Table 1.
Categorization of TB granulomas, based upon the literature.
| Type | Main findings | Mycobacteria strain | Site of granuloma(s) | Subjects | Reference |
|---|---|---|---|---|---|
| Foreign body-type (non-immune) and hypersensitivity-type (immune) granulomas (Figure 1A) | The Mtb cell component trechalose 6,6 dimycolate is a pleiotropic molecule that induces both non-immune and immune TB granulomas. | Mtb | Lung | Mice | (40) |
| Solid, caseous and cavitary granulomas (Figures 1B,C) | Characterized by region of necrosis, TNF-α composition and presence of leukotriene A4 hydrolase (LTA4H): Solid – none. Caseous – high. Cavitary – low. |
Mtb | Lung | Humans & rabbits | (5) |
| Nascent, caseous. fibrocaseous and resolved/calcified granulomas (Figures 1D,E) | Characterized based on the abundance of the proteins ADFP, ACSL1 and SapC: Nascent – low. Caseous – high. Fibrocaseous – high. Resolved – none. |
Mtb | Lung | Humans | (21) |
| Categories 1–5 granulomas (Figures 1F–J) | Characterized based upon mononuclear phagocytes, alveolar macrophages and lymphocytes, and: 1 – few lesions. 2 – scattered, discrete foci. 3 – moderate-sized lesions. 4 – enlarged, coalescing lesions with small necrotic foci and advanced fibrosis. 5 – chronic, interstitial fibrosis of the lung and thickened granuloma wall. |
Mtb | Lung | Mice | (124) |
| Primary, secondary and tertiary granulomas (Figures 2A,B) | Granuloma types explain disease severity in murine models: Primary (accumulated immune response) – beginning. Secondary (immunity acquisition) – middle. Tertiary (linkage with foamy macrophages) – late. |
Mtb | Lung | Mice | (23) |
| Type I, type II and type III granulomas (Figures 2C–E) | Characterized by immune response routes: Type I (initial) – innate. Type II (developed) – adaptive cellular. Type III (terminal) – adaptive humoral. |
Mycobacterium bovis | Bronchial lymph node | Sheep | (125) |
| Early granuloma (Figure 2F) | Early TB granuloma characterized by presence of mycobacteria and either epithelioid or foamy macrophages. | Mycobacterium marinum | Brain | Zebrafish | (90) |
| Non-necrotizing, necrotizing gummatous and necrotizing abscess granulomas (Figures 2G–I) | Characterized by size, reticulin fibers and Mtb load: Non-necrotizing – small, none and no Mtb. Necrotizing gummatous – medium, present and low Mtb load. Necrotizing abscess – large, none and high Mtb load. |
Mtb | Brain | Humans | (31) |