Source and characterization of hepatic macrophages in acetaminophen-induced acute liver failure in humans

Acetaminophen-induced acute liver failure (AALF) is associated with innate immunity activation, which contributes to the severity of hepatic injury and clinical outcome. A marked increase in hepatic macrophages (h-m?) is observed in experimental models of AALF, but controversy exists regarding their role, implicating h-m phi in both aggravation and resolution of liver injury. The role of h-m phi in human AALF is virtually unexplored. We sought to investigate the role of chemokine (C-C motif) ligand 2 (CCL2) in the recruitment of circulating monocytes to the inflamed liver and to determine how the h-m phi infiltrate and liver microenvironment may contribute to tissue repair versus inflammation in AALF. We evaluated circulating monocytes, their chemokine (C-C motif) receptor 2 (CCR2) expression, and serum CCL2 levels in patients with AALF. Cell subsets and numbers of circulation-derived (MAC387+) or resident proliferating (CD68/Ki67+) h-m phi in hepatic immune infiltrates were determined by immunohistochemistry. Inflammatory cytokine levels were determined in whole and laser microdissected liver tissue by proteome array. In AALF, circulating monocytes were depleted, with the lowest levels observed in patients with adverse outcomes. CCL2 levels were high in AALF serum and hepatic tissue, and circulating monocyte subsets expressed CCR2, suggesting CCL2-dependent hepatic monocyte recruitment. Significant numbers of both MAC387+ and CD68+ h-m phi were found in AALF compared with control liver tissue with a high proportion expressing the proliferation marker Ki67. Levels of CCL2, CCL3, interleukin (IL)-6, IL-10, and transforming growth factor-beta 1 were significantly elevated in AALF liver tissue relative to chronic liver disease controls. Conclusion: In AALF, the h-m phi population is expanded in areas of necrosis, both through proliferation of resident cells and CCL2-dependent recruitment of circulating monocytes. The presence of h-m phi within an anti-inflammatory/regenerative microenvironment indicates that they are implicated in resolution of inflammation/tissue repair processes during AALF. (HEPATOLOGY 2012)