Nonalcoholic steatohepatitis (NASH) is characterized by extensive hepatic 
monocyte infiltration and monocyte-derived macrophages have an important role in 
regulating the disease evolution. However, little is known about the functional 
changes occurring in liver macrophages during NASH progression. In this study, 
we investigated phenotypic and functional modifications of hepatic macrophages 
in experimental NASH induced by feeding C57BL/6 mice with a methionine-choline 
deficient (MCD) diet up to 8weeks. In mice with steatohepatitis liver 
F4/80-positive macrophages increased in parallel with the disease progression 
and formed small clusters of enlarged and vacuolated cells. At 
immunofluorescence these cells contained lipid vesicles positive for the 
apoptotic cell marker Annexin V suggesting the phagocytosis of apoptotic bodies 
derived from dead fat-laden hepatocytes. Flow cytometry revealed that these 
enlarged macrophages expressed inflammatory monocyte (CD11b, Ly6C, TNF-α) 
markers. However, as compared to regular size macrophages the enlarged sub-set 
was characterized by an enhanced production of arginase-1 and of the 
anti-inflammatory mediators IL-10 and annexin A1. Similar vacuolated macrophages 
producing annexin A1 were also evident in liver biopsies of NASH patients. In 
mice with NASH, the accumulation of enlarged F4/80(+) cells paralleled with a 
decline in the expression of the macrophage M1 activation markers iNOS, IL-12 
and CXCL10, while the levels of M2 polarization markers arginase-1 and MGL-1 
were unchanged. Interestingly, the lowering of IL-12 expression mainly involved 
the macrophage sub-set with regular size. We conclude that during the 
progression of NASH fat accumulation within liver macrophages promotes the 
production of anti-inflammatory mediators that influence hepatic inflammatory 
responses.