CD4 and infection: In the present study we found a clear correlation between CD4-independent use of CCR5 and macrophage tropism, inasmuch all isolates productively infected macrophages and also infected cells expressing CCR5 but not CD4 as shown by cocultivation of infected NP-2/CCR5 cells with hPBMC, infection of hPBMC with lysates and supernatants from infected NP-2/CCR5 cells.