Isolation and characterization of secretory IgA (sIgA) and free secretory component (FSC) from rat bile

Abstract

Secretory IgA (sIgA) and free secretory component (SC) have been purified from rat bile and compared to sIgA and free SC from rat and human milk. In rat bile and milk, sIgA exists in a series of polymers with S rates of 11,13 and 15 and molecular weights of 405,000, 540,000 and 690,000, respectively. These three forms have the same basic chain composition (light chains, α-chains and SC) when reduced and analysed by polyacrylamide gel electrophoresis in SDS. Rat α-chains and SC were slightly smaller than their human counterparts. SC was covalently linked to IgA in purified biliary sIgA; the latter apparently contained molecules of SC in different configurations, as revealed by antigenic analyses with anti-free-SC and anti-bound-SC antisera. There was antigenic identity between bile and milk for both FSC and sIgA. The existence of configurational determinants of SC in both sIgA and FSC was serologically demonstrated. The amino acid composition of rat bile free SC compared well to that of bovine, canine, rabbit and human free SC.