SURFACE CD4 IS CRITICAL TO IN-VITRO HIV-INFECTION OF HUMAN ALVEOLAR MACROPHAGES

The CD4 glycoprotein is the major cellular receptor for HIV. CD4 surfa ce expression of monocytes decreases with time in culture while their susceptibility to HIV-1 increases. Our aim was to investigate whether this phenomenon occurs in macrophages that have differentiated in vivo by investigating CD4 expression and HIV-1 infection of human alveolar macrophages (AMs). Using flow cytometry to detect CD4 expression by L eu-3a labeled indirectly with fluorescein isothiocyanate or allophycoc yanin, we found that CD4 was expressed at low but detectable levels, d espite the high background autofluorescence well described in AMs, Thi s finding was supported by the detection of CD4 mRNA in AMs using RT-P CR, T cell contamination of mRNA extracts of AMs was excluded by ampli fying in parallel with primers to the constant region of the T cell re ceptor, Despite this low level of surface CD4, recomibinant soluble CD 4 and anti-CD4 antibody completely inhibited HIV-1 infection of AMs. W e conclude that CD4, although expressed at low levels on the surface o f AMs, appears to be critical to HIV-1 infection of these cells.