Recently, humanity has begun to face a significant issue in response to the increasing spread of antibiotic-resistant bacteria. This situation has led to a worrying rise in mortality and the introduction of increasingly difficult-to-control diseases. Acinetobacter baumannii is regarded as one of these flexible pathogens due to an observed increase in frequency in hospitals, resistance to therapy, and association with higher mortality and morbidity rates. The occurrences of Acinetobacter baumannii outside clinical settings indicate a considerable danger related to ecological contamination [1]. Thus, the remarkable capacity of Acinetobacter baumannii to evolve resistance to a wide range of antibiotics poses a substantial concern in healthcare settings. Indeed, Acinetobacter baumannii is particularly known for causing acute and invasive hospital infections, such as bloodstream infection, ventilator-associated pneumonia (VAP), skin and soft tissue infections, meningitis, and urinary tract infections (UTIs) [2, 3]. Neonatal regions (hospital intensive care units, NICUs) and burns units are principal places where seriously sick patients develop infections from opportunistic pathogens [4, 5].

Meanwhile, cytokines and chemokines are strictly controlled, excreted proteins that govern several cellular functions, including differentiation, migration, and growth. These proteins provide cues for the trafficking of immune cells, adjust the placement of immune cells in tissues and organs, and stimulate the progression of an immune system that has been altered in response to the immune insult. Major categories of cytokines comprise interferons, interleukins, and the tumor necrosis factor (TNF) family members [6, 7]. Interleukin-7 (IL-7) is secreted from epithelial cells in host tissues, keratinocytes, stromal cells, or tumors and performs an expanded variety of immune functions controlled by the IL-7 receptor (IL-7R) [8]. The biological roles of IL-7 make this protein a pivotal adjuvant that enhances the efficiency of vaccines, as IL-7 can boost and expand systemic immune responses against microbes by lengthening the lifespan of lymphocytes, augmenting effector cell action, and increasing the production of antigen-specific memory cells [9].

Host genetics has the potential to influence the susceptibility of a person to a disease and the ability of that individual to develop an effective immune response, particularly in cases of Acinetobacter infections. Research has shown that genetic variations, such as single-nucleotide polymorphisms (SNPs), in immune-related genes can significantly influence the response of the host to infections. Thus, polymorphisms in genes producing cytokines and any associated receptors, such as IL-6, TNF-$\alpha$, and IL-10, can modify the inflammatory response, which is critical in treating bacterial infections, particularly those caused by Acinetobacter spp. [10]. A SNP is a DNA sequence polymorphism that happens because of changes to a single nucleotide in a given position at the genome level [11]. SNPs are useful indications of clinical diagnosis, and can be used to explore between-individual variances in many domains [12, 13]. Thus, this study aimed to identify the frequencies and rs231775 SNP genotypes and alleles in the selected patients and to investigate the influence of this infection on IL-7 levels in people with different rs231775 SNP genotypes.

This study involved 100 subjects, with 32 assigned to the patient group and 68 considered as controls. Males and females constituted 57 and 43 subjects, respectively. The percentages of male patients and controls were similar, at 53.1% and 58.8%, respectively. Furthermore, the females in the patient group comprised 46.9%, while those in the control group comprised 41.2%. There was no significant association between gender and the groups of subjects under study (p = 0.591) (Table 1).

Table 2 describes the distribution of participants in the patient and control groups in relation to the relevant blood group. The findings indicate no significant association (p = 0.109) between blood groups and the assigned category of the studied subjects (patients or controls). Notably, blood group A+ was the most frequently observed, while A– was the least in both patients and controls.

