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- MATERIALS AND METHODS
HIV/AIDS is currently the leading cause of infectious disease mortality around the world. Since many alleles and/or haplotypes of HLA have been reported to be associated with progressive HIV infection, more detailed information on the HLA profile in HIV-1 infected individuals in Chongqing, southwest China would facilitate further understanding of HIV-1 infection, help AIDS vaccine design and the planning of effective preventive strategies. In this study, we performed 4-digit resolution HLA-A, B, DRB1 genotyping of 759 HIV-1 seropositive individuals using PCR-SSO methods. Six alleles were found at more than 10% high frequency: A*1101, A*0201, A*2402, B*4601, B*4001 and DRB1*0901. The most common 2- and 3-locus haplotypes were A*0201-B*4601, A*1101-B*4001, A*1101-B*4601, A*3303/1-B*5801, A*0201-B*4601-DRB1*0901, A*1101-B*4601-DRB1*0901 and A*3303/1-B*5801-DRB1*0301.
690 HIV-1 seropositive individuals with records of CD4 counts were divided into two groups: an AIDS patient group comprising 216 subjects with AIDS-defining symptoms and CD4 counts below 200 cells/mm3 and an asymptomatic, HIV seropositive group of 474 subjects with a stable CD4 count of no less than 200 individuals. In the AIDS patient group, A*3303/1 and B*5801 alleles and the A*3303/1-B*5801 haplotype were significantly underrepresented as compared to the HIV-infected group, whereas A*1101-B*4001, A*1101-B*1502, A*2402-B*4801 haplotypes and five common haplotypes from two groups were significantly overrepresented. HLA-A or B and HLA-Bw6-Bw6 homozygotes were also overrepresented in the AIDS patients group. Our observations suggest that the presence of the B*3501 allele, A*2402-B*4801, common 2-locus and 3-locus haplotypes, HLA-A or B and Bw6-Bw6 homozygosity may predict a poor disease outcome in HIV-1 infection. However, HIV-1 infected individuals who have B*5801 alleles, A*3303/1-B*5801 haplotype and are heterozygous for Bw4-Bw6 are more likely to be resistant to progression of AIDS in this Chinese population.
Since the beginning of the AIDS epidemic in the 1980s, 25 million people have died of HIV-related causes worldwide (1). Globally, the annual number of new HIV infections has declined from 3.0 million (2.6–3.5 million) in 2001 to 2.7 million (2.2 –3.2 million) in 2007 (1). However developing countries such as China have been facing many challenges in attempting to prevent a nation-wide AIDS epidemic. Chongqing, located in southwest China, has a population of more than 31 million and is confronting the threat of AIDS with more than 1000 newly confirmed HIV-1 positive cases in each of the last three years, accounting for 84% of its accumulated cases. Two hundred and seventy-seven of these have been diagnosed as AIDS patients. The prevalent HIV-1 subtype in Chongqing has been classified as CRF07_BC.
HLA class I and II loci are the most polymorphic genes known in humans. HLA class I genes, located at the HLA-A, -B, and -C loci, initiate specific CTL responses. HLA class II loci, HLA-DR, -DQ, and -DP, account for cytokine production and T cell assistance with antibody production. It has been demonstrated that HLA class I, with a dominant HIV-1 subtype B, has associations with AIDS survival and HIV-1 viremia in Caucasian populations in North America, Europe and Australia (2). Studies from Caucasoids and Africans have indicated that HLA-B27 and HLA-B57 are associated with a slow progression to AIDS, while HLA-B35 is associated with rapid disease progression (3–7). Recently, it was reported that in south India HLA-A11 is associated with resistance, and B40 and DR2 with susceptibility, to HIV-1 infection (8). For HLA class II antigens, DRB1 is the most polymorphic locus among class II genes and forms haplotypes with DRB3, DRB4 and DRB5. The role of DRB alleles/haplotypes on resistance/susceptibility to HIV-1 infection remains elusive. In a study of 1090 Pumwani sex workers, it was demonstrated that three DRB1 alleles were associated with resistance, another seven alleles with susceptibility, and that certain haplotypes were associated with resistance/susceptibility to HIV-1 infection (9). These findings provide additional support for the contention that HLA-DRB-specific CD4+ T-cell responses are important in resistance to HIV-1 infection.
In this study, in order to explore potential host genetic factors involved in the pathogenesis of HIV-1 infection, the distribution of HLA-A, B, DRB1 genes in HIV-1 seropositive individuals was investigated, and the frequencies of various HLA alleles and haplotypes between an AIDS patient group and an HIV-1 infected group from Chongqing, China were compared. These data contribute to the database of HLA alleles/haplotypes from different ethnic populations, and their association with disease outcomes of HIV-1 infection.
