high TB prevalence in silicosis
Silicosis is distinguished by calcification of the rim of hilar nodes (eggshell calcification) and birefringent silica particles surrounded by fibrous tissue on histology. It has long been associated with increased risk of tuberculosis.
Silicosis impairs the macrophage effector arm of cell-mediated immunity, which is integral to the immune response against mycobacteria. It is thought that macrophage phagolysosomes are disrupted by internalized silica particles, causing release of the particles and viable mycobacteria, which inhibits the immune system's ability to control the infection. This extracellular release of lysosomal enzymes is thought to contribute to alveolar and interstitial lung injury in silicosis. Prolonged exposure of macrophages to silica particles also appears to increase macrophage apoptosis.