Correct Option
An antigen is any substance that elicits a specific immune response in the body. These substances are typically foreign to the host organism and can include proteins, polysaccharides, lipids, or nucleic acids. Upon detection by the immune system, antigens stimulate the production of antibodies and/or activate specific immune cells (e.g., T-lymphocytes) to neutralize or eliminate the perceived threat. Common sources of antigens include pathogens (bacteria, viruses, fungi), toxins, and allergens.
Incorrect Options
- Option 1 (lowers body temperatures): Antigens do not directly regulate body temperature. Fever, an increase in body temperature, can be a symptom of an immune response, but antigens themselves are not thermoregulatory agents.
- Option 2 (destroys harmful bacteria): Antigens are components of harmful bacteria or other pathogens that are recognized by the immune system. It is the immune system's components (e.g., antibodies, phagocytes, cytotoxic T-cells) that destroy bacteria, not the antigens themselves.
- Option 4 (is used as an antidote to poison): Antidotes are substances that counteract the effects of poisons. Antigens, conversely, initiate an immune response and are not used to neutralize poisons.