Outcomes of acute inflammation:ResolutionHealing by fibrosisChronic inflammation

Events in the resolution of inflammation

Return to normal vascular permeability;Drainage of edema fluid and proteins into lymphatics or by pinocytosis into macrophages;Phagocytosis of apoptotic neutrophils and necrotic debris;Disposal of macrophages. Macrophages also produce growth factors that initiate the subsequent process of repair. Note the central role of macrophages in resolution.

Serous inflammation. A skin blister showing the epidermis separated from the dermis by a focal collection of serous effusion.

Fibrinous pericarditis. A, Deposits of fibrin on the pericardium. B, A pink meshwork of fibrin exudate (F) overlies the pericardial surface (P).

Suppurative inflammation. A, A subcutaneous bacterial abscess with collections of pus. B, The abscess contains neutrophils, edema fluid, and cellular debris.

The morphology of an ulcer. A, A chronic duodenal ulcer. B, Low-power cross-section of a duodenal ulcer crater with an acute inflammatory exudate in the base.

Maturation of mononuclear phagocytes.

The roles of activated macrophages in chronic inflammationMacrophages are activated by :Cytokines from immune-activated T cells (particularly IFN-gamma), Nonimmunologic stimuli such as endotoxin.

Chronic inflammation in the lung, showing all three characteristic histologic features: (1) collection of chronic inflammatory cells (*), (2) destruction of parenchyma (normal alveoli are replaced by spaces lined by cuboidal epithelium, arrowheads), and (3) replacement by connective tissue (fibrosis, arrows).

By contrast, in acute inflammation of the lung (acute bronchopneumonia), neutrophils fill the alveolar spaces and blood vessels are congested

Mechanisms of macrophage accumulation in tissues. The most important is continued recruitment from the microcirculation.

Macrophage-lymphocyte interactions in chronic inflammation. Activated lymphocytes and macrophages influence each other and also release inflammatory mediators that affect other cells.

Typical tuberculous granuloma showing an area of central necrosis, epithelioid cells, multiple Langhans-type giant cells, and lymphocytes.