BODY’S DEFENSE MECHANISMS.pptx

The human body has a special design, it protects itself against any invaders. In this presentation you will learn about the self defense mechanisms of the body.

1. BODY’S DEFENSE MECHANISMS MR MULUNDANO@kcn

2. INTRODUCTION The study of immunology, deals with host defence reactions to foreign (nonself) entities known as antigens, antigen recognition molecules, and cell-mediated host defence functions, especially as they relate to immunity to disease, hypersensitivity (including allergy), autoimmunity, immunodeficiency, and transplantation. This presentation presents the basic principles of immunology, particularly as they relate to response to infection.

3. After the body is infected with a foreign microorganism, it attempts to fight by switching on a number of defense mechanisms. There are a number of responses involved such as; inflammation, compliment system, interferon, phagocytosis.

4. Top : The innate immune system is characterized by physiologic barriers to entry of pathogenic organisms and very fast host defense responses. Bottom : The adaptive immune system consists of cells displaying antigen recognition molecules and has the capacity for long-term memory.

5. Specific objectives Definition of terms Explain types of defense mechanisms

6. Definitions Antibody (Ab): A protein produced as a result of interaction with an antigen. The protein has the ability to combine with the antigen that stimulated its production. Antigen (Ag): A substance that can react with an antibody. Not all antigens can induce antibody production; those that can are also called immunogens. Humoral immunity: Pertaining to immunity in a body fluid and used to denote immunity mediated by antibody and complement. Opsonisation - the process of coating microorganisms with some of the proteins found in plasma, to make them more easily phagocytosable .

7. Definitions Chemokines : Low-molecular-weight proteins that stimulate leukocyte movement. Chemotaxis : A process whereby phagocytic cells are attracted to the vicinity of invading pathogens. Complement : A set of plasma proteins that is the primary mediator of antigen-antibody reactions. Cytolysis : The lysis of bacteria or of cells such as tumor or red blood cells by insertion of the membrane attack complex derived from complement activation. Cytotoxic T cell: T cells that can kill other cells, e.g , cells infected with intracellular pathogens. Endotoxins: Bacterial toxins released from damaged cells.

8. Definitions Immune response: Development of resistance (immunity) to a foreign substance ( e.g , infectious agent). It can be antibody-mediated (humoral), cell-mediated (cellular), or both. T cell (also T lymphocyte): A thymus-derived cell that participates in a variety of cell-mediated immune reactions.

9. Types of defense mechanisms The Body defends itself against being invaded and if successfully invaded, it triggers other reactions that fight off the invader. Innate Immunity Adaptive Immunity

10. A. Innate Immunity Innate immunity is the defence system which you were born with. It protects you against all antigens. ( nonspecific) Innate immunity involves barriers that keep harmful materials from entering your body.

11. A. Innate Immunity cont’d. These barriers form the first line of defence in the immune response. Examples of innate non-humoral immunity include: Cough reflex, Enzymes in tears and skin oils Mucus which traps bacteria and small particles Skin, Stomach acid

12. A. Innate Immunity cont’d. Innate immunity also comes in a protein chemical form, called innate humoral immunity. Also know as Second line of defence Examples include the body's complement system and substances called interferon and interleukin-1 (which causes fever). If an antigen gets past these barriers, it is attacked and destroyed by other parts of the immune system.

13. A. Innate Immunity ( non-humoral) cont’d. a. The Skin Both the skin and the mucous membranes form the first line of defence and belong to nonspecific The intact skin provides a barrier through which most micro-organism cannot pass, it provides a good defence against invasion. Most microorganisms enter the body through a break in the skin (cut) .

14. A. Innate Immunity ( non-humoral) cont’d. The secretions of the skin by sweat and sebaceous glands which are acidity and have chemicals which have anti-bacterial properties tend to eliminate pathogenic bacteria.

15. A. Innate Immunity ( non-humoral) cont’d. b. Mucous Membranes/Surfaces Bacteria are removed mechanically from mucous membranes such as the nose, mouth and vagina as mucus secretions trap the organism. Bacteria in the respiratory tract are trapped in the sticky secretion on the surface (mucus) and then swept away by the action of cilia, minute hair-like bodies projecting from the cells lining the cavity.

16. A. Innate Immunity ( non-humoral) cont’d. 2.Secretions: Secretions act in 2 ways: i ) Mechanical action: e.g secretions of the bronchi entrap organisms and these are propelled away from the alveoli by the action of cilia in the bronchi and expelled tears by sneezing and coughing in the eye.

17. A. Innate Immunity ( non-humoral) cont’d. ii) Chemical action: Secretions may be acidic like sweat and gastric juice or strongly alkaline like bile.

