Figure 1.

M1 and M2 Kupffer cells. Kupffer cells are stimulated by various triggering agents and become active as M1 or M2 Kupffer cells. Foreign pathogens or proinflammatory cytokines activate Kupffer cells as M1 Kupffer cells, leading to further proinflammatory cytokine secretion or production of reactive oxygen species (ROS). Other cytokines, such as IL-4 and IL-13, promote Kupffer cell activation into M2 subsets, leading to anti-inflammatory cytokine secretion, as well as transforming growth factor (TGF)-β secretion, leading to fibrogenesis. A later study has shown that M2 Kupffer cells promote apoptosis of M1 Kupffer cells via IL-10 secretion to maintain homeostasis and balance of M1/M2 Kupffer cell population.³⁶ Recent studies have demonstrated that some miRNAs can deactivate Kupffer cells or inhibit Kupffer cell activation, which may also be associated with liver diseases.41, 42, 43 LPS, lipopolysaccharide; TNF-α, tumor necrosis factor-α.