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Kupffer cells form a large intravascular macrophage bed in the liver sinusoids. The differentiation history and diversity of Kupffer cells is disputed; some studies argue that they are derived from blood monocytes, whereas others support a local origin from intrahepatic precursor cells. In the present study, we used both flow cytometry and immunohistochemistry to distinguish 2 subsets of Kupffer cells that were revealed in the context both of bone marrow transplantation and of orthotopic liver transplantation. One subset was radiosensitive and rapidly replaced from hematogenous precursors, whereas the other was relatively radioresistant and long-lived. Both were phagocytic but only the former population was recruited into inflammatory foci in response to CD8(+) T-cell activation. We propose the name "sessile" for the radioresistant Kupffer cells that do not participate in immunoinflammatory reactions. However, we found no evidence that these sessile Kupffer cells arise from immature intrahepatic precursors. Our conclusions resolve a long-standing controversy and explain how different experimental approaches may reveal one or both of these subsets.

Respiratory infections, including influenza in humans, are often accompanied by a hepatitis that is usually mild and self-limiting. The mechanism of this kind of liver damage is not well understood. In the present study, we show that influenza-associated hepatitis occurs due to the formation of inflammatory foci that include apoptotic hepatocytes, antigen-specific CD8(+) T cells, and Kupffer cells. Serum aminotransaminase levels were elevated, and both the histological and serum enzyme markers of hepatitis were increased in secondary influenza infection, consistent with a primary role for antigen-specific T cells in the pathogenesis. No virus could be detected in the liver, making this a pure example of "collateral damage" of the liver. Notably, removal of the Kupffer cells prevented the hepatitis. Such hepatic collateral damage may be a general consequence of expanding CD8(+) T-cell populations during many extrahepatic viral infections, yielding important implications for liver pathobiology.