What are pyrogens? How do they work?

• A. Fever-inducing agents that raise body temperature
• B. Substances that neutralize toxins
• C. Agents that directly kill bacteria
• D. Cells that produce antibodies

Answer: (A)

Pyrogens are substances that trigger fever by signaling the hypothalamus to raise the body's temperature set point. They can be external products from pathogens (like endotoxins from bacteria) or internal mediators released by the immune system (cytokines such as IL-1, IL-6, and TNF-alpha). When pyrogens act, they stimulate the hypothalamus to produce prostaglandin E2, which raises the temperature set point. To reach this higher set point, the body activates heat-producing responses like shivering and vasoconstriction, making you feel cold until your body warms up to the new set point. When pyrogens are cleared or the response subsides, the set point returns to normal, and heat-dissipating responses such as sweating occur. Fever can help fight infection by slowing bacterial growth and boosting immune function.

The correct statement describes fever-inducing agents that raise body temperature. Other options refer to neutralizing toxins, directly killing bacteria, or antibody-producing cells, which are different aspects of immunity and not the role of pyrogens.