INFLAMMATION. Inflammatory processes are part of the body´s natural defences. ACUTE INFLAMMATION injury -is early, immediate, response of vascularized living tissue to local - is nonspecific, may be evoked by all types of cell injury -its purpose is to localise and eliminate the injurious agent and then to restore the tissue to normal function and to normal structure SIGNIFICANCE OF INFLAMMATION 1) to destroy injurious agent 2) to reconstitute a damaged tissue (healing), repair already begins during early phases of inflammation, during repair the injured tissue is replaced by regeneration of parenchymal cells, by filling defects with fibroblastic scar tissue = scarring -acute inflammatory response is beneficial but it may also be harmful, associated with tissue damage examples: - inflammation has a beneficial effects by localising and walling off an infection, but on the other hand, the process of inflammation may cause extensive tissue damage - swelling of the brain caused by infl. response against viral infection may lead to death by increased intracranial pressure or -infl. reactions underlie genesis of autoimmune diseases (rheumatoid arthritis, fatal acute and chronic glomerulonephritis, that may lead to renal failure) -reparatory reactions may cause hypertrophic scars, or may result in an intestinal obstructions, immobilize joints (use of antiinflammatory drugs ) CAUSES OF INFLAMMATION almost all possible causes of cell injury may stimulate inflammatory response -microbial infections: bacteria, viruses, fungi, etc -hypersensitivity reactions -physical agents: burns, UV light, radition, trauma 1 -chemical agents: acids, alkalis, oxidising agents, toxins, endotoxins, even toxic catabolites derived from endogenous processes, such as in uremia, etc - tissue necrosis: ischemia MAIN CLINICAL SIGNS AND SYMPTOMS OF INFLAMMATION Acute inflammation is characterized by five major signs described by Celsus and Virchow -rubor = redness from dilatation of blood vessels -calor = increased heat and fever- redness and heat -due to an increased rate and volume of blood flow because of vasodilatation, release of pyrogens -tumor =swelling from edema -dolor =pain form edema and histamine release, pain is said to be due to an accumulation of acid metabolits that stimulate nerve endings -functio laesa = loss of function form pain and swelling These signs are manifested in acute inflammation if this occurs on the body surface, not always in inflammation of internal organs CELLS OF THE INFLAMMATORY RESPONSE Neutrophilic leukocytes -leukocytes are the first cells to appear at the site of acute inflammation -their function - is to degrade cell debris and to ingest and kill microbesphagocytosis -neutrophils contain bactericidal intracellular enzymes in lysosomes, such as myeloperoxidase, lysozyme, and acid hydrolase -lysosomes fuse with the vacuole containing the ingested materialincluding microbes, release enzymes, and destroy the contents Eosinophilic leukocytes - are associated with hypersensitivity responses and allergic reactions -they produce histaminase, aryl sulphatase and phospholipase which degrade anaphylactic chemical mediators particularly those produced by mast cells Basophils and mast cells 2 -mast cells are usually seen in tissues in type I hypersensitivity reactions mediated by IgE -mast cells have specific surface receptors for IgE -both mast cells and basophils have cytoplasmic granules which contain heparin and histamine and enzymes, such as acid hydrolase -binding of IgE to the receptor leads to degranulation and release of the granule contents into the tissues Monocytes and macrophages macrophages are major scavenger cells of the body -derived of blood monocytes -are attracted to sites of inflammation by chemotactic factors -appear 12-24 hours later than leukocytes -are long-living phagocytic cells -contain strong intracellular enzymes, such as lysozyme and hydrogen peroxide- degrade particulate material including microorganisms -they control many of the cellular, vascular and reparative responses of inflammation by releasing chemotactic factors, cytokines ( tumor necrosis factor) and growth factors ( PDGF) and transforming growth factor beta (TGF-beta) Lymphocytes and plasma cells -these are principal cells of specific immune responses- produce antibodies MORPHOLOGIC AND INFLAMMATION FUNCTIONAL CHANGES IN ACUTE -acute inflammation is defined as the early inflammatory response to an injurious agent which is characterized by the presence of neutrophils, and later macrophages -acute infl. last for a few hours or days -the early acute response is characterized by the presence of edema fluid, fibrin, and neutrophilic leukocytes -this is caused by: -arteriolar dilatation and opening up of capillary channels -increased vascular permeability (exudate formation) 3 -emigration of neutrophils from vessels -two main processes invovlved in acute infl. response are: -microcirculatory response (vascular) -cellular response 1 - microcirculatory response -vascular response is characterized by an increased blood flow in an affected area, and an increased permeability of blood vessels active vasodilatation=hyperemia -first step in microcirculation in infl. area is transient vasocontriction, that is rapidly followed by marked active vasodilatation of capillaries, small arteries and venules. Vasodilatation leads to hyperemia (= increased amount of blood in infl. area )- heat and redness increased permeability of blood vessels- next event typical of acute inflammation- associated with slowing of the circulation- called stasis in normal tissuue - blood vessel walls permeability is a function of the intercellular junctions between endothelial cells - these small gaps-pores normally permit passage of only small molecules in acute infl.