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Immunity - concepts - antigen, antibody, ag-ab reactions, vaccines

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This is a series of lectures on microbiology useful for undergraduate medical and paramedical students

This is a series of lectures on microbiology useful for undergraduate medical and paramedical students

Published in: Health & Medicine, Technology

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  • 1. IMMUNITY Concepts (Immunity, antigens, antibodies, antigen antibody reactions, vaccines) Dr. Ashish V. Jawarkar M.D.
  • 2. INFECTION
  • 3. Relationship between host and infectious agent  Saprophytes – live on dead tissue – do not cause diseases  Parasites – multiply in hosts  Pathogens – cause diseases  Commensals – donot cause diseases normally – only during immunosuppression
  • 4. Infection  Lodging of parasite in tissues of host  This is not necessarily disease
  • 5. Disease  Any deviation from good health
  • 6. Infectious disease  Any deviation from good health due to infectious agent
  • 7. Infection  Primary infection – in healthy host  Re-infection – repeat infection by the same agent  Secondary infection – second infection by a new agent
  • 8. Infection  Acute – rapid progress  typhoid  Chronic – slow onset and progress  tuberculosis
  • 9. Infection  Localised – restricted to specific area  Systemic
  • 10. Infection  Clinical – with symptoms  Subclinical – no obvious symptoms
  • 11. Infection  Oppurtunistic – when host resistance is lowered  Nosocomial – acquired from hospital, not present on admission  Laboratory acquired – from laboratory
  • 12. Sources of infection  Humans – carriers  Animals – zoonoses  Insects  Soil and water  Food
  • 13. Methods of transmission  Contact – direct, indirect, sexual  Inhalation  Ingestion  Inoculation  Insects  Congenital – vertical  Iatrogenic
  • 14. Pathogenicity  Capacity of micro organisms to cause diseases
  • 15. Virulence  Degree of pathogenicity
  • 16. Factors predisposing to pathogenicity  Adhesion – attachment due to receptors and ligands
  • 17. Factors predisposing to pathogenicity  Invasiveness  Highly invasive – septicemia following wound infection by streptococci  Less invasive – staphylococcal abscess
  • 18. Factors predisposing to pathogenicity  Toxins  Exo toxins – released outside  Endotoxins – LPS (part of cell wall)
  • 19. Factors predisposing to pathogenicity  Communicability  Ability to spread from one host to other  Ensures survival
  • 20. Types of infectious diseases  Endemic – constantly present in a particular area  Eg typhoid  Epidemic – one that spreads rapidly involving many persons at the same time  influenza  Pandemic – spreads through many areas of the world at the same time
  • 21. IMMUNITY
  • 22. Immunity  Resistance exhibited by host towards micro organisms
  • 23. Types of immunity  Innate  Immunity that a person possesses due to genetic make up  Acquired  Active • Acquired after an exposure to infection (natural) / artificially induced (vaccine)  Passive • Injection of antibodies
  • 24. Innate immunity Epithelial surfaces  Skin  Mucosa  Saliva  Urine  Antibacterial systems in blood and tissues  Complement system  Interferons  Microbial antagonism  Flora  Cells  macrophages  Neutrophils  NK cells  Inflammation  Fever  Acute phase proteins  CRP
  • 25. Acquired (Active)  Due to stimulation by an antigen (like microorganism)  Long lasting  Associated with memory
  • 26. Active immunity  Natural active  Clinical or subclinical infection  Eg chicken pox  Artificial active  vaccines
  • 27. Passive immunity  Natural passive  Placenta  Breast milk  Artificial passive  Rh iso immunisation
  • 28. HERD IMMUNITY  Overall level of immunity in a community  Useful in case of epidemics
  • 29. OVERVIEW OF STRUCTURE AND FUNCTION OF IMMUNE SYSTEM
  • 30. Lymphocytes  B lymphocytes – produce antibodies – Humoral immunity  T lymphocytes – cell mediated immunity
  • 31. T cell maturation (central lymphoid organs)
  • 32. Central lymphoid organs  Bone marrow  Thymus
  • 33. B cell maturation (Peripheral lymphoid organs)
  • 34. Peripheral lymphoid organs  Lymph nodes  Spleen  Mucosa associated lymphoid tissue (MALT)  Tonsils  Peyer’s patches
  • 35. Other cells of the immune system  ANTIGEN PRESENTING CELLS (APCs)
  • 36. Phagocytes (macrophages)
  • 37. Dendritic cells eg Langerhan’s cell
  • 38. MAJOR HISTOCOMPATIBILITY COMPLEX (MHC)  Differentiates between self and foreign
  • 39. ANTIGENS AND ANTIBODIES
  • 40. ANTIGEN  Any substance which, when introduced into the body stimulates production of antibody
  • 41. ANTIBODY  Substance that is produced by the body against the antigen is an antibody  It is a protein  Almost 25% of our body proteins are Immunoglobulins
  • 42. Types of antigens  Xenoantigens – from different species  Alloantigens – from same species  Autoantigen – lens protein, testis  Heterophile antigen – closely related antigens from different species
  • 43. Antigens – on the basis of ability to cause disease  Immunogen – develop undesired response – transplants  Tolerogens – induce immunological tolerance due to memory  Allergens – over reactions  Vaccines – protective response
  • 44. Biological classes of antigens  T cell dependent  T cell independent
  • 45. Antibodies - types  Ig G  Ig A  Ig M  Ig D  Ig E
  • 46. Structure
