From which source do endogenous pyrogens originate?

Endogenous pyrogens originate from internal body processes, specifically from immune system cells in response to certain stimuli, such as infection or inflammation. These pyrogens, which include substances like interleukins and tumor necrosis factor (TNF), are produced when the body detects pathogens or cellular damage and are responsible for raising the body's temperature set point in the hypothalamus. This increase in temperature, or fever, is a part of the body's defense mechanism, enhancing immune responses and inhibiting the growth of pathogens.

The other options refer to sources that are primarily external to the body or do not directly relate to the production of endogenous pyrogens. For instance, external pathogens and infections primarily refer to the presence of microbes that might trigger the immune response but do not directly produce endogenous pyrogens themselves. Environmental toxins may affect the body but are not related to the internal immune processes that generate pyrogens.