Association of TAP1 1177A>G and 2090A>G gene polymorphisms with latent tuberculosis infections in sheltered populations, in the metropolitan area of Guadalajara, Mexico: a pilot study

Challenges and the Way forward in Diagnosis and Treatment of Tuberculosis Infection

Globally, it is estimated that one-quarter of the world's population is latently infected with Mycobacterium tuberculosis (Mtb), also known as latent tuberculosis infection (LTBI). Recently, this condition has been referred to as tuberculosis infection (TBI), considering the dynamic spectrum of the infection, as 5-10% of the latently infected population will develop active TB (ATB). The chances of TBI development increase due to close contact with index TB patients. The emergence of multidrug-resistant TB (MDR-TB) and the risk of development of latent MDR-TB has further complicated the situation. Detection of TBI is challenging as the infected individual does not present symptoms. Currently, there is no gold standard for TBI diagnosis, and the only screening tests are tuberculin skin test (TST) and interferon gamma release assays (IGRAs). However, these tests have several limitations, including the inability to differentiate between ATB and TBI, false-positive results in BCG-vaccinated individuals (only for TST), false-negative results in children, elderly, and immunocompromised patients, and the inability to predict the progression to ATB, among others. Thus, new host markers and Mtb-specific antigens are being tested to develop new diagnostic methods. Besides screening, TBI therapy is a key intervention for TB control. However, the long-course treatment and associated side effects result in non-adherence to the treatment. Additionally, the latent MDR strains are not susceptible to the current TBI treatments, which add an additional challenge. This review discusses the current situation of TBI, as well as the challenges and efforts involved in its control.

Transporter Associated with Antigen Processing 1 Gene Polymorphisms Increase the Susceptibility to Tuberculosis

Purpose

Tuberculosis (TB) is known to result from a complex interaction between the host immune response and Mycobacterium infection. The transporter associated with antigen processing (TAP) plays an important role in the processing and presentation pathways for the Mycobacterium tuberculosis (M. tb) antigen. To investigate the possible association of the TAP1 and TAP2 genes with TB.

Patients and Methods

A total of 449 TB patients and 435 control subjects were included in this study, and single nucleotide polymorphisms (SNPs) in the TAP gene, as well as TAP1 and TAP2 alleles, were genotyped.

Results

TAP gene association analysis of TB diseases showed that rs41551515-T in the TAP1 gene was significantly associated with susceptibility to TB (P=7.96E-04, OR=4.124, 95% CI: 1.683-10.102), especially pulmonary TB (PTB, P=6.84E-04, OR=4.350, 95% CI: 1.727-10.945), and the combination of rs1057141-T-rs1135216-C in the TAP1 gene significantly increased the risk of TB susceptibility (P=5.51E-05, OR=10.899, 95% CI: 2.555-46.493). Five novel TAP1 alleles were detected in Yunnan Han people, and the allele frequency of TAP1*unknown_3 (rs41555220-rs41549617-rs1057141-rs1135216-rs1057149-rs41551515: C-A-T-C-C-T) was notably increased in all TB patients, including in the PTB and EPTB subgroups, and was significantly associated with the risk of susceptibility to TB. However, no association between the TAP2 gene and TB was found in this study.

Conclusion

Host genetic variants of rs41551515-T and the combination rs1057141-T-rs1135216-C, as well as TAP1*unknown_3 may play a critical role in susceptibility to TB disease.

Association study of TAP and HLA-I gene combination with chronic hepatitis C virus infection in a Han population in China

Host immune system genes play key roles in the progression of chronic hepatitis C virus (HCV) infection. Transporters associated with antigen processing (TAP) play an important role in the loading of viral peptides onto MHC class I molecules. This study aimed to investigate the association between TAP gene polymorphisms and chronic HCV in a Chinese Han population. A total of 232 chronic hepatitis C (CHC) patients and 362 healthy individuals were recruited from the Han population in Yunnan province in southwest China, and a TaqMan SNP genotyping assay was used to detect six single nucleotide polymorphisms (SNPs) of TAP1 and three SNPs of TAP2 genes. The association of the TAP gene with CHC was analysed at the allele, genotype, and haplotype levels. There were no significant differences in the allele and genotype frequencies of these SNPs in the TAP gene between CHC patients and controls after Bonferroni correction. A novel TAP1 allele (TAP1*unknown_1: rs41555220-rs41549617-rs1057141-rs1135216-rs1057149-rs41551515: G-G-A-G-G-G) was only present in the CHC group, and this allele significantly increased susceptibility to CHC (p = .005, odds ratio [OR] = 11.105. 95% confidence interval [CI]: 1.362-90.558). Homozygous TAP1*03:01/TAP1*03:01 was observed only in the CHC group that exhibited an obvious risk for CHC (p = .002, OR = 9.637, 95% CI: 1.153-80.574). And the haplotype TAP1*unknown_1-TAP2*01:01 was only present in the CHC group and indicated a significant risk for CHC (p = .002, OR = 9.498, 95% CI: 1.140-79.149). We observed significant interactions among HLA-A, -B,C, TAP1, and TAP2 alleles, and combination analysis revealed that the combination of TAP1*01:01-TAP2*01:01-HLA-B*35:01 was only present in the control group (2.2%) and resulted in significantly increased resistance to CHC (p = .002, OR = 0.096, 95% CI: 0.012-0.759). Whereas, the combination of TAP1*01:01-TAP2*01:01-HLA-C*07:02 and TAP1*03:01-TAP2*01:01-HLA-C*01:02 increased the susceptibility to CHC significantly (p = .001, OR = 2.016, 95% CI: 1.309-3.106 and p = .002, OR = 8.070, 95% CI: 1.018-63.997, respectively). Our results indicated that TAP and HLA-I may exert a combined effect on CHC susceptibility in the Chinese Han population.