MUM1 expression in normal activated T cells. A 50-kd band of the expected molecular size of the MUM1 protein is seen in lanes (+) corresponding to PHA-stimulated peripheral blood T cells (at days 1, 3, and 4), whereas no band is observed in lanes (–) corresponding to T cells under basal conditions (Western blotting with the MUM1p monoclonal antibody). β-tubulin levels are shown below as control for the amount of the loaded protein.