In psoriasis, the dramatic improvement of the psoriatic skin lesions by blocking IL-17s is evident, therefore IL-17 is recognized as the key cytokine in psoriatic inflammation. So many cells have been proposed as the main source of IL-17 producing cells in psoriasis, however the real IL-17 supplier in psoriasis is still controversial. Neutrophil is the majority in the psoriatic lesions, and have been suggested IL-17 producer. Presence of IL-17 immunoreactive neutrophils in the psoriatic skin lesions has been reported histopathologically as well as in peripheral blood by flow cytometric analysis. However, a report declared absence of IL-17mRNA expression by RT-PCR, but others reported presence in the severe psoriasis patients. Is there any technical issue to address this inconsistency? 
　　Neutrophil and lymphocyte are commonly separated by a gradient density cell separation. However, the neutrophil fraction by this method contains many co-migrated monocyte and lymphocyte. In contrast, the neutrophil fraction separated by specific magnetic beads shows higher purity than that by gradient density cell separation. IL-17A mRNA was amplified by PCR in monocyte and T cell, however was undetectable in the specific beads-separated neutrophil fraction from both of the healthy controls and severe psoriasis patients. The neutrophil fraction by the density gradient cell separation showed IL-17A mRNA amplification. 
    In conclusion, neutrophil is not the actual major source of IL-17A in psoriasis, but activated monocyte and lymphocyte are the dominant suppliers of IL-17A. The contaminated monocyte or lymphocyte-derived IL-17A mRNA was detected in the neutrophil fraction by a gradient density cell separation.

Is neutrophil the dominant IL-17 producer in psoriasis?