SPECIFIC IMMUNE SYSTEM T LYMPHOCYTES Immune system diseases

SPECIFIC IMMUNE SYSTEM T - LYMPHOCYTES

Immune system diseases Disease survival mechanisms Non specific immunity Physical & chemical barriers Infectious Disease Inflammatory Non-specific Cellular response Specific immunity Transmissi on Epidemiolog y Vaccination Public Health Immunological surveillance T cells B cells Clonal Selection theory Big picture

LEARNING OUTCOMES • IDENTIFY THE VARIETY OF T LYMPHOCYTES. • EXAMINE THE ACTION/FUNCTION FOR EACH T CELL POPULATION

THIRD LINE OF DEFENCE • SPECIFIC (ONLY ACTS ON PARTICULAR PATHOGEN) • INVOLVES LYMPHOCYTES Line of Specific (s) or defenc non-specific e (ns) 3 rd S Mechanism employed Function Antibodies production from B Make antibodies (humoral cells from bone marrow response)and are found in the lymphoid organs (except the thymus) Response by T cells from Cellular immunity but also with thymus gland the regulation of the humoral response

LYMPHOCYTES • LYMPHOCYTES ARE A TYPE OF WHITE BLOOD CELL. THERE A NUMBER OF DIFFERENT TYPES OF LYMPHOCYTE; • TWO OF THE MOST IMPORTANT ARE B LYMPHOCYTES AND T LYMPHOCYTES. • T LYMPHOCYTES ARE ALSO CALLED T CELLS. THEY ARE FORMED IN THE THYMUS GLAND – HENCE THEIR NAME. • T LYMPHOCYTES PLAY AN IMPORTANT ROLE IN THE IMMUNE SYSTEM AND THEY ACCOUNT FOR MORE THAN 4/5 FOUR-FIFTHS OF CIRCULATING LYMPHOCYTES. • THERE ARE TWO MAIN GROUPS OF T LYMPHOCYTES:

HELPER T CELLS (TH CELLS) • HELPER T CELLS (TH CELLS) ; SECRETE CYTOKINES THAT ACTIVATE PHAGOCYTES, T CELLS AND B CELLS. Helper T cells are not able to destroy infected cells. Instead they produce cytokines – a chemical signal that activate B lymphocytes and phagocytes, which can then act to destroy the infected cell.

CYTOTOXIC T CELLS (TC CELLS) • CYTOTOXIC T CELLS (TC CELLS) ; DESTROY INFECTED CELLS BY SEVERAL METHODS INCLUDING THE INDUCTION OF APOPTOSIS • THE CYTOTOXIC T CELLS ARE ALSO CALLED KILLER T CELLS. THEY RECOGNISE ANTIGENS ON INFECTED CELLS, BIND TO THE ANTIGEN AND CAN DESTROY THE CELLS BY APOPTOSIS. • APOPTOSIS IS A FORM OF PROGRAMMED CELL DEATH – THE CELL IS INSTRUCTED TO

Killer T-cells: Can attach themselves to cells with foreign antigens on their surface and destroy them 1. Virus attaches to and enters host cell 2. Viral DNA causes host cell to express viral anitgens on its surface 3. Killer T-cell attaches to viral antigen on infected cell 4. Killer T-cell induces death of infected cell

Killer T-cells and cancer: 1. As cell becomes cancerous mutations take place 2. Mutations cause cancerous cell to express abnormal antigens 3. Killer T-cell binds to abnormal antigens 4. Killer T-cell induces death of cancerous cell (Usually)

MEMORY CELLS • ONCE CYTOTOXIC T CELLS HAVE COMPLETED THEIR JOB, THE MAJORITY OF CELLS UNDERGO APOPTOSIS. • HOWEVER, A FEW CELLS BECOME ‘MEMORY CELLS’, WHICH WILL REMAIN ON HAND TO RESPOND SHOULD THE ANTIGEN REAPPEAR AT SOME POINT IN THE

* T HELPER CELLS Signal 2 - T cell help B YYY Signal 1 antigen & antigen receptor Th Th 1. T cell antigen receptor 2. Co-receptor (CD 4) 3. CD 40 Ligand

Summary slide SPECIFIC DEFENCES T LYMPHOCYTES • ONE GROUP OF T LYMPHOCYTES DESTROY INFECTED CELLS BY INDUCING APOPTOSIS. • ANOTHER GROUP OF T LYMPHOCYTES SECRETE CYTOKINES THAT ACTIVATE B LYMPHOCYTES AND PHAGOCYTES. • WHEN PATHOGENS INFECT TISSUE, SOME PHAGOCYTES CAPTURE THE PATHOGEN AND DISPLAY FRAGMENTS OF ITS ANTIGENS ON THEIR SURFACE. • THESE ANTIGEN PRESENTING CELLS ACTIVATE THE PRODUCTION OF A CLONE OF T LYMPHOCYTES

SUMMARY SLIDE SPECIFIC DEFENCES T LYMPHOCYTES • T LYMPHOCYTES HAVE SPECIFIC SURFACE PROTEINS THAT ALLOW THEM TO DISTINGUISH BETWEEN THE SURFACE MOLECULES OF THE BODY’S OWN CELLS AND CELLS WITH FOREIGN MOLECULES ON THEIR SURFACE.

SUMMARY SLIDE SPECIFIC DEFENCES IMMUNOLOGICAL MEMORY CELLS • SOME T AND B LYMPHOCYTES PRODUCED IN RESPONSE TO ANTIGENS BY CLONAL SELECTION SURVIVE LONG TERM AS MEMORY CELLS. • A SECONDARY EXPOSURE TO THE SAME ANTIGEN RAPIDLY GIVES RISE TO A NEW CLONE OF LYMPHOCYTES PRODUCING A RAPID AND GREATER IMMUNOLOGICAL RESPONSE. •

THIRD LINE OF DEFENCE • SPECIFIC (ONLY ACTS ON PARTICULAR PATHOGEN) • FIRST IMMUNOLOGICAL SURVEILLANCE OCCURS TO FIND/ DISCOVER PATHOGEN • THEN CLONAL SELECTION NEEDS TO OCCUR TO FIND THE CORRESPONDING LYMPHOCYTE TO COMBAT THE PATHOGEN Line of Specific (s) or Mechanism employed Function defenc e non-specific (ns) 3 rd S Antibodies production from B Make antibodies (humoral cells from bone marrow response)and are found in the lymphoid organs (except the thymus) Response by T cells from Cellular immunity but also with thymus gland the regulation of the humoral response

CYTOTOXIC T CELLS (TC CELLS) • CYTOTOXIC T CELLS (TC CELLS) ; DESTROY INFECTED CELLS BY SEVERAL METHODS INCLUDING THE INDUCTION OF APOPTOSIS • THE CYTOTOXIC T CELLS ARE ALSO CALLED KILLER T CELLS. THEY RECOGNISE ANTIGENS ON INFECTED CELLS, BIND TO THE ANTIGEN AND CAN DESTROY THE CELLS BY APOPTOSIS. • APOPTOSIS IS A FORM OF PROGRAMMED CELL DEATH – THE CELL IS INSTRUCTED TO DESTROY ITSELF. • ONCE CYTOTOXIC T CELLS HAVE COMPLETED THEIR JOB, THE MAJORITY OF CELLS UNDERGO APOPTOSIS. • HOWEVER, A FEW CELLS BECOME ‘MEMORY CELLS’, WHICH WILL REMAIN ON HAND TO RESPOND SHOULD THE ANTIGEN REAPPEAR AT SOME POINT IN THE FUTURE. •