This project was designed to investigate the cellular and molecular pathways involved in the HIV regulatory effects of cytokines/chemokines, tissue-associated factors and HIV envelope proteins. We had previously demonstrated that pro-inflammatory cytokines (PIC) and certain C-C-chemokines acted cooperatively to enhance endogenous replication of X4 strains of HIV, whereas these factors acted antagonistically in determining the level of endogenous R5 HIV strain replication. Following previous in vitro observations that IL-2 is a potent inducer of PIC and CCR5 chemokines, as well as CCR5 expression, we have analyzed various parameters in peripheral blood mononuclear cells from HIV-infected individuals receiving IL-2 subcutaneously. We have demonstrated that in vivo IL-2 administration results in significant and sustained increases CCR5 chemokine RNA and protein levels, as well as in transient increases in the expression of CCR5 in the CD4+ T lymphocyte population. Of interest, despite IL-2-associated increases in CCR5 expression, the frequency of isolation of endogenous R5 HIV from PBMC of individuals receiving IL-2 was significantly lower than that from cells of matched HIV-infected subjects not undergoing IL-2 therapy. These data suggest that, in individuals harboring predominantly R5 strains of HIV, the ability of IL-2 to induce HIV-suppressive factors in vivo, particularly CCR5 chemokines, may override HIV-inductive effects of IL-2, such as upregulation of CCR5 expression and the production of PIC. Our studies of potential effects of chemokines on HIV replication are being expanded to include analysis of numerous C-C and CXC chemokines, as well as certain lymphoid tissue (LT)-associated factors, for their effects on HIV replication in CD4+ T cells. Preliminary results suggest that certain LT-associated chemokines, such as SDF and SLC, may stimulate post-entry HIV life cycle events, such as proviral integration. Furthermore, LT-associated extracellular matrix proteins, such as laminin, appear to enhance early HIV entry events. These findings demonstrate that numerous lymphoid tissue-associated host factors are capable of upregulating HIV production from infected CD4+ T cells. The ability of HIV envelope protein (gp160) to modulate HIV expression from cellular reservoirs of HIV, such as resting latently-infected CD4+ T cells isolated from HIV-infected subjects, was investigated. HIV gp160 was found to induce infectious HIV from resting CD4+ T cells and this effect was not associated with expression of cellular activation markers, progression through the cell cycle, interferon-gamma production or apoptosis. These data suggest that the latently HIV-infected resting CD4+ T cell reservoir may serve as a source of infectious HIV while maintaining its long-lived resting T cell phenotype. Finally, the relevance of CCR7, a chemokine receptor that plays an important role in homing of cells to T cell areas of LT and in mounting an appropriate immune response, in HIV pathogenesis is being investigated. We have found that HIV disease is associated with a reduced frequency of CCR7+ cells in both memory and naive T cell compartments. We have confirmed that CCR7+, but not CCR7-, memory CD4+ T cells differentially express the X4 HIV co-receptor, CXCR4, as compared to CCR5. In this regard, we have found that CCR7+ CD4+ T cells may be preferentially depleted in HIV-infected subjects harboring X4 HIV strains. The implications of CD4+ T cells homing to LT, the primary site of HIV replication, via expression of CCR7 and the differential expression of HIV coreceptors on CCR7+ cells are being further studied.
NIH ExPorter
NIH ExPorter