ANTIGENIC SIMILARITIES BOTH INSIDE AND OUTSIDE THE CARBOHYDRATE-BINDING SITES OF TWO-CHAIN AND ONE-CHAIN LEGUMINOUS LECTINS

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Abstract
Antibodies were made against the 2-chain lectin Lath-O from the seeds of Lathyrus odoratus as well as its isolated L (.alpha.) and H (.beta.) chains. These antibodies were used to antigenically compare the Latho-O with other 2-chain lectins like Lath-S, lentil and Vicia cracca GLC specific and with 1-chain lectins like Con A [concanavalin A], PHA [phytohemagglutinin], peanut and soybean. Sensitive ELISA [enzyme-linked immunosorbent assay] tests showed that there was a distinct antigenic cross-reaction between the 1-chain and 2-chain lectins both by using antibodies against Lath-O whole molecules and its isolated .beta.-chains, while the anti-Lath-O .alpha.-chain antibodies barely reacted at all even with Latho-O .alpha.-chians. The antibodies aainst Lath-O whole molecules also strongly inhibited the mitogenic responses induced by 2-chain lectins. Antibodies reacting inside the carbohydrate-binding site of the lectins were isolated by eluting them with glucose from lectin-Sepharose columns and antibodies reacting outside the carbohydrate-binding site were subsequently eluted with guanidine or buffer with low pH. The 2 antibody fractions were separately used to antigenically compare 1-chain and 2-chain lectins, demonstrating that both kinds of antibodies showed cross-reaction between 1-chain and 2-chain lectins. Both the antibodies presumably reacting inside the carbohydrate-binding site of the lectins and those reacting outside the carbohydrate-binding site inhibited hemagglutination activity of 2-chain lectins, while hemagglutination by 1-chain lectins was unaffected. The carbohydrate-binding site specificity of the glucose-eluted antibodies was assessed by glucose-inhibition in ELISA tests. Galactose neither inhibited in these tests nor eluted antibodies from lectin-Sepharose columns. Control experiments were also performed with normal rabbit IgG.