Inflammation and wound healing -
Although the immunomodulatory effects of the two abovementioned types of cells in the inflammatory period of wound healing can be affirmed, at present, skin grafts are mostly used to seal the wound by using their proliferation and differentiation abilities.
Apligraf ® has been approved as an allograft in several countries for the treatment of acute wounds Randomized controlled trials conducted by Poinas et al.
have shown that biological dressings composed of foetal fibroblasts and keratinocytes show low immunogenicity and high regeneration efficiency, and they are expected to substitute skin allografts Vascular endothelial cells are a barrier and sensor between the circulation and basic tissue and are the key effectors that regulate the entry of circulating immune cells into the inflammatory microenvironment.
Under the stimulation of wound injury signals, circulating immune cells can pass through vascular endothelial cells through the process of capture, slow-rolling, adhesion intensity regulation, intraluminal crawling, and finally cross-cell or paracellular migration, which is a dynamic balancing process 97 , Stimulated by pro-inflammatory factors, endothelial cells express L-selectin, E-selectin, and P-selectin, which bind to ligands LFA-1 and Mac-1 on circulating immune cells These mediate circulating immune cell capture from fast-flowing blood and slow them down as they adhere to endothelial cells.
Subsequently, heterodimer adhesion molecules called integrins, such as intercellular cell adhesion molecule ICAM -1 and ICAM-2, mediate the strong adhesion of circulating immune cells to the vascular endothelium Finally, circulating immune cells crawling on the surface of vascular endothelial cells infiltrate the wound microenvironment through the paracellular pathway under the influence of chemokines In addition, vascular endothelial cells produce many cytokines and chemokines, such as TNF-α, IL-1, and IL-6 Although vascular endothelial cells expressing TLR-2, and TLR-4 can mediate inflammation through NF-κB and MAP kinases, the role of TLRs expressed by these cells in wound healing needs to be further elucidated Figure 4C.
Among a large number of skin substitutes, vascular endothelial cells partially derived from adipose matrix can achieve vascular network regeneration in diabetic wounds, but there is still no study on the mechanism of their immunomodulatory effect The ECM is a complex and dynamic structure that not only acts as a scaffold for cells and tissues but also interacts with cells to produce regulatory signals for cell migration, proliferation, differentiation, and apoptosis ECM components play an important role in every stage of wound healing and are constantly remodelled during the repair process; however, this section focuses on the function of the ECM in the inflammatory microenvironment.
In the case of tissue injury, the temporary matrix formed on the wound provides a scaffold for the infiltration of immune cells. Additionally, the ECM at the edge of the wound can transmit damage signals to immune cells and guide their infiltration.
ECM scaffolds provide mechanical support for cell regeneration and tissue repair, creating a natural microenvironmental niche In , Magnusson et al. The early, temporary matrix is formed immediately after vascular injury and consists of platelets, plasma proteins [such as fibrin, fibrinogen, fibronectin FN , hyaluronic acid HA , heparin sulfate HS ], which infiltrate the wound site, prevent blood loss, and provide a temporary scaffold for subsequent infiltration of immune and repair cells — Subsequently, neutrophils, macrophages, and lymphocytes successively enter the inflammatory microenvironment and establish the late temporary matrix , Fibrin, which is derived from profibrinogen, is the main component of the early temporary matrix and is upregulated in response to injury and inflammation In addition to providing the necessary cellular support for immune cells, fibrin can also bind to integrin receptors on the surface of immune cells to mediate cell migration, such as neutrophils and inflammatory macrophages that bind to fibrin through their αMβ2 integrin receptors As repair progresses, more plasma FN is deposited and becomes the main component of the late temporary matrix , A study of rat skin wounds showed that the level of FN mRNA increased significantly after injury FN can stimulate cell migration and adhesion by connecting actin filaments through integrins It can also activate macrophages to secrete TNF-α, IL-6, and IL-8 Besides, proteoglycan HA and HS are also present in the temporary matrix.
