Lecture 4 Micro PDF

MICROBIOLOGY AND IMMUNOLOGY (PBBS505A&B) Inflammation Fabio Re, PhD [email protected]  Learning Objectives Understand the physiologic role of inflammation Distinguish between different types of inflammation Kn...

MICROBIOLOGY AND IMMUNOLOGY (PBBS505A&B) Inflammation Fabio Re, PhD [email protected]  Learning Objectives Understand the physiologic role of inflammation Distinguish between different types of inflammation Know the components of acute and chronic inflammation. Know the mediators involved and their mode of action. Know the mechanisms of recruitment of phagocytes and other immune cells Know the event leading to resolution or chronicization of inflammation  Inflammation Inflammation is an essential immune response that is triggered by noxious stimuli and conditions, such as infection and tissue injury. Inflammation enables survival during infection or injury and maintains tissue homeostasis under a variety of noxious conditions. The Roman encyclopaedist Cornelius Celsus: described the four cardinal signs of inflammation in the 1st century AD : rubor et tumor cum calore et dolore. Rubor (redness) Increased blood flow, elevated cellular metabolism Tumor (swelling) Extravasation of fluid and leukocytes influx Calor (heat) Vasodilation, increased blood flow Dolor (pain) Release of soluble mediators, extravasation of fluid and leukocytes influx Inflammation comes at the cost of a transient decline in tissue function (functio laesa).  Inflammation The acute inflammatory response triggered by infection or tissue injury involves the coordinated delivery of blood components (plasma and leukocytes) to the site of infection or injury Recognition of infection/injury Release of soluble mediators Vasodilation, increased blood flow (Rubor, Calor) Vascular leakage and increased interstitial osmotic pressure leading to edema (Tumor, Dolor) Extravasation of fluid and leukocytes influx (mostly PMNs) Phagocytosis and release of toxic compound Elimination of infection, tissue repair, resolution  Different types of Inflammation Inflammatory Infection Tissue Injury Tissue stress and Malfunction triggers Inflammation Physiological Host defense against Adaptation to stress and purpose infection Tissue repair response restoration of a Activation of adaptive homeostatic state immunity Shift in homeostatic set Pathological Autoimmunity, inflammatory Fibrosis, metaplasia points, development of consequences tissue damage and sepsis And/or tumor growth diseases of homeostasis and/or autoinflammatory diseases Inflammation mother of all evils! Inflammation Components Medzhitov R., 2010. Cell 140: 771  Inflammation Sensors Pattern Recognition Receptors are the sensors of inflammatory inducers Toll-like Receptors Nod-like Receptors Rig-like Receptors C-type Lectin Receptors Inflammation  Inflammation Mediators Inflammatory mediators primarily alter the functionality of the vasculature and the recruitment of leukocytes  Inflammation Mediators (1) 1) Vasoactive amines (histamine and serotonin) are produced when mast cells and platelets degranulate. Complex effects on the vasculature, causing increased vascular permeability and vasodilation (or vasoconstriction, depending on the context) Edema: Swelling due to fluid collecting in tissues Increased vascular permeability hallmark of acute inflammation Leakage of plasma proteins increases extravascular osmotic pressure pulling fluid into tissues  Inflammation Mediators (2) 2) Vasoactive peptides stored in an active form in secretory vesicles (substance P) or generated by proteolytic processing of inactive precursors in the extracellular fluid (kinins, fibrinopeptide A, fibrinopeptide B and fibrin degradation products). Damage to the vascular endothelium allows plasma proteins to gain access to extravascular spaces. Hageman factor (also known as Coagulation factor XII) acts as a sensor of vascular damage It becomes activated by contact with collagen and other components of the extracellular matrix (ECM). Activated Hageman factor initiates the four proteolytic cascades that generate inflammatory mediators: 1. the kallikrein–kinin cascade generate bradykinin that affects the vasculature and have potent pro-algesic (pain- stimulating) effect 2. the coagulation cascade 3. the fibrinolytic cascade 4. the complement cascade  Inflammation Mediators (3) 3) Complement cascade generates C5a (and to a lesser extent C3a and C4a) that promotes granulocyte and monocyte recruitment and induce mast-cell degranulation, thereby affecting the vasculature.  