Figure 1. Macrophages and dendritic cells have a variety of receptor families whereby they can sense the presence of invading bacteria.

Figure 2. Both alveolar macrophages (left) and dendritic macrophages (right) readily ingest mycobacteria. In this photo the DC has a notable cluster of bacilli in its phagosome.

Figure 3. Distribution of CD4 and CD8 cells in the mouse lung granuloma. Whereas CD4 cells are distributed in aggregates across the granuloma, CD8 cells tend to occupy more peripheral sites, often along the rim of the granuloma.

Figure 4. Early (day 30) and late stage (day 100) granulomas in the guinea-pig lung. (a) By day 30 a clear core area of necrosis has already developed. It is surrounded by a layer of macrophages and further out by a large lymphocyte layer, which includes large aggregates or follicle-like structures. A fibrous capsule is beginning to develop. Most obviously on the pleural side of the structure. (b) By day 100 the central core has mineralized. A smaller region to the left may represent a smaller granuloma that has coalesced with the central structure (a common event). Around the core is a pink staining ring of extracellular fibrin which our recent research suggests contains a large number of acid-fast bacilli, some of which persist after chemotherapy; this region is also rich in iron molecules. Outside this is an obvious layer full of foamy macrophages and then a thinner, perhaps compressed layer of dark blue staining lymphocytes. A compressed vessel can be seen at the bottom right of the lesion; we have suggested that bacteria-containing cells are eroded into such vessels by mechanical force (see text).