Interleukin-33 promotes type 1 cytokine expression via p38 MAPK in human natural killer cells

David E. Ochayon; Ayad Ali; Pablo C. Alarcon; Durga Krishnamurthy; Leah C. Kottyan; Michael Borchers; Stephen N. Waggoner

IL-18 can enhance IL-12-provoked IFN- production by promoting IFNG transcript stability, which is mediated by p38 MAPK signaling 23 . To determine whether IL-33 exerts a similar effect on IFNG transcript stability, human NK cells were incubated with IL-12 alone or in combination with IL-33 for 6 hours in conjunction with pretreatment with R-1503 or vehicle control. Four hours after cytokine administration, cultures were treated with actinomycin D (5 g/mL) to halt de novo transcription, thereby permitting measurement of decay of existing IFNG transcripts. As shown in Fig. 7 , IFNG levels dropped in all experimental groups after addition of actinomycin D. Treatment of NK cells with IL-33 and IL-12 (Fig. 7 , dark purple) resulted in a significantly greater half-life of IFNG transcripts (116±3 minutes for IL-33/IL-12 versus 75±3 minutes for IL-12, p<0.0001) compared to NK cells stimulated with IL-12 alone (Fig. 7 , solid black lines, dark gray bar). The addition of R-1503 accelerated the decay of INFG transcripts ( Fig. 7 left plot, dashed lines) , and largely abrogated the enhancing effects of IL-33 (Fig. 7 , right plot, light purple bar) relative to IL-12 alone (Fig. 7 , right plot, light grey bar) in terms of half-life of IFNG transcripts (62±2 minutes for IL-33/IL-12 versus 52±2 minutes for IL-12, p=0.045). Thus, IL-33 acts to enhance IFNG transcript stability via p38 MAPK.