Synergy of interleukin-4 and interferon-γ in arginase-1 production in RAW264.7 macrophages.

Background: Interferon (IFN)-γ and interleukin (IL)-4 are considered to be important factors to regulate immune responses. Although the effects of IFN-γ or IL-4 on macrophage functions are well established, their cooperative action is not fully understood.

Objective: Inducible nitric oxide synthase (iNOS) or arginase (Arg)-1 is a representative marker of M1 or M2 macrophages and plays a role in the acceleration or suppression of inflammatory responses. In the present study, we examined the effect of simultaneous treatment with IFN-γ and IL-4 on macrophage expression of iNOS and Arg-1 using the murine macrophage cell line RAW264.7.

Methods: Protein production and mRNA expression of iNOS and Arg-1 were measured using immunoblotting and reverse transcription-polymerase chain reaction. Cell surface expression of CD86 and programmed death ligand (PD-L) 2 was analyzed using flow cytometry.

Results: IFN-γ or IL-4 increased iNOS or Arg-1 protein production, respectively. Of note, IL-4 combined with IFN-γ synergistically increased Arg-1 protein production, whereas IL-4 inhibited IFN-γ-induced iNOS production. This phenomenon was consistent with the mRNA levels. In addition, IL-4 combined with IFN-γ synergistically increased cell surface expression of PD-L2, which is involved in T cell suppression, whereas IL-4 completely inhibited IFN-γ-induced expression of CD86, which is responsible for T cell activation.

Conclusions: In the present study, we found the synergy of IFN-γ and IL-4 in Arg-1 and PD-L2 expression. Thus, macrophages highly expressing Arg-1 and PD-L2 may be induced by both IFN-γ and IL-4 at the inflammatory site, and might play a role in the regulation of inflammatory immune responses.