MICR 201 Microbiology for Health Related Sciences

1. Lecture 12: Disorders associated with the immune system Edith Porter, M.D. MICR 201 Microbiology for Health Related Sciences

2. Lecture outline • Hypersensitivity • Type I (anaphylactic) reactions • Type II (cytotoxic reactions • Type III (immunecomplex reactions) • Type IV (delayed cell-mediated) reactions • Autoimmune diseases • Tolerance • Cytotoxic autoimmune diseases • Immune complex autoimmune diseases • Cell mediated autoimmune disease • Transplant rejection • Immunodeficiencies • Congenital • Acquired

3. Hypersensitivities • Immune response against an innocuous (harmless) antigen • Antigen is now called allergen • 4 types • Type I: anaphylactic reactions (soluble allergen, IgE and mast cells)  “Allergy” • Type II: antibody mediated cytotoxicity (cellular allergen, IgG or IgM and complement) • Type III: immune complex reactions (soluble allergen, IgG, complement) • Type IV: T- cell mediated reactions (allergen, macrophages, T cells)

4. via complement activation Allergen is taken up by macrophages and activates TH cells Tuberculin reaction

5. Type I (anaphylactic) hypersensitivity • “Allergy” • Involve IgEantibodies and mast cell derived histamine • IgE is captured by mast cells in the absence of antigen • When allergen binds and cross-links surface IgE, mast cells degranulate • Release histamine containing granules • Vasopermeability increased • Mucous production increased • Constriction of airways • Localized • Hives, hay fever, or asthma from contact or inhaled antigens • Systemic • Shock from ingested or injected antigens

6. Mast cells and IgE are central for type I hypersensitivities

7. Representative allergens

8. Skin test to identify allergens • Drops of fluid containing various allergens are placed on top of the skin. • A light scratch is made with a needle to allow the substances to penetrate into the skin. • Reddening and swelling within minutes indicate hypersensitivity

9. Type II (cytotoxic) hypersensitivity • Involves allergen on cells or matrix associated, IgGantibodies, complement • Complement activation via classical pathway causes cell lysis or uptake by macrophages • Most familiar example is drug hypersensitivity

10. Type II hypersensitivity: Drug induced thrombocytopenic purpura Alternatively, complex is phagocytosed by macrophages

11. Type III (immune complex) hypersensitivity: Serum sickness • Initially observed when serum from immune animals was injected into patients • IgGantibodies and soluble allergen form complexes that lodge in basement membranes • Complement activation and inflammation • Kidney: glomerulonephritis, kidney dysfunction • Small blood vessels  arthritis

12. Type IV (cell mediated delayed) hypersensitivity • Delayed cell-mediated reactions • Do not involve antibodies • Caused mainly by T cells • Allergen is taken up by host cell and presented to T cells • Uptake by macrophages and presentation via MHC II: T helper cell response; example tuberculin test • Uptake by any nucleated cell and presentation via MHC I: CTL response; example contact dermatitis • Apparent only at least one day after allergen contact

13. Type IV hypersensitivity: T helper cell mediated- tuberculin test Cell infiltrate Used in TB diagnostic

14. Examples for positive tuberculin tests

15. Type IV hypersensitivity:CTL mediated-contact dermatitis • Example: Poison ivy contact dermatitis • Lipid soluble allergen is absorbed through skin and crosses cell membranes • Allergen modifies self peptides • Presentation of modified self peptide via MHC I to CTL • Destruction of modified cell

16. Hypersensitivities via complement activation Allergen is taken up by macrophages and activates TH cells Tuberculin reaction

17. Autoimmune diseases • Unwanted immune response to self antigens • Normally, self-reacting B-cells and T-cells are deleted during fetal development (self tolerance) • Autoimmunity is the consequence of loss of self-tolerance • Chronic disease that is continuously ongoing, since self antigen cannot be eliminated

18. Autoimmune diseases can be classified like hypersensitivities • Type II — Antibodies react with cell-surface antigens in specific organs • Type III (Immune Complex) — IgM and/or IgG react with soluble cell material, complexes are deposited, initiate complement activation, inflammation • Type IV — Mediated by cytotoxic T cells

