Use of the Lectin from Amarant hus cautiat us as a Histochemical Probe of Proliferating Colonie Epithelial Cells1

A newly isolated lectin, Amaranthus caudatus agglutinin (also called amaranthin or ACA), which binds to the Thomsen-Friedenreich antigen (T-antigen) and its sialylated variants, was used as a histochemical probe for proliferating cells in sections of human colonie tissues. Binding inhibition studies revealed that ACA binds to different sites on histolÃ3g ica! sections when compared to peanut agglutinin, which also recognizes the T-antigen. ACA bound selectively to the cells at the base of the colonie crypt [46 ±4% (SEM) of glands) which is the zone of proliferation in this tissue and preferentially labeled cytoplasmic and apical membrane glycoconjugates. Only 7 ±2% of the upper portions of the colonie crypts were labeled ( /' < 0.001 compared to the base), and this was largely a result of extensive labeling in 2 of 23 samples studies. A marked increase in histochemical labeling by ACA was seen in adenomatous polyps and adenocarcinomas of the colon, in which 82 ±7 and 97 ±2% of the glandular units were labeled, respectively. Transitional mucosa and con nective tissue adjacent to cancers were also labeled by ACA. Neuraminidase studies indicated that removal of sialic acid residues enhanced binding by peanut agglutinin, but not ACA, to glycoconjugates in cancer specimens. Specimens of colonie tissue from patients with familial ade nomatous polyposis (FAP) were examined with ACA; 83 ± 7% of adenomatous glands and 60 ±7% of glands in flat, normal-appearing tissue were labeled. Colonie tissues from persons at 50% risk for hered itary nonpolyposis colorectal cancer (HNPCC), FAP, and normal colons were studied and given "weighted average" labeling scores that ranged from 0-400 to accommodate variable intensity and distribution of label ing. Normal colons had a weighted average score of 65 ±33; FAP tissues had a score of 224 ±76 (P < 0.001 compared to normal colon) and HNPCC tissues had a score of 74 ±70 (P < 0.05 compared to normal colon). A group of five HNPCC cases had scores of 203 ±43 (P < 0.001 compared to normal colon). ACA labels glycoconjugates in the proliferative region of normal human colonie epithelium and neoplastic lesions of the colon. The results of FAP and HNPCC tissues suggest that it may be useful for identifying foci of abnormal proliferation in familial colo rectal cancer syndromes.