Lectin-binding receptors, Na+,K(+)-ATPase, and acetylcholinesterase on immunocyte plasma membrane of Limulus polyphemus.

Plasma membrane receptors are crucial for nonself tissue recognition. Using concanavalin A (Con A), wheat germ agglutinin, peanut agglutinin, soybean agglutinin (SBA), and winged pea agglutinin, five lectin-binding receptor molecules have been recognized on the plasma membrane of the granulocyte (immunocyte) of the horseshoe crab, Limulus polyphemus. Only Con A and SBA caused capping of surface receptors. On the basis of the known functions of these lectin-binding receptor molecules in other invertebrates and vertebrates, their roles in phagocytosis, encapsulation, signaling, and possibly in complement pathway activation are postulated. In addition to lectin-binding receptors, Na+,K(+)-ATPase and acetylcholinesterase were detected on the plasma membrane. Because Limulus dates back to some 200 million years, the antiquity of these molecules is suggested. Furthermore, some of the lectin-binding surface receptors have the potential to be used as markers to separate different kinds of hemocytes in higher arthropods and to distinguish between normal and neoplastic cells in humans.