Endotoxemia in horses: protection provided by antiserum to core lipopolysaccharide

An equine antiserum to core lipopolysaccharide was produced by inoculation of 6 horses with a boiled cell bacterin made from the J-5 mutant of Escherichia coli O111:B4. The antiserum immunoglobulin G titer to J-5 mutant E coli, as determined by enzyme-linked immunosorbent assay, was 1:15,006. Pooled serum prepared before inoculation (preimmune serum) had a J-5 immunoglobulin G titer of 1:350. The J-5 antiserum was tested for its protective efficacy in sublethal endotoxemia in 14 horses. Four horses served as nontreated controls and were given nothing before endotoxin challenge exposure (10 micrograms/kg of body weight, IV). Pooled preimmune serum (3 ml/kg, IV) was administered to 5 horses and J-5 antiserum (3 ml/kg, IV) was administered to 5 other horses 2 to 15 hours before endotoxin challenge exposure. During the 24 hours postendotoxin challenge exposure, endotoxemia was accompanied by significant (P less than 0.05) time-related changes in temperature, heart rate, pulse character, respiratory rate and character, capillary refill time, mucous membrane color, fecal composition, attitude, PCV, total plasma protein, WBC count, platelet count, plasma fibrinogen, prothrombin time, activated partial thromboplastin time, fibrinolytic degradation products, plasma glucose, and plasma lactate in all horses. There were no apparent treatment vs time interactions (P greater than 0.05). Two horses (1 control and 1 given J-5 antiserum) died suddenly from unknown causes immediately after endotoxin challenge exposure. Seemingly, equine antiserum to core lipopolysaccharide did not provide protection from the adverse effects of experimental endotoxemia produced by bolus IV infusion of 10 micrograms of endotoxin/kg.