Figure 4.

The effect of microgravity on macrophage polarization. M1 macrophages (left) are induced by LPS and highly express pro-inflammatory factors (TNF-α). M2 macrophages (right) are activated by IL-4 and are characterized by high expression of arginase I. Under microgravity conditions, HSF-1 and C/EBPβ are activated, resulting in a decrease of TNF-α expression and an increase of arginase I expression, respectively. Solid lines indicate the pathway affected by microgravity, whereas dashed lines indicate the pathway is not affected by microgravity. iNOS, inducible nitric oxide synthase.