Inflammation Mediators (4) 4) Lipid mediators (eicosanoids and platelet-activating factors). Arachidonic acid is metabolized to form eicosanoids either by cyclooxygenases (COX1 and COX2), which generate prostaglandins and thromboxanes, or by lipoxygenases, which generate leukotrienes and lipoxins. Prostaglandins cause vasodilation, pain Leukotriene cause recruitment of neutrophils and vasoconstriction Lipoxins inhibit inflammation and promote resolution of inflammation and tissue repair Anti inflammatory drugs  Inflammation Mediators (5,6) 5) Cytokines and Chemokines Cytokines TNF-α, IL-1b, IL-6 (and many others) are produced by many cell types, most importantly by macrophages and mast cells. They have several roles in the inflammatory response, including activation of the endothelium and leukocytes and induction of the acute-phase response. Chemokines are produced by many cell types in response to inducers of inflammation. They control leukocyte extravasation and chemotaxis towards the affected tissues. 6) Proteolytic enzymes (including elastase, cathepsins and matrix metalloproteinases) have diverse roles in inflammation, in part through degrading ECM and basement-membrane proteins. These proteases have important roles in many processes, including host defense, tissue remodeling and leukocyte migration. Inflammatory cytokines secreted by macrophages (IL-8)  Neutrophils recruitment to Inflammatory sites Neutrophils are essential effector cells of the innate immune response, forming the first line of defense against bacterial and fungal pathogens. Three major decision points presiding over the migratory fate of neutrophils: 1.exit from the bone marrow into the circulation 2.movement from the blood into the tissue 3.recruitment to the infection/tissue damage site  Neutrophils recruitment to Inflammatory sites (2) 2. Movement into tissue IL-1β, TNF, and neutrophil-active chemoattractants (chemokines and lipid mediators) produced by macrophages and mast cells activated at the infection site initiate the recruitment of neutrophils into the tissue by triggering the leukocyte adhesion cascade. The leukocyte adhesion cascade consists of distinct steps: 1. Rolling is mediated predominantly by selectins 2. Adhesion is mediated by β2-integrins LFA-1 and Mac-1 binding to ICAM-1 on the endothelial cells 3. Arrest. Activation of the neutrophil by chemokines, which are bound to the endothelium via glycosaminoglycans, enhances adhesion and induces arrest. 4. Diapedesis (transmigration through the endothelium). Paracellular transmigration is mediated by integrins, junction adhesion molecules, and degradation of ECM and vascular basement membrane Migration of monocytes, T cells, and other leukocytes is regulated in a similar way  Endothelial cells activation Phagocytes adhesion to vascular endothelium is mediated by integrins that bind to adhesion molecule expressed on activated endothelium Mutation of the b2 chain of the integrin CR3 (Mac1, CD11b/CD18) and LFA-1 cause the disease Leukocytes Adhesion Deficiency which predispose to recurrent bacterial infections and impaired wound healing.  Acute Phase Response The acute phase response is an innate body defense seen during acute inflammation. TNF-α, IL-1b, IL-6 stimulate hepatocytes to synthesize and secrete acute phase proteins  Sepsis-Septic Shock Sepsis: “Organ dysfunction caused by dysregulated host response to infection” (25% mortality) Septic shock is a subset of sepsis characterized by a drop in blood pressure that cannot be managed by vasopressors or fluid replacement and is associated with a poor outcome (60% mortality) Bacterial septicemia (Gram+/-) causes systemic activation of TLRs on monocytes and massive release of inflammatory mediators (TNFa, IL-1b, eicosanoids) and activation of coagulation and complement cascades leading to uncontrolled systemic inflammation Shock from loss of blood pressure (vasodilation and leakage of fluid into tissues), widespread coagulation (DIC via tissue factor). Immunosuppression and immunoparalysis The combination of effects can lead to multi-organ failure and death Infection Inflammatory Endothelial Vasodilation Mediators Dysfunction Hypotension Microvascular Plugging Vasoconstriction Edema Maldistribution of Microvascular Blood Flow Ischemia Cell Death Organ Dysfunction  Regulation of Inflammation In principle, the inflammatory response could be controlled at four levels, corresponding to the four components of the inflammatory pathway: inducers, sensors, mediators, and target tissues One key control point is production of inflammatory mediators. IL-10, TGF-β, and glucocorticoids are the major anti-inflammatory mediators  Regulation of Inflammation The hypothalamic-pituitary-adrenal axis (HPA axis) is a complex set of interactions among the hypothalamus, the pituitary gland and the adrenal glands that controls production of corticosteroids, hormones with potent anti-inflammatory activities.  