Chapter 4 - T cells of Adaptive Immunity At the end of this Chapter, students should be able to: . Explain the structure of the T cell receptor, and the T cell receptor complex. · Explain the process and purpose of positive and negative selection during T cell development. 1
Chapter 4 - T cells of Adaptive Immunity T cell development Precursor T cells are derived from lymphoid precursor cells in the bone marrow - they migrate to the thymus to continue their maturation and start to express the TCR and other proteins. Two major types of effector T cells: CD4 T helper cells (Th) - recognize peptides presented on MHC class Il proteins. CD8 T killer cells (or cytotoxic T lymphocytes, CTL) - recognize peptides presented on MHC class I proteins. Memory aid: 4 (CD4) x 2 (MHC II) = 8 (CD8) x 1 (MHC I) 2
Chapter 4 - T cells of Adaptive Immunity T cell recognize and respond to antigens via the receptor (TCR) complex. Different proteins in the complex have different roles. CD4 TCR T helper aß TCR: recognizes a complex of the MHC and peptide: antigen recognition. Co-receptor CD4 (T helper) or CD8 (CTL): strengthens the interaction between the antigen- presenting cell (APC) and T helper cell. CD3 (multiple subunits): relays a signal to nucleus that TCR has been engaged, resulting in new gene expression, proliferation. p56lck CD8 -CD3 4 TCR ? ? CTL p56lck (grey protein): signalling protein that works with CD3 to relay the signal CD3 p56lck 3