MODULATION OF LIPOPOLYSACCHARIDE-BINDING TO HUMAN GRANULOCYTES

Using flow cytometry and fluorescein-labelled lipopolysaccharide (LPS) from Salmonella minnesota R595 (FITC-ReLPS), we studied the role of m embrane proteins in the recognition of LPS by human polymorphonuclear granulocytes (PMN) in the absence of serum. Treatment of PMN with tryp sin, pronase E or proteinase K reduced both the binding of FITC-ReLPS to PMN at 4 degrees and the response of PMN to LPS at 37 degrees, as m easured by luminol-enhanced chemiluminescence. Neuraminidase treatment enhanced both activities. Trypsin treatment of PMN after the binding of FITC-ReLPS effectively reduced fluorescence when cells were kept at 40, while further incubation of FITC-ReLPS-labelled PMN at 37 degrees rendered fluorescence insensible to trypsin. These results indicate a protein structure of the LPS binding site, association of FITC-ReLPS with the cell membrane at 4 degrees and subsequent internalization at 37 degrees. The binding of FITC-ReLPS was not inhibited by the anti-CD 14 monoclonal antibody (mAb) 3C10, which recognizes a functional epito pe of CD14. Furthermore, binding of FITC-ReLPS was observed to PMN obt ained from a patient with paroxysmal nocturnal haemoglobinuria who lac ked membrane-bound CD14. Stimulation of PMN with tumour necrosis facto r (TNF) or LPS enhanced the binding of FITC-ReLPS at 4 degrees. This w as not observed after activation of PMN devoid of granules (cytoplasts ), indicating that the binding of LPS at the cell surface is enhanced by mobilization of LPS-binding proteins from intracellular granules. T hese studies provide evidence that LPS binding and activation of PMN i nvolves protein structures at the cell surface different from CD14, an d that granules constitute a pool of LPS-binding proteins that can be translocated to the cell surface upon stimulation.