Infectious Diseases

1. Infectious Diseases Topic 6.3 and 11.1

2. 6.3.1 Define Pathogen • Pathogen- any living organism that is capable of causing a disease. • Pathogens typically include bacteria, virus, fungi, protozoa and worms.

3. 6.3.2 – Explain how antibiotics work against bacteria • Antibiotics – chemicals that take advantage of the biochemical differences between prokaryotic and eukaryotic cells. • Common antibiotics work by blocking cell wall synthesis so new cells can’t be produced. NO EFFECT ON VIRUS! WHY???

4. 6.3.3 – Outline the role of skin and mucous membranes in defense SKIN • Skin is an obvious barrier to diseases. • Made of two layers • Dermis, bottom layer that contains sweat glands, capillaries, sensory receptors and dermal cells for structure and strength • The outer layer, the epidermis, is primarily dead skin cells, creates barrier against pathogens.

5. Role of Mucous membranes Mucous Membranes • Mucous Membranes are types of tissues that line routes of entry to the body • Produces and secretes lining of sticky mucus to trap pathogens • Lined with Cilia, also trap pathogens • Secretes Lysozyme, enzyme that chemically damages pathogens

6. 6.3.3 Continued.. • Trachea – tube carries air to lungs • Nasal Passages – tube that allows air to enter nose • Urethra – Tube that carries urine from bladder to the outside • Vagina – Reproductive tract leading from uterus to the outside.

7. Trachea

8. 6.3.4 – Outline how phagocytic leucocytes ingest pathogens in the blood and in body tissues. • Leucocytes (White Blood Cells) – cells in blood stream used to fight infection. • Macrophage – fight pathogens via phagocytosis. • Protein molecules on the bacterial membrane (antigens) identify the pathogen as either “self” or “non-self” • Pathogenic remains are digested in lysosome • This is considered a non specific immune response.

10. Antigens & Antibodies • Antigens are proteins embedded in cell membrane of a foreign invader • Antibodies are Y-shaped protein molecules produced in response to specific pathogens • Antibodies bind to Antigens and attach to pathogen

11. Antibodies are produced in response to a specific pathogen • Leucocytes that produce antibodies are B lymphocytes (b cells) • Antigen is first identified • Specific B lymphocyte is identified that can produce an antibody which will bind to antigen • B lymphocytes clone themselves and begin producing antibodies • Massive amounts of antibody production • New antibodies circulate in bloodstream and attach to antigen • Some of the new lymphocytes remain in blood stream to prevent secondary infection – known as memory cells.

13. How HIV Damages the immune system • Human immunodefeciency virus (HIV) is the virus that eventually leads to AIDS (acquired immune deficiency syndrome. • Viruses need a type of cell that is complementary to own proteins • Depending on the cell it infects, different viruses can have different symptoms/severities • HIV infects Helper T cells

14. T-Helper Cells • HIV infects T-Helper cells of the immune system. • Helper T cells help identify which antibodies need to be produced. Frequently, the virus will go undetected for years (virus has a latency period). • HIV is a retrovirus - A retrovirus is an RNA virus that is replicated in a host cell via the enzyme reverse transcriptase to produce DNA from its RNA genome. The DNA is then incorporated into the host's genome by an integrase enzyme.

15. HIV Damages Immune System • When helper T-cells begin to die  no communication between cells  no antibodies produced • Individual no longer fights off pathogens and symptoms of AIDS appear • Secondary infections ultimately take the life of someone with AIDS

16. Once detected, HIV mutates incredibly fast so it is very difficult to treat with medications.

17. Why is HIV/AIDS Difficult to treat • Virus can be hidden in body cells for years because of latency period • Virus mutates relatively quickly, vaccines may not recognize/affect it after several mutations • Association w/ Sexual Activity & Drug abuse led to reluctance in funding

18. Exercises • When a person is bitten by a poisonous snake, they are given an antivenom. The antivenom is composed of antibodies which recognize protein molecules on venom and bind to them. This type of treatment is referred to as passive immunity and does not confer long term immunity. Why is that? • Why are some viruses potentially lethal, while others cause fairly mild symptoms? • Describe how skin and mucus membranes act as barriers to pathogens?

