Phenotypic and functional changes to porcine monocyte-derived macrophages triggered by IL-1β and its receptor antagonist IL-1Ra

Pigs are attracting increasing attention as a large-animal model with translational relevance in biomedical research. They share several immunological similarities with humans, although the pig immune system has not been fully characterized yet, also at the level of macrophage polarization. A better understanding of porcine macrophage polarization could improve translational studies, allowing a better interpretation of in vitro and in vivo results. In this study, we performed a detailed characterization of the impact of two poorly studied cytokines [interleukin-1β (IL-1β) and its receptor antagonist IL-1Ra] on porcine monocyte-derived macrophage (moMФ) phenotype and functions. The effects of these IL-1 family members were investigated through microscopy, flow cytometry, enzyme-linked immunosorbent assay (ELISA), and gene expression studies. We observed that stimulation with IL-1β increased CD14, SLA-I, and SLA-II DR expression, and enhanced the release of pro-inflammatory cytokines, particularly IL-6, IL-12, and IL-1α at higher concentrations, and the expression of several antiviral and pro-inflammatory genes, including JUN, FOS, and MAP3K1. The concomitant release of IL-10 and IL-1Ra suggests that IL-1β stimulation may also activate compensatory regulatory feedback mechanisms aimed at limiting excessive inflammation. In contrast, IL-1Ra had limited effects on surface marker expression but increased IL-10 release. A small but significant release of IL-1α was also observed, as well as a trend toward enhanced IL1B expression at 24 h, suggesting a potential regulatory interaction within the IL-1 axis. MoMФ stimulated with IL-1Ra was also able to release high levels of IL-12 in response to stimulation with a TLR-3 ligand [polyinosinic–polycytidylic acid (poly I:C)], with an intensity comparable to moMФ and moMФ stimulated with IL-1β. Our data suggest that porcine macrophages attempt to maintain a balance between IL-1β and IL-1Ra, as a defense mechanism to control inflammation, by counteracting each other’s activity. Overall, in this work, we provided a better understanding of porcine macrophage polarization, which could benefit translational studies using this large-animal model.