Week 2 Fusion Session TBL Acute Inflammatory Response & Complement PDF

1/25/24, 12:55 AM Week 2: Fusion Session | TBL: Acute Inflammatory Response & Complement: Hemtlgy Onclgy Infectn Imm - January 2024 Many different types of injury (immunological insult) can trigger inflammation: these can be physical, chemical, biological, or even psychological. See the table belo...

1/25/24, 12:55 AM Week 2: Fusion Session | TBL: Acute Inflammatory Response & Complement: Hemtlgy Onclgy Infectn Imm - January 2024 Many different types of injury (immunological insult) can trigger inflammation: these can be physical, chemical, biological, or even psychological. See the table below (Table 1) for further descriptions of the types of immunological insults that exist. In this activity, we will focus on the acute inflammatory process; further types of inflammatory responses will be addressed in a separate series of activities provided by your pathologists (e.g., more detailed cellular responses, responses to chemicals, trauma, chronic inflammation, aseptic, septic, tissue repair, etc.). Noninfectious causes Infectious causes Physical: Burn Frostbite Physical trauma Foreign bodies Radiation Chemical: Glucose Fatty acids Viruses Bacteria Toxins Alcohol Chemical irritants (incl. fluoride, Fungi Protozoans Helminths nickel, & other trace elements) Arthropods (e.g., insects & mites) Biological: Damaged cells Excitement Psychological: Stress Top Inflammation is a quintessential process required by the immune system to perform its functions effectively and efficiently. All immune responses occur in the context of inflammation in one way or another; it is the environment in which leukocytes perform at their best (by increasing the https://rossmed.instructure.com/courses/3318/pages/week-2-fusion-session-%7C-tbl-acute-inflammatory-response-and-complement 10/71 1/25/24, 12:55 AM Week 2: Fusion Session | TBL: Acute Inflammatory Response & Complement: Hemtlgy Onclgy Infectn Imm - January 2024 expression of heat-shock proteins that enhance the effectiveness of leukocyte receptors & leukocyte function, & promoting the recruitment of leukocytes & the infiltration of soluble inflammatory mediators such as acute-phase reactants at the site of injury), whether occurring during innate or adaptive (acquired) immune responses. Inflammation provides an environment conducive to dealing with the injury by way of: 1. production, release, and accumulation of soluble inflammatory mediators (cytokines, complement, histamine, eicosanoid lipid mediators such as prostaglandins & leukotrienes, bradykinin, etc.) in the affected site. 2. leukocyte activation and recruitment to the site of injury, all of which are facilitated by microvascular events (increase in vascular permeability & leakage) initiated by the inflammatory response near or at the site of injury. As a result of these microvascular and inflammatory events, affected tissues swell and become erythematous (redness) and warm, which is accompanied by sensations of pain and/or pruritus (itching) and, sometimes, loss of function, thus the cardinal signs of inflammation: rubor, calor, dolor, tumor (& functio laesa). Swelling, warmth, and redness come from the influx of fluid into the affected tissue, whereas the pain and itching come from the stimulation of sensory neurons in the affected tissue (histamine stimulates itching sensation, bradykinin & prostaglandins stimulate pain, and swelling stimulates baroreceptors). It is important to consider that (1) inflammation occurs locally (restricted region of the body, e.g., sprain) and that often inflammation occurs both locally and systemically (locally and throughout the whole body, e.g., viral infections). We will address these somewhat separately. Watch these videos: Acute Inflammation | Immunology (https://www.youtube.com/watch? v=opFQgz7d1Wg) The Inflammatory Response (https://www.youtube.com/watch? app=desktop&v=qCpWXPSMBIY) The Inflammatory Response (https://www.youtube.com/watch? v=Fbzb75HA9M8) Top  Local Inflammation https://rossmed.instructure.com/courses/3318/pages/week-2-fusion-session-%7C-tbl-acute-inflammatory-response-and-complement 11/71 1/25/24, 12:55 AM Week 2: Fusion Session | TBL: Acute Inflammatory Response & Complement: Hemtlgy Onclgy Infectn Imm - January 2024 Cognition: The Inflammasome and Pathogen Recognition Receptors The first step in dealing with injury is recognizing that there is a problem in the first place. This is achieved through the convergence and integration of information initiated by at least two different signals: 1. injury detection by Pathogen Recognition Receptor (PRR)-containing