Characterization of a 180-kDa intestinal epithelial cell membrane glycoprotein, gp180. A candidate molecule mediating t cell-epithelial cell interactions.

Previous studies have shown that normal human intestinal epithelial cells stimulate CD8(+) suppressor T cell proliferation in an allogeneic mixed epithelial/T cell co-culture system, which is neither restricted by class I or class II major histocompatibility complex antigens nor by any soluble factors from epithelial cells. Two epithelial specific monoclonal antibodies (mAb), mAb B9 and mAb L12, are potent inhibitors of this mixed epithelial/T cell reaction but not of conventional mixed lymphocyte reactions. While phenotypically distinct by tissue staining, both mAbs recognize a 180-kDa epithelial membrane glycoprotein (gp180). Further characterization of gp180 revealed the following. 1) The protein migrated between 150 and 180 kDa in SDS-polyacrylamide gel electrophoresis and could be resolved by Western blot using mAb B9 or mAb L12. 2) The molecule has two forms, an apically sorted glycosylphosphatidylinositol-anchored form and a basolateral transmembrane form. 3) gp180 is heavily N-glycosylated, since N-glycanase treatment results in a >50% reduction in size. 4) Purified gp180 can bind to peripheral blood T cells and activate p56(lck). 5) gp180 can activate p56(lck) in 3G8 (a murine T cell hybridoma transfected with human CD8alpha cDNA) but not in 3G4 (CD4 transfectant), suggesting that gp180 binds to CD8. Thus, gp180 appears to be a novel regulator of mucosal immune responses.