Innate Immunity and Vaccines

1. (Non-specific) innate immunity: - provides first line of defence during the critical period just after the host's exposure to a pathogen - it is immunity you are born with 2. What are the four defensive barriers the innate immune system is comprised of ?: - Anatomic - Physiologic - Phagocytic - Inflammatory 3. Anatomic barriers - Skin: Normal skin flora: - metabolize substances secreted onto the skin - produce end products e.g., fatty acids = they discourage the colonization of skin by potential pathogens Perspiration: - contain lysozymes and other antimicrobial substances 4. Anatomic barriers - Sebaceous glands: - associated with hair follicles - produce an oily secretion = Sebum Sebum : consists of lactic acid and fatty acids maintains the skin pH 3-5 pH inhibits the growth of most microorganisms - some bacteria metabolize sebum and live as commensals on skin + can cause severe forms of acne 5. What is Sebum ?: An oily substance secreted by sebaceous glands to moisturize skin. - it consists of lactic acid & fatty acids - maintains the skin pH of 3-5 6. Anatomic barriers - Defence mechanisms of Mucous membrane: - Saliva, tears, and mucous secretions = act to wash away potential invaders + contain antibacterial or antiviral substances - Mucus (viscous fluid secreted by epithelial cells of mucous membranes) = entrap foreign microorganisms - Lower respiratory tract = mucous membrane is covered in cilia = synchronous movements of cilia propels mucous entrapped microorganisms from these tracts. 7. What tracts are lined with mucous membranes ?: - conjunctivae - alimentary - respiratory -urogenital traits 1/8 8. Physiologic barriers types:: Temperature Low pH Soluble factors e.g., Lysozyme, interferons. 9. Physiologic barriers - Chickens: - have innate immunity to anthrax because their high body temperature inhibits the growth of bacteria 10. Physiologic barriers - Gastric acidity: - innate physiological barrier to infection because very few ingested microorganisms can survive low pH condition in stomach. 11. Physiologic barriers - Lysozyme (soluble factors): a hydrolytic enzyme found in mucous secretions and in tears - it is able to cleave the peptidoglycan layer of the bacterial cell wall 12. Physiologic barriers - Interferons and innate Antiviral defences: - Viruses induce production of Interferons - Interferons alpha & beta induced by d/s RNA bind to interferons receptor = activation of RNA-ase RNA -ase can degrade viral mRNA - Interferons also induce Protein kinase R (PKR) PKR inhibit elF-2, an elongation factor involved in viral protein synthesis - Binding of of Interferon alpha & beta to NK cells enhances activity - Interferons increase MHC Class 1 and 11 activity 13. Phagocytic barriers: Mast cells, Monocytes, Neutrophils, Eosinophils, Macrophages - These kills + digest whole microorganisms in the phagolysosome. 14. Phagocytic barriers: Mast cell: - First to recognise a pathogen - found mostly in tissues that in locations that are close in contact with the environment - Activation of mast cell = release of soluble factors/ active agents (e.g. histamine, pre-formed TNF-±) - has immune effector & modulatory cells that help link innate and adaptive immunity in fight against pathogens. 15. Phagocytic barriers: Macrophage: - Phagocytic cells - Responds to endogenous stimuli due to e.g., injury or infection , signals produced by antigen-specific immune cells - Bacterial mechanism activated - antigen presentation 16. Phagocytic barriers: Neutrophil: - Phagocytosis takes place - Bacterial mechanisms are activated: degradative enzymes and other antimicrobial substances stored in their cytoplasmic granules 2/8 17. Phagocytic barriers: Eosinophil: - antibody-coated parasites are killed - may affect the progression of immune and inflammatory responses - has the ability to release immunomodulatory factors e.g., cytokines, chemokines, growth factors 18. Phagocytic barriers: Basophil: - Effector cells of the Type-2 immune response - Plays a role in allergic disease and immunity to pathogens - Activated = production of regulatory cytokines e.g., IL-4 - Plays an important role in recruiting other effector cells to the site of inflammation 19. Inflammation: A protection response intended to eliminate the initial cause of cell injury and the necrotic cells and tissues arising from the injury. - intimately associated with the repair process which includes cell regeneration and scarring 20. Inflammatory Barrier: Acute inflammation: - occurs in minutes to days - characterized by fluid and protein - main cell is the PMNs (neutrophil) 21. Inflammatory Barrier: Chronic inflammation: - occurs over weeks to years - characterized by Lymphocytes and macrophages 22. Inflammatory Barrier: Features of acute inflammation: - Vasodilation - Endothelial permeability - Extravasation of pmn's (neutrophil) 23. Inflammatory Barrier: Acute inflammation signs: Heat - Calor = caused by Vasodilation Redness- Rubor = caused by Vasodilation Swelling - Tumor = Caused by increased vascular permeability Pain - Dolor = caused by mediator release Loss of function - Functio laesa = caused by mediator release 24. Influx of phagocytes: - influx from capillaries into the tissues is facilitated by the increased permeability of the capillaries 25. Influx of phagocytes - Margination: Adherence of the cells to the endothelial wall of the blood vessels 26. Influx of phagocytes - Diapedesis or Extravasation: emigration of phagocytes between the capillary- endothelial cells into the tissue 27. Influx of phagocytes - Chemotaxis: migration of phagocytes through the tissue to the site of invasion 28. Influx of phagocytes - Pus: Accumulation of dead cells, digested material, and fluid. 