18. A. Innate Immunity cont’d. INNATE HUMORAL IMMUNITY. 1.Transferrin and lactoferrin: are substances that tie up iron, thereby preventing pathogens access to this essential mineral. 2. Fever: this augments host defence by stimulating leukocytes to deploy and destroy invaders, reducing available free plasma iron, and inducing the production of interleukin IL-1, which causes a rise in temperature and proliferation, maturation, and activation of lymphocytes in the immunologic response.

19. CONTD’ Elevated body temperature also slow down the rate of growth of certain pathogens and can even kill some especially fastidious pathogens.

20. Innate Humoral Immunity cont’d. Elevated body temperature also slow down the rate of growth of certain pathogens and can even kill some especially fastidious(difficult to grow) pathogens. 3. Interferon’s: are small, antiviral proteins that prevent viral multiplication in virus-infected cells and serve to limit viral infections.

21. Interferons

22. Innate Humoral Immunity cont’d. 4. Inflammation (inflammatory reaction/process) Inflammation is the complex biological response of vascular tissues to harmful stimuli, such as pathogens, damaged cells, or irritants. The damaged cells release chemicals including histamine , bradykinin , and prostaglandins .

23. Inflammation cont’d. These chemicals cause blood vessels to leak fluid into the tissues, causing swelling. This helps isolate the foreign substance from further contact with body tissues.

24. Inflammation cont’d. The chemicals also attract white blood cells called phagocytes that "eat" germs and dead or damaged cells. This process is called phagocytosis. Phagocytes eventually die. Pus is formed from a collection of dead tissue, dead bacteria, and live and dead phagocytes

25. Inflammation cont’d. Classic Signs of inflammation: RUBOR- Reddish appearance CALOR- Hotness at the site TUMOR- Swelling at the site DOLOR- Pain at the site of injury

26. Inflammation cont’d. By surrounding the area of infection with plasma which often contains phagocytes, the infection may be prevented from spreading. Flow of fluid to and from the area of inflammation is largely by lymph vessels.

27. Inflammation cont’d. Bacteria escaping from the area will usually enter the lymph and will be arrested at the nearest lymph node. Secondary inflammatory reaction may take place (lymphadenitis) but in many cases the infection will not become generalised.

28. Inflammation cont’d. This inflammatory response of the tissues tends to restrict the spread of infection within the body and in many cases to overcome it at the cost of inner area damage. If for some reason the inflammatory response is deficient, the infection will tend to become systemic and much more serious

29. Innate Humoral Immunity cont’d. 5. Phagocytosis. The white blood cells, together with certain tissue cells move towards the bacteria and attempt to ingest them by a process known as phagocytosis, engulfment by phagocytes and ingestion by lysosomes.

30. Innate Humoral Immunity cont’d. 6. Complement system: Complement system, Involves approximately 30 different blood proteins that interact in a step-wise manner known as the complement cascade, to try and clear off any pathogen the body comes in contact with.

31. Consequence of activation of the complement system: Initiation and amplification of inflammation. Attraction and activation of leukocytes. Lysis of bacteria and other foreign cells. Increased phagocytosis by phagocytic cells. These defences operate against a variety of micro-organisms, because it is not specific.

32. B. Adaptive Immunity Aka: Acquired; specific

33. Types of immunity

34. B. Adaptive Immunity Adaptive immunity, which occurs after exposure to an antigen (e.g., an infectious agent) is specific and is mediated by either antibody or lymphoid cells . It can be; i ) Natural ( Active or Passive or ii) Artificial ( Active or Passive) . Third line of defence

35. B. Adaptive Immunity cont’d. Specific defence mechanism is a complement to the function of phagocytes and other elements of the innate immune system. In contrast to innate defence mechanism , specific defence mechanism allows for a targeted response against a specific pathogen.

36. B. Adaptive Immunity cont’d.

37. B. Adaptive Immunity cont’d. The human body has B and T cells specific to millions of different antigens. An antigen is a foreign material that triggers a response from T and B cells.

38. B. Adaptive Immunity cont’d. We usually think of antigens as part of microbes , but antigens can be present in other settings. For example , if a person received a blood transfusion that did not match his blood type, it could trigger reactions from T and B cells. T and B cells can mature and differentiate into plasma cells that produce a protein called an antibody.

39. Blood types

40. B. Adaptive Immunity cont’d. PASSIVE IMMUNITY Passive immunity is transmitted by antibodies or lymphocytes preformed in another host . The passive administration of antibody. (in antisera) against certain viruses (e.g., hepatitis B) can be useful during the incubation period to limit viral multiplication, e.g., after a needlestick injury to someone who has not been vaccinated.

