Histochemical studies relating the activation of macrophages to the intracellular destruction of tubercle bacilli

Dermal tuberculous lesions, both primary and those of reinfection, were produced in rabbits with ¹⁴C-labeled BCG and biopsied once at various times. Macrophage activation was evaluated by the indolyl histochemical test for β-galactosidase, the number of bacilli in macrophages by acid-fast staining, and the breakdown of bacilli by autoradiography. After the rabbits became tuberculin positive, the strongly activated macrophage population contained a) fewer parasitized cells, b) fewer bacilli in each parasitized cell, and c) more 'free' ¹⁴C-label (not associated with intact bacilli) than the weakly activated macrophage population. These results suggest that the more highly activated macrophages had destroyed many of the bacilli that they once contained and that their power to do so was enhanced by immunologic mechanisms.