Studies on tubercle bacillus-monocyte relationship. III. Conditions affecting the action of serum and cells; modification of bacilli in an immune system.

Studies of the relationship of protective serum factor to cellular resistance and to tuberculin skin sensitivity have demonstrated that protective serum factor may exist independently of a high level of cellular resistance, and that both protective factor and cellular resistance may be demonstrable without a concomitant hypersensitivity of the delayed type. The experiments with absorbed sera and the globulin fraction of immune serum indicated no specific association of protective serum factor with antibody globulin. The protective factor in immune serum was found to be thermostable and non-dialyzable. In vitro exposure of virulent tubercle bacilli to the immune serum from BCG-immunized animals failed to alter the bacterial capacity for destruction of monocytes and for intracellular proliferation. In vitro cultivation of normal and immune monocytes in normal or immune serum was not effective in changing the native susceptibility or resistance of these cells. Effective manifestation of resistance to virulent tubercle bacilli by immune monocytes was found to require the continuous presence of immune serum. The intracellular passage of virulent tubercle bacilli in an immune system (immune monocytes cultivated in immune serum) resulted in a decreased bacterial potential for destruction of normal monocytes when these were cultivated in the presence of immune serum.