(a) HeLa and HeLa-Lai cells were treated with the cell membrane insoluble DTSSP cross-linker. Proteins were purified on GN lectin columns by elution with increasing concentrations (from 0.25 to 1 M) of methyl α-D-mannopyranoside. Purified complexes heavier than 100 kDa were analysed by western blot. Env purification is evident in HeLa-Lai cells and not in control HeLa cells. HLA-C molecules, containing few mannoses, are eluted in the first fractions from HeLa cells, while they are co-purified in higher amounts in the presence of Env (HeLa-Lai). No differences in flotillin-1 purification, used as negative control, were detected. (b) Membrane protein complexes from HeLa and HeLa-Lai cells were immunoprecipitated with 2G12 (anti-Env), DT9 (anti-HLA-C) and a-β2m (anti-β2m) antibodies. Western blot analysis of immunoprecipitated samples shows that HLA-C is associated either with β2m or with Env. HLA-C and α/β-tubulin expression were detected as loading control.