Basophils amplify cytokine IL-17, IL-22, and IFN-γ release in a contact-independent manner. (A) Expression of costimulatory molecules on purified basophils (CD1c-FcϵRI^highSIRP-α^low); filled histogram represents staining with isotype-matched control mAb. Data from 1 representative experiment of 5 are shown. (B) T_EM were labeled with CFSE and cocultured in the presence of IL-2 plus IL-3 with or without basophils. After 5 days, cell proliferation was assessed by CFSE cell dilution. Data from 1 representative experiment of 4 are shown. (C-D) T_EM were cocultured with or without autologous (white symbols) or allogeneic (black symbols) basophils (at a 5:1 ratio) in the presence of IL-3 and IL-2. After 4-5 days, cells were restimulated with PMA ionomycin for 6 hours. (C) Mean fluorescence intensity (MFI) of IL-17 expression in IL-17⁺CD2⁺FcϵRI⁻ cells. (D) T_EM were separated or not from basophils using a Transwell insert. IL-17, IL-22, IFN-γ, and TNF-α secretion were measured with ELISA. *P < .05; **P < .01; ***P < .001.