The galactose-binding lectin from Vatairea macrocarpa seeds induces in vivo neutrophil migration by indirect mechanism

Abstract

To explore the pathways by which lectins induce an inflammatory response, the lectin from Vatairea macrocarpa (VML) seeds was used to induce neutrophil migration in rats. The lectin was shown to cause cell migration, with the effect partially blocked when galactose was added to inhibit lectin activity. Neutrophil migration was also reduced when peritoneal cavity of the animals was depleted of their resident cells beforehand, suggesting that neutrophil migration was mediated by an indirect mechanism. Pre-treatment of rats with thioglycollate increased recruitment of neutrophils while depletion of mast cells by the addition of compound 48/80 had little effect on neutrophil infiltration, suggesting the involvement of macrophages in the inflammatory process induced by the lectin. Inhibition of the cyclooxigenase, leukotriene and PAF activities by indomethacin, MK886 and BN50730, respectively, did not modify the pro-inflammatory effect previously observed. However, dexamethasone and thalidomide significantly reduced the population of neutrophils in the peritoneal cavity after lectin injection. The present study suggests that the effects produced by a galactose-binding lectin do not involve lipoxygenase, cyclooxygenase or PAF mediators that are well known to be involved in the inflammatory process. The blocking actions of dexamethasone and thalidimide suggest that as yet unidentified pro-inflammatory mediators are involved.

Introduction

Lectins are ubiquitous (glyco)proteins, which exhibit specific and reversible carbohydrate-binding activities (Peumans & van Damme, 1995). These proteins combine, reversibly and non-covalently, with mono- or oligosaccharides free in solution or attached to cell surfaces. The functional roles of lectins have been investigated, and in animals, many of them seem to participate in important immune and physiopathological events (Kottgen et al., 1992, Tedder et al., 1995). Adhesion to the endothelium is a prerequisite for the movement of leukocytes from blood into tissues, a characteristic feature of inflammation (Colditz, 1985). Cell-specific carbohydrate recognition by membrane lectins has been shown to mediate, at least in part, the adhesion to vascular endothelial cells and the emigration of leukocytes to inflamed tissues (Tedder et al., 1995). The participation of this type of interaction has been suggested based on various observations. E-selectin has an attractive effect on neutrophils in vitro which has been shown to be similar to the effect of neutrophil chemotactic factor derived from macrophages (Cunha and Ferreira, 1986a, Cunha and Ferreira, 1986b; Lo et al., 1991). This chemotactic factor is a lectin-like molecule released from activated macrophages, which is inhibited by d-galactose (GAL) in vitro (Dias-Baruffi, Cunha, Ferreira, & Roque-Barreira, 1993). It has recently been shown that glucose–mannose and N-acetylglucosamine-binding plant lectins inhibit the neutrophil infiltration in three experimental models of inflammation (Alencar et al., 1999, Assreuy et al., 1997, Assreuy et al., 1999). Therefore, it is believed that exogenous lectins, which present similar characteristics to endogenous lectins, would be very useful for studying the protein–carbohydrate interaction involved in leukocyte migration during the inflammatory response.

The purpose of the present study was to investigate the possible interference of the galactose-binding lectin from Vatairea macrocarpa (VML) seeds, on the leukocyte migration. The roles of rat resident peritoneal macrophages and mast cells within this process were also investigated. The VML is a Gal/GalNac-specific lectin, which readily interacts with both N- and O-linked glycans in glycoproteins (Ramos et al., 1999). Interestingly, VML does not recognize these complex structures if the terminal galactose residues, in different glycoconjugates, are masked by sialic acid residues in their non-reducing extremity (Ramos et al., 2000). This property would be explored in order to characterize its receptor within cell surface glycoconjugates.