Lymphokine-induced mycobacteriostatic activity in mouse pleural macrophages

We have developed an in vitro assay to study the intramacrophage replication of Mycobacterium tuberculosis or Mycobacterium bovis BCG. In this assay, extracellular mycobacterial replication was avoided by using a small infecting inoculum and a new method for efficiently removing nonphagocytocytized bacilli. The ability of different mycobacterial strains to replicate in mouse pleural macrophages correlated with their virulence. The effect of lymphokines prepared by incubating spleen cells from BCG-immunized mice with mycobacterial antigens was tested with this assay. In the presence of lymphokines, mouse pleural macrophages were able to inhibit the intramacrophage replication of both BCG and M. tuberculosis. This assay is a useful in vitro model for studying antibacterial cellular immunity expressed by macrophages.