A novel immunohistochemical method for in vivo detection of endotoxin using horseshoe crab factor C

We developed a novel immunohistochemical method for in vivo detection of endotoxin (LPS) localization in relation to the biologically active region, by use of factor C, an initiation factor in the Limulus clotting system which is mediated by LPS, as a specific affinoligand to LPS, and using rabbit anti-factor C IgG. The competitive inhibition of various LPS, lipid A, anti-LPS factor, or polymyxin B to factor C binding indicates that the immunohistochemical reaction is specific to LPS. Investigating the time course of LPS distribution during 6 hr after IV injection of 5 mg/kg to rats, the greatest uptake of LPS was evident in the reticuloendothelial system (RES), particularly in Kupffer cells, 5 min after injection, and in adrenocortical cells 3 hr after the injection. Shortly after the injection, LPS also appeared in platelet thrombi, intravascular monocytes, and a few neutrophils, and on the surface of endothelial cells in liver, kidney, spleen, lung, and aorta. Both smooth and rough forms of LPS were detectable and there was no apparent difference in their localization. This approach facilitates immunohistochemical analyses of the mechanisms involved in development of endotoxemia.