Membrane receptors on Xenopus macrophages for two classes of immunoglobulins (IgM and IgY) and the third complement component (C3).

Using two classes of immunoglobulins (IgM and IgY) and a complement component (C3) purified from Xenopus serum and plasma, we examined the presence of receptors on Xenopus peritoneal macrophages for each ligand. Xenopus macrophages, ultrastructurally quite similar to those in higher vertebrates, were found to have different membrane receptors for both immunoglobulins as well as for C3. Whereas all of these receptors mediated the binding of the SRBC which were coated with each ligand, only the RBC coated with IgY were ingested by the macrophages. We discuss the origin and functional differentiation of phagocyte membrane receptors from the phylogenetic viewpoint, in relation to the serum factors interacting with the receptors.