- Top of page
- MATERIALS AND METHODS
Since the early days of the AIDS epidemic, many studies have been conducted focusing on the association of HLA class I and II antigens with HIV-1 infection and disease outcomes in different ethnic populations (2–8). In the subjects selected for this study, the gene frequencies for A*1101, A*0201, A*2402, B*4601, B*4001, B*1301, DRB1*0901, DRB1*1501, DRB1*1202 appear to be relatively high. However the A*01, A*23, A*68, B*08, B*27, B*57 genes, which have been reported to have a consistent association with HIV/AIDS (2, 11), occurred with a low frequency in HIV-1 seropositive individuals. Notably, B*4601 (20.88%) was the most frequently observed B allele in this group of Chinese subjects, although it rarely occurs in Caucasians and Africans, suggesting the importance of investigating ethnicity-dependent HLA polymorphisms on progression of AIDS among various ethnic populations.
The HLA haplotypes with high frequency included A*0201-B*4601, A*1101-B*4001, A*1101-B*4601 and A*3303/1-B*5801 of 2-locus and A*0201-B*4601-DRB1*0901, A*1101-B*4601-DRB1*0901 and A*3303/1-B*5801-DRB1*0301 of 3-locus. The top 20 most common HLA-A-B and HLA-A-B-DR haplotypes in this study accounted for 60% and 32% of the haplotypes, respectively. The HLA profile of the subjects in this study was similar to that of previous reports on the HLA gene distribution amongst the Han nationality of south China (12–15). In our study, it was shown that HIV-1 infected individuals who have the B*5801 and B*3501 alleles are more likely to develop progression of AIDS. Moreover, homozygosity for HLA-A or B and HLA-Bw6-Bw6 was significantly different between the two groups, suggesting an association with increased susceptibility to progression of AIDS. In addition, the presence of the common 2-locus haplotypes and 3-locus haplotypes may predict a poor disease outcome of HIV-1 infection in this Chinese population from Chongqing, China.
The B58 supertype has been the most reproducibly observed HLA association with HIV-1 viremia and prolonged AIDS survival in Caucasians and Africans who have been infected with either B or C subtype (2, 16). Previous research has confirmed that mutations occur uniquely and frequently at specific positions of certain HIV-1 gag-encoded peptides in HLA-B*58 patients, as does adaptive plasticity of T-cell receptor recognition of HIV-1 motifs, both of which could result in deficient HIV-1 replication (2, 4, 11, 17). The protective role of the B*5801 allele in regard to progression of AIDS was confirmed in this study. However, the A*3303/1 allele and A*3303/1-B*5801 haplotype were less frequently observed in the AIDS patients than in HIV-1 infected individuals. In fact, binary logistic regression analysis showed that resistance conferred by A*3303/1 may due to the presence of the B*5801 allele. Meanwhile, A*3303/1-B*5801 is in a strong linkage disequilibrium in the southwest of China (12, 13, 15).
The HLA-B*35 allele has a highly significant association with disease progression in Caucasians but not in African-Americans (11, 18, 19). Differences have been observed in a single amino acid at position 116, dividing the allele into two groups according to peptide- binding specificity: the B35-PY group and the more broadly reactive B35-Px group. Generally, possession of the B35-PY allele has no effect on AIDS progression in African-Americans (11, 20). However, the present data indicate that the B*3501 subtype allele, which belongs to the B35-PY group, may be associated with more rapid AIDS progression in the study group. B*3503 (0.7% vs. 0.4%, P= 0.68) and B*3505 (0.5% vs. 0.1%, P= 0.23) also express more in the AIDS patient group than in the HIV-1 infected group. However, our data does not support a different effect on AIDS progression between the B35-PY group and B35-Px group.
The B*4801 allele (1.39% vs. 0.53%, P= 0.10), which is not quite as common in the Chinese population, seems to be linked to accelerated progression of AIDS in this study. This allele is in linkage disequilibrium with A*2402 in the population of Chongqing, consequently, the A*2402-B*4801 haplotype was significantly different between the two groups, suggesting its association with increased susceptibility to progression of AIDS. To our knowledge, the B*4801 allele and A*2402-B*4801 haplotype have not thus far been reported to be disadvantageous factors in HIV-1 infection, the underlying mechanisms for such associations remains elusive.
