The significance of high-density lipoproteins (HDL) in the clearance of intravenously administered bacterial lipopolysaccharides (LPS) in mice.

The direct immunofluorescence technique was used to study the presence of high-density lipoproteins (HDL) in the liver, spleen and kidney of mice before and after intravenous administration of purified lipopolysaccharides (LPS) from Escherichia coli O 75, Salmonella abortus equi and Salmonella minnesota R 595, as well as free lipid A. Untreated mice had small granules of HDL in the hepatocellular cytoplasm, which appeared more pronounced after oral administration of fat. After intravenous administration of LPS, hepatocellular HDL decreased continuously and was no longer visible 1 hour after injection of LPS or lipid A. Five to ten minutes after administration, smooth-form LPS were located in sinusoidal cells, and rough form LPS and lipid A were found in both parenchymal and nonparenchymal liver cells. All toxins were demonstrated in both cell populations 1-4 hours after injection. The spleen was free of HDL, while there was a strong uptake of LPS into the cells of the reticulo-endothelial system. The kidney of experimental mice had small HDL granules in the epithelial cells of the proximal tubules, with a tendency to move to the lumen 1 hour after LPS injection, while there was a transient granular deposition of LPS in the glomeruli. The results suggest that the early uptake of circulating LPS by cells of the reticulo-histiocytic system in liver and spleen, as well as by hepatocytes, is not mediated by HDL. However, HDL located in hepatocytes or present in the circulation of experimental mice seem to be eliminated through the bile and the urine, induced by LPS.