Incidence of HIV infection in monocyte subpopulations characterized by CD4 and HLA-DR surface density

The purpose of this study was to determine any correlation between the expression of CD4 antigen on the surface of monocytes, and the frequency with which these cells are infected with HIV. CD4 surface expression on monocytes is significantly less than that expressed on CD4+ lymphocytes. Nevertheless, all monocytes express the HIV CD4 receptor and infected individuals have a significant decrease in the number of monocytes that express a higher density of CD4 surface fluorescence. Three-color flow cytometric analysis was used to characterize monocyte-enriched peripheral blood mononuclear cells (PBMC) in terms of surface expression of CD4, CD14 (macrophage antigen), and class II major histocompatibility antigen (HLA-DR). HLA-DR+ monocytes from HIV-positive individuals were sorted into two subpopulations based on either 'bright' or 'dim' CD4 surface expression. A polymerase chain reaction (PCR) assay was used to detect the presence of proviral HIV sequences within the DNA from 10(5) cells from each sorted population. Post-sort analysis revealed that the dim CD4+ monocyte subset expressed dim HLA-DR surface antigen, while the bright CD4+ monocyte subset contained both bright and dim HLA-DR+ cells. PCR results showed that four out of eight dim CD4+ monocyte subsets contained proviral HIV DNA, compared with one out of eight bright CD4+ monocyte subsets.