Three immunoglobulin classes in the pigeon (Columbia livia)

Three classes of immunoglobulins have been identified in the pigeon. IgG and IgM were purified from pigeon serum whereas IgA was isolated from pigeon hepatic bile. Pigeon IgG and IgM had the same properties and immunohistological distribution as their chicken homologues. Pigeon IgA was identified on the following grounds: (1) it contains the same light chains as pigeon IgM and IgG; (2) it is relatively abundant in exocrine secretions such as bile, egg white, cropmilk and intestinal fluid, whereas it is present only in small amounts in serum; (3) it occurs in the cytoplasm of the majority of the immunocytes from the intestinal mucosa; (4) its electrophoretic mobility and molecular size are similar to those of chicken IgA. Surprisingly, no immunoglobulin-containing cells could be detected in sections of the wall of the cropmilk gland, despite the high IgA content of the cropmilk.