Inflammatory Cytokines Drive CD4+ T-Cell Cycling and Impaired Responsiveness to Interleukin 7: Implications for Immune Failure in HIV Disease

Background. Systemic inflammation has been linked to a failure to normalize CD4(+) T-cell numbers in treated human immunodeficiency virus (HIV) infection. Although inflammatory cytokines such as interleukin 6 (IL-6) are predictors of disease progression in treated HIV infection, it is not clear how or whether inflammatory mediators contribute to immune restoration failure. Methods. We examined the in vitro effects of IL-6 and interleukin 1 beta (IL-1 beta) on peripheral blood T-cell cycling and CD127 surface expression. Results. The proinflammatory cytokine IL-1 beta induces cell cycling and turnover of memory CD4(+) T cells, and IL-6 can induce low-level cycling of naive T cells. Both IL-1 beta and IL-6 can decrease T-cell surface expression and RNA levels of CD127, the interleukin 7 receptor alpha chain (IL-7R alpha). Preexposure of healthy peripheral blood mononuclear cells (PBMCs) to IL-6 or IL-1 beta attenuates IL-7-induced Stat5 phosphorylation and induction of the prosurvival factor Bcl-2 and the gut homing integrin alpha 4 beta 7. We found elevated expression of IL-1 beta in the lymphoid tissues of patients with HIV infection that did not normalize with antiretroviral therapy. Conclusions. Induction of CD4(+) T-cell turnover and diminished T-cell responsiveness to IL-7 by IL-1 beta and IL-6 exposure may contribute to the lack of CD4(+) T-cell reconstitution in treated HIV-infected subjects.