI: 10.1016/S0065-230X(08)60483-2
[28]
HiranoKWatanabeYAdachiTItoYSugiuraMDrug binding properties of human alpha-foetoprotein. Biochem J198523118991DOI: 10.1042/bj2310189
[29]
HankePRabeCSerweMBöhmSPagenstecherCSauerbruchTCaselmannW. HCirrhotic patients with or without hepatocellular carcinoma harbour AFP-specific T lymphocytes that can be activated in vitro by human alpha-fetoprotein. Scand J Gastroenterol20023794955DOI: 10.1080/003655202760230928
[30]
Vollmer C. M. Jr Eilber F. C Butterfield L. H Ribas A Dissette V. B Koh A Montejo L. D Lee M. C Andrews K. J McBride W. H Glaspy J. A Economou J. S Alpha-fetoprotein-specific genetic immunotherapy for hepatocellular carcinoma. Cancer Res 1999 59 3064 67
[31]
MizejewskiG. JBiological role of alpha-fetoprotein in cancer: prospects for anticancer therapy. Expert Rev Anticancer Ther2002270935DOI: 10.1586/14737140.2.6.709
[32]
MizejewskiG. JAlpha-fetoprotein structure and function: relevance to isoforms, epitopes, and conformational variants. Exp Biol Med (Maywood)2001226377408DOI: 10.1177/153537020122600503
[33]
GJMizejewskiBiological roles of alpha-fetoprotein during pregnancy and perinatal development. Exp Biol Med (Maywood)200422943963DOI: 10.1177/153537020422900602
[34]
YazovaA. KGoussevA. IChristiansenMKushlinskyN. EStogovaENorgaard-PedersenBAbelevG. IHuman fetal and tumor alpha-fetoproteins differ in conformationally dependent epitope variants expression. Immunol Lett20038526170DOI: 10.1016/S0165-2478(02)00207-9
[35]
LeongS. SMiddelbergA. PThe refolding of different alpha-fetoprotein variants. Protein Sci200615204050DOI: 10.1110/ps.062262406
[36]
Bei R Budillon A Reale M. G Capuano G Pomponi D Budillon G Frati L Muraro R Cryptic epitopes on alpha-fetoprotein induce spontaneous immune responses in hepatocellular carcinoma, liver cirrhosis, and chronic hepatitis patients. Cancer Res 1999 59 5471 74
[37]
Norgaard-PedersenBAxelsenN. HAlpha-fetoprotein-like activity in sera from patients with malignant and non-malignant disease and healthy individuals. Clin Chem Acta19767134347DOI: 10.1016/0009-8981(76)90551-9
[38]
BeneduceLCastaldiFMarinoMTonoNGattaAPontissoPFaasinaGImprovement of liver cancer detection with simultaneous assessment of circulating levels of free alpha-fetoprotein (AFP. and AFP-IgM complexes. Int J Biol Markers20041915559DOI: 10.1177/172460080401900211
[39]
JingtingJChangpingWNingXyibeiZJunWMeiJBinXPeterN. EXueguanZClinical evaluation of serum alpha-fetoprotein-IgM immune complexes on the diagnosis of primary hepatocellular carcinoma. J Clin Lab Anal20092321318DOI: 10.1002/jcla.20321
[40]
ShengS. LWangQHuangGYuBQinW. XSimultaneous determination of alpha-fetoprotein immune complexes and alpha-fetoprotein concentration in hepatocellular carcinoma using dual-label time-resolved immunofluorometric assays. J Clin Lab Anal20092317985DOI: 10.1002/jcla.20316
[41]
WuJZouHJiangJ. TLiX. DZhaoX. MJarKWangHXuBWuC. PClinical application of serum alpha-fetoprotein-IgM complexes on the diagnosis of primary hepatocellular carcinoma in Kazakh and Han populations. Tumori2013995359DOI: 10.1177/030089161309900416
[42]
Butterfield L. H Koh A Meng W Vollmer C. M Ribas A Dissette V Lee E Glaspy J. A McBride W. H Economou J. S Generation of human T-cell responses to an HLA-A2.1-restricted peptide epitope derived from alpha-fetoprotein. Cancer Res 1999 59 3134 42
[43]
ButterfieldL. HMengW. SKohAVollmerC. MRibasADissetteV. BFaullKGlaspyJ. AMcBrideW. HEconomouJ. ST cell responses to HLA-A*0201-restricted peptides derived from human alpha fetoprotein. J Immunol200116653008DOI: 10.4049/jimmunol.166.8.5300
