Presence of OX40/4-1BB complex in cell lysate of PBL T-cell blasts. Total T cells were stimulated with anti-CD3 Ab (OKT3; 1 μg/mL) and anti-CD28 Ab (1 μg/mL) for 3 days. One percent NP-40 cell extracts were immunoprecipitated with anti-OX40 Ab or anti-4-1BB Ab, then analyzed by OX40-specific or 4-1BB-specific Western blotting in a reduced condition. Immunoprecipitation Abs or control Ab is indicated on the top of each panel. H indicates the position of immunoglobulin heavy chain; L, position of immunoglobulin light chain. The arrow in the top panel indicates the position of OX40 and the arrow in the bottom panel indicates the position of 4-1BB.