HIV-1 Gag proteins form intracellular complexes with endogenous CD81 and CD82 tetraspanins. Cell lysates from MOLT/HIV-1 cells were immunoprecipitated with antibodies directed against CD81, CD63 and CD82 or a control antibody. Non-immunoprecipitated (supernatants) or immunoprecipitated (IP) proteins were resolved by SDS-PAGE and blotted with an anti-HIV-1 human serum or an anti-CD82 antibody as indicated. The positions of Gag products and CD82 are indicated. The anti-CD82 blot shows the integrity of the tetraspanin web. The anti-HIV-1 blot shows intracellular Gag-tetraspanin interactions.