Evolution of low molecular weight immunoglobulins--III. The immunoglobulin of chicken bile--not an IgA.

Studies on comparison of antigenic relationships between the immunoglobulin of chicken bile--the so-called chicken IgA--and human, porcine, as well as murine IgA were performed by a series of double-antibody and solid-phase RIA systems using H chain-specific anti-chicken biliary Ig sera and alpha chain-specific anti-human IgA sera produced in rabbits and in carp. It was not possible to demonstrate a significant immunological cross-reactivity of the Ig of chicken bile to the Ig's of IgA class. Besides, we could not find an Ig type similar to this chicken biliary Ig in pooled normal sera or in the crude Ig fractions precipitated by (NH4)2SO4 of several vertebrate species (man, swine, buzzard, duck, goose, kestrel, kite, three tortoise species, frog, carp and perch); or in the bile of duck, goose, two snake species and frog. Only pooled chicken normal serum contained this biliary Ig type. Accordingly, the chicken biliary Ig can no longer be considered a precursor of mammalian IgA. This Ig of chicken bile represents a unique Ig class of birds and is to be called IgB (dominant biliary Ig of some birds).