T cell interleukin-15 surface expression in chimpanzees infected with human immunodeficiency virus

Interleukin-15 (IL-15) contributes to natural killer cell development and immune regulation. However, IL-15 and interferon-gamma (IFN-γ) production are significantly reduced during progression to AIDS. We have previously reported that HIV infected chimpanzees (Pan troglodytes) express CD3−CD8+ IFN-γ+ natural killer (NK) cells with an inverse correlation to plasma HIV viral load. To expand on our initial study, we examined a larger population of HIV infected chimpanzees (n = 10). Whole blood flow cytometry analyses showed that recombinant gp120 (rgp120) or recombinant IL-15 induces specific CD3−CD8+ IFN-γ+ NK cells at higher levels than CD3+CD8+ IFN-γ+ T cells in HIV infected specimens. Interestingly, peripheral blood T cells exhibited 0.5–3% IL-15 surface Tcell/NKT cell phenotypes, and rIL-15 stimulation significantly (P < 0.007) up-regulated CD4+CD25+ T cell expression. Importantly, these data demonstrate novel T cell interleukin-15 expression and indicate a plausible regulatory mechanism for this cell-type during viral infection.