Monocyte-derived interferon-alpha primed dendritic cells in the pathogenesis of psoriasis: new pieces in the puzzle

Psoriasis is a common chronic inflammatory skin disorder with serious clinical, psychosocial, and economic consequences. There is much evidence that different dendritic cell (DC) subsets, various proinflammatory cytokines and Toll-like receptors (TLRs) have a central role in the pathogenesis of the disease. One of the early events in psoriatic inflammation is the secretion of interferon (IFN)-α by activated plasmacytoid DCs, a special DC subset present in symptomless psoriatic skin. Secreted IFN-α along with other proinflammatory cytokines can lead to monocyte-derived DC (moDC) development, which might contribute to T-helper (Th)1 and Th17 lymphocyte differentiation/activation and to keratinocyte proliferation. Recently it was proven that interleukin (IL)-12 and IL-23 play a critical role in this process. Additionally in psoriatic lesions, Th1 and Th17 lympocytes can interact with monocytes and instruct these cells to differentiate into Th1- and Th17-promoting moDCs, further governing the formation and function of specialized moDC subsets. The concept we present here focuses on the initial and central role of IFN-α, on the importance of other proinflammatory cytokines, on TLR stimulation and on the effect of T lymphocytes in priming moDCs, which may play an important role in initiating and maintaining psoriasis.