LECOM Pharmacy School BMS-PDA II Immun 3 PDF

LECOM-Pharmacy School BMS-PDA II Immun 3 Dr. Saber Hussein Innate Immunity & Complement  Objectives 1. The early defense against infections and cancer 2. Recognition of microbes by the innate immune system 3. Components of innate immunity – Physical and chemical...

LECOM-Pharmacy School BMS-PDA II Immun 3 Dr. Saber Hussein Innate Immunity & Complement  Objectives 1. The early defense against infections and cancer 2. Recognition of microbes by the innate immune system 3. Components of innate immunity – Physical and chemical barriers (e.g. epithelial barrier, stomach acidity) – Phagocytes: neutrophils and monocytes/macrophages – Natural killer cells – The complement system – Cytokines of innate immunity – Other plasma proteins of innate immunity 4. Microbes evasion of the innate immunity 5. How does innate immunity stimulate the acquired immunity?  Innate Immunity Natural, none-adaptive Nonspecific to an antigen but recognize and fight microbes Phagocytes: Monocytes, macrophages, PMN neutrophils Natural killer (NK) cells Complement system Exterior defenses: Skin, Stomach acidity, Mucus, Cilia, Microflora, Lysozyme in tears, Flushing of urinary tract  Cytokines of Innate Immunity Cytokines are small soluble proteins produced by many cells such as macrophages They mediate immune and inflammatory reactions They are the tool of communication among leukocytes and between those and other cells Cytokines produced by macrophages Tumor necrosis factor (TNF) Interleukins (IL): – IL-1 – IL12 – IL-10 – IL-6 – IL-15 – IL-18 Type I interferons: – IFN-a – IFN-b  Cytokines of Innate Immunity Cytokine Principal cell Principal cellular targets & source biologic effect TNF Macrophage, T cell Endothelial cell: activation Neutrophil: activation Hypothalamus: fever Many cell types: apoptosis IL-1 Macrophage, Endothelial cells: activation endothelial cell, epithelial cell IL-12 Macrophages NK cells & T cells: IFN- Dendritic cells synthesis, increased cytolytic activity IFN- NK cells, T cells Activation of macrophages Type I IFN-a Macrophages All cells: antiviral activity, IFNs IFN-b Fibroblasts increased MHC I expression NK cells: activation  Innate Immunity Natural, none-adaptive, Nonspecific Phagocytes: Monocytes, macrophages, PMN neutrophils Natural killer (NK) cells Complement system Exterior defenses: Skin, Stomach acidity, Mucus, Cilia, Microflora, Lysozyme in tears, Flushing of urinary tract Physical Barriers  Toll-Like Receptors TLRs recognize different components of bacterial cell  Functions of activated macrophages Macrophages may be activated by signals from many surface receptors. inducible – Receptor for bacterial NO synthase endotoxin (LPS), which transduces signals via an attached Toll-like receptor – Receptor for the most important macrophage- activating cytokine, IFN Signals from activating receptors stimulate the production of several proteins, which mediate the important functions of macrophages. Different M surface receptors may stimulate distinct or overlapping responses Common feature is that they stimulate the production of transcription factors, which result in the production of various proteins  Functions of Natural killer (NK) cells NK cells kill host cells infected by intracellular microbes – eliminating reservoirs of infection. NK cells secrete IFN in response to IL-12 produced by macrophages IFN activates the macrophages to kill phagocytosed microbes Reticuloendothelial system & Normal flora Normal flora on Oral cavity Skin Reticuloendothelial system & Competition by Normal flora  Soluble Factors & Physiological responses Soluble Factors:➔ 1. Lysozyme 2. Complement 3. “Antiproteinases (Abs)”; ANCA 4. C-reactive protein 5. DNAse 6. RNases Physiological responses: – Chemotactic factors from infecting agents Bacteria F-Met peptides Injured tissue – Mast cells & PMN Leukotrienes & Histamines  Mechanisms of killing Toxic oxygen – Oxygen radicals – Hydrogen peroxide (H2O2) – Hypochlorous acid (HOCl)  Innate & adaptive immunity Innate Immunity Adaptive Immunity Pathogen recognized by receptors Pathogen recognized by encoded in the germline receptors generated randomly