- immediate increase of permeability of venules and capillaries (caused by active contraction of actin microfilaments in endothelial cells) - results in widening of pores (intercellular junctions)followed by an increase of amount of fluid and high-molecular-weight proteins can pass through abnormally permeable vessels into the extravascular space increased passage of fluid out of microcirculation because of increased permeability in acute inflammation –results in formation of inflammatory exudate- exudation of fluid -vascular leakage- loss of protein-rich fluid from blood vessels results in a reduction of osmotic pressure within blood vessels and in and increase within the interstitium- accumulation of fluid out of blood vesselspassage of large amounts of fluid from capillaries into the interstitium is associated with inflammatory edema- major feature of acute inflammation Composition of inflammatory exudate exudate is a fluid rich in plasma proteins, such as albumins, immunoglobulins, parts of complement, fibrinogen-when extracapillary it is rapidly converted into fibrin by tissue tromboplastin 4 Fibrin can be recognized microscopically-pink fibers or clumps, macroscopically- most easily seen on acute infl. of serosal surfaces-acute fibrinous pericarditis- „bread and butter„ appearance. in contrast Transudation= increased passage of fluids (very low level of plasma proteins, and no cells) through blood vessels with normal permeability- cause either increased hydrostatic pressure or decreased plasma osmotic pressure -composition similar to ultrafiltrate of plasma Significance of the process of exudation -Exudation helps to destroy infectious agent by its diluting, by flooding the area with blood rich in immunoglobulins and other important defensive proteins, by increasing lymphatic flow (helps to remove agents out of area)-lymphatic drainage may be however harmful, helps to spread infectious agents, and acute inflammation is complicated by -acute inflammation of lymphatics= lymphangitis -acute inflammation of lymph nodes= lymphadenitis 2 - cellular response Acute inflammation is characterized by an active emigration of inflammatory cells from the blood into the area of injury. Two most important cellular events in acute inflammatory response are: 1-active emigration to inflammed area 2-phagocytosis 1- ACTIVE EMIGRATION OF CELLS FROM THE BLOOD -early phase (first 24 hours): neutrophilic leukocytes -later phase (after first 24-48 hours): macrophages, lymphocytes and plasma cells 1. ) LEUCOCYTES: Neutrophilic leukocytes remain predominant cell type for several days in acute inflammation. Major events affecting leukocytes in inflammation -margination of neutrophils - in normal blood stream, the leukocytes are mostly confined to axial stream (separated from the endothelial surface by plasma) 5 in dilated vessel in inflammation- the rate of blood flow decreaseserytrocytes form aggregates that displace leucocytes from the centre of axial stream, in combination with a decrease of amount of plasma due to exudation- leukocytes adhere to endothelial surface -pavementing of neutrophils -dilated vessels in acute inflammation are lined by numerous adherent leukocytes (increased adhesiveness of endothelial cells in inflammation)- probably due to activity of chemical mediators of inflammation-process of leukocyte-endothelial cell adhesion is followed by -emigration of neutrophils -leukocytes actively leave the blood vessel by moving through dilated intercellular junctions, pass through basement membrane and reach the extracellular space chemotactic factors- process of active emigrating of leukocytes is governed by chemotactic factors (including C5 complement and various bacterial products), leukocytes have cell surface receptors for chemotactic factors movements of other cells: emigration of 2.) MACROPHAGES and 3.) LYMPHOCYTES is similar to that of neutrophils- chemotactic mediators for macrophagescomplement factor C5 and lymphokines (secreted by lymphocytes) different process - 4.) ERYTHROCYTES enter extracellular space passively - RBCs are pushed out from the blood vessel by hydrostatic pressure- the process is called erythrodiapedesis when large numbers of erythrocytes enter the inflammed area= hemorrhagic inflammation 2- PHAGOCYTOSIS = major mechanism by which leukocytes and macrophages inactivate noxious agents Major events in phagocytosis - recognition and attachment of bacteria by the phagocytic cells either directly (large inactive particles) or after opsonization (antigen is coated by opsonins) - opsonins-Fc fragment of IgG -C3b fragment of complement -for both molecules there are specific receptors on the surface of leukocytes 6 -engulfment - extensions of cytoplasm (pseudopods) flow around the particles - formation of phagocytic vacuole, this vacuole fuses with membrane of lysosomal vacuoles-degranulation of leukocytes -bacterial killing and degradation-killing of bacterial organisms is accomplished by activities of reactive oxygen species -Failure of oxidative metabolism during phagocytosis - leads to a severe disorder of immunity = in chronic granulomatous disease of childhood CONTROL OF RECRUITMENT OF INFLAMMATORY CELLS TO SITES OF INFLAMMATION. - it is now known that interactions can occur between different cells and between cell and connective tissue components - by CAMs- cell adhesion molecules -CAMs are involved in inflammation, cell locomotion, tumor spread, and immune processes -in inflammation- CAMs are within the endothelial cells- can bind to neutrophils and monocytes- some CAMs are present before an inflammatory response, the others are newly produced -in addition monocytes and macrophages and neutrophils have surface adhesion molecules - integrins CHEMICAL MEDIATORS OF INFLAMMATION 1.- mediators originate from plasma or from cells plasma-derived mediators: are present in plasma in precursor forms and must be activated to acquire their biologic activity cell-derived mediators: are normally within intracellular granules (histamine in mast cells) and must be secreted or even synthesized de novo - due to response to specific stimulus 2.- when activated or released from the cell, most mediators are quickly inactivated. Important for balanced and controlled mediator activity, the activity is rapid, specific but short 3.- almost all mediators perform their biologic activities by binding to specific receptor on specific cells MAJOR CLASSES OF MEDIATORS OF INFLAMMATION 7 - can be divided to the following groups according to their activities 1- Vasoactive mediators: histamine and serotonine 2- Plasma proteases: kinin system (bradykinin-kalikrein), complement systém, and coagulation-fibrinolytic system 3- So called AA metabolites (arachidonic acid metabolites): include endoperoxidases, prostaglandins, thromboxane 4- Lysosomal components ( proteases) 5- Oxygen-derived free radicals 6- Platelet activating factors (PAFs) 7- Cytokines 8- Growth factors Vasoactive mediators: „H-substances“ Histamine and serotonin are believed to mediate an immediate active phase of an increase of vessel permeability. In human, histamine is widely distributed (stored in granules of mast cells and blood basophils, in platelets). Different agents can release histamine from mast cells: -physical agents- such as cold, trauma -immunologic reactions, through well known mechanism involving the receptors on the mast cell for IgE -fragments of complement that can induce icrease of permeability of blood vessels (anaphylatoxins) -histamine-releasing interleukin-1 factors of leukocytes and platelet, Function of vasoactive substances: -Histamine- causes dilation of arterioles and in increase of permeability of venules histamine -is rapidly inactivated by histaminase, thus histamine is important mainly in early inflammatory response and in immediate IgE mediated hypersensitivity -Serotonin- second vasoactive mediator, main source of serotoninplatelets, release of serotonin from platelets is stimulated when platelets 8 aggregate after their contact with complex antigen-antibody, with collagen etc. Plasma -derived mediators: a variety of phenomena in acute inflammatory response are mediated by three interrelated systems- kinins, complement, and the clotting system -kinin system -activation of kinin system leads to a release of bradykinin-causes arterial dilatation and increase of permeability of venules, rapidly inactivated by kinases there is multi-step pathway to activate kinin system-system of activation is related to clotting systeme, key role of Hagemann factor XII of coagulation -complement system -consists of several plasma proteins and plays a role both in inflammation and immunity. Complement components ( C1-C9 ) are present in plasma in inactive form „complement cascade“- most important is C3 activation may start either complex antigen-antibody (IgG and IgM)= classic pathway or bacterial polysaccharids and endotoxins= alternative pathway complement system influences: -vascular changes in inflammation -chemotactic effect for monocytes, neutrophils -acts as opsonin-helps in phagocytosis clotting system (coagulation cascade ) coagulation is iniciated by activation of factor XII- Hagemann factor XII - cause activation of series of plasma proteins - the final step is change of fibrinogen to fibrin Platelet-activating factor (PAF) -is a mediator derived from antigen-stimulated basophils that had been sensitized by IgE and cause aggregation of plateles and release of their active constituents, such