Lectin inhibits antigen-antibody reaction in a glycoform-specific manner: Application for detecting α2,6sialylated-carcinoembryonic antigen

Carcinoembryonic antigen (CEA) is a glycoprotein marker, which is widely used for diagnosing various cancers, especially colon adenocarcinoma. In addition, CEA mediates homotypic adhesion of colon adenocarcinoma cells, which appears to favor hematogenous metastasis. CEA carries 2,6sialyl residues on its N-glycans whereas a normal counterpart, normal fecal antigen-2, does 2,3sialyl residues, suggesting that cancer-specific 2,6sialylation on CEA may play a role for cell invasion and metastasis. A simple and rapid estimation of 2,6sialyled CEA in detergent extracts from formalin-fixed colon adenocarcinoma by lectin inhibition is reported. In the lectin inhibition method, Sambucus sieboldiana Agglutinin (SSA) lectin, an 2,6sialic acid binder, was used as a glycoform-specific inhibitor for antigen-antibody reaction in ELISA. Detergent extracts from colon adenocarcinoma showed a fair amount of ELISA signal in the absence of SSA whereas the signal was markedly reduced (45 approximate to 74%) in the presence of SSA, suggesting that the extracts contains 2,6sialyled CEA. The presence of 2,6sialyled CEA in the extracts was confirmed by lectin microarray, in which SSA, Sambucus nigra agglutinin, and Trichosanthes japonica agglutinin I lectins were used as 2,6sialyl binders. Thus lectin inhibition is a simple and rapid method for detecting 2,6sialyled CEA even in crude detergent extracts from formalin-fixed adenocarcinoma tissue.