IL17A and histiocytic sarcoma: In the only case in which we had the possibility to analyze the three different sources (PB, HS lesion, and fistula curretage), we found more CD4+ IL-17- producing cells in HS lesion and fistula lesion than in PB, even if the CD4+ IFN-γ - producing cells did not differ among the different sources (Figure 3C).