How does tuberculous granuloma develop?

➢ When mycobacteria (red) resist the effects of macrophage activation, a characteristic localized inflammatory response called a granuloma develops. ➢ This consists of a central core of infected macrophages. ➢ The core may include multinucleated giant cells, which are fused macrophages, surrounded by large macrophages often called epithelioid cells. ➢ Although in the first instance the granuloma acts to constrain the infection, some bacilli can actually survive for decades inside these structures in a dormant state ➢ Mycobacteria can persist in the cells of the granuloma. ➢ The central core is surrounded by T cells, many of which are CD4-positive. ➢ The exact mechanisms by which this balance is achieved, and how it breaks down, are unknown.