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The Immune System's Thermostat: How Body Temperature Helps Fight Infection

 




Body temperature and the immune system have a close relationship. The fever response, or an increase in body temperature, is a hallmark of infection and inflammation and has been shaped over hundreds of millions of years of natural selection. In endothermic (warm-blooded) animals, the induction of fever occurs at a high metabolic cost, but it has been shown to be associated with improved survival and resolution of many infections. On the other hand, uncontrolled fever is linked to worse outcomes in patients with sepsis or neurological injuries, while treatments that induce hypothermia can have a clinical benefit.

Ectothermic (cold-blooded) vertebrates, such as reptiles, fish, and insects, also show a correlation between infection and increased temperature. Studies have shown that survival is reduced if these animals are prevented from behaviorally raising their core temperature after infection. This correlation between infection and increased temperature extends even to plants, as the temperature of infected leaves increases. The fact that fever has been retained throughout vertebrate evolution suggests that febrile temperatures confer a survival advantage.

The mechanisms by which fever protects against invading pathogens include direct effects on the infectious potential of pathogens and stimulation of both the innate and adaptive arms of the immune system. The pyrogenic cytokine interleukin-6 (IL-6) plays a key role in the febrile response, driving the rise in core temperature and orchestrating lymphocyte trafficking to lymphoid organs. Fever is also thought of as a "rheostat," dialing down systemic inflammation during the return to homeostasis. There are overlapping signaling pathways involved in thermogenesis and regulation of the immune response, and the heat shock protein response is also evolutionarily conserved.

The immune system is the body's defense against disease and foreign substances. It is made up of a complex network of cells, tissues, and organs that work together to identify and neutralize these threats. The immune system can be divided into two main arms: the innate immune system, which provides a rapid response to foreign invaders, and the adaptive immune system, which provides a more specific and long-lasting response.

The relationship between body temperature and the immune system is seen in the fever response. As previously mentioned, a fever is an increase in body temperature that is associated with improved survival and resolution of many infections. This is because fevers boost the effectiveness of the immune response during infections by stimulating both the innate and adaptive immune systems. The rise in body temperature is driven by the pyrogenic cytokine IL-6, which is released in response to an infection. IL-6 then signals the hypothalamus to raise the body's core temperature, creating a fever.

In conclusion, the close relationship between body temperature and the immune system is seen in the fever response. Fevers boost the effectiveness of the immune response during infections by stimulating both the innate and adaptive immune systems and are thought to provide a survival advantage. This relationship is driven by the pyrogenic cytokine IL-6, which signals the hypothalamus to raise the body's core temperature and stimulates the immune response.

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