HA increases in early repair stages and can both activate inflammation as a proinflammatory factor and limit inflammatory damage. The former mainly mediates cell migration and increases inflammatory cell infiltration by binding to immune cell surface receptors CD44, ICAM-1 and RHAMM , while the latter eliminates tissue damage caused by inflammation by scavenging free radicals and matrix degrading enzymes The HA content in the foetal wound microenvironment is higher and lasts longer compared to adult wounds, and exogenous HA has a beneficial effect on wound healing HS is a temporary substrate, produces growth factors needed during wound healing,such as fibroblast growth factor, platelet-derived growth factor and transforming growth factor-β And it may play an important role in promoting the migration of neutrophils to the wound site After infiltrating the wound microenvironment through the vascular endothelium, circulating immune cells need to travel through the ECM to reach the edge of the wound and then infiltrate the temporary matrix.
In this process, the ECM structure acts as a scaffold for immune cell adhesion and tissue structure, and produces cytokines, growth factors, and molecules and their derivatives, which promote the activation and migration of immune cells Because epidermal cells are closely bound to the basement membrane, the ECM of the dermis is further explored here.
Mechanical damage and pathogen invasion can cause the decomposition of macromolecular components such as fibrin, adhesive glycoproteins, and glycosaminoglycan in the ECM and release related molecules with pro-inflammatory functions Matrikines are fragments produced by partial proteolysis, and these molecules and their derivatives in the ECM can coordinate the entry of immune cells into the inflammatory microenvironment by remodelling the tissue cytoskeleton and regulating signal transduction At the same time, chemotactic gradients are formed on the wound surface to limit the access of specific cell subsets to the local inflammatory microenvironment Figure 5.
Figure 5 The role of ECM in the inflammatory microenvironment. A The early temporary matrix: mainly fibrin, playing the role of hemostasis and providing scaffold; B The late temporary matrix mainly plasma fibronectin, inducing cell activation and migration; C Dermal ECM: providing support and promoting cell migration.
Based on the importance of the ECM in wound healing, biomaterials simulating ECM have been widely used in the clinic. ECM substitutes provide temporary support and migration sites for cells to close the wound.
Harding et al. reported that a synthetic biomimetic acellular matrix was used as a substitute for ECM in the treatment of refractory leg ulcers, which proved its effectiveness and safety In addition, ECM used to treat diabetic foot ulcers can produce clinical results similar to those of human fibroblast-derived dermal substitutes, but at a lower cost It is worth noting that current research on a variety of biosynthetic materials is inseparable from the composition of the ECM, especially the application of fibrin and collagen.
Although the regulation of the behaviour and fate of immune cells by growth factors and signalling molecules in the ECM has been extensively studied, mechanical signalling is equally important in activating immune cells during tissue regeneration.
The influence of the mechanical signals of the ECM on cell behaviour is mainly mediated by integrin receptors. Integrin is a bidirectional transmembrane receptor composed of α and β subunits When mechanical signals from the ECM generated by tissue injury induce conformational changes in the extracellular domain of integrins, activated integrins activate intracellular signalling pathways to regulate gene expression , Activated integrins recruit a large number of mechanically sensitive proteins such as Talin and Vinculin to assemble into nascent adhesions NAs and deliver a reverse thrust to the ECM via actin.
αDβ2 and αMβ2 are expressed on the cell surface of macrophages and can migrate to inflammatory sites in response to the mechanical stress of the ECM , In addition, activation of mechanically gated ion channels has been shown to play a role in mechanical transduction of immune cells, for example, Piezo1 and instantaneous receptor potential cation channels TRP.
Research shows that Piezo1-deficient macrophages reduce inflammatory cell infiltration during wound healing TRPV4 is the most studied mechanically gated TRP channel and is widely expressed in immune cells.
