RESUMEN
In continuation of previous studies on the age distribution of viral antigen in spleen and kidneys of mice infected congenitally with LCM virus, the brain was subjected to a similar investigation since it participates to some extent in "late onset disease" in such animals. The antigen curve obtained differed from that for the spleen but resembled the curve for the kidneys in that an initial decrease of the antigen content in young mice was followed by a continuous rise later in live. Cerebral antigen titers in newborns and in old mice were considerably higher in carriers of the "neurotropic" strain "WCC" than in those infected with the "natural" strain "W". In old carriers of these strains there was a clear correlation between the cerebral antigen titer and the frequency and intensity of nervous symptoms which, in general, were not very striking but clearly recognizable to an experienced observer. In young congenital carriers cases of "early onset disease" characterized by spastic symptoms were observed. The latter were missing in old mice. "Early onset disease" and the temporary decrease of the cerebral and renal antigen titers in young animals are attributed to an abortive cellular immune response not strong enough to eliminate viral antigen completely from the organs. Specific antibodies, demonstrable by indirect CF in 43% of the mice reaching the age of 6-7 months, were likewise ineffective in this respect. In quantitative direct CF tests, immune sera from non-tolerant mice and, to a lesser degree, an immune serum from guinea pigs reacted better with brain extracts from congenitally infected mice than with extracts of spleens or kidneys in spite of the lower antigen content of the brain. This result seems to indicate a qualitative difference between the respective antigens.