IL-1Ra augments IFN-λ1 production by pDCs. (A) pDCs were stimulated overnight with HSV in the presence of IL-4 (50 ng/mL), IL-1 (100 ng/mL), or IL-1Ra as indicated; SNs were assayed by ELISA for IFN-λ1 (means ± SD from 3 independent experiments are shown). (B) Monocytes from 2 separate donors were incubated for 1 hour with IL-4, washed twice, and then cultured overnight. SNs were collected and used as culture medium for purified allogeneic pDCs, isolated from 2 independent donors. pDCs were incubated overnight in medium or SNs from IL-4–treated monocytes with or without neutralizing Ab to IL-1Ra, and stimulated with HSV. IFN-λ1 levels were measured by ELISA. A total of 2 independent experiments are shown (means ± SD). *P < .05 as determined by the Student t test.