10 - Innate Immunity

1. Innate Immunity

2. Immunity Ability to ward off a disease/ disease causing organism/ foreign material (pollen etc ) Susceptibility: lack of resistance to a disease INNATE IMMUNITY At birth First and Second line of defense Non-specific No Memory ADAPTIVE IMMUNITY Third line of defense Specific Memory response (to previous disease/ vaccination)

3. First line of defense Intact skin Mucous membranes and their secretions Normal microbiota Second line of defense Third line of defense Specialized lymphocytes: T cells and B cells Antibodies Phagocytes, such as neutrophils, eosinophils, dendritic cells, and macrophages Inflammation Fever Antimicrobial substances Figure 16.1 An overview of the body’s defenses.

4. Physical Barriers: First Line of Defense Skin Epidermis Outer layer – thin Layers of tightly packed epithelial cells Outermost layers dead Keratin (Protein) Sloughs off routinely Dermis Inner layer – thick Connective tissue Bacteria enter through Skin ONLY when skin is damaged

5. Top layers of epidermis with keratin Epidermis Dermis Figure 16.2 A section through human skin.

6. Mucous Membranes Line respiratory, gastrointestinal, urogenital Epithelial cells with inner connective tissue Goblet cells Secrete mucus (glycoproteins) Prevents dessication , traps microbes, enzymes to kill microbes Mucus-coated nose hairs: Trap microbes Ciliary escalator Ciliated cells of Lower Respiratory Tract Mucus-coated dust/microbes pushed outward Sneezing/ Coughing speed up process Epiglottis Covering over larynx: prevents food and microbes getting in

7. Other Physical/Chemical Barriers Tears Lacrymal Glands: Under upper eyelid Constantly wash over eye; drain into lacrymal ducts Lysozyme (breaks peptidoglycan walls of bacterial cell walls) Urine Flushing mechanism prevents colonization Contains uric acid, urea (makes pH ~6.5), lysozyme Saliva Salivary Glands Constantly washes over teeth and mouth Contains Lysozyme Peristalsis Movement of food by coordinated contractions Defecation Vomiting in response to microbial toxins

8. Lacrimal glands Upper eyelid Lacrimal canal Nasolacrimal duct Nose Figure 16.3 The lacrimal apparatus.

9. Chemical Factors Sebum: oils – protective layer on skin Low pH: unsatd . Fatty acids – inhibit path. Bacteria Sweat Regulates body temperature Flushes microbes, waste Lysozyme Gastric Juice: HCl , mucus and enzymes Low pH 1.5-3 Kills most microbes and toxins (except those of S. aureus and Botulinum ) Some bacteria enter protected by food H. pylori neutralizes acid and makes a niche for itself in stomach Vaginal Secretions: low pH

10. Normal Flora Competition/ Exclusion Compete for nutrition Alter environment to prevent pathogen growth Commensal Where one benefits (normal flora), the other is unaffected (host) Opportunistic pathogens E. coli, S. aureus , S. epidermidis

11. Second Line of Defense Formed Elements in the Blood Lymphatic System Phagocytes Inflammation Fever Antimicrobial Substances

12. Formed Element of Blood Platelets (for clotting) Erythrocytes (Red Blood Cells) Leukocytes (White Blood Cells) Granulocytes (visible granules) Neutrophils Basophils Eosinophils Agranulocytes (granules not visible) Monocytes Dendritic Cells Lymphocytes

13. Insert Table 16.1 If possible, break into multiple slides Table 16.1 Formed Elements in Blood (Part 1 of 2)

14. Insert Table 16.1 If possible, break into multiple slides Table 16.1 Formed Elements in Blood (Part 2 of 2)

15. Percentage of each type of white cell in a sample of 100 white blood cells Neutrophils 60–70% Basophils 0.5–1% Eosinophils 2–4% Monocytes 3–8% Lymphocytes 20–25% Differential White Cell Count

16. The Lymphatic System lymph : fluid Lymph vessels Lymph tissue (contain a large number of lymphocytes T cells and B cells) Red bone marrow Lymph nodes: sites of activation for T cells and B cells Tonsils/ Peyer’s patch Spleen: monitor blood for microbes and secreted products (toxins) Thymus: T cell maturation

17. Right lymphatic duct Right subclavian vein Left subclavian vein Thoracic (left lymphatic) duct Tonsil Thymus Lymphatic vessel Large intestine Red bone marrow Heart Thoracic duct Spleen Small intestine Peyer’s patch Lymph node (a) Components of lymphatic system Figure 16.5a The lymphatic system.

