Elimination of various subpopulations of macrophages and the development of multiple-organ dysfunction syndrome in mice.

OBJECTIVE To evaluate the role of specific macrophage subpopulations in the development of zymosan-induced multiple-organ dysfunction syndrome by selective elimination of liver, splenic, alveolar, and peritoneal macrophages. DESIGN Randomized animal trial. SETTING Central animal laboratory at the University Hospital Nijmegen, Nijmegen, the Netherlands. ANIMALS Male C57Bl/6 mice. INTERVENTIONS Elimination of macrophages was accomplished by administration of multilamellar liposomes that contained dichloromethylene bisphosphonate (Cl2MBP). Intravenous, intratracheal, and intraperitoneal administrations induced an elimination of liver and splenic, alveolar, and peritoneal and omental macrophages, respectively. Zymosan (1 mg/g) was injected intraperitoneally at day 0. The liposomes that contained Cl2MBP were administered before and after zymosan challenge. At day 12, all surviving mice were killed. MAIN OUTCOME MEASURES The body weights, temperatures, and mortality rates of the mice were monitored daily. Relative organ weights (ROWs) were calculated from the lungs, liver, spleen, and kidneys after the mice were killed. RESULTS The liposomes that contained Cl2MBP, administered intravenously before or after zymosan challenge, did not induce significant changes in the body weight, temperature, or mortality rate. The ROW of the liver was significantly decreased in both treatment groups. Elimination of liver and splenic macrophages after zymosan challenge induced an increased ROW of the lung and a decreased ROW of the liver. The liposomes that contained Cl2MBP, administered intratracheally before zymosan challenge, completely prevented deaths. The body weights, temperatures, and ROWs of the mice were not changed. The liposomes that contained Cl2MBP, administered intraperitoneally, did not change the body weight, temperature, or ROW. The liposomes that contained Cl2MBP, administered intraperitoneally before zymosan challenge, increased the mortality from 50% to 90%. CONCLUSIONS These data show that the elimination of specific macrophage subpopulations and the elimination on specific time points in this model had differential effects, indicating a differential role of specific macrophage subpopulations, either protective or detrimental, in the development of multiple-organ dysfunction syndrome.