LACK OF SC PIGR-MEDIATED EPITHELIAL TRANSPORT OF A HUMAN POLYMERIC IGA DEVOID OF J-CHAIN - IN-VITRO AND IN-VIVO STUDIES/

Three human polymeric IgA (pIgA) myeloma proteins of tetrameric size w ere compared for their J-chain content, their in vitro secretory compo nent (SC)-binding ability, and their capacity to be transcytosed by po lymeric immunoglobulin receptor (pIgR)-expressing epithelial cells in vitro and rat hepatocytes in vivo. One of the three pIgA preparations, pIgA-L, was shown to lack J chain and was unable to combine with puri fied free human and rat SC, whereas pIgA-G and pIgA-C contained J chai n and combined readily with SC. Furthermore, pIgA-L was not transferre d into rat bile after intravenous injection, and was hardly transporte d apically by polarized Madin-Darbey canine kidney cell monolayers exp ressing the human pIgR, whereas pIgA-G and pIgA-C were efficiently tra nsported in both test systems. Together with our recent demonstration that antibodies to human J chain block the SC/pIgR-mediated epithelial transport of pIgA, these data unanimously confirm the proposed key ro le of J chain in the epithelial transport of polymeric immunoglobulins into exocrine secretions.