[44]
LiuYDaleySEvdokimovaV. NZdobinskiD. DPotterD. MButterfieldL. HHierarchy of alpha fetoprotein (AFP)-specific T cell responses in subjects with AFP-positive hepatocellular cancer. J Immunol200617771221DOI: 10.4049/jimmunol.177.1.712
[45]
MizukoshiENakamotoYTsujiHYamashitaTKanekoSIdentification of alpha-fetoprotein-derived peptides recognized by cytotoxic T lymphocytes in HLA-A24+ patients with hepatocellular carcinoma. Int J Cancer20061181194204DOI: 10.1002/ijc.21468
[46]
PichardVRoyerP. JRichouCCauchinEGoebesKGaignerieAMasliahCGournayJGregoireMFerryNDetection, isolation, and characterization of alpha-fetoprotein-specific T cell populations and clones using MHC class I multimer magnetic sorting. J Immunother20083124653DOI: 10.1097/CJI.0b013e318169d55c
[47]
ThimmeRNeaguMBoettlerTNeumann-HaefelinCKerstingNGeisslerMMakowiecFObermaierRHoptU. TBlumH. ESpangenbergH. CComprehensive analysis of the alpha-fetoprotein-specific CD8+ T cell responses in patients with hepatocellular carcinoma. Hepatology200848182133DOI: 10.1002/hep.22535
[48]
AlisaAIvesAPathanA. ANavarreteC. VWilliamsRBertolettiABehboudiSAnalysis of CD4+ T-Cell responses to a novel alpha-fetoprotein-derived epitope in hepatocellular carcinoma patients. Clin Cancer Res200511668694DOI: 10.1158/1078-0432. CCR-05-0382
[49]
AyaruLPereiraS. PAlisaAPathanA. AWilliamsRDavidsonBBurroughsA. KMeyerTBehboudiSUnmasking of alpha-fetoprotein- specific CD4(+. T cell responses in hepatocellular carcinoma patients undergoing embolization. J Immunol2007178191422DOI: 10.4049/jimmunol.178.3.1914
[50]
AlisaABoswellSPathanA. AAyaruLWilliamsRBehboudiS Human CD4(+. T cells recognize an epitope within alpha-fetoprotein sequence and develop into TGFbeta-producing CD4(+). T cells. J Immunol2008180510917DOI: 10.4049/jimmunol.180.7.5109
[51]
EvdokimovaV. NLiuYPotterD. MButterfieldL. HAFP specific CD4+ helper T-cell responses in healthy donors and HCC patients. J Immunother20073042537DOI: 10.1097/CJI.0b013e31802fd8e2
[52]
BehboudiSBoswellSWilliamsRCell-mediated immune responses to alpha-fetoprotein and other antigens in hepatocellular carcinoma. Liver Int2010305216DOI: 10.1111/j.1478-3231.2009.02194.x
[53]
SunLGuoHJiangRLuLLiuTZhangZHeXArtificial antigen-presenting cells expressing AFP(158-166. peptide and interleukin-15 activate AFP-specific cytotoxic T lymphocytes. Oncotarget201671757990DOI: 10.18632/oncotarget.8198
[54]
JamesJ. AHarleyJ. BB-cell epitope spreading in autoimmunity. Immunol Rev1998164185200DOI: 10.1111/j.1600-065X.1998.tb01220.x
[55]
CraftJFatenejadSSelf antigens and epitope spreading in systemic autoimmunity. Arthritis Rheum199740137482DOI: 10.1002/art.1780400803
[56]
DeshmukhU. SBagavantHLewisJGaskinFFuS. MEpitope spreading within lupus-associated ribonucleoprotein antigens. Clin. Immunol200511711220DOI: 10.1016/j.clim.2005.07.002
[57]
Fernández-MadridFAutoantibodies in breast cancer sera: candidate biomarkers and reporters of tumorigenesis. Cancer Lett2005230187198DOI: 10.1016/j.canlet.2004.12.017
[58]
ZinkernagelR. MHengartnerHRegulation of the immune response by antigen. Science200129325153DOI: 10.1126/science.1063005
[59]
ShlomchikM. JCraftJ. EMamulaM. JFrom T to B and back again: positive feedback in systemic autoimmune disease. Nat Rev Immunol2001114753DOI: 10.1038/35100573
[60]
MizejewskiG. JAlpha-fetoprotein (AFP)-derived peptides as epitopes for hepatoma immunotherapy: a commentary. Cancer Immunol Immunother20095815970DOI: 10.1007/s00262-008-0548-8
[61]
WangX. WXieHAlpha-fetoprotein enhances the proliferation of human hepatoma cells in vitro. Life Sci1999641723DOI: 10.1016/S0024-3205(98)00529-3