An independent t-test was used to determine the difference between the mean values of certain demographic data for patients and controls. The comparisons revealed no significant differences between the mean age of patients (40.5 $\pm$ 1.89 years) and that of the controls (42.19 $\pm$ 1.34 years) (p = 0.474). Moreover, there were no statistically significant differences among the mean weight, height, and body mass index (BMI) of the patients and controls: the respective values of these variables in order are as follows: 93.59 $\pm$ 3.3 kg, 85.54 $\pm$ 3.03 kg (p = 0.109); 1.53 $\pm$ 5.85 m, 1.7 $\pm$ 0.01 m (p = 0.147); 32.31 $\pm$ 1.72 kg/m², 29.73 $\pm$ 1.10 kg/m² (p = 0.198), respectively (Table 3).

The Ct values ranged from 18 to 25 cycles for the first allele and 18 to 29 cycles for the second allele, signifying effective amplification. The curves with no anomalies or irregularities exhibited a typical sigmoid shape. Any observed minor variations in Ct values could be attributed to slight differences in sample preparation or pipetting accuracy.

An independence chi-square test was conducted to evaluate the relationship between a specific genotype and disease status. The results indicated that the AA genotype was markedly more common in the controls (85.4%) than in the patients (14.6%), suggesting a protective effect. A calculated odds ratio (OR) of 0.217 (p = 0.003) supports this notion, indicating that individuals with an AA genotype are significantly less likely to be patients. The possession of the AG genotype exhibited no significant association (OR = 0.800; p = 0.647), suggesting no influence on disease susceptibility. The GG genotype was significantly more frequent in patients (58.1%) than in controls (41.9%), with an OR of 5.439 (p 0.001). The A allele was significantly more common in controls (66%) and was associated with a reduced risk of disease (OR = 0.232; p 0.001). Finally, the G allele was more frequent in patients (69%) and significantly associated with a higher risk of disease (OR = 4.30, p 0.001) (Table 4).

The mean serum concentration of IL-7 (1035 $\pm$ 62.9 pg/mL) differed very highly significantly (p 0.001) from that of the controls (297 $\pm$ 32.6 pg/mL) (Table 5).

A comparison of the mean serum levels of IL-7 was conducted among the three genotypes in the patient group, namely, AG, AA, and GG. The results clarified that the respective means of these genotypes were 498 $\pm$ 79.6 pg/mL, 417 $\pm$ 63.8 pg/mL, and 720 $\pm$ 89.7 pg/mL, respectively. A significant difference was obtained (p = 0.029) (Table 6).

Connections between diseases and blood type have been explored since the 1900s, when scientists revealed that antigens and antibodies are innate components of the immune system. Nonetheless, due to the absence of antigens in some blood groups, there have been various contentious topics regarding the relationship between the ABO blood groups and an increased liability to specified noninfectious and infectious illnesses [14]. The results of the present work illustrate no significant relationship between blood groups and the occurrence of infection; this finding aligns with other studies that found no considerable connection between susceptibility to COVID-19 and ABO and D (Rh system) [15]. Conversely, several blood groups were observed to be statistically exclusive for P. aeruginosa, S. aureus, and E. coli infections [16]. Similar to age and gender, the blood group of a patient is an intrinsic factor that cannot be changed; thus, a high-risk group is defined as a blood group strongly associated with a specific disease. It is worth mentioning that the biological mechanism through which such an association occurs has yet to be completely explained [15].

Obesity, measured by BMI, has a definite but not precisely clear impact on the immune system through various immune mediators, leading to increased susceptibility to diseases and infections. The data obtained imply that obese individuals are more at risk of developing multiple types of infections, such as postoperative infections, and other hospital-acquired infections, and are more likely to develop serious infection-related complications than people of normal weight [17]. The results of the current work do not align with those presented previously [18], possibly due to the nature of the elected candidates in the study.

The SNP rs231775 in the CTLA-4 gene has previously been investigated for its potential association with various illnesses, including microbial infections. This SNP promotes the modification of the threonine amino acid to alanine at position seventeen in the leader peptide of CTLA-4 [19]. The first evidence was provided by a separate study, which identified CTLA-4 rs231775 as a predictive marker for human survival with sepsis [20]. This result is broadly consistent with the findings in this study, where patients were more likely than controls to have the rs231775 GG genotype.

