IFN-gamma modulates CD1d surface expression on intestinal epithelia.

In vivo, epithelial cells that line the intestine are intimately associated with lymphocytes, termed intestinal intraepithelial lymphocytes (iIEL). A putative ligand for iIEL on intestinal epithelial cells is CD1d, and recent studies demonstrate a surface form of this molecule exists on intestinal epithelia. At present, it is not known whether CD1d expression is regulated by cytokines in the intestinal microenvironment. Thus we examined the impact of relevant cytokines on CD1d at the level of mRNA and cell surface expression. Using a sensitive whole cell enzyme-linked immunosorbent assay, we assessed the impact of relevant cytokines on CD1d expression on intestinal epithelial cell lines. We were readily able to detect CD1d on the surface of T84 cells, a cryptlike intestinal epithelial cell line. Epithelial cell exposure to human recombinant interferon-gamma (IFN-gamma) resulted in increased CD1d expression in a dose- and time-dependent manner. Polymerase chain reaction amplification of CD1d cDNA revealed a time-dependent induction after exposure to IFN-gamma. This IFN-gamma effect on CD1d expression was cytokine specific and was evident with epithelial cell lines other than T84, including Caco-2 and HT-29 cells. Finally, we were not able to detect significant surface expression of CD1a, CD1b, or CD1c on intestinal epithelial cell lines in the presence or absence of relevant cytokines. These results indicate that CD1d cell surface protein and cellular mRNA, like other major histocompatibility complex-related molecules, is cytokine regulated in intestinal epithelial cell lines.

Composition of TCR-CD3 complex in human intestinal intraepithelial lymphocytes: lack of Fc epsilon RI gamma chain.

Human intestinal intraepithelial lymphocytes (iIEL) are a unique population of predominantly CD8 alpha beta+, TCR alpha beta+ lymphocytes and, to a lesser extent, TCP gamma delta+ lymphocytes that proliferate poorly to anti-CD3 mitogenic signals but display significant cytolytic activity. Studies in mouse model systems have shown that the gamma chain of the high-affinity receptor for IgE (Fc epsilon RI gamma) may substitute for the zeta chain in the TCR-CD3 complex of iIEL. This has suggested that the functional properties of these cells may be associated with an altered composition of the TCR-CD3 complex. We therefore analyzed the TCR-CD3 complex of normal human iIEL. One- and two-dimensional non-reducing/reducing SDS-PAGE analysis of CD3 gamma, CD3 delta, CD3 epsilon, zeta and Fc epsilon RI gamma chain immunoprecipitates of cell surface radiolabeled proteins with subunit-specific antibodies revealed a TCR-CD3 complex without associated Fc epsilon RI gamma chains. Thus, normal human iIEL contain a TCR-CD3 complex that consists predominantly of zeta homodimers in association with the alpha beta TCR and CD3 gamma, delta and epsilon, similar to the majority of peripheral lymphocytes. This indicates that the distinct properties of human iIEL are not associated with substitutions of the Fc epsilon RI gamma chain in the TCR-CD3 complex.

A major histocompatibility complex class I-related Fc receptor for IgG on rat hepatocytes.

Intestinal epithelial cells of the neonatal rat and mouse have been shown to express a major histocompatibility complex (MHC) class I-like Fc receptor, or FcRn, which transports IgG in an apical to basolateral direction. Previous studies have suggested the possible expression of this receptor beyond the neonatal period within the liver. Since bile contains high levels of IgG, we sought to determine whether the FcRn was functionally expressed by adult rat hepatocytes. Using primers specific for FcRn, which did not cross hybridize with MHC class I transcripts, FcRn DNA was amplified by reverse transcriptase polymerase chain reaction from RNA of adult rat hepatocytes. This RNA contained functional FcRn transcripts as it encoded a beta 2-microglobulin-associated cell surface protein as determined by immunoprecipitation of biotinylated cell surface proteins with a polyclonal anti-FcRn specific antiserum. Western blotting of hepatocyte canalicular (apical) and sinusoidal (basolateral) plasma membranes with an FcRn-specific monoclonal antibody further confirmed the protein expression and suggested that FcRn was enriched on the canalicular surface membranes. FcRn, on the surface of hepatocytes, was biologically functional as it bound Fc fragments of IgG at pH 6.0 but not 8.0, which is the same pH dependence observed for FcRn in rat neonatal enterocytes. Thus, FcRn is functionally expressed outside of the neonatal period on the canalicular cell surface of adult hepatocytes. This suggests that hepatocyte FcRn may bind luminal IgG, providing a potential functional communication between parenchymal immune cells and bile.

Beta 2-microglobulin-independent MHC class Ib molecule expressed by human intestinal epithelium.

A major histocompatibility complex class Ib protein, CD1d, is expressed by human intestinal epithelial cells (IECs) and is a ligand for CD8+ T cells. CD1d was found to be expressed on the surface of human IECs as a 37-kilodalton protein that was beta 2-microglobulin (beta 2M) independent with no N-linked carbohydrate. Transfection into a beta 2M- cell line confirmed that CD1d could be expressed at the cell surface in the absence of beta 2M. These data indicate that IECs use a specialized pathway for CD1d synthesis and that a beta 2M-independent class Ib protein may be the normal ligand for some intestinal T cells.