Hepatic F4/80+CD11b+CD68– cells influence the antibacterial response in irradiated mice with sepsis by Enterococcus faecalis

Gut-associated sepsis is a major problem in patients undergoing abdominal radiation therapy; the majority of pathogens causing this type of sepsis are translocated from the gut microbiota. While treating sepsis, bacterial clearance must be achieved to ensure patient survival, and the hepatic immune response is responsible for this process. In particular, Kupffer cells play a crucial role in the hepatic immune response against infectious agents. Recently, two populations of Kupffer cells have been described: liver-resident macrophages (Mϕ) (F4/80+CD11b–CD68+ cells) and hepatic Mϕ derived from circulating monocytes (F4/80+CD11b+CD68– cells). We examined the properties of both types of hepatic Mϕ obtained from irradiated and normal mice and their role in sepsis. Hepatic F4/80+CD11b–CD68+ cells from both normal and irradiated mice did not show any antibacterial activity. However, F4/80+CD11b+CD68– cells from normal mice behaved as effector cells against sepsis by Enterococcus faecalis, although those from irradiated mice lost this ability. Moreover, hepatic F4/80+CD11b+CD68– cells from normal infected mice were shown to be IL-12+IL-10–CD206–CCL1– (considered M1Mϕ), and hepatic F4/80+CD11b–CD68+ cells from the same mice were shown to be IL-12–IL-10+CD206+CCL1– (considered M2aMϕ). When normal mice were exposed to radiation, hepatic F4/80+CD11b+CD68– cells altered their phenotype to IL-12–IL-10+CD206–CCL1+ (considered M2bMϕ), independent of infection, but hepatic F4/80+CD11b–CD68+ cells remained IL-12–IL-10+CD206+CCL1– (M2aMϕ). In addition, hepatic F4/80+CD11b+CD68– cells from irradiated mice acquired antibacterial activity upon treatment with CCL1 antisense oligodeoxynucleotides. Therefore, the characteristics of hepatic F4/80+CD11b+CD68– cells play a key role in the antibacterial response against gut-associated sepsis.