Lectin-dependent recognition of foreign cells by hemocytes of the mussel, Mytilus edulis.

Phagocytosis of human erythrocytes (rbc) by hemocytes of the mussel Mytilus edulis was found to be influenced by four heterologous lectins. The effects were examined in the absence of Ca++ ions under three experimental conditions: when the lectins were bound to 1) both hemocytes and rbc, 2) only hemocytes, but not to rbc, and 3) only rbc, but not to hemocytes. The lectins used included: albumen gland agglutinin from Helix pomatia (HPA), wheat germ agglutinin (WGA), Ricinus-120 (Ric-120) and Concanavalin-A (Con A). HPA, WGA and Ric-120, for which both hemocytes and A-rbc possess receptors, strongly enhanced uptake of A-rbc. This lectin-mediated phagocytosis was abolished by addition of specific sugars either to lectin-pretreated rbc (HPA, WGA) or to a pretreated hemocyte monolayer (Ric-120); this indicated the stimulation of phagocytosis by the binding of lectin to carbohydrate determinants at the surface of hemocytes and target cells. On the other hand, HPA which binds to hemocytes, but not to O-rbc, did not influence phagocytosis of these rbc; and Con A which binds to A-rbc, but not to hemocytes, also failed to stimulate phagocytosis. These findings reveal the importance of carbohydrate determinants on the surface of hemocytes as well as on target cells in recognition and in lectin-mediated phagocytosis of foreign cells by Mytilus hemocytes.