Functional characterization of two different Kupffer cell populations of normal rat liver

Background: Kupffer cells of the liver represent the largest population of tissue macrophages. Small and large Kupffer cells were distinguished in normal liver, leading to the suggestion that they have different functions. This study intends to further characterize small and large Kupffer cells of normal rat liver in vivo and in vitro. Methods: Sections of rat liver were investigated by double-staining immunofluorescence with the monoclonal antibodies ED1 and ED2. Isolated nonparenchymal liver cells were separated according to size to obtain small and large Kupffer cells. In culture, phagocytosis was studied by zymosan ingestion and cell proliferation by incorporation of 3H-thymidine. Synthesis of the proteins C1-inhibitor, apolipoprotein E and interleukin-1 was studied by endogenous labeling of newly synthesized proteins, immunoprecipitation and sodium dodecyl-sulfate-polyacrylamide gel electrophoresis. Results: ED1+ ED2+ Kupffer cells were located in the liver along the sinusoids, ED1+ ED2- cells were found mainly located around the central vein and portal vessels. By counterflow elution, small ED1+ ED2= cells were separated from larger ED1+ ED2+ cells and cultured. The larger cells abundantly synthesized C1-inhibitor and apolipoprotein E, while the small cells synthesized only trace amounts of these proteins. Interferon-γ increased C1-inhibitor synthesis in small (5-fold) and large cells (1.5-fold). 3H-thymidine incorporation was 11-fold higher in small than in large cells. However, lipopolysaccharide-induced pro-interleukin-1α and pro-interleukin-1β synthesis and phagocytic activity were similar in both populations. Conclusions: The data demonstrate two different populations of mononuclear phagocytes in normal rat liver well distinguished by immunocytochemical and functional markers.