Activated TRPV4 binds to F-actin to mediate the extravasation of neutrophils and macrophages into injured and inflammatory sites Nuclear expression of YAP and the NF-κB pathway crosstalk up-regulate the expression of pro-inflammatory cytokines in macrophages Therefore, the proliferation and migration of immune cells require the generation and transmission of mechanical forces.
The resting stress on human skin triples during wound healing However, recent studies have found that the rigidity of the ECM environment is more likely to lead to excessive inflammation and scar hyperplasia This idea was supported by skin damage studies in Prickly African mice Acomys , where in high levels of repair were associated with low levels of inflammation associated with resting hypotonia However, some researchers have proposed that the existing models for simulating ECM structural remodeling do not take into account the mechanical plasticity caused by the change of viscoelasticity of ECM with time.
They proposed a discrete model to study the effects of ECM viscoelasticity on matrix remodeling and stress distribution Therefore, in order to simulate the role of physiological ECM in wound healing, the mechanical interaction between cells and ECM should be considered in the synthesis of ECM biomaterials.
Although the efficacy of physical therapy has widely recognised in the clinical treatment of wounds, the regulatory mechanism of this type of therapy has not yet been clearly elucidated.
In addition to mechanical forces, other physicochemical factors of the ECM humidity, temperature, oxygen, and pH also regulate immune responses.
Winter et al. proposed the concept of treating wounds with a moist microenvironment in Maintaining a wet microenvironment for the wound is beneficial to the migration of inflammatory cells , The moist environment created by saliva has been associated with rapid oral wound healing Therefore, after determining and adequately treating the cause of the wound, maintaining moisture in the wound area can better promote healing.
The use of a combination of collagen and foam helps to maintain the moist environment of the wound in patients with venous ulcers of the lower extremities, increase the perfusion of blood and oxygen into the wound, and thus promote angiogenesis The temperature of normally healed wounds peaked 3 days after injury and then gradually decreased , The wound temperature increases due to local dilation of blood vessels, allowing the body to deliver more oxygen and nutrients to the injured area Low temperature may weaken the oxidative killing ability of neutrophils and the motility of macrophages, which may easily lead to wound infection , Infrared light irradiation is a traditional wound care method, its principle is that it can promote blood circulation to accelerate wound healing through heating.
Placing diabetic ulcer patients in a heated warm room can significantly improve the wound healing rate Adequate oxygen is required for phagocytes to produce antibacterial reactive oxygen, so adequate oxygen is crucial for immune cells to phagocytose invading microorganisms , The purpose of oxygen therapy is to provide an oxygen-rich microenvironment for wound healing, such as hyperbaric oxygen therapy, which is widely used in clinic.
However, due to its limitations, researchers are developing a variety of oxygen-producing biomaterials as a source of oxygen release Acidic pH enhances acute inflammatory responses by stimulating the migration and aggregation of neutrophils and macrophages, delaying spontaneous apoptosis, and prolonging the functional life of neutrophils , In contrast, alkaline pH has been shown to adversely affect wound healing by reducing oxygen in the wound and providing an environment conducive to bacterial growth as well as by significantly inhibiting neutrophil motility , Honey has been very popular in wound treatment since ancient times.
The low PH value of honey can increase the oxygenation of the injured site, remove free radicals and promote healing After tissue injury, the platelet cascade reaction activates hemostasis and the complement system, which eventually leads to wound healing in the inflammatory phase.
When circulating immune cells migrate to the inflammatory microenvironment, they must first adhere to vascular endothelial cells and bind to selectins, integrins, or adhesion molecules 30 , This binding is an important condition for the release of TNF-α-mediated neutrophils, which increase vascular permeability They also secrete factors such as thrombin, which promote mast cell migration, proliferation, and local differentiation Neutrophils in the early inflammatory microenvironment recognise damage signals and generate H2O2 gradients through respiratory bursts that initiate an inflammatory cascade.
