MAGE-C1 (CT7) specifically interacts with NY-ESO-1. (A) Endogenous CT7-NY-ESO-1 complexes were immunoprecipitated from SK-MEL-37 cell lysates with two anti-NY-ESO-1 antibodies (E-978 and NY-41). Both proteins were detected with anti-NY-ESO-1 and anti-CT7 antibodies. Precipitation with anti-actin antibody served as a negative control. (B) Endogenous CT7-NY-ESO-1 complexes were immunoprecipitated from U266 cell lysates with an anti-NY-ESO-1 antibody (NY-41) and also with anti-CT7 antibody (CT7.33) after longer exposure (lower panel). Both proteins were detected with anti-NY-ESO-1 and anti-CT7 antibodies. Precipitation with anti-influenza hemagglutinin antibody (HA) served as a negative control. (C) CT7 could not be immunoprecipitated from SK-MEL-10 cell lysates using anti-NY-ESO-1 antibodies (E-978 and NY-41). The sizes of the proteins detected are indicated on the right. Abbreviations: ACT, actin negative control; WCL, whole cell extract.