as histamine and serotonin PAFs are not stored, they are rapidly generated after cell stimulation PAF causes - increase of vessel permeability, increase of leukocyte aggregation and adhesion to endothelium 9 PAFs appear to act directly on target cells but they can also stimulate the synthesis of other mediators, particularly prostaglandins and leukotriens Cytokines-are certain polypeptide products of activated lymphocytes and macrophages refered to as lymphokines and monokines -are involved in cellular response in immune processes, such as lymphocyte proliferation - it has been known for long time, but recently it has become clear that cytokines are involved also in inflammatory response the most important cytokines in inflammation are interleukin I tumor necrosis factor (TNF) = cachectin -because it is thought to be involved also in the cachexia in chronic inflammation and cancer their most important actions in inflammation are -1) local effects on endothelium, such as stimulation of increased adhesion of leukocytes and lymphocytes to endothelium and stimulation of synthesis of PAFs -2) induce the systemic acute inflammatory responses, such as induction of fever, release of ACTH and corticosteroids, release of neutrophils to the circulation, etc. MORPHOLOGIC PATTERNS OF ACUTE INFLAMMATION -Basic patterns of acute inflammatory response depend on severity of noxious agent, severity of reaction, type of tissue involved, site, local circumstances, composition of exsudate etc. Serous inflammation -is characterized by abundant serous fluid (exudate) that is derived either from the blood stream or from the secretory activity of mesothelial cells lining peritoneal, pleural or pericardial cavities, serous exudate is easily removed. Fibrinous inflammation -with more serious injuries, the permeability of blood vessel is greater and more proteins including large molecules of fibrinogen pass the vascular wall. 10 Fibrinous inflammation develops if highly permeable wall let pass the fibrinogen- lots of fibrin in the inflammatory fluid. Fibrin- histologically-eosinophilic meshwork or it may be amorphous. Fibrinous exsudate may be removed-this process is called resolution. When fibrinous exsudate is not removed-fibrin may stimulate the ingrowth of fibroblasts into the blood vessel wall, thus leading to scarring- this process is called organization. Fibrinous exsudate may have more serious consequencies than the serous exsudate. Suppurative or purulent inflammation -is characterized by production of large amounts of purulent exsudate (= pus ). Localized suppuration- caused mainly by staphylococci- pyogenic bacteria acute suppurative appendicitis- common example of purulent inflammation. -Abscess= localized collections of purulent exsudate pyogenic inflammation in the skin-folliculitis (furuncle) -Ulcer = is a local defect in the tissue, mainly in the mucosal or cutaneous surfaces examples: include inflammatory necrosis in mouth, stomach intestines, genitourinary tract or, peptic ulcer of stomach or duodenum, ulcers of the lower extremites due to vascular disorders acute ulcer- intense leukocyte infiltrate and vascular dilatation in the margins chronic ulcer-more developed fibroblastic reaction, infiltration of lymphocytes, macrophages and plasma cells. scarring and SYSTEMIC CLINICAL SIGNS OF ACUTE INFLAMMATION 1) fever- is one of the most prominent features of acute inflammation Fever results either of direct activity of cytokines or through local activity of prostaglandins 2) changes in the peripheral white blood cells -leucocytosis- the total number of neutrophils in the peripheral blood is increased -is common feature especially in bacterial infections 11 -under these circumstances, peripheral blood leukocytes tend to be of the less mature forms with fewer nuclear lobes ( so called „ band forms“) and they often contain large cytoplasmic granules ( so called „ toxic granulation“) the term „ shift to the left“ means the change to increased number of immature neutrophils in peripheral blood Leukocyte count-may reach levels of about 15 or 20 thousands cells per mm3- extreme levels (more than 40 thousand)- referred to as leukemoid reaction Leukocytosis occurs initially because of accelerated release from bone marrow, later proliferation of precursors in bone marrow appears, caused by stimulation by cytokines (colony-stimulating factors) on the other hand- viral infections tend to produce neutropenia (decreased number of leukocytes) with lymphocytosis- excess of lymphocytes in the blood 3) changes in plasma protein levels elevated levels of acute phase reactants, including C-reactive protein, alfa-1-antitrypsin, fibrinogen, ceruloplasmin, etc. incresed erythrocyte sedimentation rate DIAGNOSIS OF ACUTE INFLAMMATION: 1) local cardinal signs of acute inflammation (rubor, calor, dolor, tumor)enable a correct diagnosis when process involves surface structures (skin, mouth mucosa, etc) 2) acute inflammation of internal organs, such as lungs, kidney, liver may first manifest with systemic changes, such as fever, blood cell changes, etc. 12