Immune system: Acute vs chronic inflammation

Acute inflammation is induced by tissue damage due to trauma, noxious compounds, or microbial invasion. The process of acute inflammation is mediated by immune cells, important cell-signaling proteins called cytokines, and other small molecules. Anaphylatoxins, small immune-mediating molecules released at the site of inflammation, stimulate mast cells to release histamine, serotonin and prostaglandins, which bind specific receptors on endothelial cells and smooth muscle cells, promoting endothelial permeability and smooth muscle relaxation. This response allows immune cells such as neutrophils to migrate into affected tissue through the capillary wall (diapedesis) and respond to the offending agent, as shown in Figure 1; neutrophils are thus the major component of pus. Additional clinical signs of acute inflammation include swelling, redness, pain and heat at the site of the insult.

Figure 1 Neutrophil Diapedesis; adapted from Kantari et al. The role of neutrophils and monocytes in innate immunity. Contrib Microbiol. 2008;15:118-46

Chronic inflammation, in contrast, may be the only inflammatory response seen in certain viral infections and hypersensitivity reactions, particularly if the cause of inflammation is persistent. In chronic inflammation, the primary immune cells are macrophages and T lymphocytes, which produce cytokines and enzymes that cause more lasting damage to cells. Acute inflammation caused by infection or injury will also transition to chronic inflammation over a period of days to weeks.

Table 1 shows the main cell types, mediators, and symptoms observed in acute and chronic inflammation.

Table 1 Characteristics of Acute versus Chronic Inflammation

General treatments used for both types of inflammation include nonsteroidal anti-inflammatory drugs (NSAIDs), which are commonly used to reduce pain, swelling, and body temperature/fever associated with inflammation; and corticosteroids, which are potent anti-inflammatory medications that can rapidly suppress inflammation. Other treatments that can address specific types of both chronic and acute inflammation include rilonacept, a monoclonal antibody against interleukin-1, and colchicine, which interferes with microtubules and disrupts the normal cellular processes involved in inflammation.