18. Phagocytosis Greek: Phagos (eat), cyte (cell) Ingestion of a substance/ microbe by a cell Phagocytes Cells that perform phagocytosis Leukocytes and/or derivatives SEM of a neutrophil phagocytosing Aspergillus spores

19. Pseudopods Bacterium Macrophage Figure 16.6 A macrophage engulfing rod-shaped bacteria.

20. Phagocytes Neutrophils: early during infection First phagocytes at site of infection Monocytes Morph into Macrophages when infection progresses Fixed v/s Wandering Macrophages Non-motile; Specifically present in tissues/ organs Lymph nodes, bone marrow, spleen, liver Roaming through tissue, gather at site of inflammation

21. Phagocytosis: Mechanism Chemotaxis : attracted to site of infection Cytokines (released from other WBCs) Cell damage Microbial products Adherence: attachment to microbial surface Toll-like receptors (TLRs) Pathogen associated Molecular Patterns (PAMPs) Opsonins : proteins that coat microbe Ingestion: pseudopodia engulf microbe into phagosome Digestion: fusion of phagosome with lysosome Enzymes digest microbe Residual body excreted

22. Mechanism of Phagocytosis

23. PAMPs and TLRs TLRs in the plasma membrane of phagocytes attach to components commonly found on pathogens (PAMPs) LPS of gram (-) outer membrane Peptidoglycan of gram (+) cell wall DNA and RNA of viruses Fungal and parasite components Shown: Pattern Recognition Receptor of a TLR attaching to a pathogen’s PAMP

24. Inhibit adherence: M protein, capsules Streptococcus pyogenes, S. pneumoniae Kill phagocytes: Leukocidins Staphylococcus aureus Lyse phagocytes: Membrane attack complex Listeria monocytogenes Escape phagosome Shigella , Rickettsia Prevent phagosome–lysosome fusion HIV, Mycobacterium tuberculosis Survive in phagolysosome Coxiella burnettii Microbial Evasion of Phagocytosis

25. Inflammation Damage to tissue: heat, infection, chemical Four signs of inflammation: Heat ( calor ), swelling (tumor), redness ( rubor ), pain (dolor) Loss of function in some cases Acute: intense Infecting agent removed in short time S. aureus (boil) Chronic: less intense, more destructive Infecting agent cannot be removed TB lesion in lungs

26. Inflammation Purpose of inflammation: Destroy infectious agent Remove it and its byproducts from the body If #1 is impossible, confine the infectious agent and byproducts; keep from spreading Repair or replace damaged tissue Steps in the inflammatory response: Vasodilation & increased blood vessel permeability Phagocyte migration & phagocytosis Tissue repair

27. Inflammation Stage 1: Vasodilation & increased vessel permeability Histamine released from injured cell granules (basophils, mast cells) Kinins In plasma; attract phagocytic granulocytes to injured site Prostaglandins From damaged cells intensify the effects of histamine and kinins Leukotrienes Damaged basophils , mast cells increase vessel permeability; attach phagocytes to pathogens Cytokines activated fixed macrophages increase vasodilation and permeability Clotting factors enter infection site; clot prevents spread PUS: dead cells and body fluids; ABCESS: cavity after tissue breakdown

28. Histamine Vasodilation, increased permeability of blood vessels Kinins Vasodilation, increased permeability of blood vessels Prostaglandins Intensify histamine and kinin effect Leukotrienes Increased permeability of blood vessels, phagocytic attachment Chemicals Released by Damaged Cells

29. Inflammation Stage 2: Phagocyte migration and phagocytosis Phagocytes appear on the scene within ~1 hour Margination = cytokines alter blood vessel lining, cause phagocytes to stick to vessel walls at inflammation site Traverse vessel walls to get into affected area (= diapedesis ), phagocytize invading microbes Granulocytes are first on scene; die off rapidly Macrophages enter at a later stage larger and more phagocytic Phagocytize destroyed tissue, granulocytes, remnants of invaders

30. Inflammation Margination Diapedesis Macrophage Neutrophil

31. Inflammation Stage 3: Tissue repair Dead or damaged cells are replaced in affected tissues Repair capacity depends on tissue type Stroma = supportive connecting tissue Ex) capsule around the liver that encloses and protects it; not involved in liver functions Parechyma = functioning portion of tissue Ex) Hepatocyte cells of liver that perform the liver’s functions If parenchymal cells are active in repair = perfect reonstruction ; if stroma cells are more active = scar

32. Bacteria entering on knife Epidermis Dermis Subcutaneous tissue (a) Tissue damage Bacteria Blood vessel Nerve Figure 16.8a-b The process of inflammation. Chemicals such as histamine, kinins, prostaglandins, leukotrienes, and cytokines (represented as blue dots) are released by damaged cells. (b) Vasodilation and increased permeability of blood vessels Blood clot forms. Abscess starts to form (orange area). 1 2 3

33. Insert Fig 16.8d Scab Blood clot Regenerated epidermis (parenchyma) Regenerated dermis (stroma) (d) Tissue repair Figure 16.8d The process of inflammation.

