EFFECTS OF CCR5 AND CD4 CELL-SURFACE CONCENTRATIONS ON INFECTIONS BY MACROPHAGETROPIC ISOLATES OF HUMAN-IMMUNODEFICIENCY-VIRUS TYPE-1

It has been proposed that changes in cell surface concentrations of co receptors may control infections by human immunodeficiency virus type 1 (HIV-1), but the mechanisms of coreceptor function and the concentra tion dependencies of their activities are unknown. To study these issu es and to generate stable clones of adherent cells able to efficiently titer diverse isolates of HIV-1, we generated two panels of HeLa-CD4/ CCR5 cells in which individual clones express either large or small qu antities of CD 1 and distinct amounts of CCR5. The panels were made by transducing parental HeLa-CD4 cells with the retroviral vector SFF-CC R5. Derivative clones expressed a wide range of CCR5 quantities which were between 7.0 x 10(2) and 1.3 x 10(5) molecules/cell as measured by binding antibodies specific for CCR5 and the chemokine [I-125]MIP1 be ta. CCR5 was mobile in the membranes, as indicated by antibody-induced patching. In cells with a large amount of CD4, an unexpectedly low tr ace of CCR5 (between 7 x 10(2) and 2.0 x 10(3) molecules/cell) was suf ficient for maximal susceptibility to all tested HN-1, including prima ry patient macrophagetropic and T-cell-tropic isolates. Indeed, the ti ters as indicated by immunoperoxidase staining of infected foci were a s high as the tissue culture infectious doses measured in human periph eral blood mononuclear cells. In contrast, cells with a small amount o f CD4 required a much larger quantity of CCR5 for maximal infection by macrophagetropic HIV-1 (ca. 1.0 x 10(4) to 2.0 x 10(4) molecules/cell ). Cells that expressed low and high amounts of CD4 were infected with equal efficiencies when CCR5 concentrations were above threshold leve ls for maximal infection. Our results suggest that the concentrations of CD4 and CCR5 required for efficient infections by macrophagetropic HIV-I are interdependent and that the requirements for each are increa sed when the other component is present in a limiting amount. We concl ude that CD4 and CCR5 directly or indirectly interact in a concentrati on-dependent manner within a pathway that is essential for infection b y macrophagetropic HIV-1. In addition, our results suggest that multiv alent virus-receptor bonds and diffusion in the membrane contribute to HIV-1 infections.