IFN-β cooperates with IL-3 to promote monocyte survival.

Monocytes were cultured in medium alone (○) or in the presence of 50 U/mL IL-3 (▿) or 1000 U/mL IFN-β (●) or a combination of 1000 U/mL IFN-β and 50 U/mL IL-3 (▾). Apoptotic cells were enumerated by flow cytometry after staining for annexin V and PI). Results were expressed as mean ± SEM of percentages of cells negative for the expression of annexin V and PI.