Indeed, early studies using an allogeneic stimulation model implicated MHC-II expressed by IFNγ-treated ECs in enhancement of HIV infection of resting CD4+ T cells,18,19 and α4β7 has been shown to provide costimulation to TCR-activated CD4+ T cells when engaged by MAdCAM-1, thereby promoting productive HIV replication in vitro. Here, CD4 is linked to HIV infectious disease.