Monocyte-mediated T cell suppression by HIV-2 envelope proteins

© 2007 WILEY-VCH Verlag GmbH & Co. KGaA, WeinheimHIV-2 is associated with an attenuated form of HIV disease. We investigate here the immunosuppressive effects of the HIV-2 envelope protein, gp105. We found that gp105 suppresses activation of T cells through a monocyte-mediated mechanism. Suppression of T cell activation by gp105 depends on contact between monocytes and T cells, but not on CD4+CD25+ T cells. The TLR4 pathway is likely involved, since gp105 activates TLR4 signaling and induces TNF-α production by monocytes. Immunosuppression is viewed as the main pathophysiologic consequence of infection by HIV. However, the main immunologic defect caused by HIV, depletion of T cells, requires T cell activation. Our findings are consistent with a new concept that HIV-2 envelope proteins act on monocytes to suppress T cell activation and that this property may contribute to the benign course of HIV-2. We hypothesize that the HIV-2 envelope immunosuppressive properties limit bursts of T cell activation, thus reducing viremia and contributing to the slow rate of disease progression that characterizes HIV-2 disease.NIBSC Centralized Facility for AIDS Reagents supported by EU Programme EVA (contract QLK2-CT-1999–00609) and the UK Medical Research Council for providing recombinant HIV-1 gp120IIIB and HIV-2 gp105ROD; and the Portuguese Institute of Blood for providing the buffy coats. This work was supported by grants from “Funda ção para a Ciência e a Tecnologia” (FCT) and “Comissão Nacional de Luta Contra a SIDA” (PSIDA/ESP/49655/2003 to A. E. S.). R. C. received a scholarship from FCT