Figure 2. Kinetics of intracellular Mtb growth in vivo.

BAL cells and whole lung leukocytes were harvested at 1, 2, 3 and 8 weeks after aerosol infection of mice with 300 CFU Mtb Erdman delivered to the lung. Cells from both sources were counted and cytospin preparations were made for Ziehl-Neelsen staining. (A) The total number of Mtb-infected (AFB⁺) cells was derived by multiplying the % AFB⁺ cells by the total number of cells in each sample. Results for individual mice are presented as log₁₀ total AFB⁺ cells, with the line representing the mean. (B) The proportion of Mtb-infected phagocytes within the total sample was counted at each time point and expressed as % AFB⁺ cells. (C) Neutrophils infected with Mtb were identified by their typical nuclear morphology on Ziehl-Neelsen stained cytospin slides of BAL cells and whole lung leukocytes. The relative proportion of AFB in neutrophils versus monocytic phagocytes (AM, RM and mDC) is expressed as mean % AFB⁺ leukocytes ± SD from one representative experiment. All in vivo experiments were repeated twice.