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

Abstract

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.