Immunology and Pathology (Inflammation) (3) Department of Pharmacology and Biomedical Sciences Faculty of Pharmacy Petra University Instructors: Dr. luay Abuqatouseh Maysa Al-Hanbali Inflammation Inflammation is the major way by which the innate immune system deals with infections and tissue injury. Inflammation is a nonspecific response of living tissue to localize and eliminate the injurious agent. The injury may be: ➢ Physical ➢ Chemical ➢ Biological Inflammation Inflammatory response includes the accumulation of leukocytes, plasma proteins (complement proteins, antibodies, and acute-phase reactants) and fluid derived from the blood at an extravascular tissue site of infection or injury. The five cardinal signs of acute inflammation - "PRISH" • Pain The inflamed area is likely to be painful, especially when touched. Chemicals that stimulate nerve endings are released, making the area much more sensitive. • Redness This is because the capillaries are filled up with more blood than usual. • Immobility There may be some ‘loss of function’. • Swelling Caused by an accumulation of fluid. • Heat More blood in the affected area makes it feel hot to the touch. Process of inflammation Pathogen with non-self protein damages the epithelium to break through the epithelial barrier A cellular biochemical cascade system activated by bacteria (complement system) Activation of immune cells upon contact with M.O Release of substances that change morphology and permeability of endothelial cells IL-1 TNF Induce expression of integrins (ligands on blood leukocytes) chemical mediators Histamine+ kinin+ fibrin Chemokines (IL-8) Activation of integrins and their conversion to the high-affinity state Increase permeability of blood vessels Cause endothelial cells of blood vessels near site of inflammation to express Leakage of plasma Permit migration of leukocytes intracellular adhesion proteins and fluid to (neutrophils) outside blood molecules (ICAMs) tissues (edema, swelling) vessels (extravasation) Causes leukocytes to slow down and begin rolling along inner surface of vessel wall (as bonds are made & broken) Chemokine gradient stimulate adhered leukocyte to move between endothelial cells to tissues .......... (diapedesis) Movement of leukocytes within tissue ……….(chemotaxis) Start phagocytosis Extravasation Process of leukocyte movement from blood into tissues through blood vessels. Steps of extravasation: 1. Margination 2. Diapedesis 3. Chemotaxis Steps of extravasation: 1. Margination: Accumulation and adhesion of leukocytes to the inner surface of blood vessel walls in early stages of inflammation. 2. Diapedesis: Migration across endothelium (trans-migration) 3. Chemotaxis: Movement of leukocytes within tissue under influence of chemotactic factor (IL-8) Inflammation = Extravasation + phagocytosis What happens during acute inflammation? Pathogen with non-self proteins damages the epithelium to break through the epithelial barrier Epithelial cells ‘activated’ upon contact with microorganism Chemokines and cytokines are made by activated epithelial cells Inflammation Cytokines - tumour necrosis factor α (TNFα) and interleukin 1 (IL-1) change the morphology, adhesive properties and permeability of endothelial cells What happens during acute inflammation? The most abundant leukocyte that is recruited from the blood into acute inflammatory sites is the neutrophil. Blood monocytes, which become macrophages in the tissue, become increasingly prominent over time and may be the dominant population in some reactions. Neutrophils Hours Short-lived Monocytes/macrophages Hours to days Long-lived & connect with adaptive immune system Escape of cells from blood vessels Post capillary endothelial cells are impermeable to cells and plasma Phagocytes • Phagocytic neutrophils respond to an epithelial chemokine interleukin-8 (IL-8) • Cells migrate from the blood into the tissue underlying the infection The stages of neutrophil migration into sites of inflammation Diapedesis Mechanism of cell migration Tethering and rolling Cytokine activated endothelial cells express adhesion molecules Tethering Cells normally roll past resting endothelial cells Rolling Tethering and rolling are mediated by SELECTINS Leukocytes circulating in the blood interact with selectins expressed on the surface of vascular endothelial cells. In the absence of inflammation, the interaction between leukocytes and endothelial cells is weak, and leukocytes either flow past or roll along the endothelium. Neutrophil rolling is mediated by the interaction between endothelial cell E-selectin and neutrophil sialyl-Lewisx (s-Lex). Activation dependent adhesion and arrest Cytokines from epithelium activate expression of intracellular adhesion molecules (ICAMs) Rolling Neutrophil is activated INTEGRIN (adhesion molecule) has low by chemokines affinity for ICAM Cell activation changes integrin to high affinity format Integrin activation Integrin activation occurs in response to signals generated from chemokine binding to chemokine receptors. One important ligand for leukocyte function-associated antigen 1 (LFA-1), (which is an integrin), is intercellular adhesion molecule 1 (ICAM-1) expressed on cytokine-activated endothelial