Balance of Treg vs. T‐helper cells in the transition from symptomless to lesional psoriatic skin

Background In the pathogenesis of psoriasis, proinflammatory T cells are strongly involved in the inflammatory process, where regulatory T‐cell (Treg) function is impaired. Objectives As effective Treg function is associated with a numerical balance between Treg and effector T cells, we wondered whether Treg/T‐helper cell ratios may be associated with certain stages of the inflammatory process. We opted for the margin zone model as a dynamic approach. Methods From nine patients with chronic plaque psoriasis, 3‐mm punch biopsies were obtained from the centre and margin of the lesion, perilesional skin and distant uninvolved skin. Skin biopsies of 10 healthy volunteers were included as a control. Samples were analysed using immunohistochemistry and immunofluorescence. Results In the transition from symptomless to lesional skin, a significant increase of CD3+, CD4+ and Foxp3+ cells was found. In seven of nine patients the ratio of Treg (Foxp3+) vs. CD4+ T cells was higher in the distant uninvolved skin than in the perilesional and lesional skin. Interestingly, the Foxp3/CD4 ratio in the distant uninvolved skin was even higher than in the skin of healthy controls. Notably, we found that most of the interleukin (IL)‐17 expression was not related to CD4+ cells, but to mast cells. Conclusions The relatively high Foxp3/CD4 ratio in symptomless skin of patients with psoriasis suggests an active immune controlling mechanism distant from the psoriatic plaque. In the margin and centre of the plaque the ratio appears skewed towards effector cells associated with inflammation. IL‐17, an important driver of the psoriatic process, is mostly related to mast cells, and only sporadically to T cells.