Interactions of endotoxin with human blood cells and serum proteins

Endotoxin interacts with several plasma protein systems and blood cells, causing release of a multitude of endogenous mediators that contribute to the pathophysiological process of sepsis. Binding of I-125-labelled lipopolysaccharide, LPS, to human blood in vitro showed that the major part of the I-125-LPS was recovered in plasma, whereas only small amounts were retained in washed suspensions of granulocytes, erythrocytes, monocytes and lymphocytes, respectively. Whole leukocyte preparations or isolated subpopulations incubated with I-125-LPS or fluorescein-conjugated LPS followed by autoradiography, Bow cytometry or immunofluorescence microscopy showed unequivocally that monocytes bound much more LPS than did granulocytes and lymphocytes. Lipoprotein electrophoresis followed by autoradiography showed that I-125-LPS bound to all the purified lipoprotein fractions, which was also confirmed by gel filtration chromatography. These findings demonstrate that monocytes represent the most important blood cell for LPS binding and that radiolabelled LPS is able to bind to lipoproteins as well as to other serum constituents.