CD4 and infection: By using complementary biochemical and physicochemical approaches, the present study shows that, in addition to GalCer, the envelope glycoproteins of HIV-1 gp160, HIV-2 gp140, and SIV gp140 also interact with GlcCer, LacCer, and ceramide, ubiquitous glycolipids/lipids that could play an important role as receptors of attachment to promote the concentration of HIV-1, thus facilitating infection in a CD4-dependent or even CD4-independent manner, or promoting interaction with other receptors leading to activation of signaling pathways or pathogenesis.