This process occurs in combination with cytokines and chemokines e. Rapid and transient accumulation of PDCs recruited by damaged keratinocytes occurs in parallel with increased neutrophil infiltration Subsequently, mast cells are recruited and release trypsin-like enzymes, which bind to the protease-activated receptor 2 on endothelial cells, causing vasodilation and further amplification of the inflammatory response 5.
This series of reactions promotes the accumulation of M1 macrophages in the injured site and plays a role in the phagocytosis of apoptotic cells and pathogens. Meanwhile, LCs anchored to adjacent keratinocytes by the adhesion molecule E-cadherin migrate from the epidermis to the dermis in response to CXCL12 from dermal fibroblasts and MCP-1 from keratinocytes 40 , 44 , , They provide antigens to the immune response of memory T cells, which are recruited by CCL27 and produced by activated keratinocytes in the skin However, a dynamic balance in the inflammatory response is necessary for active wound healing Tregs can restrict the aggregation of pro-inflammatory macrophages, and M1 macrophages engulf apoptotic immune cells, indicating a transition from the inflammatory to the proliferative microenvironment of the wound surface Figure 6.
Figure 6 Dynamic network of cell-cell interactions in an inflammatory microenvironment. The ECM constitutes a place for tissue repair following trauma, and its macromolecules and their derivatives can regulate the activation and migration of inflammatory cells as well as the proliferation and differentiation of repair cells.
The ECM component HS participates in immune cell migration and regulates the secretion of cytokines, chemokines, and growth factors HA is involved in the regulation of macrophage phenotype Fibrin and FN mediate monocyte migration and secretion of TNF-α, IL-1β, and IL-6 and stimulate the migration and adhesion of fibroblasts, keratinocytes, and endothelial cells through integrin receptors , Various factors and enzymes released by activated cells can constantly supplement and reshape the components of the ECM , Matrix metalloproteinases and other enzymes released by activated inflammatory cells can expose the migration sites of the ECM by cleavage of the basement membrane The release of toxic particles by neutrophils causes the rapid degradation of fibrin by plasmin and elastase, and the degradation products can induce or amplify the inflammatory process The factors and proteins expressed by repair cells can fill the defects in the ECM and supplement the cell factor library of the ECM.
The ECM and its derivatives help to regulate the biological function of cells in the microenvironment, while factors, enzymes, and proteins secreted by cells modify the components of the ECM to form a dynamically balanced inflammatory microenvironment for wound healing. There are many kinds of ECM biomimetic materials for simulating wound repair that are rapidly being developed.
The incorporation of fibrinogen and collagen I into biomimetic coaxial nano-scaffolds to solve wound inflammation significantly promoted wound repair Taking advantage of the ECM scaffold potential, the ECM modified with silver nanoparticles nAg has both antibacterial and tissue regeneration abilities However, the ECM is constantly being supplemented and reshaped, and the dynamic adjustment of the composition of the ECM to simulate the microenvironment needs further research and exploration.
Active wound healing depends on an orderly and moderate immune response regulated by inflammatory cells, non-inflammatory cells, and the ECM. Disruption of any of these links can lead to persistent inflammation and prevent the repair process, leading to the occurrence of chronic wounds such as chronic venous ulcers, diabetic foot ulcers, and pressure sores.
These chronic wounds occur in the context of venous hypertension, diabetes, or angiopathy caused by prolonged tissue pressure The destruction of vascular endothelial cells reduces the amount of blood perfusion to the wound area and causes tissue hypoxia At the same time, the number of platelet-derived microvesicles in peripheral blood increases, and these microvesicles are internalised by vascular endothelial cells, thus up-regulating the expression of intercellular adhesion molecule-1 and resulting in more immune cells extravasating to the injured site Although a large number of pro-inflammatory M1 macrophages are activated, phagocytosis of apoptotic neutrophils by these macrophages is inhibited, resulting in a disturbance in the process of macrophage polarization — With increase in the number of degranulated mast cells, a sustained inflammatory response is eventually achieved The inflammatory cascade continues to cause the activation and accumulation of T cells, especially that of Th17 cells.
