Abstract

Lectins from Canavalia ensiformis (CEL) have agglutinin effect and anti-leukemic function, however, the immunomodulatory activity of CEL in regulating immune-network remains unclear. The present study clarified CEL effect on modulating the cross-reaction between monocytes and lymphocytes. The hemagglutination activity of CEL was heat-inactive and CEL at low concentrations showed no cytotoxicity to human leukemic U937 cells. However, CEL stimulated mononuclear cells (MNCs), isolated from peripheral blood, to secrete cytokines, such as TNF-a and IL-1b effectively inhibited cell growth and induced monocyte-differentiation of U937 cells. Monocytes contained in CEL-treated MNCs significantly increased the percent of macrophage morphology, formazan-positive cells, and phagocytic activity. The conditioned medium (CM) collected from CEL-treated monocytes (CEL-Mo-CM) markedly increased the viability of both monocytes, while CM from CEL-treated lymphocytes (CEL-Lym-CM) did not have this effect. The activated lymphocytes secreted IFN-g and then induced macrophage differentiation and CD40 expression through cell-to-cell interaction. Conclusively, CEL directly stimulated monocytes to produced cytokines, which may had autocrine and/or paracrine effects to activate the cross-regulation between monocytes and lymphocytes, result in inducing macrophage differentiation and may cause anti-leukemic immunity against U937 cells.

Key words: Lectins, Canavalia ensiformis, macrophage differentiation, anti-leukemic immunity.