The role of macrophages in the uptake of endotoxin by the mouse liver

Summary

The purpose of this investigation was to analyse the macrophage subpopulations involved in the uptake of endotoxin in the liver.

The results show that in normal B10.D2 mice the liver macrophages constitute a heterogeneous population of cells which, depending on their state of differentiation, are distinguished by their differential distribution in the liver acinus and by their ability to phagocytose latex.

Following the intravenous administration of endotoxin (lipopolysaccharide=LPS) from Salmonella abortus equi, endotoxin-carrying non-parenchymal cells of the liver (NPLC) were investigated immunohistochemically (in situ) and immunocytochemically (after isolation) between 1 h and 14 days after the injection. The endotoxin content of the blood and of isolated NPLC was also determined, using radioactively labeled LPS.

Following LPS injection, the total number of macrophages in the liver increased, reaching a maximum after 3 days. There was a striking increase in the ratio of mature to immature macrophages. After day 3, the number of macrophages decreased again, returning to the pre-injection values by day 14.

1 h after the administration of LPS, 41% of the isolated NPLC were already endotoxin-positive, a percentage which remained constant until the 3rd day. Thereafter, the number of LPS-bearing cells increased to a maximum of about 52% on the 5th day. This increase mostly involved macrophages which had taken up endotoxin. Concurrent with these changes there was a threefold increase in radioactively-labeled LPS from the 7th h to the 5th day after injection. Since the increase in the number of endotoxin-carrying macrophages in the liver occurred after endotoxin had been eliminated from the circulation, the increase must have resulted from endotoxin-carrying cells migrating into the liver from other organs.