First Foundations in Pathology, Part 2: Acute and Chronic Inflammation Paul G. Koles, MD Asst. Prof. Pathology and Surgery Director of Pathology Education Boonshoft School of Medicine at Wright State University
Overview of Inflammation • Definition: a protective response to injury in which blood vessels facilitate accumulation of fluid and leukocytes in extravascular tissue basophil Platelet neutrophil monocyte eosinophil lymphocyte Fig. 3-1, Pathologic Basis of Disease, 6th ed, WB Saunders, 1999.
Patterns of Inflammation • Acute • Short duration (minutes-days) with emigration of fluid, plasma proteins, and into tissue. • Chronic • Longer duration (days-months) with tissue accumulation of lymphocytes, plasma cells, & macrophages plus variable proliferation of leukocytes blood vessels and fibroblasts
Historical Milestones • Celsus, 1st century A.D., described four cardinal signs of inflammation accurately: • Metchnikoff, 1882, observed ingestion of bacteria by mammalian leukocytes called Rubor = redness Tumor = swelling Calor = heat Dolor = pain phagocytosis
3 processes involved in acute inflammation Fig. 3-2, Pathologic Basis of Disease, 6th ed, WB Saunders, 1999. 1 = vascular dilation Leading to increased blood flow 2 = structural changes in vessels permitting plasma to leak into tissues Of non-cellular components Of cellular components 3 = emigration of leukocytes
Inflammation: essential definitions exudation • = escape of fluid, proteins, and blood cells from vessels into tissues • = inflammatory fluid, high protein concentration and sp.gr. > 1.020 • = watery fluid, low protein concentration and sp. gr. < 1.012 • = excess fluid in tissues • = excess fluid in serous cavities lined by mesothelium (pleural, pericardial, peritoneal) • = inflammatory exudate rich in neutrophils and cell debris exudate transudate edema effusion purulent exudate (pus)
Vascular changes in inflammation • Altered blood vessel caliber and flow • Vasodilation slowing of flow stasis of blood cells leukocyte margination • Increased vascular permeability (leakage) • Escape of protein-rich fluid into interstitium altered osmotic pressure gradient further outflow of fluid
5 Mechanisms, Fig. 3-4, Pathologic Basis of Disease, 6th ed, WB Saunders, 1999. Mechanisms of vascular permeability
Extravasation of Leukocytes • Sequence of 3 events • In lumen of blood vessel (3 phases): • Diapedesis through endothelium of venules: • Migration into interstitium toward injury site by locomotion along a chemical gradient: Margination Rolling Adhesion transmigration chemotaxis
Mechanisms of adhesion • Complementary binding of adhesion molecules on leukocytes and endothelium • 4 families of adhesion molecules: • : on endothelial cells, platelets, and leukocytes (selectin-L) • : ICAM-1 and VCAM-1 on endothelial cells • : transmembrane heterodimeric glycoproteins on leukocytes • : on endothelial cells and leukocytes, enabling diapedesis through endothelium selectins immunoglobulins integrins CD 31 (PECAM-1)
Leukocyte emigration: overview Fig. 2-6, Pathologic Basis of Disease, 2005.
How are leukocytes induced to adhere? Redistribution of P-selectins Fig. 2-7, Pathologic Basis of Disease, 7 th edition, Elsevier, 2005. Cytokine induction of endothelial selectins TNF Increased avidity of integrins
Steps in neutrophil extravasation, 1 Margination Rolling Fig. 3-9, Pathologic Basis of Disease, 6th ed., WB Saunders, 1999.
Steps in neutrophil extravasation, 2 Adhesion Transmigration Fig. 3-9, Pathologic Basis of Disease, 6th ed., WB Saunders, 1999.
