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Introduction To The Immune System

Introduction To The Immune System. Year 10 Biomedical Science. PATHOGENS. A pathogen is anything that can cause a disease “germs” Pathogens can be grouped into: Bacteria Viruses Protozoans Fungi & Mould Worms Arthropods These living things do not necessarily cause disease.

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Introduction To The Immune System

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  1. Introduction To The Immune System Year 10 Biomedical Science

  2. PATHOGENS • A pathogen is anything that can cause a disease • “germs” • Pathogens can be grouped into: • Bacteria • Viruses • Protozoans • Fungi & Mould • Worms • Arthropods • These living things do not necessarily cause disease

  3. FIGHTING INFECTION BY A PATHOGEN • INFECTION: The pathogen has entered the host • Infection does not always result in disease • The immune system is able to fight off the pathogen before any symptoms appear • INCUBATION: the time between infection and the onset of symptoms • The immune system contains different features that fight disease including: • White blood cells • Proteins • Antibodies • Fever • Lymphatic system

  4. TYPES OF WHITE BLOOD CELLS • LEUCOCYTES – white blood cells • PHAGOCYTES – surround the pathogen and engulf it. The pathogen is broken down within the phagocyte. • Neutrophils • Basophils • Macrophage • B CELLS – produce antibodies and fight specific pathogens; B cells are produced and mature in the bone marrow • Plasma B Cells • Memory B Cells • T CELLS – do not produce antibodies; assist the B cells; T cells are produced in the bone marrow but mature in the thymus gland • T Helper Cells • Cytotoxic T Cells • Suppressor T Cells

  5. Three Lines Of Defence • The body uses many mechanisms to prevent pathogens from disabling it, including: • Barriers: prevent entry of pathogens into body. • Non-specific immune responses: try to destroy every pathogen encountered. • Specificimmune responses: only attack specific pathogens.

  6. 1st Line of Defence Barriers

  7. First Line of Defence • Barriers on skin surface • Intact Skin • Mucous membranes • Chemical barriers • Digestive enzymes • Lysozomes in saliva • Tears • Stomach acids • Physical barriers • Cilia • Blood clotting • Hair • Ear wax • Eyelashes

  8. Keeping Pathogens Out!

  9. Common Diseases & Method of Transmission

  10. 2nd Line of Defence Non-Specific Immune Response

  11. Non-Specific Immune Response • The second line of defence • The body must recognise ‘self’ from ‘non-self’ in order to respond to any invading organism • The presence of foreign ANTIGENS indicates that the cells are ‘non-self’ and must be destroyed • Pathogens can be destroyed by white blood cells, proteins or other bodily processes eg: fever

  12. Self vs Non-Self • Antigens • A molecule found on the surface of the cells of the invading pathogen • A foreign substance (‘non-self’) that activates an immune response. • A molecule whose shape triggers the production of specific antibodies • Binds to the antibodies • MHC markers • Genetically determined proteins on the surface of cells that are unique for each individual (‘self’)

  13. Phagocytes • Cells that engulf & digest foreign particles by ‘phagocytosis’ • Examples include: • Neutrophils – short life span; can squeeze between cells • Macrophages – longer life span; act on a large range of infectious agents • Basophils – secrete histamines causing inflammation

  14. Inflammation • Inflammation makes the area unfavourable for infection to occur • Blood flow to the area is increased by the dilation of the capillaries (vasodilation) • Histamines allow for easier movement of white blood cells through the blood vessels • Neutrophils, macrophages and blood proteins are more able to squeeze out of the blood vessels and into the infected tissue • This causes swelling and some pain • Pain causes reduced voluntary movement in that area, hence speeding up the repair process

  15. Fever & Interleukins • Fever is another symptom associated with infection • This rise in temperature is caused when macrophages secrete a chemical called interleukin. • Interleukin sends a message to the brain causing the body temperature to rise to around 39°C. • The higher temperature is unfavourable for the functioning of many pathogens and easier for the immune system to work on these pathogens • Interleukins also cause drowsiness, allowing more energy to be used for destroying pathogens and repairing damaged tissues.

