Natural serum haemagglutinins (lectins) in fish: physicochemical characterisation

Abstract

The present study describes natural haemagglutinins from common Indian fresh water catfish Clarias batrachus and Heteropneustes fossilis with special reference to their anti-erythrocyte and carbohydrate specificities and selected physicochemical properties. Five out of the nine species of teleosts studied possessed haemagglutinins in their sera against vertebrate erythrocytes. Serum haemagglutinins from Clarias batrachus and Heteropneustes fossilis agglutinated erythrocytes with ABH determinants, Lewis system as well as some other unknown epitope(s) on their surface. The haemagglutination reactions (HA) were calcium-ion-dependent and exhibited maximum activity at pH 8. High concentration of sodium chloride impaired HA reactions. The catfish haemagglutinins were 2-mercaptoethanol resistant but partially sensitive to heat. ABH and Lewis specificities of these two catfish species serum haemagglutinins are supported by inhibition studies with human ABH and Lewis secretor saliva and colostrum, and also by D-galactose and N-acetyl galactosamine. Furthermore, the haemagglutinins reacted with Bombay phenotype (Oh) erythrocytes and enzyme-treated amphibian and avian RBC, lacking ABH blood group determinants. The binding of catfish haemagglutinins to rabbit erythrocytes was strongly inhibited by melibiose, but not lactose, showing their specificity towards alpha-galactopyranoside residues. From the results of this study it is postulated that Indian catfish sera contain more than one haemagglutinin molecule (i.e. possess hetero or multiple agglutinins of a lectin-like nature.