Purification and characterization of a novel immunomodulatory lectin from Artocarpus hypargyreus Hance

Lectins are proteins/glycoproteins of non-immune origin, which interact specifically and non-covalently with the carbohydrate moieties of respective receptors on the cell surface. In this study, a novel 65.2-kDa tetrameric lectin (AHL) was purified from Artocarpus hypargyreus Hance (A. hypargyreus) by affinity chromatography on a galactose-sepharose column. It is a glycoprotein with carbohydrate content of 6.91%. Its maximum haemagglutinating activity was maintained after incubation at a temperature range of 20-40 °C and pH range of 5.0-9.0. AHL-induced haemagglutination of erythrocytes was inhibited strongly by carbohydrates, such as methyl-galactose, methyl-mannose, and N-acetyl-d-galactosamine, indicating the existence of more than one carbohydrate binding sites in the AHL molecule. The AHL activity was gradually lost in the presence of urea and completely lost when being treated with ethylenediaminetetraacetic acid (EDTA). The immunomodulatory activity of AHL was assessed using human peripheral lymphocytes and rat peritoneal macrophages. AHL triggered proliferation and activation of human T lymphocytes and induced the release of Th1 cytokines, including IFN-γ, TNF-α and IL-6. Furthermore, AHL significantly stimulated the production of nitric oxide (NO) and pro-inflammatory cytokines, including TNF-α and IL-12, in rat peritoneal macrophages. However, AHL did not enhance proliferation of B cell-enriched rat splenocytes. Taken together, in this study, a novel immunomodulatory lectin was purified from A. hypargyreus and was found to be capable of inducing a Th1-type immune response, and thus, it may have potential immunoregulatory application in response to infections, immune diseases and cancer.