CXCR4 and infection: To investigate whether the increased stability of the CD4 complex with gp140 contributes to infection with HIV, we compared the effects of cis-expression of DC-SIGN on in vitro infection with HIV-1 IIIB and HIV-1 IIIBx, a variant of IIIB that can bind directly to CXCR4 without CD4 [26], [37].