Multiplication of Mycobacterium tuberculosis Within Normal and “Immune” Mouse Macrophages Cultivated With and Without Streptomycin

Acquired cellular immunity to infection with Mycobacterium tuberculosis is believed to reside in the capacity of mononuclear phagocytes of immunized animals to inhibit intracellular multiplication of the parasite. However, in macrophage tissue culture systems, it has been customary to employ streptomycin in the medium for the purpose of restricting extracellular, but not intracellular, growth of M. tuberculosis. In contrast, our data show that small amounts of streptomycin markedly inhibit intracellular as well as extracellular growth of M. tuberculosis in normal mouse peritoneal macrophages, and that the degree of this inhibition is directly proportional to the concentration of streptomycin used. In the absence of streptomycin, virulent tubercle bacilli grew as rapidly in "immune" macrophages as in normal macrophages. "Immune" macrophages, however, were slightly more resistant to destruction by the intracellularly multiplying mycobacteria. In the presence of streptomycin, however, intracellular mycobacterial growth was inhibited more in "immune" macrophages than in normal macrophages, and this effect also was directly proportional to the concentration of streptomycin used. Virulent mycobacteria grew somewhat more slowly within mouse peritoneal macrophages obtained after induction of a peritoneal exudate with glycogen than in noninduced cells. The rate of multiplication, though, was the same within normal and "immune" induced peritoneal cells except in the presence of streptomycin. As with noninduced macrophages, this drug inhibited the intracellular multiplication of virulent tubercle bacilli more effectively within "immune" induced than within normal induced cells. It would appear, therefore, that the greater inhibition of intracellular multiplication of virulent tubercle bacilli in "immune" macrophages in tissue culture noted by a number of investigators in the past may have been an artifact created by the use of streptomycin in the tissue culture medium.