The in vitro activity of lectin I from mistletoe (ML I) and its isolated A and B chains on functions ofmacrophages and polymorphonuclear cells

Abstract

We investigated the effects of ML I and its isolated chains, A and B, in regard to selected functions of phagocytes (human granulocytes, paraffin-oil stimulated M from guinea pigs).On these cells, ML I has no cytotoxic effect between 10 −14 and 10 −8 M (trypan blue exclusion and ethidium bromide exclusion). Over the same concentration range, ML I and B chain diminish the negative surface charge of MΦ and agglutinate MΦ at concentrations ≥2 × 10 −8 M (ML I) and ≥ 3 × 10 −7 M (B chain), respectively. The diminishing of the negative surface charge shows two peaks, indicating the existence of two types of receptors on the MΦ surface with different affinities for sugar-binding sites. Moreover, the B chain shows athird peak at higher concentrations (3 × 10 −8 M) that could be inhibited by D-galactose(≥ 10 −4 M). In comparison, the A chain reduces the surface charge at concentrations over 3 × 10 −7 M, but D-galactose has no effect on this. By means of the agarose droplet test, the spontaneous migration of M is inhibited in the sequence ML I ≫ B chain > A chain. The phagocytic activity of human leukocytes tested with a radiometric phagocytosis technique reveals, an increasing effect only for the B chain; ML Iand the A chain have no effect. Perhaps the mechanism of the described activities of ML I and its B chain are comparable with the action of lymphokines activating M.Φ