LACK OF ASSOCIATION OF SECRETORY COMPONENT WITH IGA IN J-CHAIN-DEFICIENT MICE

J chain has been proposed to play a role in the mucosal transport of p olymeric Igs (pIg) by the polymeric Ig receptor (pIgR). We have previo usly reported the generation of J chain-deficient mice. These mice exh ibited elevated serum IgA and depleted biliary and fecal IgA levels co mpared with wild-type mice. We report here that, unlike the IgA levels in bile and feces, IgA levels in local mucosal and glandular secretio ns were not depressed in J chain-deficient mice. Breast milk, intestin al mucosal surface, and nasal wash IgA levels in the mutant mice were similar to wild-type mice while bronchoalveolar lavage IgA levels were higher in the J chain-deficient animals. Western blot analysis with a n Ab to secretory component (SC), the portion of the pIgR that remains bound to pig in secretions, and immunoprecipitation with Abs directed against IgA showed that secreted IgA was associated with SC in wild-t ype but not J chain-deficient mice. The IgA in wild-type secretions wa s polymeric while the secretion s of J chain-deficient mice contained IgA monomers and other nonpolymeric IgA forms. Thus, J chain is not es sential for IgA transport by intestinal, mammary, or respiratory epith elia but is necessary for the stable association of pIgA with SC. Furt her, we suggest that J chain-deficient IgA is transported into secreti ons by a different mechanism than wild-type IgA.