RELATIONSHIP OF ENDOGENOUS PYROGEN AND SERUM AUGMENTING FACTOR TO ENDOTOXIN TOLERANCE.

Summary Pyrogen tolerance was produced by repeated daily injections of endotoxin. As tolerance developed, the ability of the serum to augment the pyrogenic effect of endotoxin and production of endogenous pyrogen were diminished. When tolerance was produced by passive transfer, these 2 parameters were similarly affected. RES blockade did not reverse tolerance nor did it restore augmenting factor or markedly increase the animal's ability to elaborate endogenous pyrogen following injection with endotoxin. These observations suggest that serum inhibitors may mediate tolerance by inactivating the ability of serum to augment endotoxin.