Resistance to intravenous inoculation of Mycobacterium tuberculosis H37Rv in mice of different inbred strains following immunization with a leprosy vaccine based on Mycobacterium w

Abstract

Four strains of mice, namely Balb/c, C57BL/6 NCrl (Bcg^s), C3H/He NCrl and CBA/N (Bcg^r) were experimentally infected with Mycobacterium tuberculosis H37Rv (Trudeau Institute, Saranac Lake, NY) to induce sub-lethal infection. The level of infection was assessed by screening tuberculin reaction, pulmonary lesions, and viable units of mycobacteria recovered from the lung, spleen and liver. On prior immunization with 10⁷ heat-killed suspension of Mycobacterium w, an anti-leprosy vaccine currently under large scale human trials in India, protection was observed against tuberculosis in all the four strains of mice used in the study as assessed by significant reduction of both pulmonary lesions and viable units of mycobacteria recovered from different organs. In parallel experiments, live BCG was able to confer protection to mice of Bcg^s strains but not to mice of the Bcg^r strains. Results of these experiments suggest that a vaccine based on heat-killed Mycobacterium w has the potential also to confer protection against tuberculosis in mice of genetic strains whose immune system is less triggered by intravenous injection of viable BCG.