Coreceptor Dependent Signaling in Individual Primary Resting CD4+ T-cells Mediated by Low Levels of HIV Binding

Abstract

In order to enter into the target cell, HIV requires functional contact with CD4 and CCR5 or CXCR4. The last two are G-protein coupled receptors that when activated with chemokines, or HIV envelope can initiate a wide range of biological responses, including Ca2+ mobilization, cytoskeletal rearrangements and cell migration. To determine the specificity of X4-tropic gp120-mediated signaling through CXCR4, we have chosen a microscopybased approach to observe the response at the level of individual cells providing greater sensitivity. Target cells were able to activate a signaling cascade in response to both monomeric recombinant gp120 and virion-bound trimeric gp120. C2+ elevation was a direct measurement of CXCR4 engagement because it was dependent on the tropism of the envelope, engagement of CD4, and sensitive to the CXCR4 antagonist AMD-3100. Signaling required much lower levels of envelope when virion associated. Imaging analysis allowed the correlation of the pattern of virion-mediated C2+ fluxing with the exact number of viral particles bound to cells. This analysis revealed that an average of four virions, and as few as two virions associating with a primary resting T cell could mediate C2+ mobilization. The ability of several virions to stimulate signaling in primary resting T cells is physiologically relevant and has important implications for AIDS pathogenesis. Funded in part by DHHS NO1-CO-12400 and RO1AI052051. from 2005 International Meeting of The Institute of Human Virology Baltimore, USA, 29 August – 2 September 2005