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

Learning outcomes Identify the variety of t lymphocytes. Examine the action/function for each t cell population

Specific (s) or non-specific (ns) Third line of defence Specific (only acts on particular pathogen) Involves lymphocytes Line of defence Specific (s) or non-specific (ns) Mechanism employed Function 3rd S Antibodies production from B cells from bone marrow Make antibodies (humoral response)and are found in the lymphoid organs (except the thymus) 3rd S Response by T cells from thymus gland Cellular immunity but also with the regulation of the humoral response

lymphocytes Lymphocytes are a type of white blood cell. There are 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: cytotoxic T cells helper T cells.

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 destroy itself. http://www.tcells.org/scientific/killer/ http://www.nobelprize.org/educational/medicine/immunity/immune-detail.html

Killer T-cells: Can attach themselves to cells with foreign antigens on their surface and destroy them 2. Viral DNA causes host cell to express viral anitgens on its surface 1. Virus attaches to and enters host cell 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: 2. Mutations cause cancerous cell to express abnormal antigens 1. As cell becomes cancerous mutations take place 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 future.

Signal 1 antigen & antigen receptor * T Helper Cells Signal 2 - T cell help Th Th B Y 1. T cell antigen receptor 2. Co-receptor (CD4) Signal 1 antigen & antigen receptor 3.CD40 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 that move to the site of infection under the direction of cytokines.

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.

Specific (s) or non-specific (ns) 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 defence Specific (s) or non-specific (ns) Mechanism employed Function 3rd S Antibodies production from B cells from bone marrow Make antibodies (humoral response)and are found in the lymphoid organs (except the thymus) 3rd S Response by T cells from thymus gland Cellular immunity but also with 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.