Differential effect of plant lectins on mast cells of different origins

Histamine release induced by plant lectins was studied with emphasis on the carbohydrate specificity, external calcium requirement, metal binding sites, and mast cell heterogeneity and on the importance of antibodies bound to the mast cell membrane to the lectin effect. Peritoneal mast cells were obtained by direct lavage of the rat peritoneal cavity and guinea pig intestine and hamster cheek pouch mast cells were obtained by dispersion with collagenase type IA. Histamine release was induced with concanavalin A (Con A), lectins from Canavalia brasiliensis, mannose-specific Cymbosema roseum, Maackia amurensis, Parkia platycephala, Triticum vulgaris (WGA), and demetallized Con A and C. brasiliensis, using 1-300 æg/ml lectin concentrations applied to Wistar rat peritoneal mast cells, peaking on 26.9, 21.0, 29.1, 24.9, 17.2, 10.7, 19.9, and 41.5 percent, respectively. This effect was inhibited in the absence of extracellular calcium. The lectins were also active on hamster cheek pouch mast cells (except demetallized Con A) and on Rowett nude rat (animal free of immunoglobulins) peritoneal mast cells (except for mannose-specific C. roseum, P. platycephala and WGA). No effect was observed in guinea pig intestine mast cells. Glucose-saturated Con A and C. brasiliensis also released histamine from Wistar rat peritoneal mast cells. These results suggest that histamine release induced by lectins is influenced by the heterogeneity of mast cells and depends on extracellular calcium. The results also suggest that this histamine release might occur by alternative mechanisms, because the usual mechanism of lectins is related to their binding properties to metals from which depend the binding to sugars, which would be their sites to bind to immunoglobulins. In the present study, we show that the histamine release by lectins was also induced by demetallized lectins and by sugar-saturated lectins (which would avoid their binding to other sugars). Additionally, the lectins also released histamine from Rowett nude mast cells that are free of immunoglobulins.

Purification, physicochemical characterization and biological properties of a lectin from Erythrina velutina forma aurantiaca seeds

A lectin was purified from seeds of Erythrina velutina forma aurantiaca by affinity chromatography on cross-linked guargum. The lectin is a potent agglutinin for human (minimal concentration of protein able to cause visible agglutination of a 2 per cent erythrocyte suspension varying from 1 to 4 mug/ml), rabbit(4 mug/ml) and chicken erythrocytes (8 mug/ml) but presented low activity against cow (250 mug/ml) or sheep (333 mug/ml) blood cells. Hemagglutination of human O+ erythrocytes was inhibited by D-lactose (0.2 mM) > D-galactose(0.8 mM) > D-raffinose (2.1 mM). At pH 7.5, chromatography on a Superose 12 HR 10/30 column showed that the lectin was primarily a dimer (56.0 kDa) composed of two identical subunits (31.6 kDa each). A small amount of a tetrameric form was also apparently present. The lectin is a glycoprotein (7.3 per cent carbohydrate), has a pI of 4.5, contains high levels of acidic (Asp and Glu, 64.2 and 51.6 residues/mol, respectively) and hydroxy amino acids (Ser and Thr, 42.9 and 38.5 residues/mol, respectively) but relatively low amounts of sulfur amino acids (Cys and Met, 1.0 and 5.0 residues/mol, respectively) and has an N-terminal sequence of Val-Glu-Thr-Ile/Leu-Pro-Phe-Ser. Its hemagglutinating activity was abolished by heating at 70 degrees Celsius for 10 min. The activation energy (delta G') required for denaturation measured by loss of hemagglutination activity was 24.87 kcal/mol. In rats, the purified lectin (100 mug) induced neutrophil migration into the peritoneal cavity (3.7 ñ 0.6 x 10(6) neutrophils/ml) or into the air pouch (2.75 ñ 0.25 x 10(6) neutrophils/ml), 8 and 10 times greater than the negative control, respectively.