inflammasomes and 2. detection of injury by signaling PRRs engaged by Pathogen-Associated Molecular Patterns (PAMPs – e.g., LPS, peptidoglycan, flagellin, viral RNA, CpG DNA, etc.) or Damage-Associated Molecular Patterns (DAMPs – also referred to as DangerAssociated Molecular Patterns (e.g., extracellular uric acid, ATP, histones, S100 proteins, heat-shock proteins, mitochondrial DNA, calreticulin, high-mobility group box proteins & many more…); alarmins and stressorins act in a similar way to DAMPs, but these signal through specific receptors and we will only discuss one alarmin, IL-33, since it is important in the activation of mast cells in response to tissue injury. Top https://rossmed.instructure.com/courses/3318/pages/week-2-fusion-session-%7C-tbl-acute-inflammatory-response-and-complement 12/71 1/25/24, 12:55 AM Week 2: Fusion Session | TBL: Acute Inflammatory Response & Complement: Hemtlgy Onclgy Infectn Imm - January 2024 Rjoo317 (https://commons.wikimedia.org/wiki/File:3_Models_of_NLRP3_Inflammasome_Activation.png) , CC BY-SA 3.0 (https://creativecommons.org/licenses/by-sa/3.0) , via Wikimedia Commons The inflammasome is a multiprotein complex found in the cytosol of many cells (especially monocyte-derived phagocytic cells like monocytes, macrophages, & dendritic cells), and its function is to activate a caspase which is required for the proteolytic activation of the inactive precursor of InterLeukin-1-beta (IL-1ß) (or IL-18, more for intracellular pathogens, but we will focus on IL-1ß for the purpose of this discussion; also, just so you know, interleukins derive their name from their capacity to mediate inter-leukocyte communication…). The structure of the inflammasome is such that several inactive caspase subunits become activated following juxtaposition with several scaffold sensor subunits, usually Nucleotide-binding Oligomerization Domain-like Receptors (NOD-Like Receptors or NLRs), through the action of Apoptosisassociated Speck-like protein containing a CARD (ASC or PYCARD) adaptor proteins; upon engagement by a ligand (whole organism, PAMPs, or DAMPs), NLRs are activated and oligomerize to initiate the recruitment and clustering of ASC, which in turn allows for the recruitment and clustering of procaspases which are then activated by autocleavage (juxtaposed procaspase dimers cleave one another), with the resulting activated caspases free to go cleave their substrate, pro-IL-1ß or pro-IL-18. Pathway Activation Inactive IL-1ß (pro-IL-1ß) (or pro-IL-18) synthesis on the other hand, results from PRR engagement by PAMPs. For example, engagement of Toll-Like Receptors (TLRs) by PAMPs will activate the Nuclear Factor-kappa B (NF-κB) signaling pathway (further discussed in the ‘Cytokines, Chemokines, & Signaling’ activity). Nuclear factor-kappa B transcription factor DNA binding to the promoter/enhancer regions of the IL-1ß (or IL-18) gene will recruit RNApol II to yield pro-IL-1ß (or pro-IL-18) mRNA transcription. The mRNA is then translated into inactive proIL-1ß. For your information only, other PRRs, such as NLRs, also activate the NF-κB pathway, whereas Scavenger Receptors (SRs) signal through tyrosine kinases and Protein Kinase C (PKC). Top https://rossmed.instructure.com/courses/3318/pages/week-2-fusion-session-%7C-tbl-acute-inflammatory-response-and-complement 13/71 1/25/24, 12:55 AM Week 2: Fusion Session | TBL: Acute Inflammatory Response & Complement: Hemtlgy Onclgy Infectn Imm - January 2024 Watch these videos: Inflammasome (https://www.youtube.com/watch?app=desktop&v=- FNFZ9F1eB4) TLRs (https://www.youtube.com/watch?v=GXECgTLGLtI) Release of Inflammatory Mediators Top Consequently, the initial release of IL-1ß (i.e., the initiation of the inflammatory response) requires two processes to occur simultaneously: 1. synthesis of pro-IL-1ß and https://rossmed.instructure.com/courses/3318/pages/week-2-fusion-session-%7C-tbl-acute-inflammatory-response-and-complement 14/71 1/25/24, 12:55 AM Week 2: Fusion Session | TBL: Acute Inflammatory Response & Complement: Hemtlgy Onclgy Infectn Imm - January 2024 2. caspase activation. Once both have occurred, caspases can activate pro-IL-1ß by cleavage into biologically active IL-1ß. Once released by the stimulated cell, IL-1ß will engage its receptor on the surface of other cells and trigger the activation of IL-1ß-responsive genes, resulting in the synthesis and release of more IL-1ß, as well as numerous other pro-inflammatory factors. Engagement of the InterLeukin-1-Receptor (IL-1R) on the surface of macrophages triggers the NF-κB pathway (this pathway again…), with cross-talk with the Mitogen-Activated