Background: Progressive depletion of CD4⁺ and CD8⁺ T cells is a hallmark of HIV type 1 (HIV-1) infection. Viral envelope protein gp120/41 enhances the rate of apoptosis in CD4⁺ T cells. The HIV-1 env protein signals through the primary viral receptor, CD4, and its co-receptor, either CCR5 or CXCR4. In this study, we have elucidated the contribution of the CCR5 co-receptor to M-tropic (R5) envelope (env) mediated apoptosis in T cells.

Methods: T cell clones A201, A301 and A201.401 were transfected with CCR5 or empty vector. Resting primary human CD4 and CD8 T cells were isolated from healthy human donors. CD8⁺ primary lymphocytes were infected with vaccinia virus wild type (vv), with CD4 (vv: CD4), or with truncated CD4 (vv: CD4 TM). T-cell clones, primary cells and vv infected T cells were incubated with either MIP 1ß, anti-CCR5 antibodies (MAB183 or 2D7), soluble or membrane-bound R5 env with or without the caspase inhibitor Z-VAD.  Soluble CD4 (sCD4) was used to interfere with the interaction of env and CD4, and the decoy TAK779 to interfere with env and CCR5. Pyk2 activity was assayed using an immunoblot to detect tyrosine phosphorylation. FACS analysis was used to assess CCR5 expression in T cells. Cell death was analyzed by trypan blue dye exclusion and TUNEL assay.

Results: HIV gp120 in the presence of sCD4, as well as anti-CCR5 antibodies, induce Pyk2 phosphorylation through the CCR5 receptor in CD8⁺ T cells.  The HIV gp120 and anti-CCR5 antibodies also induce apoptosis in response to CCR5 stimulation in both CD4⁺ and CD8⁺ resting lymphocytes. R5env triggered apoptosis in T cell clones as well as in vv infected CD8⁺ lymphocytes through its interaction of the CCR5 co-receptor only in the presence of an inactive form of the CD4 receptor.

Conclusions:  HIV R5 env interaction with the CCR5 co-receptor induces apoptosis in T cells.  The CD4 receptor is necessary for the R5env-CCR5 interaction, but its function somehow inhibits the R5env mediated apoptosis.

Keywords: chemokines; apoptosis; ccr5