29. Inflammatory Mediators - Cell derived mediators: - Arachidonic acid derivatives - Cytokines - Vasoactive amines 3/8 30. Cell derived mediators - Arachidonic acid derivatives: - induce prostaglandins & leukotrienes this causes increased capillary permeability, vasodilation and smooth muscle constriction. 31. Cell derived mediators - Cytokines: e.g., IL 1, IL 6, IL 12, IL 17, IL 18, IL 8, Tumour Necrosis Factors, interferons - some act as endogenous pyrogens e.g., IL-1, IL-6, Tumour Necrosis Factors alpha they upregulate the synthesis of secondary mediators and pro-inflammatory cytokines by both macrophages and mesenchymal cells - they stimulate production of acute phase proteins - IL-6 or - attract inflammatory cells e.g., neutrophils IL-8 32. Cell derived mediators - Vasoactive Amines: Histamine: - released by a variety of cells in response to tissue injury - a principal mediator of the inflammatory response binds to receptors on nearby capillaries & venules = causing vasodilation and increased permeability 33. Inflammatory Mediators: Plasma derived factors types: - Acute Phase Proteins - Kinin system - Clotting & fibrinolytic system - Complement 34. Plasma derived factors: Acute Phase protein: - CRP (a key acute phase protein) - produced in liver - useful inflammatory marker - CRP levels are raised in infection/inflammation - CRP activates complement 35. Plasma derived factors: Kinin system: - small peptides - normally present in blood in an inactive form - tissue injury activates the peptides - then cause vasodilation and increased permeability of capillaries - particular kinin called bradykinin = also stimulates pain receptors in the skin This effect probably serves a protective role, because pain normally causes an individual to protect the injured area. 36. Plasma derived factors: Clotting & Fibrinolytic System: - Vasodilation and the increase in capillary permeability in injured tissues = enable enzymes of the 4/8 blood-clotting system to enter the tissues - these enzymes activate an enzyme cascade that results in the deposition of insoluble strands of fibrin (main component of a blood clot) - fibrin strands wall off the injured area from the rest of the body + prevent the spread of infection 37. Plasma derived factors: Complement (Role in immunity): - Membrane Attack Complex (MAC C5-9) - MAC attack + punch a hole in the membrane - Deficiency of terminal complement components (C5-8) predisposes to Neisseria infection 38. Plasma derived factors: Complement (Role in inflammation): - C3a & C5a - increasing vascular permeability and vasodilation are similar to histamine - Activates lipoxygenase pathway of arachidonic acid metabolism (C5a) - C5a causes = leukocyte activation, adhesion and chemotaxis 39. Plasma derived factors: Complement (Role in Phagocytosis): C3b: - acts as opsonin - promotes phagocytosis by cells bearing receptors for Cb3 40. What are the consequences of inflammation ?: - tissue repair - regeneration of new tissue begins - Capillaries grow into fibrin of a blood clot - New connective tissue cells 'fibroblasts' replace the fibrin as the clot dissolves - fibroblasts and capillaries accumulate = scar tissue forms 41. What are the outcomes of Acute Inflammation ?: - Resolution - Fibrosis = scarring - Abscess Formation = walled of collection of pus - Progression to chronic inflammation 42. What are the main types of Vaccines ?: - Live attenuated (LAV) - Inactivated (killed antigen) - Subunit (purified antigen) - Toxoid (inactivated toxins) They are capable of stimulating enough memory T and B lymphocytes 43. Vaccines: Live Attenuated Vaccines: - Tuberculosis (BCG) - Oral polio vaccine (OPV) - Measles - Rotavirus - Yellow fever 44. Vaccines: Inactivated (killed antigens): - Whole-cell pertussis (wP) - Inactivated polio virus (IPV) 5/8 45. Vaccines: Subunit (purified antigen): - Acellular Pertussis (aP) - Haemophilius influenzae type B (Hib) - Pneumococcal (PCV-7, PCV-10, PCV-13) - Hepatitis B (HepB) 46. Vaccines: Toxoid (inactivated toxins): - Tetanus toxoid (TT) - Diphteria toxoid 47. Whole organism vaccines: - can be attenuated - there is loss of pathogenicity but the vaccine can grow within the host - virulent pathogen is grown under abnormal culture conditions/ different host tissues to select for avirulent organisms: e.g., BCG strain of TB is grown in increasing bile concentrations; MMR vaccine - provide prolonged exposure to epitopes + shows increased immunogenicity & memory cell production = usually no boosters needed 48. Whole organism vaccines: Attenuated Sabin vaccine: - colonizes gut and induces slgA production - vaccine boosters required: due to 3 polio strains used interfere with each other's replication in the gut 49. What are the issues with whole organisms attenuated vaccines?: - Reversion to the wild type - Contamination with other viruses 50. Inactivated vaccines:: - safer method - pathogen is inactivated by heat/ chemicals - requires repeated boosters - induces a mainly humoral response 51. What are the issues associated with inactivated vaccines ?: - use of heat/chemical can cause problems for maintaining of epitope structure - can also be problems of inadequate formaldehyde killing when inactivated vaccines are prepared. 