Turnover of Tritiated-Thymidine-labeled Mononuclear Cells in Tuberculous Lesions of Rabbits: A Comparison of Primary Dermal BCG Lesions and Those of Reinfection

Rabbits were infected or rein-fected intradermally in multiple sites with BCG. One day before the BCG infection they were injected iv with a single pulse of tritiated thymidine (³HT). At various times thereafter, the BCG lesions were biopsied and evaluated for ³HT-labeled mononuclear cells (MN), which are mostly macrophages but include some lymphocytes. Periodically Old Tuberculin (OT) was injected intradermally, creating MN traps, which were biopsied and evaluated 1 day after their onset. These traps monitor the population of ³HT-labeled MN in the blood stream that readily enters sites of inflammation. During the first 5 days after the ³HT pulse, a higher percentage of labeled MN accumulated in tuberculin traps on rabbits reinfected with BCG than in traps on rabbits with primary infection. The high percentage of labeled MN in the former was probably due to the more intense inflammation caused by preexisting tuberculin hypersensi-tivity. By 8 days after the ³HT pulse, a lower percentage of labeled MN had accumulated in BCG lesions of reinfection than in primary BCG lesions. Evidently the presence of delayed hypersensitivity increased the turnover of MN in tuberculous lesions. By 15 days after the ³HT pulse, the percentage of ³HT-labeled MN was much higher in BCG lesions than in 1-day traps, suggesting that such MN had accumulated in the lesions over a period of several days.