HLA-DRB1 and HIV-1 infection: Although neither of them showed any difference between the HIV-1 positive and population control group, several 3-locus haplotypes containing B*4001G (B60) such as A*11-B*4001G-DRB1*15, A*02-B*4001G-DRB1*04 and A*02-B*4001G-DRB1*12, were significantly overrepresented in the HIV positive group than that in the population control group, suggesting this allele might be another risk factor of HIV-1 infection in Chongqing Han, in consistent with the observation that HLA-B*40 correlated with susceptibility to HIV-1 infection in South India [9].