Effects of Small-Molecule Inhibitors of TNFR2 Signaling Pathways On TNF-Mediated Expansion of CD4+FoxP3+ Regulatory T Cells

Abstract 4722

TNF is a pleiotropic cytokine with biphasic proinflammatory and immunosuppressive effects. Previous work clearly demonstrated that TNF has the capacity to preferentially activate and promote the proliferative expansion of CD4+FoxP3+ regulatory T cells (Tregs), which represent a basis for the paradoxical anti-inflammatory action of TNF. Our studies also indicate that TNFR2, one of the TNF receptor which is preferentially expressed by Tregs, mediates the Treg-activating effect of TNF. However, the molecular mechanism and signaling pathways mediated Treg-activating effect of TNF remain to be understood.

In this study, we first further verified that TNFR2 transduces the activating signal of TNF on Tregs, based on the evidence that 1) human TNF, known to only bind to mouse TNFR1, did not activate mouse Tregs; 2) a blocking anti mouse TNFR2 Ab, but not TNFR1 Ab, dose-dependently inhibited TNF-mediated proliferation of mouse Tregs at concentrations of 2.5–500 ng/ml. We next examined the signaling pathways of TNFR2 leading to the proliferation of Tregs, by using specific small-molecule inhibitors. It is well established that the activation of IKK-NFkB is a major consequence of activation of TNFR2. However, small molecule inhibitors of NFkB signaling pathway, namely BAY11–7082 and Sulfasalazine, did not block TNF-mediated proliferation of Tregs. In contrast, small molecule inhibitors of MAPK signaling pathway, SB203580 (P38 MAPK inhibitor), SP600125 (JNK inhibitor) and PD98059 (Erk1/2 inhibitor), potently suppressed TNF-induced replication of Tregs in a dose-dependent manner.

Our results indicate that TNF selectively stimulates the expansion of FoxP3+ Tregs through TNFR2. Activation of MAPK (ERK1/2,P38 and JNK), rather than NFkB, is responsible for this activity of TNF.