Th17 cells secrete IL to maintain the activity of M1 macrophages, leading to persistent inflammatory wound healing On the contrary, increasing the number of LCs in the wound of diabetic mice has been shown to improve healing A large number of pro-inflammatory factors increased the release of MMPs and accelerated the degradation of the ECM, which further reduced the proliferation and collagen deposition of fibroblasts 4 , In this pathological inflammatory microenvironment, inflammatory genes expressed by fibroblasts are up-regulated and keratinocytes release IL-1α and type I interferon, triggering an inflammatory chain reaction in adjacent stromal cells 92 , This, in turn, promotes the flow of immune cells into the injured site.
In summary, the delay of chronic wound healing can be attributed to the failure of ECM remodelling caused by the uncontrolled immune regulation of inflammatory and non-inflammatory cells. We briefly reviewed the effects of the interaction of inflammatory cells, non-inflammatory cells, and the ECM on the inflammatory microenvironment of skin wounds.
The spatial coexistence of functionally specialised cell types is a basic feature of multicellular organisms, and the different anatomical locations and degrees of interaction with other cells determine the functional differences in similar cells during the process of wound healing i.
cellular heterogeneity. For example, before circulating macrophages arrive, some tissue resident macrophages are already involved in the inflammatory response Although different fibroblast subsets in human skin have been revealed, the unique gene expression changes in this population in skin wounds, especially in the inflammatory microenvironment, remain unknown In addition, a wide range of cell types in wounds have significant plasticity under the influence of the ECM, which complicates the dynamic study of different cell subsets and their effects on wound healing.
Single cell technology and space transcriptome technology, which are widely used because of the development of genomics technology, can solve the above problems step by step. The development and application of multiple sequencing technology can realise the unsupervised analysis of interactions among different cell types in skin wounds on the basis of restoring the spatial characteristics of tissue structure in vivo Correct and coordinated actions in the inflammatory microenvironment ensure proper wound healing.
However, when this process is disrupted, skin healing is delayed, which eventually leads to chronic wounds. Compared with acute wounds, marrow-like cells neutrophils and macrophages in chronic wounds exist in large numbers for a long time, accompanied by the degranulation of mast cells and high expression of inflammatory T cell subtypes The signal molecules and proteases secreted by these immune cells can also lead to the over-expression of pro-inflammatory cytokines and chemokines and continuous degradation of the ECM in non-inflammatory cells such as keratinocytes Although many research groups have successfully promoted healing by regulating inflammatory cells, it is possible to induce an inappropriate immune response by directly regulating the immune system.
Therefore, designing functional regulation based on non-inflammatory cells and the ECM provide a potential therapeutic approach for chronic wound healing. Understanding the inflammatory microenvironment of skin wounds will help to develop a comprehensive understanding of the processes affecting wound healing.
This information can provide personalised guidance for the strict control of wound immune response. In particular, research on the immune function of non-inflammatory cells and the ECM in wounds may reveal new strategies for the clinical development of innovative wound treatments.
Several studies have shown that the inflammatory microenvironment is composed of inflammatory cells, non-inflammatory cells, and the ECM, which collaborate to scavenge necrotic cell fragments and prevent infection.
The activation of repair-related cells promotes wound healing through the secretion of cytokines that lead to the proliferation stage. However, there is a need for further evidence to support the interactions between non-inflammatory cells and the ECM, which are involved in the immune regulation of the inflammatory microenvironment.
Additionally, the functional advantages of all the inflammatory factors that control the inflammatory response needs to be elucidated. As the evidence that the reduction of inflammation can promote wound healing comes from the study of inflammatory cells, it is not clear whether the regulation of non-inflammatory cells and ECM can achieve the same or perhaps even a better immunomodulatory effect.