19. Antivenom • Antibodies produced by another organism. The memory cells that are capable of producing these antibodies are located in the organism that produced them, not in the organism who receives the antivenom. Long term immunity comes from memory cells. This is called passive response

20. Severity of Symptoms • Severity of symptoms depends on two factors: • Tissue type that is the target of a particular virus, some tissue types are potentially more dangerous when infected • How quickly virus replicates could result in less time the immune system has to respond

21. Skin/Mucous Membrane Barriers • Skin is a physical barrier to entry, dry skin inhibits growth of bacterial cells; bacteria on skin prevents growth of other bacterial cells; sweat contains anitmicrobial/lysozyme to keep bacterial growth in check • Mucous Membrane traps bacteria in sticky mucus; cilia sweep/trap bacteria; secretes lysozyme to destroy bacteria; contain macrophages to perform phagocytosis

22. Defense Against Infectious Diseases

23. 11.1.1 Describe the process of blood clotting • When your skin is punctured, typically you puncture the capillary bed that is delivering blood to that area. With that, you release blood (remember—capillary walls are only 1 cell thick) • The plasma portion of your blood contains many different proteins that are involved in the clotting. The clotting of blood stops blood loss and prevents pathogens from entering body.

25. Blood Clotting – platelets stick together to damaged/torn area and seal the “leak” • If wound is more serious  clotting process takes over • Platelets release thromboplastin(clotting factors) • Thromboplastin converts prothrombin (plasma protein) into thrombin • Thrombin converts fibrinogen into fibrin • Fibrin forms a network of strands that trap RBCs and platelets to form clot • Once the healing is complete, plasmin (enzyme) dissolves the fibrin clot

27. Blood Clotting

28. Antibody Production • Macrophage recognizes pathogen as non-specific “not-self ” organism • Engulfs pathogen by phagocytosis and partially digest it • Remaining pieces are displayed in manner called “antigen presentation” • Helper T cells recognize the antigen and turn immune response from non-specific to specific • T cells chemically communicate to specific B lymphocytes to produce antibodies

29. Cell Cloning • When Helper T Cells signal for production of B lymphocytes, Cell cloning begins • Clone Two types of cells • Antibody-secreting cells – cells secret antibodies immediately to fight primary infection • Memory Cells – cells have long life in bloodstream waiting for secondary infection

30. Principles of Immune System • Challenge and response: Immune system is challenged by antigen, response by macrophage, helper t cells, b lymphocytes. • Clonal Selection: Identification of B lymphocytes that secrete specific antibody and multiple cell divisions • Memory Cells: Cells provide long term immunity

32. Vaccinations • Bodies cannot be immune to a pathogen they have not been exposed to. • Vaccines act as first exposure • Pathogen is weakened by exposure to heat or chemical treatment • Leucocytes respond to “not-self” pathogen and primary immune response occurs • Memory Cells form capable of producing antibodies if there is a real infection

33. Vaccinations • Do not prevent infection but speed up secondary response of immune system

34. Benefits and Dangers of Vaccinations • Pg. 289 in Text book

35. Active vs. Passive Immunity • Active Immunity: • Always leads to the production of memory cells. • Process listed on previous slide is example of active immunity. • Passive immunity: • Obtaining immunity through some other means. • Passing of Ab’s from mother to fetus. • Colostrums – breast milk • Injection – antisera (anti-venom)

36. Polyclonal vs. Monoclonal Ab’s • Polyclonal • Pathogens made up of several membrane proteins • Several antibodies produced and several memory cells formed • Monoclonal • Produce single type of antibody (see next slide) • Used for pregnancy tests (Human Chorionic Gonadotrophin, HCG) • Treatments: Cancer cells produce specific antigens, modified monoclonal antibodies can target cancer-cell antigen directly

37. Monoclonal Antibody Production • Inject mouse with antigen, undergoes primary immune response • Spleen is harvested • B leucocytes fused with myeloma cellsform hybridoma cells • Hybridoma cells carry specific antibodies and can be cultured for extended periods of times

38. Uses of Ab’s in research • Western Blot

39. ELISA – Enzyme linked immunosorbant assay

40. Medical uses of Ab’s