TLR9 and rheumatoid arthritis: In particular, we observed an increase in IL-12 in both PsA and RA DC in response to CPG (TLR9) stimuli and TNFα in PsA in response to TLR3 stimuli (Poly I:C); both cytokines having a key role in DC immuno-biology, conferring a more mature phenotype to DC, leading to T cells activation (49, 50).