Final answer:
Fever can be both beneficial and harmful; it helps fight infection by inhibiting pathogen growth and speeding up cellular repair, but if it's too high, it can cause organ damage and even be life-threatening. Superantigens from certain bacteria can cause an overactive immune response leading to dangerously high fevers.
Step-by-step explanation:
Why is fever often considered not beneficial, and what are the reasons mentioned regarding its effects on cellular metabolic rate and antigen-antibody reactions? While fever is a defense mechanism that the body uses to fight off infection, an elevated temperature can sometimes be detrimental. The increased temperature can inhibit the growth of pathogens and speed up cellular repair processes. However, a fever can also increase the cellular metabolic rate, which may result in damage to tissues and organs if the temperature becomes excessively high.
One of the dangers of fever is in the case of a response to bacterial superantigens, which can lead to life-threatening conditions such as toxic shock syndrome and scarlet fever. Superantigens trigger an excessive immune response, causing too many T cells to activate and the release of large amounts of cytokines, which can be harmful to the body. High fevers exceeding 42 °C (108 °F) can be extremely dangerous and may require medical intervention.
To maintain core body temperature, the hypothalamus acts as a thermostat. Endogenous pyrogens, released during infections, tell the hypothalamus to increase the body's set point, resulting in fever. This increase in body temperature conserves iron (limiting bacterial growth), boosts the activity of enzymes and protective cells, and in some cases, directly kills pathogens. However, the body also has mechanisms for cooling down, like vasodilation and sweating, to prevent the temperature from rising too high.