Malignant CTCL cell lines express IL-17F and/or IL-17A. Nonmalignant (MySi) and malignant (MF2000, PB2B, SeZ-4, and SeAx) T-cell lines established from patients with CTCL were cultured for 24 hours in the absence (−) or presence (P + I) of PMA (50 ng/mL) and ionomycin (1 µg/mL). Subsequently, the concentrations of (A) IL-17F, (B) IL-17A, and (C) IL-17A/F heterodimers in the cell culture supernatants were determined by enzyme-linked immunosorbent assay. Bars represent mean + SEM.