Biology · MU Pleven

43.The genetic basis of T-cell receptor. Ontogeny of T-lymphocytes.

Covers the two-chain T-cell receptor, its alpha and beta chains compared with antibody light and heavy chains, and how the variable regions are built from V, D and J gene segments. It explains MHC I and MHC II antigen presentation, the roles of CD4, CD8 and CD3, and how T cells develop in the thymus through selection for self-tolerance and MHC restriction. It closes with a point-by-point comparison of immunoglobulins and T-cell receptors.

Inside: 3 sections · 3 labelled pictures · 20 flashcards · 3 min

Topic 43 of 63 in the MU Pleven syllabus for Biology (Medicine, Year 1). The free AceMed note covers it in 3 sections, about 448 words (3 min of reading), with 20 flashcards.

In this note

  1. The genetic basis of T-cell receptor. Ontogeny of T-lymphocytes.
  2. T-Cell Receptor (TCR)
  3. T-Cell Ontogeny

The genetic basis of T-cell receptor. Ontogeny of T-lymphocytes.

Role of T Cells in the Immune Response

T cells play a crucial role in defending the body against protein components of foreign antigens that enter cells. They achieve this through two major mechanisms:

  • By releasing soluble factors called cytokines, which influence the function of multiple cell types.
  • By directly killing cells that have been penetrated by antigens.

T-Cell Receptor (TCR)

The T-cell receptor consists of two chains, α and β, and is structurally similar to an antibody molecule: the α-chain corresponds to the light chain, and the β-chain corresponds to the heavy chain. Key features of TCRs include:

  • Chains connected by a disulfide bond
  • Variable and constant regions
  • A short cytoplasmic tail

Most T cells express αβ TCRs, but some specialized T cells express γ and δ chains (γδ T cells). The variable regions are encoded differently in each chain:

  • α-chain: composed of V and J gene segments
  • β-chain: composed of V, D, and J gene segments

Antigen Recognition

TCRs recognize antigens only when they are presented by MHC molecules (Major Histocompatibility Complex), first identified in transplantation immunology. There are two main types of MHC molecules:

  • MHC I, which presents endogenous peptides, such as those encoded by viruses, intracellular microorganisms, or tumor antigens.
  • MHC II, which presents exogenous peptides, taken up through phagocytosis and processed in phagolysosomes.

Additional Molecules in Antigen Recognition

  • CD8 interacts with MHC I, and CD4 interacts with MHC II.
  • CD3 is a multimolecular complex that transduces signals after antigen binding.

All T cells, whether αβ or γδ, express TCRs on their surface along with CD3. αβ T cells also have coreceptor molecules (CD4 or CD8), dividing them into two subsets:

  • αβ+ CD4+ T cells
  • αβ+ CD8+ T cells

The coreceptors serve two main functions:

  • Bind MHC molecules on antigen-presenting cells
  • Act as signal transduction molecules after antigenic stimulation

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