Macrophage turnover, division and activation within developing, peak and "healed" tuberculous lesions produced in...

This review is a synthesis and analysis of our nine experimental pathology papers on macrophage kinetics in dermal tuberculous lesions produced in rabbits by BCG. It is presented at this time to summarize the macrophage kinetics in both active and essentially healed tuberculous lesions and to suggest that the bacilli frequently multiply and are destroyed in the viable granulation tissue of many small arrested tuberculous lesions. The turnover of mononuclear cells (MN)-which were mostly macrophages with some medium and large lymphocytes-was most rapid in BCG lesions at 2-3 weeks (when tuberculin sensitivity and acquired cellular resistance were at their peaks). At this time, more macrophages entered, more died or left, more remained at the site, and more became activated than before or afterwards. Before this time, the host had no delayed-type hypersensitivity (DTH) and cell-mediated immunity (CMI), so that no antigen-specific enhancement of the inflammatory response occurred. After this time, the bacilli and their antigenic products had decreased, so that the stimuli for cell infiltration and activation were reduced. In "healed" lesions, the MN turnover still occurred, but was decreased. The continuous entry of live non-activated macrophages into the viable parts of tuberculous lesions provides fresh intracellular sites where tubercle bacilli may multiply before they are again inhibited by the DTH and CMI of the host. In tuberculosis, bacillary dormancy of long duration may only be present in caseous necrotic tissue where no live host cells exist.