Co-expression of CXCR4/fusin and galactosylceramide in the human intestinal epithelial cell line HT-29

Objective: To detect the expression CXCR4/fusin in human intestinal epithelial cells and to assess its potential role in the pathway of HIV-1 infection mediated by the alternative gp120 receptor galactosylceramide (CalCer). Methods: CalCer+ (HT-29, HT-29/CD4+) and GalCer-(Caco-2/Cl2, Cl14 and C114/CD4+) human intestinal cell lines were analysed for CXCR4/fusin expression using the monoclonal antibody (MAb) 12C5. This MAb was then evaluated for its ability to inhibit HIV-1 infection in permissive cells. HIV-1 infection was measured by detection of p24 antigen, polymerase chain reaction amplification, and cocultivation with CD4+ cells. Results: CXCR4/fusin was detected on the surface of HT-29 and HT-29/CD4+, but not on Caco-2/Cl2, C/14 and Cl74/CD4+ cells. Ninety per cent of CXCR4/fusin+ HT-29 and HT-29/Cd4+ cells co-expressed GalCer. Infection of HT-29 cells by laboratory isolates of HIV-l was inhibited by both anti-GalCer and anti-CXCR4/fusin MAbs. Expression of CD4 rendered HT-29 cells sensitive to HIV-1(89.6), a macrophage-tropic isolate that does not recognize GalCer. The 12G5 MAb blocked HIV-1 infection of HT-29/CD4+ cells. In contrast, the expression of HIV-1 receptors, i.e., CD4, CalCer or both, into CXCR4/fusin-negative intestinal cells did not confer sensitivity to HIV-1 infection. The resulting receptor-positive cell lines could, however, bind HIV-1, whereas the original cell lines could not. Conclusion: HIV-1 entry into human intestinal cells involves both GalCer and CXCR4/fusin. HIV-1 isolates such as 89.6 that are able to use CXCR4/fusin as coreceptor, but do not bind to CalCer, do not infect these cells. These data raise the possibility that CXCR4/fusin may function as a coreceptor for HIV-1 entry into CD4-/GalCer+ intestinal epithelial cells.