Chemotaxis • Definition: locomotion of leukocytes toward site of injury along chemical gradient • Chemical attractants, exogenous: bacterial products (proteins, lipids) • Chemical attractants, endogenous: • Complement components, esp. • (LTB4) • Cytokines, esp. chemokines like IL-8 C5a leukotrienes
Time-related cellular response to MI Later response: (48 hrs-2 weeks) Early response (12-48 hrs.) neutrophils Mononuclear cells
Leukocyte Locomotion Extension of cytoplasm which pulls cell in direction of the extension: Pseudopod (filopodium) Pseudopod motion mediated by assembly & disassembly of which contractile proteins? actins
Phagocytosis by neutrophils and macrophages: three steps opsonins • Recognition and attachment to particle • Microbes coated by which promote binding to leukocyte receptors: • Engulfment & formation phagocytic vacuole • Membrane phagocytic vacuole merges with limiting membrane of: • Killing/degradation of ingested material • Mainly by oxygen-dependent mechanisms with release of from azurophilic granules in neutrophils Fc fragment of IgG; C3b; plasma lectins lysosome myeloperoxidase
Phagocytosis: mechanism Activation NADPH-oxidase generates H2O2, which converts to HOCl in presence of Cl- and myeloperoxidase; H2O2-MPO-halide system is bactericidal in: neutrophils Fig. 3-13, Pathologic Basis of Disease, 6th ed, WB Saunders, 1999.
Leukocyte-mediated injury: too much of a good thing can be bad • Amplified inflammatory response releases neutrophil products into extracellular space: • Lysosomal enzymes • O2-derived active metabolites • Products of arachidonic acid metabolism
Genetic defects in leukocyte function Leukocyte adhesion Chronic granulomatous disease Myeloperoxidase Chediak-Higashi
Neutropenia: decreased concentration of neutrophils in peripheral blood (absolute neutrophil count < 1600/ul) What is most frequent pathophysiologic mechanism of neutropenia? Decreased production of neutrophils by bone marrow What are two most common specific etiologies of neutropenia caused by this mechanism? Drug-induced myelosuppresion (esp. chemotherapy) Myelophthisis (replacement of hematopoietic cells by neoplastic cells and/or fibrosis)
Chemical mediators of inflammation histamine serotonin lysosomal enzymes prostaglandins nitric oxide cytokines anaphylatoxins Fig. 2-12, Pathologic Basis of Disease, 7th ed, Elsevier, 2005.
Histamine: in granules of mast cells, basophils, and platelets • Triggers for degranulation/release histamine • Physical injury • Immune reactions • Anaphylatoxins: • Neuropeptides, eg. Substance P • Cytokines IL-1, IL-8 • Function histamine: dilation arterioles and creation of gaps in for increased vascular permeability C3a and C5a endothelium
Plasma-derived mediators of inflammation (synthesized by liver) Complement • system of 20 component proteins and cleavage products • system, generating vasoactive peptides from plasma proteins by specific proteases called kallikreins. • system, divided into two pathways that converge, culminating in activation of thrombin & formation of fibrin Kinin Coagulation
Complement activation pathways C3b: Opsonin for coating microbes Functions of complement in inflammation: C5-9 MAC: Cell lysis by attacking membrane C3a and C5a Increased vascular permeability
Plasma mediators: summary Initiates four systems involved in inflammation XIIa (Hageman f.) Brady kinin Powerful mediators of increased vascular permeability C3a Fig. 3-17, Pathologic Basis of Disease, 6th ed, WB Saunders, 1999.
Role of arachidonic acid metabolites steroids Inhibited by: Selective Cox-2 inhibitors: celecoxib rofecoxib Cox 1&2 inhibitors: Aspirin ibuprofen Fig. 3-18, Pathologic Basis of Disease, 6th ed, WB Saunders, 1999.
2 Major cytokines of inflammation Actions of IL-1 and TNF may be: 1) On the same cell that produces them: autocrine IL-1 and TNF 2) On cells in nearby vicinity: paracrine 3) systemic: endocrine Fig. 3-21, Pathologic Basis of Disease, 6th ed, WB Saunders, 1999.
Nitric Oxide: synthesized in endothelial cells & macrophages Two types of nitric oxide synthase (NOS): endothelialNOS expressed at low levels in endothelial cells; is induced when macrophage activated by cytokines (TNF-a or IFN-y) iNOS Fig. 3-22, Pathologic Basis of Disease, 6th ed, WB Saunders, 1999.
Neutrophil: lysosomal granules Spccific granules Smaller, dump into phagocytic vacuoles within cell but also easily release contents extracellularly Azurophilic granules Larger, dump granule contents primarily into phagocytic vacuoles within cell Fig. 3-23, Pathologic Basis of Disease, 6th ed, WB Saunders, 1999.
