The regulation of dendritic cell maturation and survival by tumour necrosis factor receptors 1 and 2

Abstract

Dendritic cells (DC) are potent antigen presenting cells which have been implicated in a number of autoimmune diseases. Tumour necrosis factor (TNF) is a key mediator of inflammatory diseases such as rheumatoid arthritis (RA) and plays a central role in DC biology. My aim was to identify the individual contributions of the two TNF receptors (TNFR1 and TNFR2) in regulating the maturation and survival of human inflammatory monocyte-derived (moDC) and steady-state myeloid DC. To address this, I have made use of TNFR-selective ligands in order to dissect the individual contributions of the two receptors. In moDC, TNFR1-selective, but not TNFR2-selective stimulation resulted in increased expression of DC maturation markers CD83 and CD86, and enhanced T cell stimulatory capacity. A DNA binding assay was used to demonstrate that in moDC TNFR1, but not TNFR2, activates the classical p65 NFB pathway whereas both TNFR1 and TNFR2 activate the alternative p100/p52 NFB pathway, highlighting differences in signalling downstream of the receptors. Furthermore, moDC survival was prolonged by selective stimulation of either TNFR1 or TNFR2 as shown by reduced intracellular levels of active caspase-3, indicating that innate signals can promote DC survival in the absence of DC maturation. Accordingly, the p65 NFB pathway was involved in the pro-survival effect of TNFR1 whereas the Bcl-2/Bcl-xL pathway (identified by the use of small molecule inhibitors) was essential to survival mediated by both TNFR. In contrast, in myeloid DC, maturation was mainly mediated through TNFR1, whereas TNFR2 was superior in protecting DC from cell death. Antagonistic TNFR1-specific antibodies were used to confirm that cell death protection via TNFR2 was independent of TNFR1-mediated signalling and vice versa confirming that the two receptors can act independently of one another. Understanding the immunoregulatory properties of signalling through these two TNF receptors is important for the design of more targeted anti-TNF therapy.