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 µg/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%, 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.
Sementes de Dioclea rostrata Benth. Têm uma lectina que é melhor extraída em tampão acetato de sódio a pH 4,0 e é seletivamente adsorvida em Sephadex G-50, apresentando um alto título de hemaglutinação contra eritrócitos de coelho. A lectina também aglutina inespecificamente hemácias de carneiro e humanas. A atividade hemaglutinante é inibida por glicose, frutose, manose e alfa-metil-D-manosídeo, sendo os dois últimos os mais potentes inibidores. A lectina é uma metaloproteína, uma vez que a atividade hemaglutinamente desaparece na presença de EDTA.
Seeds of Dioclea rostrata Benth. Have a lectin which is best extracted with Na-acetate buffer at pH 4.0 and that is selectively adsorbed in a Sephadex G-50 matrix, yielding a protein fraction of high hemagg lutinating titre against rabbit erythrocytes. It also agglutinates sheep, and human cells inespecifically. Its hemagglutinating activity is inhibited by glucose fructose, mannose and O-methyl-D-mannopyranoside the latter two being the most active inhibitors. The lectin seems to be a metaloprotein since the hemagglutinating activity is lost in the presence of EDTA.
Sementes de Parkia platycephala Benth.possuem uma lectina que é melhor extraída a pH 4,0 e pode ser isolada por cromatografia de afinidade em coluna de Sephadex G-50. A lectina aglutina eritrócitos de coelho mas não aglutina hemácias humanas (A, B e O), de boi, de carneiro ou de galinha. D-glicose, D-manose, D-frutose e derivados mostraram ser açúcares inibidores da atividade hemaglutinante, sendo que alfa-metil-glicosídeo e alfa-metil-manosídeo foram os mais potentes inibidores entre os açúcares testados.
Seeds of Parkia platycephala Benth. have a lectin which is best extracted at pH 4,0 and partially purified using a Sephadex G-50 column as an affinity adsorbent. The lectin .agglutinates rabbit erythrocytes but not those of cow, sheep, chicken or human D-glucose, D-mannose, D-fructose and derivatives act as inhibitors of the lectin with o-methyl-glucopyranoside and O-methyl-mannopyranoside being the most potent ones.