Protection of guinea pigs inoculated with Tacaribe virus against lethal doses of Junin virus.

Guinea pigs were protected against lethal doses of Junin virus by a previous inoculation with Tacaribe virus. Fourteen guinea pigs were infected with 10(6) 50% lethal doses (LD50) of Tacaribe virus and superinfected 45 days later with 10(3) LD50 of Junin virus. Appropriate control groups for both infections were also studied. The replication of Junin virus was impaired, as no virus was isolated from blood and organs of animals killed on days 9 and 11 after infection. High levels of neutralizing antibodies to Tacaribe virus were present by day 45, and no cross-reacting neutralizing antibodies to Junin virus were detected. However, three days after challenge with Junin virus, a typical secondary immune response to this virus was established. From these results it was concluded that the protection observed was mainly due to a specific immune response that was triggered by the Junin virus but primed by Tacaribe virus, which is antigenically similar to Junin virus.