MONOCLONAL ANTIBODY-M3 USED IN TISSUE POLYPEPTIDE-SPECIFIC ANTIGEN-ASSAY FOR THE QUANTIFICATION OF TISSUE POLYPEPTIDE ANTIGEN RECOGNIZES KERATIN-18

Recently, a new 'specific tissue polypeptide antigen (TPA)' test was i ntroduced and designated tissue polypeptide-specific antigen (TPS); it is based on the monoclonal antibody (MAb) anti-TPS, M3. We have teste d the specificity of this antibody by immunocyto- and immunohistochemi stry, gel electrophoresis and immunoblotting. MAb M3 bound to intermed iate filaments of epithelial cells and revealed a staining pattern ide ntical to cytokeratin (CK) 18-specific MAb (DE-K18) on tissue sections of various human tissues. On immunoblots of proteins extracted from v arious epithelial cell lines, M3 reacted with a 45-kD protein correspo nding to CK18, and on immunoblots of proteins isolated from MCF-7 cult ure fluid M3 stained three bands, 45, 33 and 29 kD. The same bands wer e stained with CK18-specific MAb, indicating that they represent CK18 and its degradation products. TPA, used as a tumor marker in clinical diagnoses and follow-up, was shown to be a degradation product of CK 8 , 18 and 19. In contrast to TPA, MAb M3 did not stain CK8 and CK19 pre sent on immunoblots.