HUMAN COLORECTAL CARCINOMA-SPECIFIC GLYCOCONJUGATES DETECTED BY POKEWEED MITOGEN LECTIN

Pokeweed mitogen (PWM) lectin, known to bind branched poly-N-acetyllac tosamines, has a highly selective affinity for human colorectal carcin omas. We performed light microscopic (LM) histochemistry with PWM lect in on paraffin sections of human colorectal tissues. In histological s ections, normal mucosae and adenomas with mild dysplasia exhibited neg ative reaction (0/10, 0/13, respectively) with of without neuraminidas e pre-digestion, whereas adenomas with moderate dysplasia showed a sma ll increase in PWM lectin reactivity after neuraminidase digestion (41 23). In contrast, we observed a high incidence of positive reactivity in colorectal carcinoma without neuraminidase pre-digestion (38/44). A fter digestion with neuraminidase, there was increased reactivity of c olorectal carcinomas in situ (7/12) and invasive carcinomas (13/32). T hese results imply that human colorectal carcinomas consistently conta in substantial amounts of PWM-reactive branched poly-N-acetyllactosami ne glycoconjugates structures. We also compared the staining patterns of PWM lectin and monoclonal antibodies (MAb) directed to Lewis X (Le( X)) or Lewis Y (Le(Y)) antigen. PWM lectin reactivity was largely conf ined to the apical membranes of carcinoma tissues. MAb-Le(X) or MAb-Le (Y) immunoreactivity was seen on the apical membranes and in the cytop lasm of both adenomas and carcinomas. Therefore, histochemical studies with this lectin should be useful for identification of carcinoma tis sues and analysis of glycoconjugates associated with colorectal carcin oma.