Relation of Resistance and Allergy in Tuberculosis as Shown by Vaccinating Rabbits with B. C. G

Abstract

Resistance. Resistance to a subsequent inoculation of a virulent bovine strain of the tubercle bacillus was developed by vaccinating with B. C. G. Four rabbits were inoculated at 4 weekly intervals with 1 mg. of B. C. G. in 1 cc. of salt solution in each of the following methods: (1) living organisms, subcutaneously; (2) living organisms, intravenously; (3) heat killed (60° C. for 30 minutes) organisms, subcutaneously; and (4) heat killed organisms, intravenously. The basis of the 4 methods of administering the vaccine was suggested by previous experiments with streptococcic vaccination in which it was found that the intravenous method of giving the vaccine was superior to the subcutaneous method in developing resistance and in not producing allergy. This was true with both living and heat-killed organisms. Three weeks after the last injection of the B. C. G. vaccine, 9 nonvaccinated rabbits, 4 rabbits vaccinated intravenously with the timothy grass bacillus, and the 16 rabbits vaccinated with B. C. G. were inoculated intravenously with 0.01 mg. of virulent bovine tubercle bacilli. The length of life following the injection of the virulent strain and the degree of involvement, if tuberculous lesions were present, were compared in the nonvaccinated and vaccinated injected animals. The 9 nonvaccinated rabbits died with extensive pulmonary and generalized tuberculosis, 27, 30, 31, 36, 44, 54, 71, 76, and 97 days respectively after receiving the lethal dose of the virulent bovine strain. The average length of life in these 9 animals after injection was 52 days. The 4 animals which were vaccinated with the timothy grass bacillus were used for controls for specificity of any resistance which might develop from the vaccination. Following the inoculation with the bovine bacillus these 4 animals rapidly developed pulmonary and generalized tuberculosis and died 26, 33, 35, and 45 days respectively after the virulent injection. The average length of life after injection was 35 days. No protection was evident from vaccination with this organism. It was even suggested that the vaccination with the timothy grass bacillus might in some way have hastened the course of the infection. One of the 4 rabbits vaccinated subcutaneously with living B. C. G. died the night following the injection. At necropsy no tuberculosis was found. The animal had a positive Mantoux test. It is possible that death was due to an allergic shock. The remaining 3 animals of this group were in good condition 142 days after the injection at which time they were killed. One had multiple firm tubercles in the lungs and kidneys. The amount of involvement was much less, however, than in the non-vaccinated animals. The remaining 2 animals, when killed, had no lesions. Not including the animal which died on the day of inoculation, it is seen that the average length of life of the rabbits in this group was more than 142 days.