Endotoxin-induced protection against experimental Junín virus infection

Summary

The effects of the administration of a bacterial endotoxin on the course of the Junín viral infection in the mouse were studied. The results showed that maximal protection against the disease was produced when both endotoxin and the virus were given on the day of birth. If endotoxin was administered first (on the day of birth) and was followed by the virus 24 hours later, a lesser degree of protection was obtained, but with a 48-hours interval there was no protection. If the virus was administered first (on the day of birth), followed by endotoxin 1 to 8 days later, the mortality was the same as with virus alone. If the interval between the administration of the virus and the endotoxin was 9 to 10 days, a very high mortality was observed in 24 hours, possibly due to an increased sensitivity of the infected mouse to the lethal effect of endotoxin.

Viral titrations showed that the brains of endotoxin-protected mice contained enough virus to kill normal mice, indicating that the mere presence of the virus is not sufficient to produce death in the infected animals. Circulating antibodies to the virus were detectable 28 days after infection, i.e., about 13 days after the signs of the disease had disappeared. This fact and the failure of endotoxin-protected mice to survive a new challenge with Junín virus suggest that the protective phenomenon is not antibody-related.

Since endotoxin fails to protect when given to mice either simultaneously with the virus 2 days after birth or one or more days after infection on the day of birth, it is very unlikely that an enhanced release of interferon might be responsible for the observed protection.

Thymic function and its possible alteration by endotoxin is discussed.