Receptors have broad specificity, Receptors have very narrow i.e., recognize many related specificity; i.e., recognize a molecular structures called PAMPs particular epitope (pathogen-associated molecular Most epitopes are derived from patterns) polypeptides (proteins) and PAMPs are essential reflect the individuality of the polysaccharides & pathogen polynucleotides that differ little Receptors are B-cell (BCR) and from one pathogen to another but T-cell (TCR) receptors for are not found in the host (mannose) antigen Receptors are PRRs (pattern Slow (3 -5 days) response recognition receptors) (because of the need for clones Immediate response of responding cells to develop) No memory of prior exposure Memory of prior exposure Occurs in all metazoans? Occurs in vertebrates only  Innate & Adaptive Immunity C-Reactive CRP belongs to the pentaraxin family of proteins Protein – so-called because it has five identical subunits, encoded by a single gene on chromosome 1, which associate to form a stable disc-like pentameric structure It reacts with the somatic C polysaccharide of Streptococcus pneumoniae In the presence of calcium, CRP Pentameric structure specifically binds to phosphocholine of CRP moieties – phosphocholine is found in phospholipid membranes of many organisms  CRP role in innate immunity Binding phosphocholine gives CRP a host-defensive role because: – Phosphocholine is found in microbial phospholipids ➔CRP-binding activates the classical complement pathway ➔Opsonizes ligands for phagocytosis – It neutralizes the pro-inflammatory platelet-activating factor (PAF) – It down-regulates polymorphs (neutrophil, eosinophil, basophil)  CRP made in the liver CRP is exclusively made in the liver Secreted in increased amounts within 6 hours of an acute inflammatory stimulus (e.g. infection) The plasma level can double at least every 8 hours, reaching a peak after about 50 hours After effective treatment or removal of the inflammatory stimulus, levels can fall almost as rapidly as the 5-7- hour plasma half-life of labeled exogenous CRP The only condition that interferes with the "normal" CRP response is severe hepatocellular impairment  Defensins Definition: – A family of abundant, modestly potent cationic proteins that is found in the primary granules of neutrophils and in the lysosomes of some mononuclear phagocytes Bactericidal – can kill fungi and viruses too One defensin is chemotactic for monocytes – Neutrophils help to attract the "second wave" of leukocytes- Mononuclear phagocytes  Defensins All of the following are protected by defensins 1. our epithelial surfaces 2. skin 3. lining of the GI tract 4. lining of the genitourinary tracts 5. lining of the nasal passages and lungs  Inflammation WBCs extravasation to infected tissue where they: Acute inflammation Destroy microbes Immediate response Clear damaged cells to infections and Promote inflammation and repair tissue damage Redness, swelling and heat Macrophages, dendritic cells and Chronic inflammation mast cells release cytokines and other mediators (NCF, ECF) ➔ Increase permeability of blood vessels Plasma proteins enter tissues https://studentconsult.inkling.com/read/basic-immunology- abbas-lichtman-pillai-4th/chapter-2/figure-215 Leukocytes extravasation Blood vessel Infected tissue  Dr. Saber Hussein Complement Classic Pathway Alternative Pathway  Objectives 1. Define complement 2. Activation of the classical pathway 3. Activation of the lectin pathway 4. Activation of the alternative pathway 5. Describe the three functions of complement in body defense 6. Complement deficiencies and disease The complement system: (Chapter 2) The enzymatic cascade Activation of the complement cascade 1. The alternative pathway 2. The classical pathway 3. The lectin pathway Anaphylactic and chemotactic products of the complement system Membrane attack complex Evasion of innate immunity by microbes Role of innate immunity in stimulating adaptive immune responses  What is Complement? Non-immunoglobulin serum proteins Involved in: i. Control of inflammation ii. Stimulation of phagocytosis iii. Activation of cell lysis Opsonization (“Eat Me” tag) & phagocytosis