The human body is a complex and sophisticated machine in which all components must maintain an intricate balance to ensure optimal functioning. This balance at a specific set point is known as homeostasis. There are many homeostatic variables and the one I find most interesting is temperature, more specifically how our bodies respond to environmental and internal threats by means of thermoregulation. Many different syndromes such as heat stroke, neuroleptic malignant syndrome, malignant hyperthermia and fever can lead to elevation of body temperature. Fever is usually triggered by infection or inflammation while the other syndromes are a result of an imbalance between heat production and heat loss rather than a change in the body temperature set point (Prewitt, 2005). This paper aims to describe the different elements that originate a fever in the human body.
As mentioned above, fever is a defense mechanism the immune system uses to get rid of invading pathogens. The infectious organisms or their products that cause fever are called pyrogens and they can be exogenous (from the outside) and endogenous (internally produced). They are low-molecular-weight proteins that modulate immune, inflammatory and hematopoietic processes in the body (Biddle, 2006). Pyrogenicity is a fundamental biologic property of several cytokines and hence the property of fever links host perturbations during disease with fundamental perturbations in cell biology (Dinarello, 1999). When a microbial infection occurs, it usually causes localized tissue death or injury stimulating the release of inflammatory mediators that attract white blood cells which phagocytize the pathogen and initiate the release of cytokines and prostaglandins: small proteins that facilitate the fever and inflammation reactions to pathogens (Broom, 2007).
Out of all the products of the inflammatory process, cytokines are the most closely related to fever. The most relevant cytokines are: Interleukin 1 (IL-1) which activates the vascular epithelium and increases vascular access to where the infection is taking place so the lymphocytes can fight pathogens. Interleukin 6 (IL-6) stimulates the production of antibodies while TNF –α (Tumor necrosis factor) acts as a cytolitic (destroys cells) and a cytostatic (inhibit cell growth) and increases permeability to capillaries. When the immune system has been affected by a viral attack, Interferon is present to assist cell communication to enhance cell resistance to viral attacks (Broom 2007). In addition, the discovery of the existence of TLRs which are specific toll-like receptors for specific stimuli, explains why diverse microbial products with different chemical and physical characteristics can evoke fever; the cytoplasmic domains of TLR exhibit the same signaling areas of IL-1 (Dinarello, 2004).
These cytokines are the first responders to infection, but how does the brain interpret their signals? The blood-brain barrier (BBB) is a network of capillary...