Reactivities of Shark 19S and 7S IgM Antibodies to Salmonella typhimurium

LOWER vertebrates such as sharks can synthesize humoral antibodies in response to antigenic stimulation with a wide variety of antigens 1 . Physicochemical studies have shown that sharks can synthesize both 19S and 7S immunoglobulins and that these two proteins belong to the same immunoglobulin class, which seems to be structurally homologous to IgM as defined for higher animals. Thus the shark immunoglobulins have been designated 19S IgM and 7S IgM 2–4 . Because the predominant immunoglobulin (IgG) of most mammals is absent from sharks, the shark monomeric (7S) IgM might be functionally analogous to IgG. One example of the functional differences between IgM and IgG antibodies is the greater reactivity of the former in agglutination and bactericidal reactions 5,6 . We have isolated and characterized functionally the relatively high levels of agglutinating antibodies which the nurse shark, Gingly-mostoma cirratum , synthesizes in response to Salmonella typhimurium “O” antigens.