FIG 4.

Confocal microscopy of internalized M. tuberculosis bacilli in neurons in brain sections of C57BL/6 mice 7 days after intracerebral infection. (B, D, and F) Orthogonal projections representing 3-dimensional data sets provide a view of the x-y, as well as the z, dimensions of the original z-stack. Cell nuclei are labeled with DAPI (blue). (A, C, and E) DIC images showing the tissue localization of H37Rv-GFP (green). (B) H37Rv-GFP bacilli are contained within β-III-tubulin-positive neuronal structures (red), indicated by partial colocalization (yellow) of the red and green fluorescence signals. (D) Bacilli are found within MAP2-positive neuronal structures (red, resulting in a yellow colocalization signal), but also disassociated from MAP2 (green). The latter may represent internalized or free bacilli, as it is not possible to delineate cell boundaries in these preparations. (F) Brain macrophages (identified by CD11b immunoreactivity) (red) contain large numbers of bacilli (green). CD11b is a cell surface antigen; therefore, no signal colocalization is observed. Scale bars, 10 μm.