INVIVO EXPERIMENTS INVOLVING SECRETORY COMPONENT IN THE RAT HEPATIC TRANSFER OF POLYMERIC IGA FROM BLOOD INTO BILE

Abstract

Human or rat purified secretory IgA (sIgA) injected i.v. into rats is transferred to bile much less (7-24 times) than human or rat polymeric IgA (pIgA) devoid of secretory component (SC). A polymeric Fc.alpha. [Ig A Fe portion] (pFc.alpha.) fragment of a human IgAl myeloma protein, obtained by IgA-protease digestion, bound in vitro to rat SC and was actively transferred in vivo into bile, in contrast to the corresponding Fab.alpha.. The IgA recovered in bile was not degraded, as judged by sedimentation in density gradients. Purified rabbit IgG anti-rat SC antibody was also efficiently transported in vivo into bile, about 40 times more than normal rabbit IgG. The biliary anti-SC antibody transport could be reduced and retarded by the simultaneous i.v. injection of purified rat SC or human pIgA. Rat 125I-pIgA transfer into bile was also significantly reduced and retarded by the concomitant i.v. injection of purified rat or human SC. Injection (i.v.) of purified rat or human SC induced a marked and prolonged decrease of the sIgA level in bile. Rat SC was more effective than human SC in this respect. All these in vivo experiments confirm the in vitro findings showing that SC is the IgA-receptor on the hepatocyte membrane for the transfer of pIgA from rat plasma into bile.