Guinea pigs can be immunized against
lymphocytic choriomeningitis by 2 or 3
injections with formolized
vaccines prepared from a variety of infected guinea pig tissues.
Vaccines prepared from the consolidated areas of diseased lungs gave the best results. The immunity produced was partial in the majority of the cases, in that the vaccinated animals as a rule showed
fever after the test of immunity and virus was present in the circulation during the febrile period.
Vaccines prepared from infected mouse tissue had no, or very little, immunizing power for guinea pigs, even when prior to formolization they contained at least as much virus as guinea pig tissue
vaccines. This failure to immunize appears to be due to the interference by
heterologous antigens, since the immunity induced by homologous
vaccines was often inhibited when formolized normal mouse tissue
suspensions treated in the same manner as the guinea pig tissue
vaccines were added to the latter before inoculation. The inhibitory effect of the heterologous tissue was less marked when it was not mixed with the
vaccine but injected simultaneously on the opposite side of the body. The immunizing power of homologous
vaccines did not parallel their virus content prior to formolization. A high degree of immunity, characterized by protective
antibodies in the serum, was produced in some guinea pigs by prolonged treatment with large doses of homologous
vaccine, while sera of guinea pigs vaccinated in the ordinary manner contained no detectable
neutralizing antibodies. It is possible, therefore, that the immunity produced by inactive virus differs only quantitatively from that induced by an
infection.