Literature search and manuscript drafting, ZW and GX. Figures, ZW and HL. Manuscript editing and revision, GX, FQ, and DW. All authors contributed to the article and approved the submitted version. This work was supported by the National Natural Science Foundation of China [grant numbers and ], the Science and Technology Plan Project of Guizhou Province [grant numbers 4Y], the PhD Fund of Scientific Research Foundation of Affiliated Hospital of Zunyi Medical University[grant numbers ], and the Chinese Ministry of Education [grant numbers ].
The authors declare that the research was conducted in the absence of any commercial or financial relationships that could be construed as a potential conflict of interest.
All claims expressed in this article are solely those of the authors and do not necessarily represent those of their affiliated organizations, or those of the publisher, the editors and the reviewers.
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pdf Russell Childs. Recently uploaded 20 Inflammation and Healing wound healing 1. INDEX 1. CAUSES The agents causing inflammation may be as under: 1. Physical agents like heat, cold, radiation, mechanical trauma.
Chemical agents like organic and inorganic poisons. Infective agents like bacteria, viruses , and their toxins.
Immunological agents like cell-mediated and antigen- antibody reactions. Thus inflammation is distinct from infection — the former is the protective response by the body while the latter is invasion into the body by harmful microbes and their resultant ill effects by toxin.
Inflammation involves two processes: a inflammatory response b healing. Redness 2. Swelling 3. Heat 4. Pain 5.
Loss of function. Acute inflammation is a short duration and represents the early body reaction and is usually followed by repair. The main features of acute inflammation are: a accumulation of fluid and plasma at the affected site. b intravascular activation of the platelets c polymorphonuclear neutrophils as inflammatory cells.
Chronic inflammation is of longer duration and occurs either after the causative agent of acute inflammation persists for a long time or the stimulus is such that it induces chronic inflammation from the beginning.
The characteristic feature of chronic inflammation is presence of chronic inflammatory cells such as lymphocytes plasma cells and macrophages. Vascular events 2. Cellular events Vascular events Alteration in the microvasculature is the earliest response to tissue injury.
These alterations include : a Haemodynamic changes b Changes in vascular permeability. A Haemodynamic changes — the earliest features of inflammatory response result from changes in the vascular flow and calibre of small blood vessels in the injured tissues. The sequence of these changes is as under: 1.
Irrespective of the type of injury immediate vascular response is of transient vasoconstriction of arterioles. With mild form of injury the blood flow may be re-established in secs while with more severe injury vasoconstriction last for about 5 mins.
Next follows persistent progressive vasodilatation which involves mainly the arterioles. Vasodilatation results in increased blood volume in microvascular bed of the area which is responsible for redness and warmth at the site of acute inflammation.
Progressive vasodilatation in turn may elevate local hydrostatic pressure resulting in transudation of fluid into extracellular space. This is responsible for swelling at local site. Slowing or stasis of microcirculation occurs. Slowing is attributed to increased permeability of microvasculature the results in increased concentration of red cells.
Stasis or slowing is followed by leucocytic margination or peripheral orientation of leucocytes along the vascular endothelium after this these move and migrate through gaps between endothelial cells into. the extravascular space.
This process is called as emigration. The reaction elicited is known as triple response or red line response consisting of following : 1. Red line appears within a few seconds following stroking and results from local vasodilatation of capillaries and venules.
Flare is the bright reddish appearance or flush surrounding the red line and results in vasodilatation of adjacent arterioles. Wheal is the swelling or edema of the surrounding skin occuring due to transudation of fluid into the extravascular space.
In the initial stage the escape of fluid is due to vasodilatation and consequent elevation in hydrostatic pressure. This is transudate in nature. The presence of edema due to increased vascular permeability of microvascular bed. The endothelial cells develop temporary gaps between them due to their contraction resulting in vascular leakiness.
This change too affects the venules and is mediated by cytokines such as interleukin Process of thrombosis is intiated at the site of endothelial cells. The activated leucocytes release proteolytic enzymes and toxic oxygen species which may cause increased vascular leakiness and endothelial injury.
