Binding of Staphylococcal Enterotoxin B (SEB) to B7 Receptors Triggers TCR- and CD28-Mediated Inflammatory Signals in the Absence of MHC Class II Molecules

The inflammatory activity of staphylococcal enterotoxin B (SEB) relies on its capacity to trigger polyclonal T-cell activation by binding both T-cell receptor (TCR) and costimulatory receptor CD28 on T cells and MHC class II and B7 molecules on antigen presenting cells (APC). Previous studies highlighted that SEB may bind TCR and CD28 molecules independently of MHC class II, yet the relative contribution of these interactions to the pro-inflammatory function of SEB remained unclear. Here, we show that binding to MHC class II is dispensable for the inflammatory activity of SEB, whereas binding to TCR, CD28 and B7 molecules is pivotal, in both human primary T cells and Jurkat T cell lines. In particular, our finding is that binding of SEB to B7 molecules suffices to trigger both TCR- and CD28-mediated inflammatory signalling. We also provide evidence that, by strengthening the interaction between CD28 and B7, SEB favours the recruitment of the TCR into the immunological synapse, thus inducing lethal inflammatory signalling.

Inhibition of Arterial Allograft Intimal Hyperplasia Using Recipient Dendritic Cells Pretreated with B7 Antisense Peptide

Background. Low expression or absence of dendritic cell (DC) surface B7 molecules can induce immune tolerance or hyporesponse. Whether DCs could induce indirect allogeneic-specific cross-tolerance or hyporesponse to recipient T cells remains unclear.Methods. Generated from C3H/He mice bone marrow cells pulsed with donor antigen from C57BL/6 mice, recipient DCs were incubated with B7 antisense peptide (B7AP). Immune regulatory activities were examinedin vitroby a series of mixed lymphocyte reactions. Murine allogeneic carotid artery orthotopic transplantation was performed from C57BL/6 to C3H/He. Recipients were given B7AP-treated DCs 7 days before transplantation. Allograft pathological analysis was done 2 months after transplantation.Results. B7AP-pretreated DCs markedly inhibited T-cell proliferation compared with untreated group. Pretreated T cells exhibited markedly reduced response to alloantigen versus third-party antigen. Pathological analysis of arterial allografts demonstrated significant reduction of intimal hyperplasia in B7-AP pretreated group versus control.Conclusion. Blockade of B7 molecules by B7AP could induce indirect allogeneic-specific hyporesponse and inhibit arterial allograft intimal hyperplasia, which may be involved in future strategies for human allograft chronic rejection.

Mantle Cell Lymphoma Cells Express B7 Family Molecules and B7-H1 Expression Are up-Regulated After LPS Exposure Via MEK-Dependent and PI3K/Akt-Dependent Pathways In Mantle Cell Lymphoma Cells

Abstract 3114 Mantle cell lymphoma (MCL) is a distinct subtype of B-cell non-Hodgkin lymphomas characterized by a specific t(11;14) (q13;q32) translocation, causing over-expression of cyclin D1. Recent studies demonstrated that B7 family molecules were not only expressed on antigen presenting cells but also on various hematopoietic malignancies, solid tumors and infiltrating immune cells and may play important roles in tumor immunology. Many cytokines could upregulate the expression of B7 molecules, however, the molecular mechanism of regulating expressions of B7 molecules is still unknown. In this study, we analyzed B7 family molecule expression on cultured mantle cell lymphoma cells and primary MCL cells by RT-PCR. We confirmed that B7 family molecules were detected in mantle cell lymphoma cell lines SP53, Jeko-1 and Mino and primary MCL cells. We next used LPS to activate TLR4 signaling pathway. Although B7 family molecules were detected in mantle cell lymphoma cells, only B7-H1 expression was greatly enhanced after LPS exposure. B7-H1 mRNA was constitutively expressed on MCL cells and was further up-regulated after LPS stimulation in dose and time dependent manners. Western blot also indicated that total and surface B7-H1 protein expression were up-regulated after stimulated by LPS. Flow cytometry demonstrated that surface B7-H1 protein expression were up-regulated after stimulated by LPS. When we knockdown TLR4, LPS stimulation did not up-regulate B7-H1 expression. To clarify the signaling pathways of LPS induced B7-H1 up-regulation in MCL cells, we incubated the SP53 and Jeko-1 cells with LPS after pretreatment with different signal transduction pathway inhibitors for 1h and detect the activity of each inhibitor. Pretreatment and coincubation of SP53 and Jeko-1 cells with the MEK1/2 inhibitor UO126 and PI3K/Akt inhibitor LY294002 strongly reduced LPS induced B7-H1 expression, indicating that the MEK1/2 and PI3K/Akt pathway are crucial for B7-H1 expression in MCL cells. We also tested whether JNK or p38, respectively, are involved in controlling the expression of B7-H1 in MCL cells. Blocking of JNK and p38 MAPK with specific inhibitors reduced B7-H1 mRNA expression, but B7-H1 protein expression was not obvious, which may be regulated after transcriptional factors. To confirm that LPS induced B7-H1 expression through a MEK and PI3K/Akt pathway pathways in MCL cells, we stimulated SP53 and Jeko-1 with LPS and analyzed the phosphorylation of ERK1/2, p38, and JNK at different time. ERK1/2, p38, and JNK phosphorylation were significantly up-regulated following LPS treatment. We confirmed that pretreatment of the cells with these specific inhibitors inhibited LPS-induced phosphorylation of ERK1/2, p38 MAPK, and JNK, respectively. In conclusion, our study demonstrated that mantle cell lymphoma cells express B7 family molecules. B7-H1 expression were up-regulated after LPS exposure via MEK-dependent and PI3K/Akt-dependent in mantle cell lymphoma cells. Disclosures: No relevant conflicts of interest to declare.