Bacterial isolates from CTCL patients contain SEs. (A) Mixed bacterial isolates from patients were tested for SE expression (SEA, SEB, SEC, SED, and TSST-1) and categorized accordingly as either positive or negative. Cocultures with malignant T cells (SeAx) and nonmalignant T cells (MF1850) were then stimulated with SE-positive or SE-negative isolates and incubated for 24 hours. IL-17 concentration in the supernatants was determined by ELISA. (B) Malignant (SeAx) and nonmalignant (MF1850) T-cell lines were mono- and cocultured in the absence (Media) or presence (Isolate) of a mixed bacterial isolate from a CTCL patient. IL-17A protein was measured in the supernatant after 24 hours of incubation with ELISA. (C-D) Malignant (SeAx) and nonmalignant (MF1850) T-cell lines were mono- and cocultured with vehicle (PBS) or recombinant SEA (50 ng/mL) (C), or with PBS, SEAwt, or the toxins SEAD227A, SEAF47A/D227A, SEB, SEC2, SED, SEE, SEI, or TSST-1 (50 ng/mL) (D). IL-17A protein was measured in the supernatant after 24 hours of incubation with ELISA. (E) Malignant (SeAx) and nonmalignant (MF1850) T-cell lines were mono- and cocultured with SEA (50 ng/mL) and tofacitinib (0.3 μM) or vehicle (dimethylsulfoxide [DMSO]) for 24 hours. After incubation, IL-17A protein concentration was determined by ELISA. Error bars represent standard error of the mean of 3 independent experiments. *P < .05. Malign., malignant; Neg, negative; Non-malign., nonmalignant; Pos, positive.