ASSOCIATION BETWEEN SERUM CYTOTOXICITY AND SELECTED CLINICAL-VARIABLES IN 240 HORSES ADMITTED TO A VETERINARY HOSPITAL

A total of 378 serum samples from 240 hospitalized horses and 47 sera from healthy control horses were assayed for growth effects on actinomycin D-treated L929 cells. On average, patient and control sera stimulated cell growth; however, mean percentage of the relative growth index (RGI) of sera from clinical cases was significantly (P < 0.001) lower than that of control sera. Approximately 35% of patient sera and 6% of control sera had tumor necrosis factor-like cytotoxic activity for L929 cells (ie, RGI < 100%). Sera from horses with either peritoneal leakage of gastrointestinal tract contents or any bacterial infection were significantly (P < 0.05) more cytotoxic than sera from horses that did not have these clinical factors. A clear tendency was evident for horses that had the highest serum CytotoxiCity (RGI < 75%) to also have clinical profiles suggestive of endotoxemia. Fever, leukopenia, diarrhea, and gastrointestinal tract leakage were significantly (P < 0.05) overrepresented among these horses, compared with horses without serum cytotoxicity. Bacterial infections and abdominal surgeries were also increased in this group, but not significantly. Of the 14 horses with serum RGI < 75%, 13 had some form of gastrointestinal tract disease and the other had gram-negative septicemia. Survival to discharge was significantly (P < 0.05) lower among horses in the high-cytotoxicity group than among horses without serum cytotoxicity. Diarrhea and bacterial infections were the only clinical factors found more frequently in horses with low serum cytotoxicity than in horses without serum cytotoxicity. The finding of circulating cytotoxic activity in horses at risk for endotoxemia was consistent with the proposed role for tumor necrosis factor as an important mediator of inflammation.