However, we acknowledge that the cross-sectional design limits our ability to infer a causal relationship between the CTLA-4 rs231775 polymorphism and Acinetobacter baumannii infection. As noted, the possibility of reverse causality and unmeasured confounding factors remains.

Interleukin-7 is a pleiotropic molecule, primarily generated by stromal cells [21], which is an important factor to T and B cell growth in primary lymphoid organs, as well as to the control of proliferation of mature T cells in the periphery [22]. The findings of the present study align with the above-mentioned discoveries, which indicate the significance of IL-7 in regulating the inflammatory response initiated by microbial infections. The rs231775 SNP, located in the CTLA-4 gene, can affect cytokine levels, including IL-7 [23]. This finding is supported by the present study, which demonstrated a significant difference in IL-7 serum levels among individuals with the rs231775 genotype.

IL-7 also regulates proinflammatory cytokines IFN-$\gamma$ and TNF-$\alpha$, both essential in the immune response to infection. Indeed, IL-7 promotes Th1 differentiation and CD8+ T cell activity, enhancing IFN-$\gamma$ production. Additionally, IL-7 upregulates TNF-$\alpha$ in activated immune cells. Thus, IL-7 variations linked to the rs231775 SNP in the CTLA-4 gene may impact both cellular and cytokine-mediated immunity, contributing to infection susceptibility and highlighting the broader immunological relevance of this polymorphism [24, 25].

The impact of rs231775 on disease vulnerability and development underscores the significant role of genetic factors in the normal functioning of the immune system and overall disease progression. Such associations will be immensely useful for understanding how genetic variations influence the host immune response to infection, for developing evidence-based therapy practices, and for further developing treatments specifically targeted at these associations. Thus, thoroughly outlining these connections is fundamental to effectively incorporating genetic data into medical practice and care for the sick [26]. In conclusion, the present work shows the status of genetic polymorphism (rs231775) in the susceptibility to infectious diseases and emphasizes the crucial role of IL-7 in modulating immune responses.

(1) A key limitation of this study is the small sample size, which may reduce statistical power and limit the detection of subtle associations. This was due to strict inclusion criteria, focus on a specific patient population (e.g., those infected with A. baumannii), and logistic challenges such as limited sample availability and resources. While these measures ensure data quality, these measures may also limit generalizability. Therefore, future studies with larger and more diverse cohorts are recommended to validate these findings.

(2) IL-7 levels were compared across CTLA-4 rs231775 genotypes using appropriate statistical tests. Multiple comparison correction (e.g., Bonferroni) was not applied due to the limited number of planned, hypothesis-driven tests and the small sample size. Moreover, unadjusted p-values are presented due to the risk of increased Type II error, meaning the results should be interpreted with caution.

(3) Antimicrobial susceptibility testing (AST) was not performed in this study due to several limiting factors and resource and logistic limitations. Our study focused on genetic susceptibility (CTLA-4 rs231775), and clinical isolates were limited and not preserved for further testing. Therefore, we recommended that further research include both host and pathogen factors.

In conclusion, this study presents the status of the rs231775 genetic polymorphism regarding susceptibility to infectious diseases and emphasizes the critical role of IL-7 in regulating immune responses.

The data supporting the findings of this study are available from the corresponding author upon reasonable request.

MMRA-R formulated the study design and was responsible for writing the manuscript, WA-EB and ZFA did the practical section of this work, and RSA-S was responsible for the statistical analysis. All authors contributed to editorial changes in the manuscript. All authors read and approved the final manuscript. All authors have participated sufficiently in the work and agreed to be accountable for all aspects of the work.

The study was conducted in accordance with the principles of the Declaration of Helsinki and was approved by the local ethics committee of the Microbiology Department at the Medical College of Mustansiriyah University (approval number 153, dated 20/03/2024). Verbal informed consent was obtained from all participants prior to sample collection, and this procedure was specifically approved by the ethics committee.

This research received no external funding.

The authors declare no conflict of interest.