  16. INTERFERON Protein that is secreted by virally infected cells Induces resistance to viral infection in the surrounding cells Acts as a warning signal from the affected cell to other cells Non-specific in their effects

  17. 3rd Line of Defence Specific Immune Response ~Humoral Response ~Cell Mediated Response

  18. Humoral Immune Response • B lymphocytes (B cells) are the cells involved in humoral immunity • B cells produce antibodies that combine with specific antigens • B cells originate as stem cells and differentiate within the bone marrow • This process starts when we are embryos • Each type of B cell only produces one type of antibody • None of the antibodies react against the body’s own antigens

  19. Antibodies and Antigens • Antigens are on the surface of pathogens. Cause the production of antibodies. • Antibodies are produced by plasma cells and recognise specific antigens. • Antibodies and antigens fit together with a special lock and key system of identification. • The lymphocyte then disposes of the pathogen through the lymph glands

  20. Structure of Antibodies

  21. B lymphocytes (B cells) • Produced in the bone marrow. • Produce large quantities of antibodies when stimulated by specific antigens. • B cells divide when stimulated • Produce plasma B cellsand memory B cells. • Plasma cells secrete large amounts of antibody to destroy pathogen. • Memory cells remain in the body to quickly identify pathogen upon reinfection.

  22. Cell-Mediated Immune Response • Involves T lymphocytes • Able to distinguish self from non-self • React with antigens • T cells do not bind directly with antigens, but with the antigens presented on the MHC markers

  23. T lymphocytes (T cells) • Produced in the bone marrow but mature in the thymus gland. • There are different kinds of T cells: • T-helper cells (TH), • Cytotoxic T cells (TC) • T-suppressor cells.

  24. T Helper Cells (TH Cells) • Help by producing and secreting chemicals to make activated B or T cells divide and increase their numbers. • Can also stimulate macrophages to engulf pathogens more easily. • HIV is deadly because it disables TH cells.

  25. Cytotoxic T Cells (TC cells) • Directly kill infected or foreign cells. • Able to destroy tumour cells • Release powerful cytotoxins • These are the major cells involved in fighting off viruses by killing infected cells (cells that are hosts to the virus) • Can cause problems in organ transplant patients - cause transplant tissue rejection. To combat this, patients take high levels of immunosuppressant drugs.

  26. T Suppressor Cells • Regulate the action of lymphocytes. • Can suppress phagocytes. • Help prevent immune system overreacting to pathogen.

  27. OVERVIEW OF THE IMMUNE RESPONSE

  28. Helping The Immune System • Preventing infection - antiseptic, disinfectants, safe sex, insect repellent, dry skin. • Assisting immunity - chemotherapy, antibiotics (for bacteria only), surgery. • Enhancing immunity - vaccinations use dead or weakened (attenuated) pathogens. Passive immunity is when antibodies are passed from mother to foetus via placenta.

  29. Active Immunity • Immunity due to the production of antibodies by the organism itself after the body’s defence mechanisms have been stimulated by the invading pathogen • Takes time to develop • Permanent • NATURAL ACTIVE IMMUNITY • Made the antibody as a result of infection • ARTIFICIAL ACTIVE IMMUNITY • Made the antibody as a result of vaccination

  30. Passive Immunity • Immunity due to the acquisition of antibodies from another organism in which active immunity has been stimulated • Passive immunity gives immediate protection • NATURAL PASSIVE IMMUNITY • Obtained antibody via the placenta before birth • ARTIFICIAL PASSIVE IMMUNITY • Obtained antibody from another organism

  31. Misdirected Immunity • This refers to when the immune system reacts against its own tissues as it does not recognise self from non-self • Autoimmune diseases • Rheumatoid arthritis – • Chronic inflammation of joints • T cells & B cells respond to the collagen in the joints • Myasthenia gravis – • Progressive loss of muscle control • Antibodies bind to receptors on skeletal muscle cells • Multiple sclerosis – • Impaired nerve transmission • Antibodies develop against the myelin sheath of the nerve axons

  32. Overreaction Of The Immune System • Exaggerated immune responses to the antigens of normally harmless substances that may be found on pollen, food, cosmetics, drugs or animals • Symptoms include inflammation & excessive mucus production • Anaphylactic shock: • life-threatening response to an allergy • the constriction of the airways • loss of fluid from capillaries into body tissues • Sudden drop in blood pressure which may lead to a heart attack

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