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Oral tolerance can prevent unnecessary immune responses against dietary antigens. Members of the B7 protein family play critical roles in the positive and/or negative regulation of T cell responses to interactions between APCs and T cells. V-set and Ig domain-containing 4 (VSIG4), a B7-related co-signaling molecule, has been known to act as a co-inhibitory ligand and may be critical in establishing immune tolerance. Therefore, we investigated the regulation of VSIG4 signaling in a food allergy and experimental oral tolerance murine models. We analyzed the contributions of the two main sites involved in oral tolerance, the mesenteric lymph node (MLN) and the liver, in VSIG4-mediated oral tolerance induction. Through the comparative analysis of major APCs, dendritic cells (DCs) and macrophages, we found that Kupffer cells play a critical role in inducing regulatory T cells (Tregs) and establishing immune tolerance against oral antigens via VSIG4 signaling. Taken together, these results suggest the possibility of VSIG4 signaling-based regulation of orally administered antigens.

Background and purpose: Cilostazol is a specific inhibitor of 3′-5′-cyclic adenosine monophosphate (cAMP) phosphodiesterase, which is widely used to treat ischemic symptoms of peripheral vascular disease. Although cilostazol has been shown to exhibit vasodilator properties as well as antiplatelet and anti-inflammatory effects, its cellular mechanism in microglia is unknown. In the present study, we assessed the anti-inflammatory effect of cilostazol on the production of pro-inflammatory mediators in lipopolysaccharide (LPS)-stimulated murine BV2 microglia. Experimental approach: We examined the effects of cilostazol on LPS-induced nuclear factor-kappaB (NF-κB) activation and phosphorylation of mitogen-activated protein kinases (MAPKs). Key results: Cilostazol suppressed production of nitric oxide (NO), prostaglandin E2 (PGE2) and the proinflammatory cytokines, interleukin-1 (IL-1), tumour necrosis factor-α, and monocyte chemoattractant protein-1 (MCP-1), in a concentration-dependent manner. Inhibitory effects of cilostazol were not affected by treatment with an adenylate cyclase inhibitor, SQ 22536, indicating that these actions of cilostazol were cAMP-independent. Cilostazol significantly inhibited the DNA binding and transcriptional activity of NF-κB. Moreover, cilostazol blocked signalling upstream of NF-κB activation by inhibiting extracellular signal-regulated kinases 1 and 2 (ERK1/2) and c-Jun N-terminal kinase (JNK), but without affecting the activity of p38 MAPK. Conclusion and implications: Our results demonstrate that suppression of the NF-κB, ERK, JNK signalling pathways may inhibit LPS-induced NO and PGE2 production. Therefore, cilostazol may have therapeutic potential for neurodegenerative diseases by inhibiting pro-inflammatory mediators and cytokine production in activated microglia.

Granulocyte colony-stimulating factor (G-CSF)-mobilized donor graft tissue used for peripheral blood stem cell transplantation contains a large number of immature myeloid cells that suppress alloreactive donor T cells, resulting in an inhibition of acute graft-versus-host disease (GVHD). However, the molecular mechanism underlying the suppressive function of immature myeloid cells is not fully understood. Here, we investigated whether indoleamine 2,3-dioxygenase (IDO) is related to the suppressive mechanism of G-CSF-induced immature myeloid cells (gMCs). We found that Gr-1(+) CD11b(+) cells were highly induced in G-CSF-injected donor graft tissue, which is a phenotype of immature myeloid cells, resulting in an inhibition of acute GVHD lethality by suppressing alloreactive donor T-cell expansion. IDO was not detected in primary isolated gMCs; however, this enzyme was markedly induced after treatment with interferon-gamma (IFN-gamma). This level was significantly higher in IFN-gamma-treated gMCs than in bone marrow myeloid cells, which promote alloreactive T-cell responses. We next investigated the functional role of IDO in gMC-mediated inhibition of acute GVHD lethality. We found no changes in gMC-mediated survival or alloreactive donor T-cell suppression when IDO activity was blocked using 1-methyl tryptophan. In addition, there was no difference in gMC-mediated survival rates between recipients transferred with either wild-type gMCs or IDO(-/-) gMCs. Taken together, our data suggest that gMC-mediated inhibition of lethal acute GVHD is through an IDO-independent mechanism.

B7-H1 (also known as CD274 and PD-L1) is a cosignalling molecule regulating T-cell immunity positively or negatively in vivo. However, little is known about the role of endogenous B7-H1 in bacterial infection. We found that B7-H1 expression was up-regulated in various cell populations including CD4+ and CD8+ T cells, natural killer (NK) cells and macrophages following Listeria monocytogenes infection. Administration of the antagonistic B7-H1 monoclonal antibody resulted in a significant increase in mortality in mice infected with a lethal dose of L. monocytogenes compared with mice given the control immunoglobulin. In vivo blockade of B7-H1 greatly inhibited the production of tumour necrosis factor (TNF)-alpha and nitric oxide, key effector molecules responsible for intracellular killing by macrophages. B7-H1 blockade also suppressed the expression of granzyme B and interferon (IFN)-gamma by NK cells. Interestingly, blocking of endogenous B7-H1 selectively inhibited CD8+ T cells rather than CD4+ T cells in response to L. monocytogenes infection, as evidenced by the reduction of IFN-gamma production and the expression of effector surface markers including CD62L(int/low) and CD44(high) in CD8+ T cells from mice given anti-B7-H1 monoclonal antibody. In addition, we found that the proliferation of listeriolysin-O (LLO)-specific and IFN-gamma-producing L. monocytogenes-reactive CD8+ T cells was significantly decreased not only in the effector phase but also in the memory phase in the presence of anti-B7-H1 antibody. Our findings thus suggest that endogenous B7-H1 can provide positive costimulatory signals for innate and adaptive immunity leading to protection against intracellular bacterial infection.

Silibinin is the primary active compound in silymarin. It has been demonstrated to exert anti-carcinogenic effects and hepato-protective effects. However, the effects of silibinin on the maturation and immunostimulatory activities exhibited by dendritic cells (DCs) remain, for the most part, unknown. In this study, we have attempted to determine whether silibinin can influence surface molecule expression, dextran uptake, cytokine production, capacity to induce T-cell differentiation, and the signaling pathways underlying these phenomena in murine bone marrow-derived DCs. Silibinin was shown to significantly suppress the expression of CD80, CD86, MHC class I, and MHC class II in the DCs, and was also associated with impairments of LPS-induced IL-12 expression in the DCs. Silibinin-treated DCs proved highly efficient with regard to Ag capture via mannose receptor-mediated endocytosis. Silibinin also inhibited the LPS-induced activation of MAPKs and the nuclear translocation of the NF-kappaB p65 subunit. Additionally, silibinin-treated DCs evidenced an impaired induction of Th1 response, and a normal cell-mediated immune response. These findings provide new insight into the immunopharmacological functions of silibinin, especially with regard to their impact on the DCs. These findings expand our current understanding of the immunopharmacological functions of silibinin, and may prove useful in the development of therapeutic adjuvants for acute and chronic DC-associated diseases.