Western blot analysis of OX40. OX40-expressing CEM cells (CEM/OX40), in vitro activated PBMCs and MT-2 cells were cell-surface labeled with biotin, lysed and immunoprecipitated with anti-OX40 (B-7B5). The precipitates were subjected to 10% PAGE and blotted onto nitrocellulose sheets. The sheets were then probed with HRP-labeled anti-HIV-1 p24 (as a control), anti-OX40 (B-7B5) or streptavidin. Mol. Wt. markers are shown on the right. Data shown are representative of 3 independent experiments.