Human immunodeficiency virus (HIV) type 2 infection is associated with a better clinical outcome, slower rates of CD4 T cell decline, and lower viremia than is HIV-1. This study compares HIV-1 and HIV-2 in regard to the percentages of interleukin (IL)-2-, interferon (IFN)-gamma-, and IL-4-producing cells at the single-cell level, as determined by flow cytometry. At a given degree of CD4 T cell depletion, the frequency of T cells able to produce IL-2 is better preserved in HIV-2 than in HIV-1 infection, particularly within the CD4 T cell subset. As described for HIV-1 immunodeficiency, HIV-2-positive patients exhibit a marked expansion of terminally differentiated effector CD8 T cells (CD28(-)CD27(-)IFN-gamma(+)). However, the proportion of CD8 T cells able to simultaneously produce IL-2 and IFN-gamma is higher in HIV-2 disease. Considering the central role of IL-2 as a lymphocyte proliferative and survival factor, these findings provide a possible immunologic basis for the distinct course of HIV-2 immunodeficiency.

The immunosuppressive properties of the HIV envelope proteins could be beneficial rather than detrimental to the host by interfering with the heightened state of immunocellular activation that characterizes HIV infection and by limiting the bursts of viral replication. This hypothesis could in part explain the slower decline of CD4 cell numbers in HIV-2 infection and deserves further exploration.

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