Endogenous alpha2M-peptide complexes are immunogenic. alpha2M was purified from the sera of male C57BL/6 mice as described. Syngeneic female mice were immunized twice with 7 µg of protein or PBS. Spleens were removed from immunized mice and cytotoxic assays were performed after two restimulations against male (filled squares) and female (open squares) target cells.