Human intestinal epithelial cell-derived interleukin (IL)-18, along with IL-2, IL-7 and IL-15, is a potent synergistic factor for the proliferation of intraepithelial lymphocytes.

Intestinal epithelial cell (IEC)-derived cytokines, such as stem cell factor (SCF), interleukin (IL)-7 and IL-15 are known to be required for the development of intestinal intraepithelial lymphocytes (IELs). A newly described cytokine, IL-18, has also been shown to be produced by intestinal epithelial cells. To demonstrate the functional effects of IL-18 on human IELs, we assessed IL-18/IL-18 receptor expression in IEC/IEL and proliferation following stimulation of intestinal IELs by IL-18. IL-18 transcripts were detected both in freshly isolated human colonic epithelial cells and in various colonic epithelial cell lines. IL-18 protein was also detected by ELISA and flow cytometric analysis using antihuman IL-18-specific monoclonal antibody (MoAb). Furthermore, IELs constitutively expressed the IL-18 receptor in addition to the IL-2 and IL-7 receptors. More importantly, IL-18 augmented significant proliferative responses of IEL in combination with IL-2, IL-7 and IL-15 both in the presence and in absence of anti-CD3 MoAb. These results suggest that IL-18 might play a crucial role in the proliferation and maintenance of intestinal IELs.

Normal development of the gut-associated lymphoid tissue except Peyer's patch in MyD88-deficient mice.

MyD88 is a key adaptor molecule for signalling via Toll-like receptors (TLRs) and the response to gut commensal microbes. To investigate the role of TLRs/MyD88 pathway in the development of the gut-associated lymphoid tissue (GALT), we examined the development of Peyer's patches (PPs) and cryptopatch (CP), and also one of effector compartment, intraepithelial lymphocyte (IEL) in MyD88-/-, TLR2-/- and TLR4-/- mice. In MyD88-/- mice, the organogenesis of PPs was not disturbed. However, PPs in 2-week-old MyD88-/- mice were significantly smaller than those in MyD88+/- mice. Also, in 2-week-old TLR4-/-, but not TLR2-/- mice, PPs did not develop rapidly. The development of PPs in MyD88-/- and TLR4-/- mice was completely recovered in 10 weeks. PP cells from MyD88-/- mice showed significant decrease in proliferation when stimulated with lipopolysaccharide. The development of CP and IEL was also normal in 10-week-old MyD88-/- mice. These results suggest that the TLRs/MyD88 pathway might be involved in the development of PPs only at early postnatal stage, and TLRs/MyD88-independent signalling is critically involved in the development of GALT in adult mice.

The role of cryptopatch-derived intraepithelial lymphocytes in the development of chronic ileocecitis.

Lympho-haemopoietic progenitors residing in murine gut cryptopatches (CPs) have been shown to generate intestinal extrathymic intraepithelial lymphocytes (IELs). However, the role of CPs in the development of intestinal inflammation remains unclear. To investigate the role of CPs in the development of intestinal inflammation, we examined SAMP1/Yit mice, which spontaneously develop a chronic intestinal inflammation localized to the terminal ileum and cecum. Here, we showed the sharp correlation between the disease onset and the decreased number of CPs, resulting in decreased number of both thymus-independent IELs including T-cell receptor gammadelta+ (TCRgammadelta+) and CD8alphaalpha+TCRalphabeta+ cells but not thymus-dependent CD8alphabeta+TCRalphabeta+ and CD4+TCRalphabeta+ cells in SAMP1/Yit mice. These data provide the first suggestion that thymus-independent IELs derived from CP might play protective role against the onset and the development of intestinal inflammation.

The role of inducible co-stimulator (ICOS)/B7-related protein-1 (B7RP-1) interaction in the functional development of Peyer's patches.

T-cell co-stimulatory molecule, inducible co-stimulator (ICOS)/B7-related protein-1 (B7RP-1) interactions play an essential role of T-cell-dependent B-cell activation in peripheral lymphoid organs such as spleen and lymph nodes. Here, we investigate the role of ICOS/B7RP-1 interactions in the development of Peyer's patches (PPs). In ICOS(-/-) mice, the number of PPs was not decreased, although PPs in ICOS(-/-) mice were significantly reduced in size. Phenotypic analysis showed no obvious differences between ICOS(-/-) and ICOS(+/-) mice in the distribution of T-cells, B-cells, macrophages and dendritic cells. However, PNA(+) cells characteristic of intestinal germinal centers were totally absent in ICOS(-/-) mice. Moreover, production of IgA and IgG, but not IgM was significantly reduced in PPs in ICOS(-/-) mice. These data suggest that ICOS/B7RP-1 interactions may not affect the organogenesis, but involve in the functional development of PPs.

Therapeutic effect of anti-OX40L and anti-TNF-alpha MAbs in a murine model of chronic colitis.

Interaction of OX40 (CD134) on T cells with its ligand (OX40L) on antigen-presenting cells has been implicated in pathogenic T cell activation. This study was performed to explore the involvement of OX40/OX40L in the development of T cell-mediated chronic colitis. We evaluated both the preventive and therapeutic effects of neutralizing anti-OX40L MAb on the development of chronic colitis in SCID mice induced by adoptive transfer of CD4(+)CD45RB(high) T cells as an animal model of Crohn's disease. We also assessed the combination of anti-OX40L and anti-TNF-alpha MAbs to improve the therapeutic effect. Administration of anti-OX40L MAb markedly ameliorated the clinical and histopathological disease in preventive and therapeutic protocols. In vivo treatment with anti-OX40L MAb decreased CD4(+) T cell infiltration in the colon and suppressed IFN-gamma, IL-2, and TNF-alpha production by lamina propria CD4(+) T cells. The combination with anti-TNF-alpha MAb further improved the therapeutic effect by abolishing IFN-gamma, IL-2, and TNF-alpha production by lamina propria CD4(+) T cells. Our present results suggested a pivotal role of OX40/OX40L in the pathogenesis of T cell-mediated chronic colitis. The OX40L blockade, especially in combination with the TNF-alpha blockade, may be a promising strategy for therapeutic intervention of Crohn's disease.