Endotoxin-Induced Modification of Plasmodium Berghei Infection in Mice

Abstract

Pretreatment of mice with bacterial endotoxin markedly enhanced resistance to P. berghei infection. The degree of enhancement was related to the dose of endotoxin and decreased with increasing time between endotoxin and malarial infection. Parasite counts appeared later and rose more slowly in the endotoxin-treated group than in controls. Reticuloendothelial system clearance was markedly enhanced by endotoxin, but similar acceleration of clearance induced by zymosan or stilbestrol failed to modify the infection. No fluorescent antibodies were detectable in either endotoxin-treated or control mice through the 7th day after infection, when most controls died. Attempts at passive transfer of protection with serum failed. Endotoxin tolerance abolished the protective effect, showing that the toxic effect of endotoxin was related in some way to the protective effect. Possible mechanisms responsible for endotoxin's protective effect were discussed.