Granuloma formation begins with the recognition of a persistent antigen by the immune system. This leads to the recruitment of macrophages and lymphocytes to the site of infection or inflammation. The macrophages then attempt to phagocytose the antigen. When they fail to degrade the antigen, they undergo morphological changes to become epithelioid cells or fuse to form giant cells. Over time, a fibrous capsule may form around the granuloma, isolating it from the surrounding tissue.