In our study, most of the common HLA-A-B and HLA-A-B-DR haplotypes were overrepresented in the AIDS patients group, such as A*1101-B*4001, A*1101-B*4601, A*1101-B*1502, A*0201-B*4001, A*2402-B*4601 and A*1101-B*1501 for 2-locus haplotypes and A*1101-B*1502-DRB1*1202, A*1101-B*4001-DRB1*1101, A*1101-B*4601-DRB1*0803, A*0201-B*4001-DRB1*0901, A*1101-B*4001-DRB1*1501 and A*2402-B*4601-DRB1*0901 for 3-locus haplotypes. These common haplotypes consisted of common alleles such as A*1101, B*4001, B*1501, DRB1*1501, DRB1*1202 and DRB1*0803. Most of them were observed with higher frequencies in the AIDS patient group, although the differences were not significant. It has been reported that possession of certain common HLA alleles confers a disadvantage in regard to progression of AIDS (21–23). A possible reason for the association of these common HLA alleles with a more rapid onset of AIDS in HIV-1 infected individuals is frequency-dependent selection, in which a pathogen has evolved to escape an efficient immune response mediated by common alleles in the population, but remains susceptible to responses mediated by low-frequency alleles (11, 21). Therefore, HIV is more likely to adapt to the most common HLA types in a given population. However, we also observed that common alleles such as A*0201, B*4601, DRB1*0901 and the most common, A*0201-B*4601-DRB1*0901, haplotype of this population did not occur at greater frequencies. Even the most common HLA-A-B haplotype, A*0201-B*4601, occurred slightly less frequently in the AIDS patient group, the difference not being significant. Moreover, the frequency of common A*0201-B*4601-DRB1*1401 (1.86% vs. 2.69%) and A*1101-B*4601-DRB1*0901 (1.79% vs. 3.31%) haplotypes was less in AIDS patients. These observations suggest that common alleles of A*0201, B*4601, DRB1*0901 are not risk factors for the development of AIDS.
It has been reported that HLA class I homogeneity accelerates disease progression in HIV-1 infection (18, 25). Accordingly, homozygosity at class I loci can reduce the repertoire for such HLA-dependent interactions, leading to accelerated disease progression. The high population diversity in HLA alleles implies low frequencies of homozygosity in individuals. Complete absence of class I homozygosity would maximize the likelihood of receiving at least one of the less frequent, but more effective, alleles mediating a favorable CTL response. On the other hand, higher frequencies of class I homozygosity may reduce the CTL repertoire, and the effectiveness of the CTL response to the constantly evolving HIV-1 antigen profiles (11, 24). Our data suggest a significant association of HLA class I homozygosity with rapid progression to AIDS in the Chinese population of Chongqing.
The Bw4 and Bw6 serotype differ in their antigen recognition properties, resulting in differences in association with different viral epitopes presented, and in intensity of the cytotoxic T lymphocyte response. It had been reported that HLA-Bw4 homozygosity is associated with slow progression to AIDS and less likelihood of HIV-1 transmission in heterosexual couples (26, 27). Some HLA-Bw4 molecules serve as ligands for NK cell receptors. The interaction between the HLA-Bw4 epitope and the NK cell receptors induces elimination of HIV-1 infected cells by NK-mediated lysis (28, 29). In this study, homogeneous Bw6-Bw6 occurred significantly more often in the AIDS patient group than in the HIV-1 infected group. This association with accelerated disease progression had been confirmed in Chinese HIV-1 infected patients (30). In contrast, heterogeneous Bw4-Bw6 was underrepresented in the AIDS patients, implying that HLA-Bw4-Bw6 heterozygosity may be a protective factor in regard to progression of HIV-1 infection.
Differences were observed between AIDS patients and HIV-1 infected individuals in other host factors such as gender and age. There were more AIDS patients in the 50–59 age group and more female patients in the AIDS patient group than that in the HIV-1 infected group. Previous reports have shown that older age is associated with lower CD4+ counts at a similar time from seroconversion, which may explain the relationship between age and disease progression (31). In this study, older or female patients were subject to poorer disease outcomes of HIV-1 infection. However, binary logistic regression analyses also demonstrated the associations of the alleles and genotypes identified in this study were independent of these two host factors.
Our results not only revealed consistent HLA associations with AIDS progression, including increased susceptibility with B*3501 and some common haplotypes, HLA A or B and Bw6-Bw6 homozygosity, and a protective effect of the B*5801 allele and A*3303/1-B*5801 haplotype, but also suggested that the B*4801 allele and A*2402-B*4801 haplotype are unique disadvantageous factors. However, since the time since infection had occurred was unknown, it was difficult to estimate the duration of infection in each individual. Meanwhile, virus loads in the plasma were not determined in this study. Therefore, these two aspects restrict the application to other populations of conclusions from this study.
In summary, we observed the HLA profile of HIV-1 seropositive subjects from Chongqing, China, and identified differences between AIDS patients and HIV-1 infected individuals. Our study also suggests that HLA alleles and haplotypes may be associated with progression of HIV-1 infection to AIDS for the predominant HIV-1 CRF07_BC clade in China. These data are consistent with evidence that the progression of infectious disease is associated with host genetic factors, indicating that the HLA-mediated immune response determines the course of AIDS. Thus, our investigation of polymorphism in HLA alleles and haplotype analysis in HIV-1 seropositive individuals from Chongqing, China may provide further insight into other potential associations and linkages between protective/susceptible alleles, as well as the effect of whole haplotypes on anti-HIV-1 immunity, and finally, contribute to predicting rates of disease progression, the development of therapeutics, and future vaccine design for this Chinese population.