T-cell

t-cell maturation MHC MOLECULES

1. PRESENTED BY: REHNUMA K. GHORI

2. IMMUNOLOGY T-CELL: TCR,DIFFERENTIATION AND IMPORTANCE

3. 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.

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

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 (T H cells) Cytotoxic T cells (T C cells, or CTLs) Regulatory T cells (T reg cells), formerly known as suppressor T cells Memory T cell

12. Helper T Cells Helper T cells release molecules (cytokines) into the bloodstream to warn the immune system of the presence of a dangerous cell or virus. “CD4 positive”

13. Cytotoxic T Cells Cytotoxic T cells attach themselves to other cells in the body; if a cytotoxic T cell learns that a cell is diseased or pathogenic it will do one of two things: Force the cell to commit suicide (apoptosis). or Secrete enzymes that will kill the cell. “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. Class I MHC Class II MHC RBCs APCs Nucleated cells

21. 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.

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

23. 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

24. 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