[62]
GeisslerMMohrLWethRKöhlerGGrimmC. FKrohneT. UWeizsäckerF. vonBlumH. EImmunotherapy directed against alpha-fetoprotein results in autoimmune liver disease during liver regeneration in mice. Gastroenterology20011219319DOI: 10.1053/gast.2001.28019
[63]
CooperJ. DMoving towards therapies for juvenile Batten diseases? Exp. Neurol20082132931DOI: 10.1016/j.expneurol.2008.02.016
[64]
IsosomppiJLysosomal localization of the neuronal ceroid lipofuscinosis CLN5 protein Human Molecular Genetics20021188589DOI: 10.1093/hmg/11.8.885
[65]
HaltiaMThe neuronal ceroid-lipofuscinoses: from past to present. Biochim Biophys Acta,2006176285056DOI: 10.1016/j.bbadis.2006.06.010
[66]
Pardo C. A Rabin B. A Palmer D. N Price D. L Accumulation of the adenosine triphosphate synthase subunit C in the mnd mutant mouse. A model for neuronal ceroid lipofuscinosis. Am J Pathol 1994 144 829 35
[67]
ChanC. HRamirez-MontealegreDPearceD. AAltered arginine metabolism in the central nervous system (CNS. of the Cln3-/- mouse model of juvenile Batten disease. Neuropathol Appl Neurobiol200935189207DOI: 10.1111/j.1365-2990.2008.00984.x
[68]
MatsumotaSHaberleJKidoJMitsubuchiHEndoFNakamuraKUrea cycle disorders-update. J Hum Genet20196483347DOI: 10.1038/s10038-019-0614-4
[69]
CollinsJHolderG. EHerbertHAdamsG. G. WdiseaseBatten features to facilitate early diagnosis. British Journal of Ophthalmology200690111924DOI: 10.1136/bjo.2006.091637
[70]
LuiroKKopraOBlomTGentileMMitchisonH. MHovattaITornquistKJalankoABatten disease (JNCL. is linked to disturbances in mitochondrial, cytoskeletal, and synaptic compartments. Journal of Neuroscience Research200684112438DOI: 10.1002/jnr.21015
[71]
NarayanS. BRakhejaDTanLPastorJ. VBennettM. JCLN3P, the Batten's disease protein, is a novel palmitoyl-protein Delta-9 desaturase. Annals of Neurology20066057077DOI: 10.1002/ana.20975
[72]
Leman A. R Pearce D. A Rothberg P. G Gene symbol: CLN3. Disease: Juvenile neuronal ceroid lipofuscinosis (Batten disease). Human Genetics 116: 2005 544
[73]
PhillipsS. NBenedictJ. WWeimerJ. MPearceD. ACenter for aging and developmental biology, University of Rochester School of Medicine and Dentistry, Rochester, New York 14642, USA. CLN3, the protein associated with batten disease: structure, function and localization. Journal of Neuroscience Research20057957383DOI: 10.1002/jnr.20367
[74]
MoleS. EWilliamsR. EGoebelH. HCorrelations between genotype, ultrastructural morphology and clinical phenotype in the neuronal ceroid lipofuscinoses. Neurogenetics 6:200510726DOI: 10.1007/s10048-005-0218-3
[75]
WeimerJ. MCusterA. WBenedictJ. WAlexanderN. AKingsleyEFederoffH. JCooperJ DPearceD. AVisual deficits in a mouse model of Batten disease are the result of optic nerve degeneration and loss of dorsal lateral geniculate thalamic neurons. Neurobiology of Disease20062228493DOI: 10.1016/j.nbd.2005.11.008
[76]
PontikisC. CCotmanS. LMacDonaldM. ECooperJ. DThalamocortical neuron loss and localized astrocytosis in the Cln3 Deltaex 7/8 knock-in mouse model of Batten disease. Neurobiology of Disease20052082336DOI: 10.1016/j.nbd.2005.05.018
[77]
KatzM. LShibuyaHLiuB. CKaurSA mouse gene knockout model for juvenile ceroid lipofusinosis (Batten's disease). J. Neurosci Res19995755156DOI: 10.1002/(SICI)1097-4547(19990815)57:4<551::AID-JNR15>3.0. CO;2-R
[78]
ChattopadhyaySItoMCooperJ. DBrooksA. LCurranT. MPowersJ. MPearceD. AAn autoantibody inhibitory to glutamic acid decarboxylase in the neurodegenerative disorder Batten disease. Hum Mol Genet200211142131DOI: 10.1093/hmg/11.12.1421