19. Type II autoimmune disease: Graves’ disease • Stimulating auto-antibodies against growth receptors on thyroid gland • Cross reactive autoantigens in the eyes • Patients develop goiter, bulging staring eyes

20. Type II autoimmune disease: myasthenia gravis • Autoantibodies against acetylcholine receptor on muscle cells • Muscle weakness • Repetitive movements very difficult! • In particular eye bulb muscles affected • Life threatening when muscles for respiration are affected • Can be transferred to fetus

21. Auto-antibodies against nuclear components (DNA, histones, ribosomes, snRNP, etc) Immune complexes activate complement Complexes transported via Fc-rec. on phagocytes or via complement rec. on erythrocytes to spleen/liver for sequestration Excess complexes are deposited in small blood vessels Local inflammation in skin, joints and kidneys, multi-organ damage Type III autoimmune disease: systemic lupus erythematosus

22. Insulin Dependent Diabetes Mellitus Early, sudden onset (adolescence) Initially mediated by autoantibodies against beta cell antigen Later phases include cytotoxic T-cell response Type IV autoimmune disease: diabetes mellitus type I Immunohistochemistry Insulin = brown Glucagon = black

23. Transplant rejection • Unwanted normal response against foreign antigen • Mainly MHC I based • Every nucleated cell expresses MHC Type I molecules • MHC I molecules differ from person to person • MHC I molecules from a different person are recognized as foreign • Cytotoxic T cells attack the transplant • Cross reactive antibodies • NK cell dependent cytotoxicity • Complement attack with lysis • Macrophage attacks Lymphocyte Infiltrate

24. Transfusion rejection due to blood group antigen incompatibility

25. Hemolytic disease of the newborn due to rhesus factor incompatibility • Formerly erythroblastosisfetalis • Can be prevented by i.v anti-rhesus at the time of delivery

26. Graft-versus-host • Immune competent cells are transplanted • Bone marrow transplant • Immune cells from graft attack the host • Typical symptoms include diarrhea and kidney failure

27. Stem cell and induced pluripotent cell technoilogy might make transplantation unneccessary

28. Immune deficiencies • Opportunistic infections • Recurrent infections with otherwise harmless organisms

29. Immune deficiencies • Inherited • Chronic granulomatous disease • Neutrophil defect • Lack of oxidative burst • Complement deficiencies • Agammaglobulinemia • No antibodies • Severe Combined Immune Deficiency • No B-cells, no T-cells • Acquired • Immunosuppressive drugs • HIV infection Chronic granulomatous disease Burst + Burst – Neutrophils

30. Acquired immunodeficiency syndrome (AIDS) • 1981: In US, cluster of Pneumocystis and Kaposi's sarcoma in young homosexual men discovered • The men showed loss of immune function • 1983: Discovery of virus causing loss of immune function • HIV • By Montagnier (France) and Gallo (US)

31. The origin of AIDS (1) • Evidence indicates HIV-1 and HIV-2 arose from different evolutionary lines • HIV-2: mutation in a simian immunodeficiency virus (SIV) of mangabey monkeys in West Africa • HIV-1: SIV carried by chimpanzees in Central Africa • Chimpanzee virus appears to be a hybrid of two mangabeySIVs

32. The origin of AIDS (2) • Crossed the species barrier into humans in Africa in the 1930s • Humans eating infected monkeys • Humans being bitten by infected monkeys • Patient who died in 1959 in Congo is the oldest known case • Spread in Africa as a result of urbanization • Spread in world through modern transportation and unsafe sexual practices • Norwegian sailor who died in 1976 is the first known case in Western world

33. HIV structure • Enveloped with protein spikes • gp 120 • gp 41 • 2 copies of RNA • Reverse transcriptase • Integrase • Protease

34. HIV infection of T cells • Requires CD4 and a chemokine receptor • Individuals with certain mutations in one of the chemokine receptors are immune to HIV infection • Primarily, T cells are infected • Additional cell targets are monocytes and macrophages, epithelial cells • Major steps of infection • Attachment via gp 120 • Fusion via gp41 • Entry of virion without envelope • Uncoating • Reverse transcription • Incorporation of viral cDNA into host genome • Viral RNA and viral mRNA production • Capsid and enzyme production (reverse transcriptase, integrase, protease) • Assembly , packaging, and release

