An experimental study on problems of immunity and allergy in postvaccinal encephalitis

Fifty-four harvests of 7 different strains of vaccinia virus present in calf lymph used as smallpox vaccine have been examined for virulence, antigenicity, and resistance to neutralizing antibody, and the results were compared with those of a similar examination of smallpox vaccines that had initiated postvaccinal encephalitis. In 3 of 6 cases of post vaccinal encephalitis, the antibody level was poor, and did not agree with the high antigenicity of the virus. In one case, a child that had been vaccinated with a vaccine of low antigenicity, vaccinia virus was recovered from the blood on the 15th day following vaccination. It is suggested, that individual factors may inhibit the production of neutralizing antibody, and in animal experiments, guanidin appeared to exert such an inhibitory effect, although slight and transient. A considerably higher antibody level was obtained when rabbits and children were revaccinated on the 7th day following primary vaccination, but then the virus could be recovered from the blood from the second to the eighth day following revaccination, which proves, that the virus is not rapidly inactived in spite of the high antibody level. Immunization experiments with heat-inactivated neurovaccinia, even when incorporated in vaseline and lanoline, were unsuccessfull, since the resistance to challenge with living neurovaccinia, particularly of the central nervous system, proved unsatisfactory, although antibodies had developed. Softened foci of the brain and encephalitis could be produced by intracerebral inoculation of rabbits with mixtures of neurovaccinia, vaccinia immune serum and brain tissue, but no demyelination was observed. Bovine protein, vaccinia virus grown on the chorioallantoic membrane of the chick-embryo, and bacteriologically sterile calf lymph failed to produce demyelination after repeated injection into rabbits. Only in one rabbit, that had been injected intracerebrally with calf lymph, and that received two subsequent intramuscular injections with the same material, developed a demyelinating encephalopathy, which, however, was not identical with the demyelinating lesions in human beings suffering from postvaccinal encephalitis. It is suggested, that the vaccinia virus may produce the inflammatory lesion in the wall of the blood vessels, but that the virus particle itself has no direct action on the myelin sheaths.