PRESENTED BY:

REHNUMA K. GHORI

IMMUNOLOGY

T-CELL: TCR,DIFFERENTIATION

AND IMPORTANCE

Type of blood cell Belong to a group of white blood cells (WBCs) called lymphocytes.WBCs protect the body from infection. The main job of T-cells is to fight infection. There are a number of different types of T-cells that act in many ways to identify, directly attack and destroy infectious agents. Along with other WBCs, they play a major role in the immune system, which guards the body against infection.

T- CELL

Two types of lymphocytes◦ B lymphocytes – oversee humoral immunity

◦ T lymphocytes – non-antibody-producing cells that constitute the cell-mediated arm of immunity

Antigen-presenting cells (APCs):◦ Do not respond to specific antigens

◦ Play essential auxiliary roles in immunity

Lymphocytes

Immature lymphocytes released from bone marrow are essentially identical

Whether a lymphocyte matures into a B cell or a T cell depends on where in the body it becomes immune competent◦ B cells mature in the bone marrow

◦ T cells mature in the thymus

Thymus

•The thymus is an organ located in the upper chest.•Immature lymphocytes leave the bone marrow and find their way to the thymus where they are “educated” to become mature T-lymphocytes.

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Thymocytes at different developmental stages are

found in distinct parts of the thymus

Matu

ratio

n

PositiveSelection Ensures MHC Restriction

death by neglect !

(double positive cells)

class I

class II

NegativeSelectionEnsures Self-tolerance

Types of T-cell•T helper cells (TH cells)

•Cytotoxic T cells (TC cells, or CTLs)•Regulatory T cells (Treg cells), formerly

known as suppressor T cells•Memory T cell

“CD4 positive”

“CD8 Positive”

T-cell receptor

The T cell receptor or TCR is a molecule found on the surface of T lymphocytes (or T cells)that is responsible for recognizing antigens bound to major histocompatibilitycomplex (MHC) molecules.

Structure of T-Cell Receptor

Heterodimer(α+β chain linked together by a disulfide bridge)

Constant Region(anchor the receptor to the plasma membrane)

Variable Region(contact the antigen)

Structure of the T cell Receptor

Each T cell bears TCRs of only one specificity (allelic exclusion)

Structure of the T cell Receptor

Both α and β chains have a variable (V) and constant (C) region

V regions of the αand β chains contain hyper variable regions that determine the specificity for antigen

Major HistocompatibilityComplex (MHC)

There were three kinds of molecules encoded by the MHC◦ Class I◦ Class II◦ Class III

Class I MHC molecules are found on all nucleated cells (not RBCs)

Class II MHC molecules are found on APC◦ Dendritic cells, Macrophages, B cells, other cells

Class I MHC

Class II MHC

RBCs

APCs

Nucleated cells

THE ROLE OF THE MHC

In infected cells, MHC molecules bind and transport antigen fragments to the cell surface, a process called antigen presentation.

A nearby T cell can then detect the antigen fragment displayed on the cell’s surface

Depending on their source, peptide antigens are handled by different classes of MHC molecules:

Class I MHC molecules are found on almost all nucleated cells of the body

They display peptide antigens to cytotoxic T cells Class II MHC molecules are located mainly on dendritic

cells, macrophages, and B cells Dendritic cells, macrophages, and B cells are antigen-

presenting cells that display antigens to cytotoxic T cells and helper T cells.

Infected cell

Antigenfragment

Class I MHCmolecule

T cellreceptor

(a)

Antigenassociateswith MHCmolecule

T cellrecognizescombination

Cytotoxic T cell (b) Helper T cell

T cellreceptor

Class II MHCmolecule

Antigenfragment

Antigen-presentingcell

Microbe

1

11

2

22

Key Steps in T cell Activation

APC must process and present peptides to T cells T cells must receive a costimulatory signal Accessory adhesion molecules help to stabilize

binding of T cell and APC Signal from cell surface is transmitted to nucleus Cytokines produced to help drive cell division

◦ IL-2 and others

REFERENCE http://lymphoma.about.com/od/glossary/g/tcells.htm

http://www.tcells.org/beginners/tcells/

http://en.wikipedia.org/wiki/T_cell

http://www.nobelprize.org/educational/medicine/immunity/immune-detail.html

https://www.britannica.com/nobelprize/article-215578

https://www.google.co.in/imghp