Intestinal and systemic immune responses in rats to dietary lectins

Structure-function and application of plant lectins in disease biology and immunity

Lectins are proteins with a high degree of stereospecificity to recognize various sugar structures and form reversible linkages upon interaction with glyco-conjugate complexes. These are abundantly found in plants, animals and many other species and are known to agglutinate various blood groups of erythrocytes. Further, due to the unique carbohydrate recognition property, lectins have been extensively used in many biological functions that make use of protein-carbohydrate recognition like detection, isolation and characterization of glycoconjugates, histochemistry of cells and tissues, tumor cell recognition and many more. In this review, we have summarized the immunomodulatory effects of plant lectins and their effects against diseases, including antimicrobial action. We found that many plant lectins mediate its microbicidal activity by triggering host immune responses that result in the release of several cytokines followed by activation of effector mechanism. Moreover, certain lectins also enhance the phagocytic activity of macrophages during microbial infections. Lectins along with heat killed microbes can act as vaccine to provide long term protection from deadly microbes. Hence, lectin based therapy can be used as a better substitute to fight microbial diseases efficiently in future.

Natural human antibodies to dietary lectins

Natural antibodies to self and non-self proteins, including dietary proteins, are a significant part of the immune repertoire of humans. Antibodies to three structurally related legume lectins (Erythrina corallodendron lectin (ECorL), peanut agglutinin (PNA), and soybean agglutinin (SBA)) and to one cereal lectin (wheat germ agglutinin (WGA)) were purified by affinity chromatography from human sera and their binding specificity examined. The anti-SBA, anti-ECorL and anti-WGA antibodies exhibited high specificity, whereas the anti-PNA antibodies were polyreactive. Although the anti-WGA antibodies were highly specific for WGA, they also crossreacted slightly toward some other proteins. The anti-ECorL antibodies bound to native SBA, but the anti-SBA antibodies failed to bind to the native ECorL. Although the anti-SBA and anti-ECorL antibodies both exhibited specificity when interacting with native lectins, they bound to a wider range of denatured lectins, indicating a common or universal epitope which is recognized by many natural antibodies. Interestingly, the natural antibodies did not interfere with the agglutination properties of the lectins. These findings may provide a basis for studying the in vivo biological effects of anti-dietary protein antibodies, including those against carbohydrate-binding proteins.