Comparative Phenotypic and Functional Analyses of the Effects of IL-10 or TGF-β on Porcine Macrophages

Abstract

Simple Summary Macrophages play a central role in innate immune response to both infectious and non-infectious stressors. They respond to different agonists modifying their phenotype and functions. In humans and mice, the regulatory cytokines IL-10 or TGF-β are both known to drive macrophage polarization into an anti-inflammatory phenotype, referred to as M2c. However, the immune systems of animal species each have their own peculiarities and the M2c subsets has never been investigated in pigs. A deep knowledge of the porcine immune system is required to design vaccines or control strategies against pathogens, which are a major constraint to pork production. Due to anatomical, physiological, and immunological similarities, swine are attracting increasing attention as a model for human diseases. To better characterize porcine macrophages, we evaluated the effects of IL-10 or TGF-β on the phenotype and function of monocyte-derived macrophages. Both cytokines downregulated the expression of MHC II DR and CD14. IL-10, but not TGF-β, statistically significantly reduced the ability of macrophages to respond to Toll-like receptor 2 (TLR2) or TLR4 agonists. Whilst these data suggest differentiation to an M2c-like immunosuppressive phenotype, the responses, and differences between IL-10 and TGF-β also reveals species-specific differences. Abstract Macrophages are phagocytic cells involved in maintaining tissue homeostasis and defense against pathogens. Macrophages may be polarized into different functionally specialized subsets. M2c macrophages arise following stimulation with IL-10 or TGF-β and mediate anti-inflammatory and tissue repair functions. M2c macrophages remain poorly characterized in the pig, thus we investigated the impact of these regulatory cytokines on porcine monocyte-derived macrophages (moMΦ). The phenotype and functionality of these cells was characterized though confocal microscopy, flow cytometry, ELISA, and RT-qPCR. Both cytokines induced CD14 and MHC II DR down-regulation and reduced IL-6, TNF-α, and CD14 expression, suggestive of an anti-inflammatory phenotype. Interestingly, neither IL-10 or TGF-β were able to trigger IL-10 induction or release by moMΦ. Differences between these cytokines were observed: stimulation with IL-10, but not TGF-β, induced up-regulation of both CD16 and CD163 on moMΦ. In addition, IL-10 down-regulated expression of IL-1β and IL-12p40 4h post-stimulation and induced a stronger impairment of moMΦ ability to respond to either TLR2 or TLR4 agonists. Overall, our results provide an overview of porcine macrophage polarization by two immunosuppressive cytokines, revealing differences between IL-10 and TGF-β, and reporting some peculiarity of swine, which should be considered in translational studies.