Increased antibacterial activity against Escherichia coli in bovine serum after the induction of endotoxin tolerance.

Small amounts of endotoxin injected intramuscularly into cows induced endotoxin pyrogenic tolerance and an increase in the rate at which the serum killed a strain of Escherichia coli. Most of the difference between normal serum and serum from the endotoxin-tolerant animal was shown to be due to a bentonite-adsorbable factor other than lysozyme or beta-lysin. The antibacterial activity was not completely removed from either type of serum after bentonite adsorption. Electron microscope studies and measurement of the rate of release of radioactively labeled cytoplasmic contents showed that the bentonite-adsorbable factor was important in the final breakdown of the cell membrane and release of cellular contents. The antibacterial system was totally dependent on complement, and the importance of antibodies could not be entirely ruled out because adsorption at O C with homologous cells eliminated the killing activity.