Immune activation is associated with CD8 T cell interleukin-21 production in HIV-1-infected individuals.

Interleukin-21 (IL-21) can be produced by CD8 T cells from HIV-1-infected individuals and those with autoimmune disease, but the mechanism remains poorly understood. Here we demonstrate that IL-21-producing CD8 T cells are not associated with CD4 depletion and are absent in patients with idiopathic CD4 lymphocytopenia. Instead, IL-21 production by CD8 T cells was associated with high levels of activation, suggesting that these cells emerge as a consequence of excessive chronic immune activation rather than CD4 lymphopenia.