70 Both these events are necessary Selleckchem PD0325901 for the activation of the IKK complex and further activation of the NF-κB pathway; however, they may occur independently of each other.70 Carma1, BCL10, MALT1, IKK components and Tak1 have

been shown to localize to the immunological synapse.71,72 An alternative pathway of NF-κB activation involves stabilization of NF-κB inducing kinase (NIK) owing to proteosomal degradation of tumour necrosis factor receptor-associated factor 3 following TCR stimulation. The NIK activates IKKα, which phosphorylates p100 leading to proteosomal processing of p100 to p52.65 Proteosomal processing of the C-terminal half of p105 into p50 occurs constitutively in unstimulated cells.64 Nuclear factor-κB is shown to regulate a number of genes involved in immunity, cell

proliferation and apoptosis.59,73,74 Which NF-κB dimers specifically target particular genes has not been resolved.64 Studying the immune responses in mice deficient in NF-κB proteins has revealed that NF-κB plays a very important role in regulating immune responses. However, a specific role for NF-κB in regulating T-cell differentiation is not known. There are reports that suggest that NF-κB components may regulate both Th1 and Th2 responses. T cells lacking p50 failed to produce IL-4, IL-5 and IL-13 as a result of failure to induce GATA-3 under Th2-polarizing conditions and at the same time they have been shown to affect Th1 responses.75,76 RelB-deficient T cells have defects in Th1 differentiation.77 Deficiency of c-Rel in T cells has been shown to affect IFN-γ and find more IL-2 production, and so to affect Th1 responses.78–81 c-Rel plays a role in autoimmunity and allogeneic transplants as revealed from studies on c-Rel-deficient mice.78,82,83 Deficiency of p50 and c-Rel in CD4 T cells has revealed a role of these transcription

Interleukin-3 receptor factors in CD4 T-cell survival in vivo.78,84 RelA-deficient T cells have reduced proliferation in response to TCR stimulation.85 There is a general consensus that all NF-κB members affect TCR-induced proliferation of T cells to some extent.86 NFAT, AP-1 and NF-κB are not the only family of transcription factors that are activated downstream of TCR. Among the other transcription factor family members that are directly regulated by TCR signalling are the forkhead family of transcription factors Foxo1, Foxo3 and Foxo4.87 Their nuclear export is regulated by phosphorylation by Akt, which is activated by phosphatidylinositol 3-kinase signalling known to occur downstream of TCR.87 Mef2 is a transcription factor that is activated downstream of TCR by calcium signalling.47 It is maintained in an inhibitory state in the cytoplasm in complex with a protein called cabin1 which is an inhibitor of calcineurin.88 Intracellular calcium increase leads to dissociation of MEF2 from Cabin1 through competitive binding of calmodulin.88 The Mef2 regulates apoptosis in T cells by regulating the expression of the Nur77 family of orphan nuclear receptors.