Establishment of a functional secretory IgA transcytosis model system in vitro for functional food screening.

Abstract

A characteristic mucosal immune response involves the production of antigen-specific secretory immunoglobulin A (SIgA) antibodies. In order to study transcytosis by mimicking the SIgA secretion and to screen for SIgA secretion-promoting substances, we developed a model system of a transfected Madin-Darby canine kidney (MDCK) cell line that expresses the human polymeric immunoglobulin receptor (pIgR). We thus isolated the human dIgA (dimeric IgA)/pIgA (polymeric IgA) complex as the binding ligands. In the present study, a recombinant vector encoding the human pIgR gene was constructed and infected into MDCK cells. Following reverse transcription polymerase chain reaction (RT-PCR), immunoblotting, and immunofluorescence staining, we confirmed that pIgR was expressed in the transfectant MDCK-pIgR cells and was located at the basolateral side of the cell surface. We also confirmed the coexistence of the dIgA/pIgA complex in the IgA myeloma serum. The covalent dIgA/pIgA complex was then isolated from the serum of an IgA multiple myeloma patient using an ÄKTA purifier operation system with a HiPrep 16/60 Sephacryl S-300 HR column, in order to utilize the complex as transcytosis ligands for human pIgR. Finally, we confirmed the uptake of the isolated human dIgA/pIgA complex into MDCK-pIgR cells. We demonstrated that the human dIgA/pIgA complex was transcytosed into the apical side of the monolayer cells. Therefore, our MDCK-human pIgR cell transcytosis model is an operational system and can be used for screening functional food components that promote dIgA/pIgR transcytosis as well as SIgA secretion.