BCG modulation of delayed type hypersensitivity, humoral response and acquired resistance after rabies vaccination.

The immunopotentiating action of BCG was evaluated in rabies. The maximum enhancing effect on delayed type hypersensitivity (DTH) was obtained 14 days after rabies immunization when different BCG vaccination schedules were tested in mice. A stable form of specific sensitization to rabies antigen under the modulation of BCG pretreatment was obtained. High concentrations of rabies antigen were found to be inhibitory for the DTH reaction. Levels of protection were evaluated in rabies vaccination after BCG modulation. One single injection of rabies vaccine in BCG pretreated mice was as effective as two injections of rabies vaccine in normal mice. However, in the latter, increase of protection was correlated with the levels of neutralizing antibody. On the other hand, the BCG pretreated mice, protection was not associated with a significant increase in antibody. Pretreatment with BCG alone influenced the outcome of fixed rabies as well as street rabies by enhancing the natural resistance to rabies infection.