Characterization of release of tumor necrosis factor, interleukin-1, and superoxide anion from equine white blood cells in response to endotoxin.

Direct effects of endotoxin (lipopolysaccharide [LPS]) on equine WBC are known to stimulate the release of a variety of mediators including thromboxane, prostacyclin, and leukotrienes. In this study, 0.1 microgram of LPS/ml stimulated an early increase in tumor necrosis factor, succeeded by an increase in interleukin-1, but concentrations of LPS up to 5.0 micrograms/ml caused no significant increase in superoxide anion release. The concentration of LPS (0.1 microgram/ml) used in this experiment was in the range of concentrations measured in plasma of some horses with gastrointestinal problems. These results indicate that mediators released in response to low concentrations of LPS may be responsible for many of the LPS-induced pathophysiologic effects. This is indicated because concentrations of LPS detected in plasma of some horses with severe gastrointestinal problems are approximately 0.1 microgram/ml, a concentration that will stimulate cells to produce tumor necrosis factor, but will not stimulate any other measurable cytotoxic effect.