Preparation for eating Phagocytosis facilitating process Opsonins are deposited on the Ag (bacteria or virus infected cell) Important opsonins can label bacteria: IgG Complement fragments (e.g. C3b)  Sites of synthesis Hepatocytes Macrophages, various tissues Epithelial cells, GI tract Monocytes, in blood  Functions of complement Direct killing of bacteria & virus-infected cells by lysis mediated by MAC Indirect killing by opsonization followed by phagocytosis & intracellular killing Immunization does NOT increase complement concentration in the serum  Role of C3 in bacterial clearance and killing 1. C3 bound to bacteria as C3b or iC3b binds to CR1 on erythrocytes, which transport bacteria through circulation 2. C3 acts as focus for the deposition of lytic MAC on bacterial cell membrane intermediate 3. It ligates complement receptor on phagocytes 4. Complement, in turn, activates the phagocyte leading to Bacterial phagocytosis, Respiratory burst generation and Bacterial killing  Activators of the alternative pathway (AP) Lipopolysaccharides (LPS) Bacterial cell walls Cell walls of yeasts Aggregated IgA Cobra venom NO need for Ab-Ag complex or IgM for activation Activation cascade of the Alternative Pathway Alternative Pathway C3b binds foreign substance C3b + Serum’s Factor B ➔ C3bB Factor D cleaves Factor B ➔ C3bBb C3bBb acts as C3 convertase: C3 → C3a + C3b – Properdin regulates the process; stabilizes C3bBb. – Factor I & H inactivate free C3b  Activation of Classical Pathway (CP) CP is activated by: – Antigen-IgG complex – Pentameric IgM Non-activators of CP: – IgG4 – IgA – IgE – They lack C1q receptors ➔ they Classical pathway cannot bind C1q  Steps of CP activation Step 1: Activation of C1 – C1q-FcIgG activates C1r &C1s – C1s activates C4 → C4a + C4b Step 2: Activation of C4 – C4 → C4a + C4b Step 3: Activation of C2 by C4b – C4b + C2 → C4b2a (C3- convertase) + 2b Step 4: Activation of C3 Step 5: Activation of C5, C6 & C7 Classical pathway Step 6: Activation of C8 & C9  Complement Classic Pathway Common Pathway Alternative Pathway MAC & Cell Lysis Activities of complement fragments Split Products and Their Activity  The Lectin Pathway (LP) Activator: Mannose-binding lectin (MBL), a plasma protein that is similar to C1q MBL binds to terminal mannose (sugar) on the surface glycoprotein of microbes This lectin activates the classical pathway proteins Difference between LP and CP: – LP activation does not require antibodies → Therefore, LP activation is part of the innate immune system Three functions of complement in host defense 1. Opsonization: – C3b binds to microbes and so enables the phagocytes to grab the microbe, via their C3b receptor, and phagocytose it 2. Chemotactic activity of C5a: – This complement fragment attracts neutrophils and monocytes to the site of infection – C5a promotes inflammation at the site of complement activation 3. Formation of membrane attack complex(MAC) – MAC forms a pore (hole)in the membrane of the microbe leading to the loss of cellular contents, lysis of the microbe and death of the microbe  Complement Proteins’ Deficiencies Alternative pathway defects ➔ Susceptibility to Haemophilus influenzae Defects of Factor D & Properdin increase Neisseria infection C5 deficiency, less severe consequences, but increases susceptibility to Neisseria gonorrheae & N. meningitidis  Complement & disease pathogenesis Complement may cause disease pathogenesis by: 1. Systemic production of anaphylaxis such as after Gram-negative sepsis 2. Insertion of MAC into host cell membrane leading to cellular activation and stimulation of membrane arachidonic acid metabolism 3. Fixation of C3b to immune complexes located in tissues causing recruitment and activation of tissue and circulating WBCs  Heritable angioedema (HAE) C1-inhibitor deficiency Autosomal dominant trait inheritance Edema in various organs & tissues Especially bad: – Edema of intestine and throat Treatment – Epinephrine for emergency treatment  Acquired angioedema Caused by an autoantibody to C1 inhibitor, This leads to inactivation of C1 inhibitor – A result similar to HAE: C1 inhibitor becomes deficient Bacteria evade of innate immunity