三级片视频播放,精品三级片在线观看,A级性爱视频,欧美+日韩+国产+无码+小说,亲子伦XX XX熟女,秋霞最新午夜伦伦A片黑狐,韩国理伦片漂亮的保拇,一边吃奶一边做边爱完整版,欧美放荡性护士videos

The T cell receptor （TCR） α and β proteins are essential components of the αβ T cell receptor, a heterodimeric surface protein expressed on T lymphocytes that recognizes antigenic peptides presented by major histocompatibility complex （MHC） molecules. The TCR α chain is encoded by the TRAC （T cell receptor alpha constant） and TRAV （T cell receptor alpha variable） genes, while the TCR β chain is encoded by the TRBC （T cell receptor beta constant） and TRBV （T cell receptor beta variable） genes, along with diversity （TRBD） and joining （TRBJ） segments, enabling extensive combinatorial diversity. Structurally, both chains consist of a variable （V） domain responsible for antigen recognition and a constant （C） domain that anchors the receptor to the cell membrane. The TCR αβ heterodimer associates with the CD3 complex （CD3γε, CD3δε, and CD247 ζζ） to form a functional TCR-CD3 signaling unit, which transmits activation signals upon peptide-MHC engagement. TCR β undergoes V（D）J recombination during thymic development, contributing to the receptor's antigen specificity, whereas TCR α lacks a D segment but still undergoes recombination for diversity. Mutations or dysregulation in TCR α/β genes can lead to immune disorders, including T cell malignancies and autoimmune diseases. TCR αβ T cells are critical for adaptive immunity, mediating responses against infections, tumors, and self-antigens in autoimmune conditions.