No differences in cellular immune responses between asymptomatic HIV type 1-and type 2-infected Gambian patients

Fewer people infected with human immunodeficiency virus (HIV) type 2 progress to acquired immunodeficiency syndrome, compared with those infected with HIV-1. To understand the immune mechanisms leading to slow progression in HIV-2 infection, cell-mediated immune responses were compared between the 2 infections in asymptomatic subjects with a CD4 cell count greater than or equal to20%. Interferon-gamma release from T lymphocytes and the cytotoxicity of CD8(+) T lymphocytes were measured by ELISPOT and Cr-51 release assays. The level of responses and the proportion of responders were similar in the 2 infections, despite a 20-fold difference in their geometric mean plasma virus loads. The proliferation of CD4(+) T helper cells, which was evaluated by thymidine incorporation, was not different between the 2 infections. Contrary to widely held views, our results suggest that nonprogression in HIV-2 infection may not be due to more vigorous immune responses.