CELLULAR EVENTS The cellular phase of inflammation consists of 2 processes: 1. Exudation of leucocytes 2. Phagocytosis 1. Exudation of leucocytes- the escape of leucocytes from the lumen of microvasculature to the interstitial tissue is the most important feature of inflammatory response.
the acute inflammation includes first line of body defense followed by monocytes and macrophages. The changes leading to migration of leucocytes are: a Changes in the formed elements of blood- in the early stage of inflammation the rate of flow of blood is increased due to vasodilatation.
But subsequently there is slowing of blood stream. due to slowing and stasis the central stream of cells widens and peripheral plasma zone becomes narrower because of loss of plasma by exudation.
This phenomenon is known as margination. b Rolling and adhesion- Peripherally margination and pavemented neutrophils slowly roll over the endothelial cells lining the vessel walls. This is followed by transient bond between the leucocytes and endothelial cells becoming firmer.
It includes 3 phases: 1 selectins 2 integrins 3 immunoglobulins superfamily adhesion molecules c Emigration —after sticking of neutrophils to endothelium the former move along the endothelial cells is found where the neutrophils throw out cytoplasmic pseudopods.
Subsequently the neutrophils lodged between the endothelial cells and basement membrane cross the basement membrane by damaging it locally with secreted collagenases and escape into the extravascular space this is known as emigration. d Chemotaxis-The chemotactic factor cytokines, platelet factor etc mediated transmigration of leucocytes after crossing several barriers endothelium, basement membrane , etc to reach the interstitial tissues is called chemotaxis.
Phagocytosis-phagocytosis is defined as the process of engulfment of solid particulate material by the cells cell-eating. The cells performing this function are called phagocytes.
There are mainly two types of phagocytic cells: a Polymorphonuclear neutrophils PMNs which appear early in acute inflammatory response also called as microphages. b Circulating monocytes and fixed tissue mononuclear phagocytes called macrophages.
The process of phagocytosis is similar for both polymorphs and macrophages and involves the following 4 steps: 1. Recognition and attachment stage opsonisation 2. Engulfment stage 3. Secretion stage 4. Digestion or degradation stage. However, currently many chemical mediators have been identified which partake in other processes of acute inflammation as well eg: vasodilatation , chemotaxis, fever, pain etc.
The substances acting as chemical mediators of inflammation may be released from the cells , the plasma, or damaged tissue itself. They are broadly classified into 2 groups: 1 Mediators released by cells 2 Mediators originating from plasma.
histamine and serotonin. The main action of histamine are vasodilatation , increased vascular permeability, itching, and pain. Stimulation of mast cells and basophils also releases products of arachidonic acid metabolism including release of slow-reacting substances of anaphylaxis.
Serotonin is less potent mediator of increased vascular permeability and vasodilatation than histamine. b Arachidonic acid metabolites-arachidonic acid is fatty acid, eicosatraenoic acid and it has two main sources i. from diet directly and conversion of essential fatty acids c Lysosomal components-the inflammatory cells neutrophils and monocytes contain lysosomal granules which on release elaborate a variety of mediators of inflammmation.
d Platelet activating factor PAF - it is released from IgE- sensatised basophils or mast cells endothelium and platelets. They increase vascular permeability , vasodilatation in low concentration , bronchoconstriction, chemotaxis e Cytokines.
Each of these systems has its inhibitors and accelerators in plasma with negative and positive feedback mechanisms respectively.
Such self damaging effects are kept in check by the host mechanisms so as to resolve inflammation. Mechanisms are: a Acute phase reactants-these are released in plasma in response to tissue trauma and infection.
These are mainly synthesised in liver and to some extent in macrophages. b Corticosteroids — glucocorticoids act as anti inflammatory agents.
c Free cytokine receptors- cytokines in serum correlates with disease activity. d Suppressor T cells- prohibition of suppressor t cells is seen which inhibits the function of T and B cells. e Anti-inflammatory chemical mediators-it has an anti- inflammatory action. as a result of denudation of epithelium , plasma exudes on the surface where it coagulates and together with necrosed epithelium.
