Background: Prurigo nodularis (PN) is a chronic dermatitis characterized by discrete, raised, and firm papulonodules with intense pruritus. The pathogenesis still remains to be elucidated. Objectives: To clarify the role of Th1 and Th2 cytokines in the pathogenesis of PN. Methods: We examined the cytokine signatures, such as phosphorylation of STAT1, STAT3 and STAT6, HLA-DR and hyaluronan accumulation, to reveal the Th1 and Th2 cytokine influence on the lesional epidermis of PN. Results: We first optimized antigen retrieval methods to detect these signatures with antibodies for phospho-STAT1 (pSTAT1), phospho-STAT3 (pSTAT3), phospho-STAT6 (pSTAT6), HLA-DR and hyaluronic acid binding protein (HABP) on the formalin-fixed paraffin-embedded sections of psoriasis, lichen planus and atopic dermatitis biopsy samples. Activation of STAT1 and STAT6 in epidermis by Th1 and Th2 cytokines was further confirmed in a cultured skin equivalent model treated with interferon-γ or interleukin (IL)-4/IL-13. With the relevant immuno-staining methods, we examined the cytokine signatures in 22 cases of PN. The results revealed that (i) the entire epidermis of 19 cases was stained with anti-pSTAT6 antibody, (ii) 21 cases demonstrated nuclear staining with anti-pSTAT3 antibody, (iii) the entire epidermis of 21 cases was stained with HABP, (iv) the epidermis of eight cases showed scattered staining with anti-pSTAT1 antibody, and (v) six cases were positive for HLA-DR membrane expression. Conclusions These data indicated that Th2 cytokines related to STAT6 activation together with some unknown stimuli that activate STAT3 play a principal role in the pathogenesis of PN.
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