To the Editor:
Genetic factors like HLA influence the infection and progression of HIV disease. 1 Mutations in chemokine receptor genes have been found to be associated with the progression of HIV disease. Refractoriness to HIV infection in case of Δ32 mutation in the gene encoding mL chemokine receptor-5 has been reported. 1 Various HLA alleles have been linked with rapid (A11 and B35) and slow (B27 and B57) disease progression in HIV infection. 2 Thus, genetic factors might be significant in acquisition of HIV infection. The paucity of data on HLA association with HIV-1 infection in India, where HIV-1 subtype C is predominant, prompted us to undertake the present study.
Thirty-eight HIV-1-infected individuals enrolled in the ongoing study on clinical progression of HIV infection were studied for anti-HIV cytotoxic T-lymphocyte (CTL) activity and class I HLA alleles. None of the patients had AIDS-defining illnesses. The CD4 counts of these patients ranged between 48–938/ mm3, with a median of 598/mm3.
This study was approved by Institutional Ethics Committees of National AIDS Research Institute and Institute of Immunohaematology. A total of 128 age- and sex-matched unrelated healthy normal Maharashtrian subjects acted as controls. The diagnosis of HIV infection was made by 2 different enzyme-linked immunosorbent assays (Labsystems HIV EIA as a screening test and either Immunocomb II HIV1 and 2 BiSpot /HIV TRI-DOT/Capillus HIV-1 and HIV-2/CombAids-R5 as a confirmatory test) according to the National AIDS Control Organization guidelines. Genomic DNA was extracted from frozen peripheral blood mononuclear cells by Quiagen blood mini kit and subtyped for its A, B, and C allele subtypes by PCR reverse line strip sequence specific oligonucleotide hybridization (PCR-SSOP) strips (Roche Molecular, Oakland, CA). Genomic DNA was amplified using HLA locus-specific biotinylated primers and hybridized with the SSO strips. The alleles were determined using the Pattern Interpretation software supplied along with the kit (Roche Molecular). Statistical significance and association of HLA alleles and HIV infection status were computed. To overcome chance deviate frequency of HLA allele, the P value is corrected by use of Bonferroni inequality method, i.e., by multiplying it with the number of alleles compared. The HLA Cw*1507, B*3520, and B*1801 subtypes were more commonly observed among HIV-infected individuals compared with controls, which reached statistical significance (P < 0.01) (Table 1). The allele frequencies of B35 and B18 in Maharashtrian population had been earlier reported to be 26.3 and 2.42%, respectively, by serologic method. 3 Serologic methods are not adequate to determine finer differences in the subtypes of alleles. However, molecular methodology in the present work allowed us to further subtype these alleles as it has been reported for HLA A19 in our earlier study. 4 Out of 42 allele subtypes of HLA B*35, HLA B*3503 was found to be common among the controls while B*3520 was more common in HIV-infected individuals. Out of 18 allele subtypes of B*18, B*1801 was more common in HIV-infected individuals (Table 1).
Genes that are involved in protective immunity seem to have been under greater selective pressure and show greater variability than other genes. Genetic epidemiology data indicate that there might be major susceptibility genes that account for a significant proportion of genetic contribution to disease susceptibility. HLA loci evolve very fast, probably as a result of selective pressure from pathogens, and polymorphism in these loci has been associated with altered susceptibility to infectious diseases. Polymorphisms are seen in HLA molecules predominantly at crucial sites such as peptide binding motifs, which may influence the CTL responses against HIV antigens. The CTL is prime response attributed for control of HIV infection and disease progression. Hence, population-based diversity of HLA molecules might actually be an advantage. 5 Evidence now exists that HLA heterozygosity is associated with protection against viral diseases, including delayed progression of HIV infection. 2 Association of HLA alleles with susceptibility to HIV infection and progression of disease has been studied in diverse populations. HLA alleles B*27 and B*57 have been associated with slow disease progression. Conversely, allele B*35 has been found to be associated with rapid progression of the disease. This is the first report on the association of distinct HLA allele subtypes with HIV-1 infection in an Indian population. Moreover, association of Cw allele with HIV infection is reported for the first time. Our results might have important implications in understanding the host genetic factors responsible for HIV acquisition and disease progression in India. Further, the results of this study might be important in designing and testing effective vaccines in Indian patients.
We would like to thank the staff of the NARI clinic for their support in counseling and obtaining blood samples from the enrolled patients and the laboratory staff for HIV serology and sample preparation for HLA typing. Conflict of interest: none. Dr. Dipika Mohanty, Dr. Ramesh S. Praranjape, Dr. Sanjay Mehendale, Dr. Madhuri Thakar, and Dr. Umapathy Shankarkumar conceived and designed the study. Dr. Umapathy Shankarkumar carried out blinded tissue typing and did the statistical analysis. Dr. Madhuri Thakar was involved in planning and coordination of the study. All authors contributed in the preparation of the manuscript.
Ramesh S. Praranjape
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