ULCER- ulcers are local defects von the surface of an organ produced inflammation. Common sites for ulceration are the stomach, intestinal ulcers in typhoid fever , ulcers of legs.
in the acute stage there is infiltration by polymorphs with vasodilatation while long standing ulcers develop infiltration by lymphocytes and macrophages. A cavity is formed which is called abscess and contains a pus and process of abscess formation is called suppuration.
FEVER- occurs due to bacteraemia. It is thought be mediated through release of factors like prostaglandins, interleukins and tumor necrosis factor in response to infection. Typhoid fever is an acute inflammation however induces leucopenia with relative lymphocytosis.
The lyphatics and lymph nodes that drain the inflamed tissues show reactive inflammatory changes in the form of lymphangitis. SHOCK- It may occur in severe cases. Massive release of cytokine a mediator of inflammation in response to severe tissue injury results in profuse systemic vasodilatation , increased vascular permeability and intravascular volume loss.
The net effect of these changes is hypotension and shock. This occur when tissue changes are slight and cellular changes are reversible. HEALING-This takes place when tissue destruction in acute inflammation is extensive so that there is no tissue regeneration but there is actually healing by fibrosis.
Intially there is intense neutrophillic infiltration. Causes: 1. Chronic inflammation following acute inflammation —when the tissue destruction is extensive or the bacteria survive and persist in small numbers at the site of acute inflammation.
Recurrent attacks of acute inflammation- when repeated bouts of acute inflammation culminate in chronicity of the process e. recurrent urinary tract infection. Chronic inflammation starting de novo- when the infection with organism of low pathogenicity is chronic from the beginning.
infection with Myobacterium tuberculosis. The blood monocytes on reaching the extravascular space transform into tissue macrophages. besides the role of macrophages in phagocytosis they may get activated in response to stimuli such as cytokines.
This is brought by activated macrophages which release a variety of biologically active substances. protease, lipase. Eventually healing by fibrosis and collagen laying takes place. FEVER-Invariably there is mild fever often with loss of weight and weakness.
ANAEMIA-Chronic inflammation is accompanied by anaemia of varying degree. ESR- It is elevated 5. NON-SPECIFIC-When the irritant substance produces a non-specific chronic inflammatory reaction with formation of granulation tissue and healing by fibrosis , like chronic ulcer.
SPECIFIC-When injurious agent causes a characteristic histologic tissue response like, tuberculosis. HEALING Injury to tissue may result in cell death and tissue destruction.
Healing on the other hand is the body response to injury in an attempt to restore normal structure and function. The process of healing involves 2 processes: 1. Regeneration-when healing takes place by proliferation of parenchymal cells and usually results in complete restoration of the original tissue.
An is Energy-boosting foods standard, initial owund of the Muscle building tips to injury. Whether biological, chemical, physical, or radiation burns, all injuries lead to wounv Inflammation and wound healing sequence of physiological events. Inflammation limits the extent of injury, partially or fully eliminates the cause of injury, and initiates repair and regeneration of damaged tissue. Necrosisor accidental cell death, causes inflammation. Apoptosis is programmed cell death, a normal step-by-step process that destroys cells no longer needed by the body. Wound healing refers amd a living Boost thermogenesis naturally replacement of helaing or damaged Inflammation and wound healing by woubd produced tissue. In undamaged Inflammation and wound healing, an epidermis surface, epithelial layer and Energy-boosting foods deeper, connective layer form Fat loss for busy individuals protective barrier against the external environment. When the barrier is broken, a regulated sequence of biochemical events is set into motion to repair the damage. Blood clotting may be considered to be part of the inflammation stage instead of a separate stage. The wound-healing process is not only complex but fragile, and it is susceptible to interruption or failure leading to the formation of non-healing chronic wounds.
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