T cell, t cell receptor, t cell differentition, and its importance

1. T-CELL
TCR,DIFFERENTIATION
AND IMPORTANCE
R.KrishnaMoorthy
Bharathidasan University

2. 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

4. 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

5. 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

6. 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.

7. 8

8. Thymocytes at different developmental stages are
found in distinct parts of the thymus
Matration

9. Positive
Selection
Ensures MHC
Restriction
death by
neglect !
(double positive
cells)
class
I
class
II

10. Negative
Selection
Ensures
Self-tolerance

11. 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

12. “CD4 positive”

13. “CD8 Positive”

14. 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 histocompatibility
complex (MHC) molecules.

15. 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)

16. Structure of the T cell Receptor
Each T cell bears
TCRs of only one
specificity (allelic
exclusion)

17. Structure of the T cell Receptor
Both α and β
chains have a
variable (V) and
constant (C) region
V regions of the α
and β chains contain
hyper variable
regions that
determine the
specificity for
antigen

18. Major Histocompatibility
Complex (MHC)

19. 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

20. RBCs
Class II
MHC
APCs
Nucleated cells
Class I MHC

22. 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.

23. Infected cell
Antigen
fragment
Class I MHC
molecule
T cell
receptor
(a) Cytotoxic T cell (b) Helper T cell
T cell
receptor
Class II MHC
molecule
Antigen
fragment
Antigen-
presenting
cell
Microbe
1 Antigen
associates
with MHC
molecule
1
1
2 T cell
recognizes
combination
2
2

24. 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

26. 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/me
dicine/immunity/immu ne-detail.html
 https://www.britannica.com/nobelprize/article-215578
 https://www.google.co.in/imghp