Characterization of two F4/80-positive Kupffer cell subsets by their function and phenotype in mice

Liver Kupffer cells have been suggested to be heterogeneous macrophage lineage cells. We explored this possibility by classifying the mouse Kupffer cells into subpopulations and characterizing them by their phenotype and function.Liver mononuclear cells (MNCs) from C57BL/6 mice were isolated and their phenotypes and functions were analyzed. The effects of clodronate liposomes and gadolinium chloride (GdCl(3)) on Kupffer cells were also investigated.Approximately 25% of liver MNCs were F4/80(+) Kupffer cells. Of these, 46% were CD11b(-)CD68(+), 22% were CD11b(+)CD68(-), and 6% were CD11b(+)CD68(+). CD68(+) cells showed potent phagocytic activity and reactive oxygen species (ROS) production capacity after lipopolysaccharide (LPS) stimulation, whereas CD11b(+) cells did not. CD11b(+) cells showed a strong capacity for the production of cytokines (TNF and IL-12), which was much less prominent in CD68(+) cells. At 24h after LPS or Escherichia coli injection into mice, the proportions of CD11b(+)CD68(-) and CD11b(+)CD68(+) cells increased but that of CD11b(-)CD68(+) cells decreased. The increase in CD11b(+)CD68(+) cells appeared to be derived from the CD11b(+)CD68(-) subset. Although the CD11b(+) cells augmented phagocytic activity after LPS injection, they did not increase ROS production, suggesting their weak lytic activity. Injection of clodronate or GdCl(3) into mice depleted the CD68(+) cells but increased CD11b(+) cells proportionally because CD68(+) cells may phagocytose these toxic reagents and undergo apoptosis. GdCl(3)-treated mice also consistently increased serum TNF after LPS challenge.Two F4/80(+) Kupffer cell subsets may exist, a CD68(+) subset with phagocytic activity and a CD11b(+) subset with cytokine-producing capacity.