Summary: important mediators Tissue damage mechanism used by all leukocytes Tissue damagemechanism used by which leukocytes? Macrophages
Outcomes of acute inflammation Fig. 3-24, Pathologic Basis of Disease, 6th ed, WB Saunders, 1999.
Chronic Inflammation • Definition: inflammation of prolonged duration (weeks-months-years) in which active inflammation, tissue destruction, and tissue repair are simultaneously present. • Clinical settings of chronic inflammation: • Persistent infections (eg, M. tuberculosis) • Prolonged exposure to toxins (silicosis) • Autoimmunity (rheumatoid arthritis) • Neoplasia
Histopathology of chronic inflammation Mononuclear cell infiltration (3 cell types): Macrophages, lymphocytes, plasma cells Tissue destruction with replacement of damaged tissue by well-vascularized young fibrous tissue Giant-cell arteritis (temporal arteritis) Biopsy temporal artery, H&E Diagnosis?
Origin & Distribution of Macrophages Anatomic sites: Microglia: Kupffer cells: Sinus histiocytes: Osteoclasts: Brain Liver Lymph node Bone
Activation of Macrophages Activated CD4 Th1cell Interferon-gamma Result: Tissue injury Result: Fibrosis
Macrophage arsenal: friend & foe Friend: potent destroyer of unwanted substances: bacteria, fungi, foreign particles Foe: significant tissue destruction accompanies the chronic inflammatory response
Cells of chronic inflammation (1) Lymphocytes • : mobilized by Ab-mediated and cell-mediated immune reactions; use adhesion molecule pairs and chemokines to migrate into sites of inflammation • : mature, fully differentiated B-cells, manufacture and secrete specific immunoglobulin directed against persistent antigen or altered tissue components. Plasma cells
Cells of chronic inflammation (2) Mast cells • : have surface receptors for Fc portion of IgE antibody. Binding of antigen-specific IgE causes degranulation and release of histamine. • : seen in immune reactions mediated by IgE and parasitic infections. Chemotaxis mediated by eotaxin. Large cytoplasmic granules contain which is toxic to parasites and epithelial cells. Activated by cytokine Eosinophils Major basic protein IL-5
Reciprocal activation of lymphocytes and macrophages MØ activates Tcells by secreting CD4+ Th1 IL-12 INF-gamma and which autocrine cytokine? IL-2 TNF and TNF, IL-1 and Fig. 2-31, Pathologic Basis of Disease, 7th ed, Elsevier, 2004.
Granulomatous inflammation macrophages • Definition: distinctive pattern of chronic inflammation mediated by • Why important to recognize in tissue? • Limited number of causes (narrows the differential diagnosis) • Identification of specific cause (by various methods) allows specific treatment for potentially serious disease
Name this structure: Granuloma Definition: microscopic aggregate of macrophages with epithelioid features, usually encircled by peripheral collar of lymphocytes and plasma cells
Disease Tuberculosis Leprosy Sarcoidosis Syphilis Histoplasmosis (& other fungi) Cat scratch disease Brucellosis undulant f. Berylliosis Cause Diseases with granulomatous inflammation Mycobacterium tuberculosis Mycobacterium leprae ?? Treponema pallidum Histoplasma capsulatum Bartonella henselae (gram-neg rod) Brucella spp. Beryllium
Variant forms of granuloma Foreign body granuloma : incited by inert foreign materials that can’t be destroyed by single macrophages and do not incite much inflammation or immune response Foreign body giant cell : formed by fusion of activated macrophages; contains haphazardly arranged multiple nuclei Lung biopsy, H&E and polarized light
Morphologic type of granuloma 2 Immune granulomas: :incited by poorly soluble particles which induce cell-mediated immune response involving activated macrophages processing and presenting Ag to T-lymphocytes Langhans-type giant cell : formed by fusion of activated macrophages; showing peripheral wreath arrangement of multiple nuclei + central necrosis: Caseating g. No central necrosis: Non-caseating g.
Role of lymphatics in inflammation • Function: lymphatics and lymph nodes are secondary defense to contain inflammation when local reaction fails to neutralize injury • = inflammation of lymphatics • = inflammation of lymph nodes draining a focus of injury • may result when local infection is not contained by lymphatics and regional lymph nodes. Lymphangitis Lymphadenitis Sepsis