A Ghon complex is caused by
Mycobacterium tuberculosis, which is the bacteria that causes TB. When the Mycobacterium enters the lungs,
macrophages recognize the Mycobacterium as foreign and attempt to phagocytize them. Typically, a
macrophage does this by engulfing the foreign material and packaging them into a structure called phagosome. The macrophage then fuses the phagosome with a lysosome, or organelle of the cell that contains enzymes that break down biochemical molecules. However, Mycobacterium can produce a protein that inhibits this fusion, thereby allowing the Mycobacterium to survive, proliferate, and create a localized infection called
primary tuberculosis. Nevertheless, approximately three weeks after the initial infection, more specific immune cells (e.g.,
T cells,
B cells, and
Neutrophils) surround the site of TB infection, creating a wall of immune cells known as a
granuloma, which isolates the bacteria and prevents it from spreading. The tissue inside the granuloma then dies during a process referred to as caseous necrosis, or cheese-like necrosis. This necrotic area is known as a Ghon focus. TB infection can also spread to nearby hilar lymph nodes, either carried through the lymph or by direct
extension of the Ghon focus. Together, the caseating tissue and associated lymph node involvement make up the characteristic “Ghon complex.”