BCR, or B-cell receptor, is a protein complex found on the surface of B cells, a type of white blood cell. It plays a crucial role in the immune system by recognizing specific antigens, which are foreign substances that can trigger an immune response. When a BCR binds to its corresponding antigen, it activates the B cell, leading to the production of antibodies that help neutralize or eliminate the threat. In addition to its role in immunity, BCR is important for the development of B cell memory. This allows the immune system to remember past infections and respond more effectively if the same antigen is encountered again. Understanding BCR is essential for research in immunology and the development of vaccines.