What are foreign substances that trigger immune responses called?

The term that denotes foreign substances triggering immune responses is "antigens." Antigens are typically proteins or polysaccharides found on the surface of pathogens like bacteria and viruses, as well as substances that come from non-pathogenic sources, such as pollen or certain foods. When antigens enter the body, the immune system recognizes them as foreign and initiates a response that may include the production of antibodies by B cells and activation of T cells.

Understanding antigens is crucial for grasping how the immune system works. They play a fundamental role in the identification of what is non-self, allowing the immune system to mount a targeted response. The specificity of immune responses is largely determined by the unique molecular structures of various antigens.

While pathogens refer to the organisms that can cause disease, such as bacteria and viruses, they are not synonymous with antigens, as not all antigens are pathogens. Antibodies are the proteins produced by the immune system in response to antigens, serving to neutralize or tag them for destruction. Allergens specifically refer to antigens that trigger allergic responses and are a subset of antigens, but they do not encompass all immune responses. Thus, antigens are the broad category that includes any substance capable of invoking an immune reaction