Further characterization of IgA in chicken serum and secretions with evidence of a possible analogue of mammalian secretory component.

Immunochemical studies of the intestinal secretory immune system of the chicken have led to further characterization of IgA in bile, intestinal contents and serum. A component was detected in late Sephadex G-200 fractions of caecal and intestinal contents which showed partial identity with bile, intestinal and a high molecular weight fraction of serum IgA. This component showed similar sedimentation characteristics to bovine serum albumin in sucrose density gradients, a fast electrophoretic mobility on polyacrylamide gel and is a possible analogue of mammalian secretory component (SC). Fractionation of serum from birds affected with infectious synovitis revealed two moleculare classes of IgA. Comparative double diffusion studies produced a reaction of complete identity between bile IgA and high molecular weight serum IgA (15S) and partial identity with low molecular weight serum IgA (7S), suggesting a lack of an SC determinant on the latter. A spur of partial identity between 15S and 7S serum IgA was also observed. Although no direct structural homology with mammalian or human IgA could be demonstrated by immunological cross-reactivity, the similarities of molecular characteristics, particularly emphasized by the presence of a secretory component, favour a functional analogy between the secretory immune system of the fowl and mammalian species.