52. Purified macromolecules: E.g., polysaccharide of meningococci/ pneumococci & acellular pertussis vaccine - Polysaccharide vaccines activate B cells - Mainly IgM is produced with little to no memory cells 53. Purified macromolecules: Conjugation to a protein carrier: - vaccine can be conjugated to a protein carrier e.g., Haemophilius type B vaccine where the capsular polysaccharide is covalently linked to tetanus toxoid - enables activation of Th cells and class switching 54. Purified macromolecules: Prevention of Whooping cough: - an acellular vaccine is made from highly purified macromolecules of Bordetella pertussis is used 6/8 These components are treated with: - formaldehyde or glutaraldehyde - then absorbed onto adjuvants aluminium phosphate or aluminium hydroxide, to improve immunogenicity 55. Recombinant antigen vaccine: - involve cloning the DNA coding for the relevant antigen in a suitable expression vector E.g., Hepatitis B vaccine where the gene for the major surface antigen of hepatitis B is cloned in yeast cells - antigen vaccine induces protective antibodies 56. Recombinant vector vaccines: Genes coding for major antigens of especially virulent pathogens are inserted into the genome of attenuated bacteria and viruses 57. Recombinant vector vaccines: Vaccinia vaccine: - Vaccinia virus is used as a vector - made by inserting genes from hepatitis B, herpes simplex, influenza into vaccinia induced antibody responses - gene coding for envelope protein = cell mediated & antibody response can be generated 58. Recombinant vector vaccines: What is Vaccinia ?: - a large complex virus - 200 genes = can carry several dozen foreign genes without impairing its capacity to infect and replicate 59. Recombinant vector vaccines: Issues with using Vaccinia ?: - could cause disease in immunodeficient patients Another problem example: - use of attenuated strain of S.typhimurium with genes from V.cholerae = vaccine will infect mucosal lining of gut and induce a slgA response. 60. What diseases have been reduced due to immunisation ?: - Diphtheria - Measles + Mumps - Pertussis (Whooping cough) - Rubella - Polio myelitis - Tetanus - Smallpox 61. Passive immunisation:: Involves transfer of antibodies and immune cells to recipients (Antibodies received have been produced by another individual) - recipient's immune system does not engage with the vaccine to produce an immune response = no memory cells produced 62. Passive immunisation: Natural: - trans placental transfer of maternal antibody. (Rubella, diphtheria, mumps) antibodies are transferred to foetus via the placenta or to the baby via breast milk 7/8 63. Passive immunisation: Artificial: - Transfer of preformed antibody in tetanus, hepatitis, rabies 64. Problems associated with Passive immunity ?: - Response to isotypes of foreign antibody e.g., Systemic anaphylaxis due to IgE produced against foreign antibody - IgM / IgG producing Complement activating immune complexes - childhood immunizations requiring multiple boosters due to persistence of maternal antibodies that can block epitopes e.g., DPT vaccine 65. Active immunisation: Generation of a primary immune response which involves the proliferation of T/B cells resulting in memory cell formation which can give rise to a protective heightened secondary immune response upon exposure to the pathogen 66. Active immunisation: Natural: - generation of memory cells following a childhood infection e.g., chicken pox 67. Active immunisation: Artificial: - Most vaccines in current use - a killed or attenuated microorganism or a component of a microorganism is used as a vaccine to generate memory cells following a primary immune response 68. Vaccine Design: - Primary aim is the induction of a memory response Short incubation period of pathogen: - the vaccine should be designed to maintain high levels of neutralizing antibody by repeated immunizations 69. Vaccine design: Why is activation of appropriate branch of the immune system important ?: - some pathogens are destroyed by the humoral immune responses , others require cell mediated mechanisms 70. Vaccine design: Generation of antibody responses: - Antigenic epitopes should be accessible to B cells 71. Vaccine design: Generation of T helper responses: - antigens should be processed by APC's for the T helper cell activation - vaccine must be able to replicate in host cell to activate T cytotoxic cells. 8/8