Binding of C4 by IgM.
D000818:Animals; D003181:Complement C4 / Q000378:metabolism*; D006801:Humans; D007075:Immunoglobulin M / Q000378:metabolism*; D011817:Rabbits; D011951:Receptors, Complement
D003181:Complement C4; D007075:Immunoglobulin M; D011951:Receptors, Complement