Specific acquired resistance and activity of migration inhibition factor (MIF) in spleens of mice with chronic tuberculosis.

The antimycobacterial resistance of the host (as evaluated by mycobacterial counts in spleens) and the in vitro cell-mediated immunological mechanisms ((cellular immune reactivity) assayed by the activity of migration inhibition factor in splenic fragments) were compared in the course of experimental chronic tuberculosis infection. Mice, either unvaccinated or vaccinated with killed mycobacteria suspended in saline and then either untreated or treated with azathioprine, were used in the study. The treatment with azathioprine caused a relative depression of specific resistance accompanied by less pronounced inhibition of migration in vitro. Although a higher level of specific resistance was detected in mice vaccinated with non-living vaccine, no enhancement of cellular reactivity in vitro could be estimated in the splenic cells of these animlas. The participation of humoral mechanisms in mice vaccinated with the non-living vaccine plausibly explains the discrepancy. The results indicate furthermore, that the migration inhibition test reflects delayed hypersensitivity rather than other components of cellular immune reactivity.