BACTERIAL LIPOPOLYSACCHARIDE INDUCES ENDOTHELIAL-CELLS TO SYNTHESIZE A DEGRANULATING FACTOR FOR NEUTROPHILS

Enzymes and other factors secreted by degranulating neutrophils (polym orphonuclear leukocytes, PMNs) mediate endothelial injury, thrombosis, and vascular remodeling. In bacteremia and sepsis syndrome and their consequent complications (including acute respiratory distress syndrom e and systemic ischemia-reperfusion resulting from septic shock), neut rophil degranulation is an important mechanism of injury. In related s tudies, we found that human endothelial cells regulate neutrophil degr anulation and that inflammatory cytokines induce synthesis of degranul ating factors by human endothelial cells. Here we show that lipopolysa ccharides (LPS) from gram-negative bacteria were the most potent agoni sts for release of degranulating activity by endothelial cells when co mpared to several cytokines and stimulatory factors. LPS also induced the release of degranulating signals for PMNs from a human endothelial cell line, EA.hy 926. Interleukin 8 (IL-8) is synthesized by endothel ial and EA.hy 926 cells in response to LPS and induces neutrophil degr anulation. However, complementary strategies using receptor desensitiz ation, translation of messenger RNA by Xenopus laevis oocytes, and pur ification and analysis of factors from conditioned supernatants demons trated that degranulating factors distinct from IL-8 are generated in response to LPS. The characteristics of a partially purified degranula ting factor isolated from conditioned supernatants distinguished it fr om known chemokines and other factors that induce PMN degranulation an d are generated by endothelial cells in response to LPS. Thus, culture d human endothelial cells and endothelial cell lines synthesize severa l unique signaling molecules that can trigger neutrophil granular secr etion. If produced in vivo in response to LPS or other pathologic agon ists, these degranulating signals may activate PMNs in combination or in sequence, initiating or propagating vascular damage.