CD4 and infection: Recently, our study on differential infection of cultured peripheral and CNS cells by distinct T/F HIV-1 infectious molecular clones (IMC) revealed that T/F variants in AHI show different efficiencies of replication in CNS cells (microglia and astrocytes) compared to peripheral cells (CD4+ cells and macrophages) in vitro and that p24 production by these variants is differentially influenced by TNFα [42].