34. Fever Fever = abnormally high body temperature a systemic response Hypothalamus = brain region that controls body temp Raises temp in response to cytokines by: - blood vessel constriction - increased metabolism - shivering M aintained until cytokines (and infection) are eliminated Heat loss by vasodilation and sweating  Drop in body temperature

35. Fever benefits: Intensifies the effect of antiviral interferons Increases production of transferrins - decreases iron available to microbes Increased speed of tissue repair - speeds up all of the body’s reactions Fever complications: Increased metabolism effects: Tachycardia = rapid heart rate Acidosis = increased acidity of blood/tissue Seizures, delirium, coma Death (temp above 112-114 o F) Fever

36. Antimicrobial Substances Complement system = defensive system of >30 proteins produced in the liver that circulate the blood & tissues “Complements” the action of immune cells Destroy microbes by: Cytolysis Inflammation Phagocytosis Act in a cascade with one reaction triggering another Activated by one of 3 possible pathways

37. The Complement Cascade C3 splits into C3a and C3b C3b coats the microbe to promote phagocyte attachment ( opsonization ) C3b initiates formation of membrane attack complex (MAC) on invading cell MAC causes cytolysis = bursting of invading cell due to inflow of extracellular fluid C3a and C5a bind mast cells stimulate release of histamine  increase blood vessel permeability C5a also attracts phagocytes

38. Complement-induced cytolysis before cytolysis after cytolysis

39. Antibodies bind antigens  antigen-antibody complexes activate C1 Active C1 splits (activates) C2 and C4 into C2a, C2b, C4a, C4b C2a and C4b combine and split C3 into fragments C3a and C3b  Active fragments initiate the complement cascade Complement activation: classical pathway

40. Steps: C3 combines with factor B, D and P (complement proteins) on the surface of a microbe C3 splits into C3a and C3b  complement cascade No antibodies involved Direct contact between complement proteins and pathogen Complement activation: alternative pathway

41. Lectins = proteins produced by the liver that bind carbohydrates Mannose binding lectin (MBL) = binds mannose ( in bacterial cell walls and some viruses) Steps: MBL binds an invader Activates C2 and C4 C2a and C4b combine and activate C3  complement cascade Complement activation: The lectin pathway

42. Interferons Interferons = class of cytokines produced by certain animal cells after viral stimulation Interfere with viral multiplication Three types in humans: Alpha and Beta interferon = produced by infected host to induce antiviral protein synthesis in neighboring cells Oligoadenylate synthetase = degrades viral mRNA Protein kinase = inhibits viral protein synthesis Gamma interferon = produced by lymphocytes; induces neutrophils and macrophages to kill invaders; suppresses tumor cell proliferation

43. Interferons Interferon complications: Stable for only short time periods Side effects of injection: Nausea, fatigue, vomiting, fever Toxic in high concentrations heart, kidneys, liver, red bone marrow Medical usage: Limited or no effect on tumors in clinical trials Alpha interferon  some virus-associated disorders Kaposi’s sarcoma Chronic Hepatitis B and C

44. Iron-binding proteins Humans use iron in many ways: component of cytochromes in the ETC cofactor of many enzymes component of hemoglobin Iron-binding proteins = transport and store iron Transferrin = blood and tissue fluids Lactoferrin = milk, saliva, mucus Ferritin = liver, spleen, red blood marrow Hemoglobin = red blood cells deprives pathogens of available iron!

45. Iron-binding proteins Siderophores = proteins released into the medium by bacteria to capture iron from transport proteins Forms iron- siderophore complex, recognized by bacterial receptors and taken into cell Splits iron from siderophore and utilizes it Other mechanisms of obtaining iron: R elease toxins when iron is low  Kills host cells, releasing their iron Ex) Strep pyogenes Hemolysins  lysis of red blood cells Hemoglobin broken down to capture iron

46. Antimicrobial Peptides Antimicrobial peptides (AMPs) = short chains of amino acids synthesized on ribosomes Synthesized by neutrophils when TLRs contact PAMPs - B road spectrum killing of bacteria, viruses, fungi - Attract other phagocytes - Sequester endotoxins What makes them interesting? Work together with other antimicrobials (synergy) Stable over a wide range of pH Microbes don’t develop resistance