Covers the molecules of cell-mediated immunity centred on T cells: the T cell receptor and its two forms (alpha-beta and gamma-delta), how the receptor is structured and compared with antibodies, and how the CD3 and zeta chains transmit signals. It then explains antigen recognition through peptides presented by MHC molecules, the HLA genes and the classes of MHC, their structure and tissue distribution, and the CD4 and CD8 co-receptors. The note ends with four mnemonics summarising receptor types, signalling partners, MHC types and peptide binding sizes.
Topic 50 of 105 in the MU Sofia syllabus for Biology (Medicine, Year 1). The free AceMed note covers it in 15 sections, about 1,098 words (8 min of reading), with 10 flashcards.
In this note
Molecules of cell-mediated immunity.
Overview of Cell-Mediated Immunity
The T Cell Receptor (TCR)
Types of T Cell Receptors
Structure and Function of TCR2
Comparison with Antibodies
Gamma Delta (γδ) T Cells
TCR Signal Transduction
How T Cells Recognize Antigens
Major Histocompatibility Complex (MHC)
Genetics of the MHC
Structure of MHC Molecules
MHC Expression and Tissue Distribution
MHC Co-receptors on T Cells
MNEMONICS
Overview of Cell-Mediated Immunity
Cell-mediated immunity is the arm of the immune system primarily carried out by T lymphocytes (T cells).
These T cells detect and respond to infected or abnormal cells, rather than free-floating pathogens in bodily fluids.
T cells rely on a specialized surface protein called the T cell receptor (TCR) to recognize antigens presented to them by other cells.
The T Cell Receptor (TCR)
T cells have surface receptors that are structurally distinct from the immunoglobulins found on B cells.
The T cell receptor is never secreted; it is anchored in the cell membrane.
TCR belongs to the immunoglobulin superfamily of proteins but functions exclusively on the cell surface.
The receptor allows T cells to recognize processed fragments of protein antigens presented by other cells.
Types of T Cell Receptors
There are two main types of TCRs:
TCR2, which is composed of alpha (α) and beta (β) chains, is found on over 90 percent of T cells.
TCR1, which is composed of gamma (γ) and delta (δ) chains, is present on a small population of T cells.
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