Question

Explain how pyrogens are believed to cause a fever, and give two examples of pyrogens. (p. 399)

Short answer

Provide two examples of pyrogens. Answer: Pyrogens are substances capable of inducing fever in an organism, typically produced by bacteria or released from damaged host cells. They cause fever by stimulating the production of prostaglandin E2 (PGE2), which then travels to the hypothalamus and results in a change in the body's temperature set point. Two examples of pyrogens are lipopolysaccharide (LPS), an exogenous pyrogen from the outer membrane of Gram-negative bacteria, and interleukin-1 beta (IL-1β), an endogenous pyrogen produced by immune cells like macrophages.

Step-by-step solution

Define pyrogens

Pyrogens are substances, typically produced by bacteria or released from damaged host cells, that are capable of inducing fever in an organism. They act by stimulating the production of prostaglandins, a group of hormone-like substances involved in a variety of body processes, including inflammation and fever.

Explain the mechanism of pyrogens causing fever

When pyrogens enter the body, they bind to receptors on immune cells known as macrophages. This binding stimulates the production of prostaglandin E2 (PGE2) by the macrophage through a cascade of molecular events involving the activation of enzymes such as cyclooxygenase-2 (COX-2). PGE2 then travels through the bloodstream to the hypothalamus, a region of the brain responsible for regulating body temperature. In the hypothalamus, PGE2 binds to specific receptors, resulting in a change in the set point of the body's temperature control system. This change leads to an increase in body temperature, which is sensed by the thermoregulatory center in the hypothalamus, resulting in the activation of heat-producing mechanisms, such as increased metabolic rate and shivering. Consequently, fever occurs as the body attempts to reach the new temperature set point.

Provide two examples of pyrogens

There are two main categories of pyrogens: endogenous and exogenous pyrogens. 1. Exogenous pyrogens: These are substances produced by infectious agents, such as bacteria, viruses, and fungi. One well-known example of an exogenous pyrogen is lipopolysaccharide (LPS), also called endotoxin, which is a component of the outer membrane of Gram-negative bacteria. When released during a bacterial infection, LPS triggers fever by stimulating the production of PGE2. 2. Endogenous pyrogens: These are substances produced by the host organism's own cells in response to infection or injury. A common example of an endogenous pyrogen is interleukin-1 beta (IL-1β), which is a cytokine produced by various immune cells, including macrophages. IL-1β plays a key role in the inflammatory response, and it also acts as a pyrogen by inducing the production of PGE2 in cells.