Recognition of yeast cell wall glucan by Atlantic salmon (Salmo salar L.) macrophages.

Phagocytosis of yeast (Saccharomyces cerevisiae) glucan particles by Atlantic salmon (Salmo salar L.) pronephric macrophages was studied. The particles contained > 95% glucose linked through beta-1,3- and beta-1,6-glycosidic linkages. The macrophages rapidly phagocytized both native and opsonized glucan particles although the latter were taken up at a higher rate. Within 30 min, 40-60% of the macrophages had taken up > 1 native glucan particle. The uptake of native glucan particles could be inhibited by preincubating the macrophages with laminarin, a soluble beta-1,3-linked glucan, and a soluble yeast glucan made by partial formolysis of glucan particles. Soluble yeast glucan, on the other hand, did not inhibit uptake of serum opsonized glucan particles or sheep red blood cells, which showed that it did not interfere with phagocytosis in general or inhibit phagocytosis through complement receptors. Polyglucoses with glycosidic linkages other than beta-1,3, like dextran, glycogen, and pustulan or the polymannose mannan, showed little or no inhibition of phagocytosis of native glucan particles. Altogether these observations indicate that Atlantic salmon macrophages may have a specific receptor for yeast glucan. Studies with chelator- and heat-treated salmon serum showed that glucan particles were opsonized primarily by activation of the alternative complement pathway. However, the data indicate that serum components other than complement may also be involved in the opsonization of glucan particles.