Supernatant obtained from an ex vivo culture of healthy human colonic mucosa was used to condition monocyte-derived DC in an in vitro model as to mimic the exposure of DC to intestinal microenvironment. Conditioned–DC (C-DC) were analyzed by flow cytometry for the expression of HIV-1 receptors and activation markers, and incubated in vitro with either R5 or X4 HIV-1 to study their susceptibility to infection.
C-DC displayed an activated phenotype, a significant down-regulation of CCR5 and CD4 an up-regulation of CXCR4 and a moderate modulation of DC-SIGN expression compared to unconditioned DC. Interestingly, both R5 and X4 HIV-1 integrated their genome and replicated less efficiently in C-DC compared to unconditioned DC. Colonic supernatants contained the CCR5-binding chemokines Mip1b and MCP-1 whereas the CXCR4 ligand SDF-1a was absent. IL-10 and IL-2, described to induce CXCR4 up-regulation on DC, were also detected. This specific intestinal milieu may partially explain the observed phenotype. Interestingly, the CDK inhibitor p21Cip1/WAF1, described to restrict HIV replication in human macrophages, is induced upon conditioning at both transcriptional and protein level.
Our results point to a role of p21Cip1/WAF1 as an inhibitory factor of HIV-1 infection in intestinal DCs.