In Vitro Studies on the Mechanism of Acquired Resistance to Tuberculous Infection

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Abstract
The relationship between lymphocytes and macrophages in cellular immunity against tuberculous infection was studied in an in vitro cell culture system without streptomycin addition. The peritoneal macrophages were obtained from normal mice or mice immunized with heat-killed tubercle bacilli in paraffin oil, boosted with live BCG and infected with [Mycobacterium tuberculosis] H37Rv cells in vitro. The infected monolayers of macrophages were cultivated for 48 h with immune lymphoid cells obtained from immunized mice. The intracellular growth of H37Rv cells 3,5 and 7 days after infection was examined by counting tubercle bacilli within infected macrophages under a microscope. The increase of bacilli within macrophages derived from immunized mice was slightly smaller than that in normal macrophages. The addition of immune lymph node cells to the macrophage monolayers resulted in a marked decrease in the number of bacilli within normal and immune macrophages. Normal lymph node cells exhibited an enhancing effect on the intracellular bacillary growth. Immune lymph node cells caused greater macrophage suppression of intracellular growth of bacilli than that of splenic lymphoid cells or thymocytes after addition to macrophage monolayers. The treatment of lymphoid cells with inhibitors of protein synthesis, cycloheximide or streptovitacin A, resulted in a remarkable reduction of the ability of sensitized lymphocytes to cause macrophages to suppress multiplication of intracellular bacilli.