Bacterial lipopolysaccharides alter human endothelial cell morphology in vitro independent of cytokine secretion.

Lipopolysaccharides derived from six bacterial species were found to alter human endothelial cell morphology in vitro in a species-dependent and dose-dependent manner. Lipopolysaccharides derived from Salmonella enteritidis (SeLPS) induced the strongest response, whereas lipopolysaccharides from Vibrio cholerae produced no effect. Cell-shape changes induced by SeLPS (10 micrograms/ml) were noticeable by 24 hours and reached a maximum by 72 hours, thus paralleling the effects produced by the recombinant cytokines interferon gamma (IFN-gamma) (10(3) U/ml), tumor necrosis factor (10(2) U/ml), and interleukin-1 (5 to 10 U/ml). Pretreatment of human endothelial cells with IFN-gamma (10(3) U/ml) for 24 hours induced an accelerated morphologic response to subsequent SeLPS (10 micrograms/ml) stimulation and vice versa, suggesting independent pathways of action. Simultaneous treatment of human endothelial cells with SeLPS and IFN-gamma produced a more rapid onset of morphologic changes and a stronger overall effect. Culture medium containing polymyxin B inhibited cell-shape changes induced by lipopolysaccharides but not those induced by the cytokines. Conditioned medium generated over a 12-hour period following a 24-hour SeLPS/IFN-gamma stimulation did not contain measurable cytokine antigens, nor did it induce biologic responses associated with interleukin-1, IFN-gamma, and tumor necrosis factor alpha. The results indicate that lipopolysaccharides act directly on endothelial cells as well as synergistically with IFN-gamma to alter cell morphology and may, therefore, contribute to the vascular pathology of gram-negative infections.