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Studies on the secretory immunologic system of fowl. 3. Serum and secretory IgA of the chicken.


 A new immunoglobulin (IgA) was purified from chicken serum and secretions by using immunoabsorbent columns, Sephadex G-200 gel filtration and DEAE-cellulose chromatography. The immunoglobulin nature of IgA was confirmed by the presence of heavy (H) and light (L) chains, and antibody activity of serum IgA obtained from immunized chickens.
 In chicken serum, IgA exhibited size heterogeneity, the major portion eluting from Sephadex G-200 in a volume corresponding to τ; 200,000 with a minor peak of approximately 170,000 to 180,000. In secretions IgA was mainly of high molecular weight (350,000 to 360,000). The IgA/IgY ratio in all secretions examined was greater than that in serum. Secretory IgA found in the bile contains an additional antigenic determinant not found in serum IgA, perhaps indicating the presence of secretory piece and/or J chain.
 Serum IgA was dissociated by partial reduction to a size comparable to that of IgMs (∼175,000). Gel filtration in 8 M urea—0.05 M propionic acid separated H and L chains. The α H chains were approximately the size of µ chains (∼70,000). These results indicate that IgA is composed of H and L polypeptide chains and suggest the polymeric nature of most serum and secretory IgA.
 The demonstration of an immunoglobulin in the chicken similar to mammalian IgA reconfirms the presence of a secretory immunologic system in the fowl.