SummaryThe vast majority of peripheral T cells exist as resting lymphocytes until a signal for activation has been received. In response to antigen, this involves ligation of the T cell receptor (TCR) and signal transmission through the CD3 complex, which then initiates a cascade of intracellular events that leads to the expression of genes used in T cell activation. T cell activation also requires soluble mediators in the form of cytokines and chemokines that regulate the process in both positive and negative ways, and costimulatory signals received in conjunction with TCR/CD3 signaling are important in the activation of T cells. Unlike T cells in other peripheral immune compartments, small and large intestinal intraepithelial lymphocytes (IELs) bear some but not all properties of activated T cells, suggesting that they constitute a large population of 'partially-activated' effector cells. Because of that, regulation of the IEL activation process must be held in tight check, yet it must be ready to respond to foreign antigen rapidly and effectively. We discuss how costimulatory molecules may hold the key to controlling IEL activation through a multi-phase process beginning with cells that have already entered into the early stage of activation.

Murine intestinal intraepithelial lymphocytes (IELs) can be classified according to expression of a CD43 glycoform recognized by the S7 monoclonal antibody. In this study, we examined the response of S7+ and S7-IELs in mice during acute reovirus serotype 3 (Dearing strain) infection, which was confirmed by virus-specific real-time PCR. In vivo proliferation increased significantly for both S7and S7+ IELs on day 4 post-infection as determined by BrdU incorporation; however, expression of the inducible costimulatory (ICOS) molecule, which peaked on day 7 post-infection, was upregulated on S7+ CD4+ T cells, most of which were CD4+8-IELs. In vitro ICOS stimulation by syngeneic peritoneal macrophages induced IFN-γ secretion from IELs from day 7 infected mice, and was suppressed by treatment with anti-ICOS mAb. Additionally, IFN-γ mRNA increased in CD4+ IELs on day 6 post-infection. These findings indicate that S7-and S7+ IELs are differentially mobilized during the immune response to reovirus infection; that the regulated expression of ICOS is associated with S7+ IELs; and that stimulation of IELs through ICOS enhances IFN-γ synthesis during infection.

Background and Objective Porphyromonas gingivalis infection is strongly associated with periodontitis. Although P. gingivalis is known to elicit a strong inflammatory response, details of that remain fragmentary. To understand the local response to P. gingivalis, primary cell lines derived from mouse gingival tissues were exposed to P. gingivalis or E. coli lipopolysaccharide (LPS), and cytokine production for interleukin-6 (IL-6) and tumor necrosis factor-α (TNFα were measured. CCL25 gene expression was measured by real-time PCR. Cells stimulated with combinations of IL-6, soluble IL-6 receptor (sIL-6R), and/or soluble gp130 (sgp130) were assayed for CCL2 and TNFα secretion. Methods Primary cell lines were generated from mouse gingival tissues. Enzyme-linked assays were used to determine cytokine levels, and real-time PCR was used to quantify CCL25 gene expression. Results Exposure to P. gingivalis but not E. coli LPS resulted in significantly elevated levels of both IL-6 and TNFα, and P. gingivalis LPS-stimulation also upregulated CCL25 gene expression. In one of three experiments, IL-6 induced CCL2 secretion, whereas IL-6 with sIL-6R induced CCL2 secretion in all three experiments, suggesting that both direct IL-6 signaling and IL-6 trans-signaling may be involved. However, because sgp130 did not inhibit trans-signaling, and because direct stimulation of gingival cells with sgp130 resulted in CCL2 secretion, the possibility exists that sgp130 forms binary complexes with soluble IL-6R that promote direct IL-6 stimulation. Conclusion These findings define a pathway in which exposure of gingival cells to P. gingivalis induces the release of IL-6 and TNFα; IL-6 in turn induces CCL2 secretion.

The involvement of the CD43 molecule in the activation of mouse small intestinal intraepithelial lymphocytes (IELs) has been studied using a panel of twenty-two regulatory and effector immune response analytes. In the absence of stimulation in vitro, IELs produced low levels of CCL5 only. Upon CD3 stimulation, the activity of seven of twenty-two analytes were elevated relative to unstimulated cultures, including several proinflammatory cytokines and chemokines. Notably, CD3 stimulation in the presence of CD43 costimulation resulted in elevated levels of five analytes (interleukin-2, interferon-γ, CCL5, granulocyte colony-stimulating factor, and granulocytemonocyte colony stimulating factor) above that produced by CD3 stimulation alone. That CD43 costimulation was responsible for elevated cytokine/chemokine activity was confirmed at the transcriptional level by real-time PCR for IFN-γ and CCL5, and by ELISA assay for IFN-γ. These findings open the way to a better understanding of the process by which T cells are activated in the intestinal epithelium.

Summary Soluble gp130 (sgp130) has been shown to suppress the inflammatory response of autoimmune pathologies; however, its effects on virus infection are not known. Here, we report that intraperitoneal treatment of mice with sgp130-Fc fusion protein at the time of oral reovirus serotype 3 infection resulted in altered morphopathological changes that were evident by less shortening of intestinal villi length and crypt depth after infection. That the effect mediated by sgp130 treatment was due to an increase in intestinal crypt cell proliferation was demonstrated by an increase in the number of crypt mitotic figures. This was further confirmed by increased immunoreactivity to the Cdc47 proliferation-associated antigen in crypts of sgp130-treated virus-infected mice compared to infected non-treated mice. These findings suggest that sgp130 may have a beneficial effect during intestinal virus infection by disrupting IL-6 trans-signaling, thereby reducing the local inflammatory response.