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 immune system's ability to adapt and respond to new infections.