Synthesis of Secretory IgA in the Rabbit

Abstract

Abstract A fragment (γAt) of rabbit colostral IgA which differs from the parent molecule primarily in that it lacks most of the original T chain has been prepared by chromatography of IgA on Sephadex G-200 in 5 M guanidine. This fragment is capable of combining specifically with free T chain in vitro. When mammary tissue from homozygous b4 rabbits is incubated in the presence of 14C amino acids and varying concentrations of b5γAt, the latter competes with an endogenous b4γA subunit for newly synthesized T chain, suggesting that the γA and T chain molecules are synthesized in different cells. Furthermore, γAt stimulates the synthesis of T chain, whereas intact IgA does not. On the basis of these and other data we have proposed a model for the synthesis and secretion of colostral IgA in the rabbit which agrees in most respects with the model developed by Tourville and co-workers from immunofluorescence studies in human tissues.