  • 47. IgG  Can be transported across placenta, provides immunity to new born  Neutralize viruses  Encourage phagocytosis
  • 48. IgA  Main immunoglobulin in mother’s milk, saliva and tears  Called secretory Ig  Local immunity
  • 49. IgM  Earliest Ig to be synthesized by fetus  Not transported across placenta  Presence useful in diagnosis of congenital infections such as syphilis, rubella, HIV and toxoplasmosis  Responsible for protection from blood invasion by microorganisms
  • 50. IgD  Occur on the surface of B lymphocytes (with IgM) and act as receptors for antigens
  • 51. IgE  On mast cells and basophils  Responsible for anaphylaxis (hypersensitivity)
  • 52. In short  IgG - protects body fluids  IgA – protects body surfaces  IgM – protects the blood stream  IgD – receptor on surface of B lymphocytes  IgE – mediates anaphylaxis
  • 53. Antigen – Antibody reactions  Antigen and antibody can react and cause  Precipitation  Agglutination  Lysis  Killing of live antigens (micro organisms)
  • 54. Precipitation
  • 55. Agglutination
  • 56. Lysis
  • 57. Killing of microorganisms
  • 58. General features of antigen – antibody reaction  Reaction is specific  Combination occurs at surface – so surface antigens are relevant  Combination is firm but reversible  Antigen and antibody can combine in variable proportions
  • 59. Combinations occur at surface
  • 60. Combination is reversible  Affinity – intensity of attraction
  • 61.  Avidity – strength of bond
  • 62.  Combine in variable proportions
  • 63. Applications  Precipitation reactions  Agglutination reactions  Complement fixation tests  Neutralization tests  Labelled immunoassays  Immunofluorescence  Radio immunoassay  Enzyme linked immunosorbent assay (ELISA)
  • 64. Precipitation reactions  Precipitation – when a soluble antigen combines with its antibody – antigen antibody complex forms an insoluble ppt in the medium
  • 65. Prozone
  • 66.  Ring test – to group streptococci
  • 67.  Slide test – VDRL for syphilis  Tube test – Widal test
  • 68. Agglutination reactions  For blood grouping
  • 69. Labelled immunoassays
  • 70. Radio immuno assay
  • 71. ELISA  HIV
  • 72. HYPERSENSITIVITY REACTIONS (ALLERGY) .
  • 73. Definition • Hypersensitivity – exaggerated immune response • Allergen – substance which causes hypersensitivity
  • 74. • Hypersensitivity reaction occurs after second exposure to antigen • First exposure causes sensitisation
  • 75. Types • Based on time between second exposure and clinical reaction – – Immediate hypersensitivity – Delayed hypersensitivity
  • 76. Types • Type I – anaphylactic • Type II – cytotoxic • Type III – immune complex • Type IV – delayed type
  • 77. Type I hypersensitivity (Allergy) • a/k/a anaphylaxis (ana – without, phylaxis – protection)
  • 78. degranulation • Releases histamine, serotonin, cytokines and prostaglandins • These cause – Smooth muscle contraction (larynx, lungs) – Leaky blood vessels (rhinorrhoea, oral secretions) – Intestinal fluid secretion (diarrhoea and vomitting)
  • 79. • Systemic anaphylaxis is fatal within minutes • Unless given adrenaline immediately
  • 80. allergens • Nuts • Seafood • Eggs • Insect venom • Drugs
  • 81. Atopy • Anaphylaxis in a localised area • Eg asthma, hay fever • Allergens here include – Dust – Pollen – Eggs – milk
  • 82. TYPE II HS • Mediated by IgG or IgM (with complement) antibodies • Examples are autoimmune hemolytic anemias and hemolytic disease of newborn
  • 83. Type III HS • Complexes of antigen and antibody get deposited in various sites of the body like – Kidneys – Joints – Skin – Eye
  • 84. • Examples – Vasculitis – Arthus reaction – Serum sickness
  • 85. Type IV HS • Take 2-3 days to occur • Delayed HS • Mediated by T cells – antibodies not involved • Examples – Tuberculin reaction – Contact dermatitis
  • 86. Tuberculin reaction (Montaux test) • To know whether the person is infected by TB • Injection of PPD into skin • Look for raised area (induration) after 48 hours
  • 87. Contact dermatitis • Skin reaction caused by application of various chemicals such as nickel, chromium, drugs such as penicillin and toiletries.
  • 88. Contact dermatitis
  • 89. Granulomatous reactions • Occur due to intracellular pathogens such as Mycobacteria, fungi and Leishmania • Phagocytes are unable to remove and digest them and become giant cells with multiple nuclei
  • 90. Summary
  • 91. VACCINES AND IMMUNISATION
  • 92. Immunising agents • Vaccines (active – slower, long lasting) • Immunoglobulins (passive – faster, short lasting)
  • 93. Vaccine • Substance designed to induce production of antibodies against a specific disease causing organism
  • 94. Types • Live – live but attenuated organisms – Eg BCG, oral typhoid vaccine, oral polio vaccine • Killed – typhoid, cholera, injectable polio vaccine • Toxoids - DPT
  • 95. Immunoglobulins (Passive) • Administering directly antibodies • Newborns receive passive immunisation from colostrum • Eg – Hep B antibodies given after accidental exposure • Protect immunodeficient individuals
  • 96. Vaccines available
  • 97. Herd immunity
  • 98. Contact immunity • Children immunised with live OPV shed virus in feces • An unimmunised family member / community member who is exposed to this shed virus develops immunity as well
  • 99. National immunisation schedule (Indian academiy of Paediatrics)
  • 100. Optional immunisation • Chicken pox • Influenzae • HPV • Yellow fever • Japanese encephalitis • Pneumococcal vaccine