CD4 and HIV-1 infection: In conclusion, our data support a mechanism whereby MPA, at concentrations found in serum of DMPA-IM users, unlike NET, directly increases R5 but not X4 HIV-1 replication in CD4+ T cells via increasing expression of CD4 and CCR5 co-receptors on T cells and activation of monocytes, to increase HIV-1 infection in cervical tissue.