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Biology LibreTexts

11.3I: Fever

 Skills to Develop

  1. Describe the mechanism behind fever induction and indicate its possible benefits.
  2. Define hyperpyrexia.

Activated macrophages and other leukocytes release inflammatory cytokines such as TNF-alpha, IL-1, and IL-6 when their pattern-recognition receptors (PRRs) bind pathogen associated molecular patterns or PAMPs - molecular components associated with microorganisms but not found as a part of eukaryotic cells. These include bacterial molecules such as peptidoglycan, teichoic acids, lipopolysaccharide, mannans, flagellin, and bacterial DNA. There are also pattern-recognition molecules for viral double-stranded RNA (dsRNA) and fungal cell walls components such as lipoteichoic acids, glycolipids, mannans, and zymosan.

These cytokines stimulate the anterior hypothalamus of the brain, the part of the brain that regulates body temperature, to produce prostaglandin E2, which leads to an increase bodily heat production and increased vasoconstriction. This, in turn, decreases the loss of heat from the skin and increases body temperature. Up to a certain point, fever is beneficial:

  1. Fever increases the environmental temperature above the optimum growth temperature for many microorganisms. If the microorganisms are growing more slowly, the body's defenses have a better chance of removing them all.
  2. Fever leads to the production of heat shock proteins that are recognized by some intraepithelial T-lymphocytes called delta gamma T-cells, resulting in the production of inflammation-promoting cytokines.
  3. Fever elevates the temperature of the body increasing the rate of enzyme reactions, and speeding up metabolism within the body. An elevation in the rate of metabolism can increase the production and activity of phagocytes, speed up the multiplication of lymphocytes, increase the rate of antibody and cytokine production, increase the rate at which leukocytes are released from the bone marrow into the bloodstream, and speed up tissue repair.

Too high of a body temperature, however, may cause damage by denaturing the body's enzymes. Hyperpyrexia is a fever with an extreme elevation of body temperature greater than or equal to 41.5 °C (106.7 °F). Body temperature this elevated often indicates a serious underlying condition and may lead to potentially hazardous side effects. As a result, hyperpyrexia is considered as a medical emergency.

Summary

  1. Activated macrophages and other leukocytes release inflammatory cytokines such as TNF-alpha, IL-1, and IL-6 when their pattern-recognition receptors (PRRs) bind pathogen associated molecular patterns or PAMPs.
  2. These cytokines stimulate the anterior hypothalamus of the brain, the part of the brain that regulates body temperature, to produce prostaglandin E2, which leads to an increase bodily heat production and increased vasoconstriction.
  3. Vasoconstriction decreases the loss of heat from the skin and increases body temperature.
  4. Fever increases the environmental temperature above the optimum growth temperature for many microorganisms.
  5. Fever leads to the production of heat shock proteins that are recognized by some intraepithelial T-lymphocytes resulting in the production of inflammation-promoting cytokines.
  6. Fever elevates the temperature of the body increasing the rate of enzyme reactions, and speeding up metabolism within the body including that involved in innate and adaptive immunity as well as tissue repair.

Contributors

  • Dr. Gary Kaiser (COMMUNITY COLLEGE OF BALTIMORE COUNTY, CATONSVILLE CAMPUS)