cells. During the inflammatory response Endothelial cells up-regulate their expression of intercellular adhesion molecules (ICAMs). ICAM expression increases the potential for strong binding interactions between leukocytes and the activated endothelial cells. ICAM-1 on endothelial cells binds tightly to lymphocyte function-associated antigen-1 (LFA-1) on neutrophils. The enhanced cell–cell interaction leads to margination of leukocytes onto endothelial cell surfaces and initiates the process of leukocyte diapedesis and transmigration from the vascular space into extravascular tissues. Leukocytes migrate through injured tissue in response to chemokines such as IL-8. Migration and diapedesis Firm adhesion causes the neutrophil to flatten and migrate between the endothelial cells (diapedesis) Neutrophil migrates towards site of infection by detecting and following a gradient of chemokine (chemotaxis) Neutrophils migrate readily to IL-8 made by epithelilal cells that have encountered microorganisms Phagocytosis Neutrophils and macrophages that are recruited into sites of infections ingest microbes into vesicles by the process of phagocytosis and destroy these microbes. Phagocytosis is an active process of engulfment of large particles into vesicles. Phagocytic vesicles fuse with lysosomes, where the ingested particles are destroyed, and in this way, the mechanisms of killing, which could potentially injure the phagocyte, are isolated from the rest of the cell. Neutrophils and macrophages express receptors that specifically recognize microbes, and binding of microbes to these receptors is the first step in phagocytosis. Recognition of microorganisms by phagocytes Mannose receptor Mac-1 Scavenger receptors Mannose receptor Mac-1 Neutrophils Scavenger receptors Toll-like CD14 receptors Macrophages • Neutrophils and macrophages express receptors that specifically recognize microbes (pattern recognition receptors). • Specialised recognition of classes of molecules and structures not present in or on self tissues (pathogen-associated molecular patterns [PAMPs]). • Selective specificity for microbial ‘patterns’. Process of Phagocytosis 1- Chemotaxis and attachment A- Attraction by chemotactic Subst. ( microbes, inflam. tissues) B- Attachment by receptors on surfaces of phagocytes 2- Ingestion - Phagocyte produce pseudopodia surround organism forming phagosome - Opsonins and co-factors enhance phagocytosis - Fusion between phagosome and lysozomal granules and release digestive, toxic contents 3- Killing (two microbicidal routes) A- Oxygen depended system (powerful microbicidal agents) Oxygen converted to superoxide, anion, hydrogen peroxide, activated oxygen and hydroxyl radicals. B- Oxygen-independent system (anaerobic conditions) Digestion and killing by lysozyme. Lactoferrin, low pH, cationic proteins and hydrolytic and proteolytic enzymes Phases of phagocytosis Chronic inflammation When neutrophils and macrophages are strongly activated, they can injure normal host tissues by release of lysosomal enzymes, reactive oxygen species (ROS), and nitric oxide. The microbicidal products of these cells do not distinguish between self tissues and microbes. As a result, if these products enter the extracellular environment, they are capable of causing tissue injury Chronic inflammation • Acute inflammation can develop in minutes to hours and last for days. • Chronic inflammation is a process that takes over from acute inflammation if the infection is not eliminated or the tissue injury is prolonged. • It usually involves recruitment and activation of monocytes and lymphocytes. Chronic inflammatory sites also often undergo tissue remodeling, with angiogenesis and fibrosis. Chronic inflammation - Chronic bacterial infections may lead to the formation of granuloma— collections of specialized macrophages surrounded by T cells. - Granulomata occurs in tuberculosis and takes 2 to 3 days to develop (time it takes for the T-cell response to develop). - Necrotic lesions subsequently cavitate and these cavities are produced when necrotic material is coughed up, which allows the mycobacteria contained to be spread from person to person. Chronic inflammation - Chronic viral infection leads to more diffuse inflammation, although macrophages and T cells are still present. - This typically occurs in infections with Hepatitis B virus, where acute inflammation occurs initially as a result of antiviral activity, and chronic inflammation can follow as the inflammatory response continues in a failed attempt to eliminate the pathogen. - This chronic stage results in damage to the host organs. Overview of immune responses to microbes The early innate immune response to microbes: ➢ Barriers to prevent the entry of microbes from the external environment. ➢ Cells of innate immunity: cellular innate immune response to microbes consists of two main types of reactions—inflammation and antiviral defense. ➢ Microbes that are able to withstand these defense reactions in the tissues may enter the blood, where they are recognized by the circulating proteins of innate immunity. Among the most important plasma proteins of innate immunity are the components of the alternative pathway of the complement system.
