Inflammatory Processes

macrophages include microglial cells in the central nervous system, Kupffer cells in the liver, alveolar macrophages in the lungs, and peritoneal macrophages in the abdomen.

INFLAMMATORY PROCESSES

Inflammation is part of the innate immune response. It happens when there are pathogens in the body or damaged tissue. Inflammation is both necessary and helpful in the immune response, although excessive inflammation is not always helpful and can be lethal to the human host.

In acute inflammation, the response is nearly instantaneous. There will be vasoconstriction in order to limit blood loss. It does not last long and will later become vasodilation and an increase in vascular permeability because of histamine release in the mast cells. The process will dilute both bacteria and toxins.

The overall inflammatory response involves five visible signs: redness or erythema, heat, swelling or edema, pain, and alteration of function. Phagocytes enter the system through an increase in vascular permeability. These will release inflammatory mediators that further the response to infection. The complement system gets activated and complement factor C5a, also called anaphylatoxin, increases the inflammatory response. Bradykinin increases tissue edema, neutrophils rush in, and sometimes there can be pus formation.

Chronic inflammation happens when the body cannot clear the pathogen. This leads to a chronic battle between the immune system and the pathogens. One phenomenon of chronic inflammation is granuloma formation. This is a pocket of infection and white blood cells in a cluster. Figure 53 shows a granuloma:

Figure 53.

Granulomas often occur in the setting of tuberculosis, in which the granuloma is called a tubercle. Viral infections can also lead to this type of inflammation, with granulomas forming when the infection does not clear out.

Fever is another part of inflammation that can affect the whole body. There are some pathogens that result in pyrogen formation in the body, which resets the thermostat in the hypothalamus of the brain. Pyrogens can involve the endotoxin lipopolysaccharide of gram-negative bacteria, which causes leukocytes to release some of their own pyrogens. These can include tumor necrosis factor, certain interleukins, and interferongamma. These lead to prostaglandin formation that ultimately causes the fever. Fever makes leukocytes more effective and decreases the growth of many pathogens.

There can be a crisis phase, when the fever is said to “break”. Vasodilation and sweating occur, which help to cool the body. Sometimes the fever is too extensive; this can be