The mechanism behind the selective depletion of CD4+ cells in HIV infections remains undetermined. Although HIV selectively infects CD4+ cells, the relatively few infected cells in vivo cannot account for the extent of CD4+ T cell depletion suggesting indirect or bystander mechanisms. The role of virus replication, Env glycoprotein phenotype and immune activation (IA) in this bystander phenomenon remains controversial. Using samples derived from HIV-infected patients; we demonstrate that while IA in both CD4+ and CD8+ subsets correlates with CD4 decline, apoptosis in CD4+ and not CD8+ cells is associated with disease progression. As HIV-1 Env glycoprotein has been implicated in bystander apoptosis, we cloned full length Envs from plasma of viremic patients and tested their Apoptosis Inducing Potential (AIP). Interestingly, AIP of HIV-1 Env glycoproteins were found to correlate inversely with CD4:CD8 ratios suggesting a role of Env phenotype in disease progression. In vitro mitogenic stimulation of PBMCs resulted in upregulation of IA markers but failed to alter the CD4:CD8 ratio. However, co-culture of normal PBMCs with Env expressing cells resulted in selective CD4 loss that was significantly enhanced by IA. Our study demonstrates that AIP of HIV-1 Env and IA collectively determine CD4 loss in HIV infection.

CCR5 is the major co-receptor for HIV and polymorphisms in the CCR5 gene as well as promoter region that alter cell surface expression have been associated with disease progression. We determined the relationship between CCR5 promoter polymorphisms and CD4 decline and other immunopathological features like immune activation and CD4+ T cell apoptosis in HIV patients. CCR5 promoter haplotype HHC was significantly associated with higher CD4 counts in patients. The relative promoter activity (RPA) of each haplotype was determined in vitro and combined promoter activity based on both alleles (CRPA) was assigned to each patients. Interestingly, CCR5 CRPA correlated inversely with CD4 counts and CD4:CD8 ratio specifically in viremic patients. In normal individuals, the CRPA correlated with the number of CCR5+ CD4+ T cells in the peripheral blood suggesting an effect on CCR5 expression. In a subset of high viremic patients harboring R5 tropic HIV, there was a strong correlation between CCR5 CRPA and both CD4 counts and CD4 T cell apoptosis. Our study demonstrates that, CCR5 promoter polymorphisms correlate with CD4 T cell loss possibly by regulating CD4 T cell apoptosis in HIV patients. Furthermore, assigning CRPAs to each patient is a new method of translating genotype to phenotype.