Outcomes of Inflammation Granuloma Tertiary lymphoid organs Scarring Chronic inflammation Fibrosis Loss of function Failure to eliminate infection Persistence of inducers Positive feedback loops Acute inflammation Resolution (Homeostasis) Elimination of infection Tissue repair  Resolution of Inflammation The acute inflammatory response is normally terminated once the triggering insult is eliminated, the infection is cleared, and damaged tissue is repaired. Key regulatory mechanisms of resolution switch from proinflammatory prostaglandins to anti-inflammatory, resolution-inducing lipoxins. transition from neutrophil to monocyte recruitment that results in clearance of the dead cells and other debris and initiation of tissue repair at the affected site Phases of acute inflammation  Possible outcomes of acute inflammation Complete resolution –Tissues capable of regeneration. Little tissue damage Abscess formation –occurs with some bacterial or fungal infections Scarring (fibrosis) –In tissues unable to regenerate. Excessive fibrin deposition organized into fibrous tissue Progression to chronic inflammation  Granulomatous Inflammation A distinctive pattern of chronic inflammatory reaction in which the predominant cell type is an activated macrophage with a modified epithelial like (epithelioid) appearance A granuloma is a focal area of granulomatous inflammation. It consists of a microscopic aggregation of macrophages that are transformed into epithelium like cells (epithelioid cells) surrounded by a collar of mononuclear leukocytes Granulomas are typical of mycobacterial infections (TB, leprosy) and of certain fungal infections Granulomas can contain syncytial giant cells (polykaryons)  Chronic “Low Grade” Inflammation A growing number of chronic inflammatory conditions have been described (including obesity and type 2 diabetes, atherosclerosis, neurodegenerative diseases, and cancer) where the initiating trigger is not well defined but does not seem to involve infection or tissue damage. In these disease the inflammation is “low grade, smoldering”.  Summary Inflammation is an essential immune response that is triggered by noxious stimuli and conditions, such as infection and tissue injury. Inflammation involves the coordinated delivery of blood components to the site of infection or injury Various classes of inflammatory mediators are produced at idfferent time point and by different cell types Inflammatory mediators primarily alter the functionality of the vasculature and the recruitment of leukocytes The leukocyte adhesion cascade consists of distinct steps The acute phase response is an innate body defense seen during acute inflammation. Massive release of TNFa and IL-1b leads to uncontrolled systemic inflammation and sepsis Failure to remove the infection or repair tissue may result in chronic inflammation that has features distinct from acute inflammation  Which neutrophil function is impaired by mutation of the b2 subunit of integrins? A. Neutrophils rolling on inflamed endothelium B. Neutrophils adhesion to endothelium and extravasation C. Neutrophils respiratory burst 0% 0% 0% 0% 0% D. Cytokine signaling E. Release of g alin........... to n. pr ign ry ni ion ils to es go neutrophils proteases ph ira es kin llin ro sp dh to ro ut re a Cy ne ils ils ils ph ph ph of ro ro ro se ut ut ut lea Ne Ne Ne Re 10  The anti-inflammatory action of aspirin is due to inhibition of: A. Synthesis of cytokines B. Synthesis of prostaglandins and thromboxane C. Synthesis of histamine and serotonin D. Generation of anaphylatoxins through 0% 0% 0% 0% 0% the complement cascade E. TLR activation by es i..... kin i..... ob an nd lat to microbial products icr hy gla ine cy ym ap sta m of an ta nb ro sis his p of he tio of ion of nt va sis Sy sis rat cti he he Ra ne nt nt Ge TL Sy Sy 10  Production of TNFa and IL-1b by phagocytes is regulated by: A. Activation of Complement cascade B. Activation of TLR and NLR by microbial products C. Antimicrobial peptides D. Expression of selectins on activated endothelium E. Release of histamine and 0% 0% 0% 0% 0% serotonin es i..... kin i..... ob an nd lat to icr hy gla ine cy ym ap sta m of an ta nb ro sis his p of he tio of ion of nt va sis Sy sis rat cti he he Ra ne nt nt Ge TL Sy Sy 10