Western blotting reactivity of monoclonal anti-NPM antibodies. (A) Wild-type NPM (38 kD) is detected in lysates of both normal cells (tonsil) and of the t(2;5)-positive cell line SU-DHL-1 with each of the three antibodies. However, only the two antibodies to the N-terminal region (NA24 and NPMa) react with the hybrid NPM-ALK protein (80 kD). (B) The two antibodies to the N-terminal region (NA24 and NPMa) detect recombinant NPM-ALK and also recombinant NPM-MLF1 and NPM-RAR proteins. Antibody NPMc (against the C-terminal region) is unreactive with any of these fusion proteins.