A B Cell Receptor (BCR) is a protein found on the surface of B cells, a type of white blood cell involved in the immune response. BCRs are responsible for recognizing specific antigens, which are foreign substances like bacteria or viruses. When a BCR binds to its corresponding antigen, it triggers the B cell to activate and proliferate, leading to the production of antibodies. Antibodies are proteins that help neutralize or eliminate pathogens. Each B cell has a unique BCR that can recognize a specific antigen, allowing the immune system to target a wide variety of threats. This specificity is crucial for effective immune responses and long-term immunity.