[79]
CotmanS. LVrbanacVLebelL. ALeeR. LJohnsonK. ADonahueL. RTeedA. M Cln3(Deltaex7/8. knock-in mice with the common JNCL mutatio8n exhibit progressive neurologic disease that begins before birth. Hum Mol Genet200211270921DOI: 10.1093/hmg/11.22.2709
[80]
Persaud-SawinD. ABoustanyR-M. NCell death pathways in juvenile Batten disease. Apoptosis20051097385DOI: 10.1007/s10495-005-0733-6
[81]
RajhejaDNarayanS. BBennettM. JJuvenile neuronal ceroid-lipofuscinosis (Batten disease): a brief review and update. Curr Mol Med200766038DOI: 10.2174/156652407781695729
[82]
Ramirez-MontealegreDChattopadhyaySCurranT. MWasserfalCPritchardLSchatzDPetittoJHopkinsDSheJ. XRothbergP. GAtkinsonMPearceD. AAutoimmunity to glutamic and acid decarboxylase (gad. in the neurodegenerative disorder Batten disease. Neurology20056474345DOI: 10.1212/01. WNL.0000151973.08426.7E
[83]
LimM. JBeakeJBibleECurranT. MRamirez-MontealegreDPearceD. ACooperJ. DDistinct patterns of serum immunoreactivity as evidence for multiple brain-directed autoantibodies in juvenile neuronal ceroid lipofuscinosis. Neuropathology & Applied Neurobiology20063246982DOI: 10.1111/j.1365-2990.2006.00738.x
[84]
Toran-AllerandC. DRegional differences in intraneuronal localization of alpha-fetoprotein in developing mouse brain. Brain Res198228121317DOI: 10.1016/0165-3806(82)90161-4
[85]
VillacampaM. JLampreaveFCalvoMNavalJPineiroAUrielJIncorporation of radiolabelled alpha fetoprotein in the brain and other tissues of the developing rat. Brain Res19843147782DOI: 10.1016/0165-3806(84)90177-9
[86]
MitchisonH. MBernardD. JTargeted disruption of the Cln3 gene provides a mouse model for Batten disease. Neurobiol Diseases1999632134DOI: 10.1006/nbdi.1999.0267
[87]
BennoR.WWilliamsT. HEvidence for intracellular intracellular localization of alpha-fetoprotein in the developing rat brain. Brain Res197814218286DOI: 10.1016/0006-8993(78)90189-0
[88]
BakkerJDeMeesCAlpha-fetoprotein protects the developing female mouse brain from masculinization and defeminization by estrogens. Nature Neurosci,2006923036DOI: 10.1038/nn1624
[89]
DeMeesCLaesJ. FAlpha-fetoprotein controls female fertility and prenatal development of the gonadotropin-releasing hormone pathway through an antiestrogenic action. Mol Cell Biol,200626201218DOI: 10.1128/MCB.26.5.2012-2018.2006
[90]
SchachterB. SToran-AllerandC. DIntraneural alpha-fetoprotein and albumin are not synthesized in the developing brain. Brain Res19822819398DOI: 10.1016/0165-3806(82)90116-X
[91]
MizejewskiG. JLevels of alpha-fetoprotein during pregnancy and early infancy in normal and disease states. Obstet Gynecol Surv20035880426DOI: 10.1097/01. OGX.0000099770.97668.18
[92]
MizejewskiG. JAutoimmune disorders during pregnancy: effect of biomarkers on maternal serum screening and course of disease. Curr. Women's Health Reviews20161295104DOI: 10.2174/1573404812666160727122345
[93]
RuoslahtiEPihkoHBeckerMa-fetoproteinO. Makela: Rabbitnormal levels and breakage tolerance with haptenated homologous a-fetoprotein. Eur J Immunol19755710DOI: 10.1002/eji.1830050103
[94]
Taga H The effect of active immunization of rats with heterologous a-fetoprotein upon hepatocarcinogenesis induced by 39-methyl-4-dimethylaminoazobenzene. Gann 1983 74 248 57
[95]
LaffertyK. JToleranceL. S. Gazdaa case of self/not self discrimination maintained by clonal deletion? Hum. Immunol19975211926DOI: 10.1016/S0198-8859(96)00294-7
Publisher’s Note: IMR Press stays neutral with regard to jurisdictional claims in published maps and institutional affiliations.
Share
Back to top