Cycling Memory CD4+ T Cells in HIV Disease Have a Diverse T Cell Receptor Repertoire and a Phenotype Consistent with Bystander Activation

The mechanisms of increased memory CD4(+) T cell cycling in HIV disease are incompletely understood but have been linked to antigen stimulation, homeostatic signals, or exposure to microbial products and the inflammatory cytokines that they induce. We examined the phenotype and V beta family distribution in cycling memory CD4(+) T cells among 52 healthy and 59 HIV-positive (HIV+) donors. Cycling memory CD4(+) T cells were proportionally more frequent in subjects with HIV infection than in controls, more often expressed CD38 and PD-1, and less frequently expressed OX40 and intracellular CD40L. OX40 expression on memory CD4(+) T cells was induced in vitro by anti-CD3, interleukin-2 (IL-2), IL-7, or IL-15 but not by Toll-like receptor ligands. In HIV+ donors, memory CD4(+) T cell cycling was directly related to plasma lipopolysaccharide (LPS) levels, to plasma HIV RNA levels, and to memory CD8(+) T cell cycling and was inversely related to peripheral blood CD4(+) T cell counts but not to the levels of IL-2, IL-7, or IL-15, while in HIV-negative donors, memory CD4(+) T cell cycling was related to IL- 7 levels and negatively related to the plasma levels of LPS. In both controls and HIV+ donors, cycling memory CD4(+) T cells had a broad distribution of V beta families comparable to that of noncycling cells. Increased memory CD4(+) T cell cycling in HIV disease is reflective of generalized immune activation and not driven primarily by cognate peptide stimulation or exposure to common gamma-chain cytokines. This cycling may be a consequence of exposure to microbial products, to plasma viremia, or, otherwise, to proinflammatory cytokines.