FIG 5.

Confocal microscopy of internalized M. tuberculosis bacilli in cultured murine primary neurons and in brain sections. (B and E) 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) Overview of MAP2-positive neurons (red), established from the hippocampi of 17-day-old C57BL/6 mouse embryos, containing an H37Rv-GFP bacillus (arrowhead). (B) Bacilli (green) are found associated with MAP2-positive neuronal structures, such as the cortical cytoplasm and neurites (red), resulting in a partial colocalization signal (yellow). (B1 to B3) Detailed images reveal localization of the bacillus within the MAP2-positive neuronal structure. Panels A and B represent a 24-h time point. (C and D) In brain sections (14 days postinfection), colocalization of bacilli (green signal in DIC image) (C) and MAP2 signal (D) is evident (yellow signal in panel E), indicating internalization of bacilli by the neurons. However, it is not possible to resolve the relevant structures in brain sections at the level seen in vitro. Scale bars, 5 μm.