The Resistance-Promoting Activity of Endotoxins and Other Microbial Products

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Abstract
Summary: The resistance-promoting activity of typhoid vaccine, xerosin and bacterial endotoxin against the neurotoxic action of influenza virus is similar in many respects to the effect of these compounds on resistance to cerebral typhoid infection of mice. Minute doses of endotoxin or vaccine injected intracerebrally produce marked protection against neurotoxic challenge whereas large doses injected intraperitoneally increase resistance to virus neurotoxicity only slightly. The protective effect against the neurotoxic action of virus develops by 2–4 hr after intracerebral injection of endotoxin and persists for about a week. The refractory state is not related to suppression of infectious virus in brains and it has not been possible to demonstrate virus neutralizing factors in cerebral tissue of resistant mice. Intracerebral injection of aleuronat, an irritant, did not alter resistance to neurotoxic challenge. A prior intracerebral injection of endotoxin or typhoid vaccine did not alter susceptibility to cerebral infection with lymphocytic choriomeningitis or neurotropic influenza viruses. Although these studies shed no light on the mechanism of altered resistance after injection of endotoxin, they emphasize the importance of local factors in determining the protective effect.

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