Characteristics of the strongly Ia-positive cells in rat liver

The expression of MHC class II antigens (Ia) on rat liver non-hepatocytic cells were analysed by the Staphylococcus aureus rosette method using monoclonal antiserum to the common part of the class II molecules. Of the non-hepatocytic liver cell population, the passenger lymphocytes and monocytes were strongly anti-Ia binding but the most reactive were large mononuclear cells, morphologically macrophages. The characteristics of the strongly Ia-positive cells of rat liver were tested with different 'macrophage markers'. Of the macrophage-like cells, 55% were Ia-positive in the Staph. aureus rosette 84% had intracytoplasmic lysozyme, 100% of them were positive for alpha-naphthyl acetate esterase (ANAE) reaction, and 92% had Fc-receptors on the cell surface. As functional tests of macrophages, phagocytosis and adhesion were used: 79% of the cells were able to phagocytose antibody-coated human red cells and 56% of the cells adhered on glass. As most of the tested cells were positive for the markers the results demonstrate that the most antigenic component of rat liver has the characteristics of macrophages and thus the strongly Ia-positive cells are probably liver tissue macrophages (Kupffer cells).