Fill in the Blank QuestionFill in the blank question.Any molecule that triggers an immune response is called a(n) .

Any molecule that triggers an immune response is called an antigen.

Antigens are typically foreign substances such as proteins, polysaccharides, or nucleic acids that are found on the surface of pathogens like bacteria, viruses, fungi, and parasites. When the immune system detects these antigens, it mounts a response to eliminate or neutralize the invader. This involves the activation of various immune cells such as lymphocytes, which produce antibodies that specifically target the antigens. The interaction between antigens and antibodies is crucial for the adaptive immune response, allowing the body to remember past infections and respond more rapidly to subsequent exposures to the same pathogen. Understanding antigens is fundamental in immunology and is a key concept in vaccines, where harmless versions of antigens are introduced to prompt immunity without causing disease.