Ligation of intestinal epithelial CD1d induces bioactive IL-10: Critical role of the cytoplasmic tail in autocrine signaling

The intestinal epithelium is anatomically positioned to serve as the critic al interface between the lumen and the mucosal immune system. In addition t o MHC class I and II antigens, intestinal epithelia constitutively express the nonclassical MHC molecule CD1d a transmembrane molecule with a short cy toplasmic tail expressed as a beta(2)-microglobulin-associated 48-kDa glyco protein and novel beta(2)-microglobulin-independent 37-kDa nonglycosylated protein on intestinal epithelia. At present, it is not known whether extrac ellular ligands can signal intestinal epithelial CD1d. To define signaling of CD Id cytoplasmic tail, retrovirus-mediated gene transfer was used to ge nerate stable cell lines expressing wild-type CD1d or a chimeric molecule ( extracellular CD1d and cytoplasmic CD1a), and surface CD1d was triggered by antibody crosslinking. Although wild-type CD1d was readily activated (tyro sine phosphorylation), no demonstrable signal was evident in cell lines exp ressing the chimeric molecule. Subsequent studies revealed that anti-Cold c rosslinking specifically induces epithelial IL-10 mRNA and protein and is b locked by the tyrosine kinase inhibitor genistein. Further studies addressi ng epithelial-derived IL-10 revealed that anti-CD1d crosslinking attenuates IFN-gamma signaling and that such attenuation is reversed by addition of f unctionally inhibitory IL-10 antibodies. These results define signaling thr ough surface CD1d, and, importantly, they demonstrate that this pathway may serve to dampen epithelial proinflammatory signals.