35. HIV infection of T cells

36. Latent and active infection of CD4+ Th cells

37. via CD4 and chemokine Receptor CCR HIV also infects macrophages

38. Latent and active infection of HIV • Viral RNA is reverse transcribed into DNA • Viral DNA is integrated into host genome • Latent infection as provirus • Latent virion • Viruses are not released but remain in a vacuole in the cell • Active production • Budding and release of infectious virions • Cell to cell fusion

39. Classification of HIV • HIV-1 • USA, Western Hemisphere • HIV-2 • Western Africa • Almost normal life span • Clades • No proof reading • High mutation rate of HIV • Many new subtypes • Clades differ from each other by ~ 30% or more

40. The stages of HIV infection • Category A • Asymptomatic or persistent lymphadenopathy • Category B • Persistent Candida albicans infections • Category C • Clinical AIDS • CMV, TB, Pneumocystis, toxoplasmosis, Kaposi's sarcoma

41. The progression of HIV infection

42. Protozoa Cryptosporidium Toxoplasma Viruses Herpes simplex Varizella zoster Bacteria Mycobacterium tuberculosis Mycobacterium avium intracellulare Fungi Pneumocystis Histoplasma Candida Cryptococcus Opportunistic infections associated with AIDS Intracellular organisms that require T-mediated defense!!!

43. Tumors associated with HIV infection • Deficient tumor control • T-helper cells activate NK cells • CTL can kill specific tumor cells • New Herpes viridae are involved • Lymphoma, Kaposi sarcoma

44. HIV diagnostics • Antibody detection • Seroconversion takes up to 3 months • HIV antibodies detected by ELISA, confirmed by western • Rapid (20 min) test available • Plasma viral load is determined by PCR or nucleic acid hybridization

45. HIV therapy • Types of drugs • Reverse transcriptase inhibitors • Prevent viral DNA synthesis • Protease Inhibitors • Fusion inhibitors which target gp41 • Integraseinhibitors prevent integration of HIV cDNA into host chromosome • Virus decoys (material to which virus binds instead of to cells) • Boosting immune system • Combination therapy • HAART (highly active anti-retroviral therapy) • Often requires up to 40 pills a day

46. Prevention of HIV infection • Use of condoms and sterile needles • Health-case workers use universal precautions • Wear gloves (double glove during invasive surgery), gowns, masks, goggles • Do not recap needles • Risk of infection from infected needle stick injury is 0.3% • Vaccine development • So far unsuccessful: > 30 vaccine candidates tested • Rapid mutation, differing clades • Infected cells not very susceptible to CTL attack • Latent infections

47. The pandemic AIDS ~20,000,000 have already died 14,000 new infections every day http://www.who.int/vaccine_research/diseases/hiv/en/

48. Prevalence of HIV infection

49. Important to remember • Hypersensitivities are immune responses to an innocuous antigen, which is called allergen. • Autoimmune diseases are immune responses to self antigens. • Transplant rejection: normal but harmful and unwanted immune reactions • Immune deficiencies can be acquired or inherited and result in recurrent infections due to opportunistic organisms.

50. Check your understanding 2) The chemical mediators of anaphylaxis are A) Found in mast cells. B) Antibodies. C) Antigens. D) Antigen-antibody complexes. E) The proteins of the complement system. 9) A healthy immune system destroys cancer cells with A) Tumor-specific antigens. B) CTLs. C) IgG antibodies. D) IgE antibodies. E) CD4+ T cells. 16) Which of the following statements about type I hypersensitivities is false? A) They are cell-mediated. B) They involve IgE antibodies. C) The symptoms are due to histamine. D) Antibodies are bound to host cells. E) The symptoms occur soon after exposure to an antigen. 33) During asymptomatic phase I of HIV disease, HIV infection is diagnosed by A) Measuring viral RNA. B) Measuring antibodies against HIV. C) Counting CD4+ T cells. D) Counting CD8+ T cells. E) Testing for seroconversion.