T cells recognize antigens presented on MHC proteins by antigen presenting cells such as macrophages, dendritic cells, and B cells. Activated T cells clone and differentiate into cytotoxic T cells that directly attack pathogens and infected cells, or helper T cells that coordinate both innate and adaptive immune responses. Cytotoxic T cells express CD8 and kill infected cells, while helper T cells express CD4 and stimulate B cell antibody production, macrophage activation, and proliferation of other immune cells through cytokine signaling. Suppressor T cells regulate the immune response to prevent excessive damage to self tissues.

1. Cellular Immunity T lymphocyte respond to antigen when they bond to specific antigen called MHC proteins (major histocompatibility complex proteins) on the surface of the antigen presenting cells T cells do not recognize free antigen but do recognize antigens combined with an MHC protein MHC: Cell surface molecule that present antigen to T Cell

4. Helper T cells

5. Memory T cellsDirect physical & chemical attack Antigens bacteria viruses

6. Cellular Immunity Lymphocyte can be divided into two major classes based on cell surface proteins called CD proteins One class of lymphocyte has CD4 and the other CD8 About one third of all T cells are CD8 and the other two third have CD4

7. Activated CD8 cells become cytotoxic T cells Activated CD4 become Helper T cells CD8 bind to the class I MHC proteins CD4 bind to class II MHC proteins

9. T Cells Only Recognize Antigen Associated with MHC Molecules on Cell Surfaces

10. Once a T cell is activated by the presentation of the combined MHC/Antigen, it will clone differentiate into: Activated CD8 cells become cytotoxic T cells – seek out the specific pathogen/infected cell that contains the targeted Antigen and destroys it by secreting various chemicals Activated CD4 becomes helper T cells – necessary for coordination of both specific & non-specific defenses, as well as for stimulating both cell-mediated & antibody-mediated immunity.

11. Helper T cell The most numerous of T cells Help regulate immune system by forming protein called lymphokines, that act on other cells of the immune system Some of lymphokines are: Interleukin-2 Interleukin-3 Interleukin-4 Interleukin-5 Interleukin-6

12. T-Helper Cell function Forming lymphokines Immune system is paralyzed in the absence of lymphokines Stimulation of growth and proliferation of cytotoxic T cells and suppressor T cells Interleukin-2 has strong effect in causing growth and proliferation of both cytotoxic and suppressor T cells

13. Stimulation of B cells growth and differentiation Have direct effect to cause B- cell growth, proliferation, formation of plasma cells and secretion of antibodies Activate macrophage system They slow / stop the migration of the macrophages after they have attracted to the inflamed tissue Stimulate effect on the helper cells Interleukin-2 have direct effect in stimulating activation of helper T cells themselves T-Helper Cell function

14. Humoral Response to T Dependent Antigens

15. Central Role of Helper T Cells

16. Antibody Mediated (Humoral) Immunity

17. Review of Immune Response

18. Overview of the Immune Response

19. Cytotoxic T Cells Also called Killer cells Capable of killing microorganism and even some of the body’s own cells Cytotoxic T cell secret whole forming proteins called perforins that punch holes in the membrane of attacked cell Cytotoxic T cell releases cytotoxic substance into the attacked cell causing lysis of infected cell

20. Cytotoxic T cell recognize and destroy cancer cells Recognize and destroy transplanted tissue Undergo apoptosis when stimulating antigen is gone Apoptosis Programmed cell death, eliminate cells that are unneeded, infected or cancerous Cytotoxic T Cells

21. Cytotoxic T Cells Lyse Infected Cells

22. Suppressor T cells They are capable of suppressing the function of both cytotoxic and helper T cell They serve functions of preventing the cytotoxic cells from causing excessive immune reactions that may damage the body own tissues, this called immune tolerance Immune Tolerance The condition of not mounting an immune response against the antigens that normally found within one’s own body. Lack of self tolerance underlies autoimmune diseases