A T-cell receptor (TCR) is a protein found on the surface of T-cells, a type of white blood cell that plays a crucial role in the immune system. TCRs are responsible for recognizing specific antigens, which are molecules from pathogens like viruses and bacteria. When a TCR binds to an antigen presented by other immune cells, it triggers an immune response to help eliminate the threat. Each TCR is unique, allowing the immune system to target a wide variety of pathogens. The diversity of TCRs is generated through a process called V(D)J recombination, which rearranges gene segments to create different receptor combinations. This diversity is essential for the adaptive immune response, enabling the body to remember and respond more effectively to previously encountered pathogens.