Necrotic liver induces pyroptosis through Caspase-1 in eosinophils

Abstract

Abstract During sterile inflammatory reactions damage associated molecular patterns (DAMPS) are released from necrotic cells and recruit immune cells to the sites of tissue injury. We found that necrotic liver homogenates, when injected intraperitoneally, can recruit large numbers of immune cells. Among these immune cells were activated eosinophils. Eosinophils are polymorphonuclear leukocytes typically found within tissues of the gastrointestinal and respiratory tracts. While eosinophils are well known to accumulate in the lungs of asthmatics or in response to helminths and parasites, several studies have shown the presence of eosinophils in liver biopsies of drug-induced liver injury, chronic hepatitis C and liver fibrosis. The prevalence of eosinophilic infiltrates in the liver points to a correlation between infiltration and disease outcome. Our results demonstrated eosinophil activation upon exposure to necrotic liver components. Exposure to necrotic liver cells induced eosinophil degranulation as measured by expression of CD107a and eosinophil peroxidase release as measured by ELISA. Further study of eosinophil activation during necrotic liver exposure showed IL-1β and IL-18 release as well as cell death. All of these responses were dependent upon caspase-1 activation. Caspase-1 mediated cell death accompanied by IL-1β and IL-18 release are hallmarks of pyroptosis, an inflammatory cell death pathway. We verified eosinophil pyroptosis in vivo using a liver fibrosis model involving Schistosoma mansoni infected mice. Eosinophils extracted from S. mansoni infected livers showed caspase-1 activation and cytokine release indicating that these cells undergo pyroptosis in vivo in response to hepatocyte injury.