TCRs

TCRs, or T-cell receptors, are proteins found on the surface of T cells, a type of white blood cell crucial for the immune system's adaptive response. They play a pivotal role in recognizing and responding to foreign substances, such as viruses, bacteria, and cancer cells. TCRs are composed of two chains: an alpha (α) chain and a beta (β) chain, which are encoded by the T-cell receptor genes. These chains are non-covalently associated with CD3 molecules, which are essential for signal transduction upon antigen recognition.

TCRs are highly diverse, allowing T cells to recognize a vast array of antigens. This diversity is achieved through a process called V(D)J recombination, which rearranges the genes encoding the TCR chains during T-cell development. The diversity is further enhanced by somatic hypermutation and junctional diversity, which occur during the T-cell's maturation process.

There are two main types of T cells based on their TCRs: CD4+ T cells and CD8+ T cells. CD4+ T cells express TCRs that recognize antigens presented by major histocompatibility complex (MHC) class II molecules, primarily assisting in the activation of other immune cells. CD8+ T cells, on the other hand, express TCRs that recognize antigens presented by MHC class I molecules, directly killing infected cells.

TCRs are not only essential for the immune response but also play a role in autoimmune diseases and cancer. Dysregulation of TCR signaling can lead to excessive immune activation, contributing to conditions like rheumatoid arthritis and multiple sclerosis. In cancer, TCRs can recognize and eliminate tumor cells, making them a target for cancer immunotherapy.