Endogenous pyrogens are essential information molecules that cause regulated body temperatures. At present, the known endogenous pyrogens belong to proinflammatory cytokines, such as interleukin 1 (IL-1), interferon (IFN), IL-1, tumor necrosis factor (TNF), interleukin 6 (IL-6), etc. In addition to the pyrogenic effect on the body, it also mediates acute phase reactions closely related to fever, including changes in the number of neutrophils, hypoferremia, hypozincemia, hypercopperemia, and increased synthesis of various acute phase reaction proteins. In addition, these cytokines play an important regulatory role in the immune system.
As early as 1948, Beeson et al. extracted a thermogenic substance that is not heat-tolerant, non-thermogenic tolerant, and can be inactivated by proteolytic enzymes from the supernatant of leukocyte culture in the peritoneal cavity of rabbits, which is essentially different from the bacterial endotoxin, a heat-activator commonly called pyrogen, and is named leukocytic pyrogen. It has been made clear that this endogenous thermogenic information molecule is mainly produced by activated mononuclear macrophages, which is a protein component, and can lose its pyreogenic activity when heated for min, and the general dose of intravenous injection causes monophasic heat, and its fever latency is significantly shorter than that of bacterial endotoxin, and there is no thermotoxin tolerance, and injection into rabbits that have been tolerant to bacterial endotoxin can still cause febrile reaction, and there is cross-thermogenicity in some species of animals.