Herve Bazin , and Brian

Polymeric IgA is t ransported from blood to bile by the rat liver (1, 2) in a manner which may be analogous to the transport of polymeric IgA across the mucosal epithelium. Such transport is thought to be mediated by secretory component (SC) 1 an epithelial cell glycoprotein which acts as a receptor for polymeric IgA on these cells (3-8). Fisher et al. (9) recently reported that Ig transport by the rat liver is selective for polymeric IgA and that secretory component is involved in this process because prior addit ion of SC to polymeric IgA reduced its transport. Moreover, a l though IgG is not tran',ported, IgG which could bind SC (i.e., anti-SC antibodies) was t ransported by the liver (9). Recently, Birheck et al. reported that transport of polymeric IgA by the rat liver proceeds through hepatic parenchymal cells (10). Thus, if SC is involved in the IgA receptor which mediates transport, it should be expressed on rat hepatocytes. The experiments presented in this paper indicate that SC is synthesized by rat hepatocytes and is involved in mediat ing the b inding of polymeric IgA to these cells.