Circulating dendritic cell subsets in psoriatic patients before and after biologic therapy

Psoriasis is an immune-mediated skin disease affecting approximately 2% of the population;1 its pathogenesis is characterized by a complex interplay of cells and cytokines.2 Recently, attention has focused on two main subpopulations of dendritic cells (DC), myeloid DC (mDC) and plasmacytoid DC (pDC), which represent a critical link between the innate and the adaptive immune systems.3 In the inflamed psoriatic dermis, there is an increase in mDC,4 probably derived from circulating DC precursors which migrate into the skin in response to chemotactic signals and synthesize high levels of pro-inflammatory cytokines (e.g. interleukin [IL]-12 and IL-23).5 pDC have been identified in the lesional and in the non-lesional psoriatic skin. Activated pDC produce interferon (IFN)-α in the early phase of the development of a psoriasis lesion with a strong amplification of a pathogenetic role of T lymphocytes.6 The antimicrobial peptide LL37 is expressed in high concentrations in psoriatic skin and through its binding with self-DNA is a potent activator of pDC.7 In a previous work, we have reported a reduction of both mDC and pDC in psoriatic lesions upon treatment with biologic therapies,8 but to date no studies have compared blood DC before and upon biologic treatment. Our purpose was to monitor the blood DC compartment in psoriatic patients before and during biologic therapy with infliximab (an anti-tumor necrosis factor-α molecule). Our analysis could better focus the activity of this drug on the number and phenotype of DC.