Down-regulation of CXCR-4 and CCR-5 expression by interferon-γis associated with inhibition of chemotaxis and human immunodeficiency virus (HIV) replication but not HIV entry into human monocytes

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Abstract
Alterations in the expression of CXCR4 and CCR5, the co‐receptors for HIV entry, may be associated with susceptibility of monocytic cells to HIV infection. Interferon (IFN)‐γ has been shown to inhibit HIV replication in monocytic cells, but the molecular mechanism involved is not well understood. To determine if IFN‐γ regulates HIV replication by altering CXCR‐4/CCR‐5 expression and hence virus entry into monocytic cells, we investigated the effects of IFN‐γ on CXCR‐4 and CCR‐5 expression and its biological implications with respect to HIV entry, replication and chemotaxis towards the CXCR‐4 and CCR‐5 ligands SDF‐1 and MIP‐1α, respectively. IFN‐γ decreased CXCR‐4 and CCR‐5 expression on monocytes derived from HIV‐negative adults, HIV‐positive adults and HIV‐negative cord blood. This down‐regulation of chemokine receptor expression did not result in a corresponding change in mRNA expression but was associated with elevated levels of the endogenously produced chemokines SDF‐1 and RANTES. Furthermore, IFN‐γ inhibited chemotaxis in response to SDF‐1 and MIP‐1α, inhibited HIV replication, but failed to inhibit virus entry in monocytic cells. These results suggest that although IFN‐γ‐induced down‐regulation of CXCR‐4 and CCR‐5 expression is associated with an inhibition of SDF‐1‐/MIP‐1α‐mediated chemotaxis, IFN‐γ‐induced inhibition of HIV replication may be mediated at levels subsequent to the virus entry.