Evolution of low molecular weight immunoglobulins--IV. IgY-like immunoglobulins of birds, reptiles and amphibians, precursors of mammalian IgA.

Radioimmunochemical studies on the comparison of the immunological cross-reactivity between the 7-S Igs of birds, reptiles and amphibians (IgY-like Igs) and the IgA of mammals (man and pig) using 125I-chicken IgY and anti-chicken IgY(Fc) or anti-chicken IgY(H) antibodies from rabbits and carp for the detection led to the conclusion that there are close antigenic relationships between them. Therefore, the IgY-like Igs seem to be the precursors for the IgA class of mammals. From that, we give a phylogenetic tree of Igs in accordance with the evolutionary development of vertebrates.