The effects of activin-A on NK-cell IFN-γ production. Purified NK cells were cultured at 105 in 96-well plates in media supplemented with IL-2 (20 U/mL) alone or IL-2 + IL-12 (10 ng/mL) with or without the addition of poly I:C (12.5 μg/mL) in the absence or presence of increasing concentrations of activin-A. (A) NK-cell production of IFN-γ by ELISA. (B) NK-cell production of IFN-γ by ELISA after pretreatment with the activin type I receptor antagonist SB431542 (10 μmol/L) for 30 minutes before addition of activin-A. Data represents the mean plus or minus 1 SD of 3 separate donors. *P < .01 versus no activin-A and versus SB431542 pretreatment.