Human intestinal epithelial cell-induced CD8+ T cell activation is mediated through CD8 and the activation of CD8-associated p56lck.

Abstract

SummaryThe activation of CD8 + suppressor T cells by normal intestinal epithelial cells in antigen-specific or allogeneic mixed cell culture systems has significant implications for the regulation of mucosal immune responses. In this study, we found that the capacity of epithehal cells to induce CD8 + suppressor T cell activation appeared to be linked to the binding of CD8 molecules on the T cell surface. This appears to be mediated by a non-class I molecule expressed on the epithelial cell surface, which binds to CD8 and results in the activation of the CD8-associated src-like tyrosine kinase, p56 lck. Epithehal cell-stimulated p56 lck activation is an early event (in contrast to monocytes) and is essential for T cell activation, since proliferation could be completely abrogated by pretreatment of T cells with genestein or herbamycin, both of which are protein tyrosine kinase inhibitors. Pretreatment ofT cells with anti-CD8 or of intestinal epithelial cells with an anti-epithelial cell mAb B9 inhibited p56 lck activation and further confirmed that CD8 on the T cell and a CD8 ligand on the epithelial cell were involved in this T cell activation event. The specificity of this reaction was confirmed in experiments in which murine transfectants 3G4 and 3G8, expressing CD4 or CD8, respectively, were used. Coculture of 3G8 with epithelial cells but not with monocytes activated p56 lck in this cell line, whereas p56 lck was preferentially activated in 3G4 cells when monocytes were used as the stimulator cells. Although stimulation through CD8-and CD8-associated p561ok was important for epithelial cell-induced T cell activation, T cell proliferation could not be induced by crosslinking CD8 alone with monoclonal antibody anti-CD8. These data suggest that a second signal, possibly through the T cell antigen receptor since activation of the T cell receptor-associated kinase fyn was also seen, is required for epithelial cell-driven T cell proliferation. O ver the past several years, it has become increasingly apparent that the rules governing mucosal immune responses differ from those of the peripheral immune system. First, antigen priming via the oral route most frequently results in the development of immunologic suppression or oral tolerance rather than in an active immune response. Second, the cell types in the gastrointestinal tract are not typical of what one would find systemically. Intraepithelial lymphocytes are predominantly CD8 + T cells that are, in general, anergic despite exposure to inordinate numbers of disparate foreign antigens in the gut lumen (1-3). In contrast, lamina propria T cells are activated memory cells, a rich source of cytokines, but with limited prohferative capacity to specific antigen (4, 5). An understanding of the underlying mechanisms responsible for these phenomena has been slow to evolve, partly because of our limited This manuscript is in partial fulfillment of a Ph.D. thesis (3(in Li and Xian Yang Yio). knowledge of how the primary trigger of an immune response, antigen, is handled b...

Activation of CD8+ Regulatory T Cells by Human Placental Trophoblasts

“…We have previously characterized a subset of CD8 ϩ regulatory T cells in the intestine that require a complex of the nonclassical class I molecule, CD1d, and a costimulatory molecule of the CEA subfamily for activation (11,23). In agreement with previous data showing the expression of CD1d on human trophoblasts (10), quantitative PCR of mRNA isolated from human trophoblasts showed increasing CD1d transcripts present from gestational age wk 7-12 ( Fig.…”

“…These cells were described originally in the intestine where they are activated by an interaction with IEC through a combination of the nonclassical class I molecule CD1d and a costimulatory molecule of the CEA family recognized by the B9 mAb (11,23). CD1d has been reported to be expressed by trophoblasts during the early stages of pregnancy (10).…”

Defective expression of gp180, a novel CD8 ligand on intestinal epithelial cells, in inflammatory bowel disease.

“…As described previously, when NL IEC are cocultured with 3G4 cells, no upregulation of p56lck is seen when compared with baseline at 0 min (Fig. 6 A) (13). In contrast, p56lck is activated in 3G8-IEC cocultures at 1-5 min, supporting the concept that IEC express a molecule capable of binding to CD8, allowing for kinase activation (Fig.…”

“…Importantly, neither blocking anti-class I nor anti-class II mAbs can inhibit this activation event. Only antibody to gp180 (mAb B9) can inhibit the activation of p56lck in this system (13). The increase in the baseline phosphorylation in 3G8 cells appears to reflect the dimerization of CD8␣ chains but does not affect the response of these cells to CD8 ligation.…”

“…We have identified previously a molecule expressed on normal IEC that appears to play a role in the activation of antigen nonspecific CD8 ϩ suppressor T cells (11,12). This molecule, recognized by two mAbs, B9 and L12, is a 180-kD glycoprotein (gp180) that mediates binding to CD8 and results in the activation of the src-like tyrosine kinase p56 lck (13). Activation of this kinase is necessary but not sufficient for the proliferation of CD8 ϩ T cells induced by normal epithelial cells.…”