noun, plural: endogenous pyrogens
Pyrogens are substances that act on the hypothalamic thermoregulatory center inciting a febrile response. There are two types of pyrogens. These are the endogenous pyrogen and the exogenous pyrogen. The endogenous pyrogens are produced by the immune cells that are activated by the presence of infectious agents (e.g. bacteria, viruses, prions, and viroids).
Endogenous pyrogens are usually cytokines, such as interleukin-6, interleukin-1, tumour necrosis factor, interferon-alpha, gp130 Receptor Ligands, and so on. They are released by monocytes, neutrophils, lymphocytes, endothelium glial cells, mesangium, and mesenchymal cells.1 The pyrogenic cytokines act on the fenestrated endothelium of the circumventricular organs releasing prostaglandin E2, which in turn act on the thermoregulatory center of the hypothalamus. In response, the hypothalamus increases the temperature of the body above the normal range resulting to fever. Increase in body temperature is thought to help defend the body against infection by stimulating the activity of the immune cells.2
1 Dinarello, C. A. Cytokines as Endogenous Pyrogens The Journal of Infectious Disease 1999 179: S294-S304.
2 The Editors of Encyclopædia Britannica. 2014. Fever. Britannica.com. Retrieved from http://www.britannica.com/EBchecked/topic/205674/fever