41. Passive Immunity cont’d. The main advantage of passive immunization with preformed antibodies is the prompt availability of large amounts of antibody; Disadvantages are the; Short life span of these antibodies and Possible hypersensitivity reactions if antibodies (immunoglobulins) from another species are administered.

42. Passive Immunity cont’d. I. Naturally acquired passive immunity Here the antibody is obtained by the child from the mother either across the placenta or in breast milk. The human placenta allows maternal antibodies to pass into the foetal circulation.

43. Naturally acquired passive immunity The baby is born having maternal antibodies against the diseases to which the mother is immune. This provides the baby with defence immediately after birth. The antibodies do not persist. They disappear after a few months.

44. Passive Immunity cont’d. Artificially acquired passive immunity In here the antibody is obtained or protection is derived from the injection (serum) of prepared or readymade antibodies . e.g administering preformed antibodies of rabies vaccine following a rabies dog bite.

45. B. Adaptive Immunity cont’d. Active Immunity Active immunity is induced after contact with foreign antigens (e.g., microorganisms or their products). This contact may consist of clinical or subclinical infection, immunization with live or killed infectious agents or their antigens, exposure to microbial products (e.g., toxins, toxoids), or transplantation of foreign cells.

46. Active Immunity cont’d. In all these instances the host actively produces antibodies, and lymphoid cells acquire the ability to respond to the antigens. Advantages of active immunity include; Long-term resistance (based on memory of prior contact with antigen and The capacity to respond faster and to a greater extent on subsequent contact with the same antigen) Disadvantages include; The slow onset of resistance and the need for prolonged or repeated contact with the antigen.

47. Naturally acquired active immunity This is the type of immunity which is acquired in response to the entry of a live pathogen into the body (i.e., in response to an actual infection) It has long duration (has memory). Examples are typhoid fever, measles and small pox.

48. Artificially acquired Active immunity In here the antibody is obtained or protection is derived from introducing antigens such as vaccines which are live attenuated or dead into the body and then the body produces specific antibodies against them. Expanded Program of Immunization (EPI) is aimed at stimulating the bodies of children to produce specific antibodies against the common childhood killer diseases such as measles, poliomyelitis etc

49. Antibody isotypes of mammals Immunoglobulin A or ( IgA) Immunoglobulin D or IgD Immunoglobulin E or IgE Immunoglobulin G or IgG Immunoglobulin M or IgM

50. Immunoglobulin A or ( IgA) Found in mucosal areas, such as the gut, respiratory tract and urogenital tract, and prevents colonization by pathogens. Also found in saliva, tears, and breast milk. IgD : Functions mainly as an antigen receptor on B cells that have not been exposed to antigens . It has been shown to activate basophils and mast cells to produce antimicrobial factors. IgE : Binds to allergens and triggers histamine release from mast cells and basophils, and is involved in allergy. Also protects against parasitic worms. IgG: In its four forms, provides the majority of antibody-based immunity against invading pathogens. The only antibody capable of crossing the placenta to give passive immunity to the foetus. IgM: Expressed on the surface of B cells and has very high avidity (is a measure of the overall strength of binding of an antigen with many antigenic determinants). Eliminates pathogens in the early stages of B cell mediated (humoral) immunity before there is sufficient IgG.

51. CONTD’ This protein or antibody is specifically targeted to a particular antigen. However, B cells alone are not very good at making antibody and rely on T cells to provide a signal that they should begin the process of maturation.

52. CONTD’ When a properly informed B cell recognizes the antigen it is coded to respond to, it divides and produces many plasma cells. The plasma cells then secrete large numbers of antibodies, which fight specific antigens circulating in the blood.

53. CONTD’ T cells are activated when a particular phagocyte known as an antigen-presenting cell (APC) (the APC-is a trigger for the various elements of the specific immune response) displays the antigen to which the T cell is specific.

54. Other cells A subtype of T cell known as a T helper cell performs a number of roles. T helper cells release chemicals to Help activate B cells to divide into plasma cells Call in phagocytes to destroy microbes Activate killer T cells

55. CONTD’ Once activated, killer T cells recognize infected body cells and destroy them. Regulatory T cells (also called suppressor T cells) help to control the immune response. They recognize when a threat has been contained and then send out signals to stop the attack.

56. Organs and Tissues of defence mechanisms The cells that make up the specific immune response circulate in the blood, but they are also found in a variety of organs. These immune tissues and organs allow for maturation of immune cells, trap pathogens and provide a place where immune cells can interact with one another and mount a specific response.

57. CONTD’ Organs and tissues involved in the immune system include the thymus , bone marrow , lymph nodes, spleen , appendix, tonsils, and Peyer’s patches (in the small intestine).

58. The End