Human neutrophils activated by TLR8 agonists, with or without IFNγ, synthesize and release EBI3, but not IL‐12, IL‐27, IL‐35, or IL‐39
The IL‐12 family of cytokines plays crucial functions in innate and adaptive immunity. These cytokines include heterodimers sharing distinct α (IL‐12A, IL‐23A, and IL‐27A) with two β (IL‐12B and Epstein‐Barr virus induced gene 3 [EBI3]) chains, respectively, IL‐12 (IL‐12B plus IL‐12A) and IL‐23 (IL‐12B plus IL‐23A) sharing IL‐12B, IL‐27 (EBI3 plus IL‐27A), IL‐35 (EBI3 plus IL‐12A), and IL‐39 (EBI3 plus IL‐23A) sharing EBI3. In this context, we have recently reported that highly pure neutrophils incubated with TLR8 agonists produce functional IL‐23. Previously, we showed that neutrophils incubated with LPS plus IFNγ for 20 h produce IL‐12. Herein, we investigated whether highly pure, TLR8‐activated, neutrophils produce EBI3, and in turn IL‐27, IL‐35, and IL‐39, the IL‐12 members containing it. We report that neutrophils incubated with TLR8 ligands, TNFα and, to a lesser extent, LPS, produce and release remarkable amounts of EBI3, but not IL‐27A, consequently excluding the possibility for an IL‐27 production. We also report a series of unsuccessful experiments performed to investigate whether neutrophil‐derived EBI3 associates with IL‐23A to form IL‐39. Furthermore, we show that neutrophils incubated with IFNγ in combination with either TLR8 or TLR4 ligands express/produce neither IL‐12, nor IL‐35, due to the inability of IFNγ, contrary to previous findings, to activate IL12A transcription. Even IL‐27 was undetectable in supernatants harvested from IFNγ plus R848‐treated neutrophils, although they were found to accumulate IL27A transcripts. Finally, by immunohistochemistry experiments, EBI3‐positive neutrophils were found in discrete pathologies only, including diverticulitis, cholecystitis, Gorham disease, and Bartonella Henselae infection, implying a specific role of neutrophil‐derived EBI3 in vivo.