An in vitro modelling of resolving macrophage with Raw 264.7 macrophage cell line

In acute inflammation, macrophages polarises its phenotype in order to participate effectively in the inflammatory, anti-inflammatory and resolving phases. Particularly, the resolving phase is vital for homeostatic recovery. The in vivo murine peritonitis model had identified various subtypes of resolving macrophages. However, the in vivo model has limitations in deciphering the molecular mechanisms required for resolving macrophage polarisation. Therefore the aim of this study is to establish an in vitro model that could simplify the reproduction of resolving macrophage polarisation. This model will be a useful tool to screen for molecular mechanisms essential for triggering resolution. Our in vitro model showed Raw 264.7 cells exhibited classical inflammatory-like (M1-like) phenotype between 2-24 h with increased interleukin-1β expression and tumour necrosis factor-α secretion. Concurrently, at 22-24 h there was an increase in Raw 264.7 cells polarising to anti-inflammatory like (M2-like) phenotype. These M2-like macrophages were increased in arginase activity and interleukin-10 expression. By 48 h, Raw 264.7 cells were polarised to resolving-like (Mres-like/CD11b low) phenotype. These macrophages were characterised by high efferocytic index and a decrease in inflammatory cytokine expression, low arginase activity and low CD11b expression. In summary, this in vitro resolution model showed resolving-like polarisation in a macrophage cell line.