Protein Kinase (MAPK) pathway; the combined effect of these two pathways yields the activation of the two following transcription factors: NF-κB and Activator Protein 1 (AP-1, which are c-jun/c-fos homo or heterodimers). Activation of these transcription factors leads to the synthesis and release of the following proinflammatory cytokines, chemokines, and inflammatory mediators in the inflammatory cascade, namely Tumor Necrosis Factor-alpha (TNF-α), IL-6, CXCL8 (IL-8), as well as LeukoTrienes (LT and prostaglandins) and adhesion molecules among others. Top https://rossmed.instructure.com/courses/3318/pages/week-2-fusion-session-%7C-tbl-acute-inflammatory-response-and-complement 15/71 1/25/24, 12:55 AM Week 2: Fusion Session | TBL: Acute Inflammatory Response & Complement: Hemtlgy Onclgy Infectn Imm - January 2024 The importance of these events can be illustrated by the amount of anti-inflammatory drugs and biologicals (mostly monoclonal antibodies) currently on the market. The accompanying figure below shows a subset of these treatment options and some of the diseases they are meant to treat. At this stage, you are not required to learn the drugs and biologicals listed or the diseases they are used to treat, for that matter; this will come in later Pharmacology lectures. Gain of function of elements of the inflammasome is involved in many autoimmune diseases. Transcript Top Inflammatory Allergy Asthma C t ki l d https://rossmed.instructure.com/courses/3318/pages/week-2-fusion-session-%7C-tbl-acute-inflammatory-response-and-complement 16/71 1/25/24, 12:55 AM Week 2: Fusion Session | TBL: Acute Inflammatory Response & Complement: Hemtlgy Onclgy Infectn Imm - January 2024 Cytokine release syndrome Multicentric Castleman disease Autoimmune Rheumatoid arthritis Systemic lupus erythematosus Crohn disease Psoriasis Ankylosing spondylitis Systemic juvenile idiopathic arthritis Giant cell arteritis Autoinflammatory Neonatal-onset multisystem inflammatory disease Familial Mediterranean fever Cryopyrin-associated periodic syndromes (Hereditary period fevers) Leukocyte Recruitment and Hemodynamic Changes Coordination of these inflammatory mediators, coupled with the effects of soluble complement fragments 5a and 3a (C5a & C3a – see The Complement System Handout and Study Guide), work on the microvasculature (postcapillary veinules) to induce vascular permeability and vascular leakage (endothelial cell activation & transendothelial migration), which allows the influx of leukocytes (mainly neutrophils and monocytes during an innate response, & lymphocytes & other leukocytes during the acquired stage) and the infiltration of more soluble inflammatory mediators to the injured site. The resulting vasodilation and fluid influx produce the swelling that is characteristic of inflammation. In addition to these events, inflammation also initiates the extrinsic coagulation pathway and microvascular thrombosis, as well as the kallikrein-kinin system (bradykinin) to further enhance the inflammatory response. Top https://rossmed.instructure.com/courses/3318/pages/week-2-fusion-session-%7C-tbl-acute-inflammatory-response-and-complement 17/71 1/25/24, 12:55 AM Week 2: Fusion Session | TBL: Acute Inflammatory Response & Complement: Hemtlgy Onclgy Infectn Imm - January 2024 Transcript Local inflammation triggers a complex interplay between the immune response and coagulation pathways, where inflammatory signals can induce clotting mechanisms, influencing immune cell recruitment and tissue repair. In the absence of infection, cellular injury releases DAMPs, which attract tissue-resident phagocytic cells, e.g., macrophages, that home into the site of injury and initiate the inflammatory process described above. Additionally, cellular injury triggers the release of the Top nuclear cytokine IL-33 (IL-1 family), whose main target is mast cells, which are important in inflammatory processes. During infections, bacteria release chemotactic peptides (e.g., Nformylmethionyl-leucyl-phenylalanine or fMLF, fMLP, or N-formyl-met-leu-phe – all synonyms) which attract neutrophils and activate macrophages; furthermore, activation of complement by https://rossmed.instructure.com/courses/3318/pages/week-2-fusion-session-%7C-tbl-acute-inflammatory-response-and-complement 18/71 1/25/24, 12:55 AM Week 2: Fusion Session | TBL: Acute Inflammatory Response & Complement: Hemtlgy Onclgy Infectn Imm - January 2024 microbial surfaces further enhances phagocytic cell recruitment since C3a and C5a are chemotactic. Release of macrophage-derived proinflammatory mediators such as IL-1β, IL-6, TNF-α, CXCL8, LTB4, and prostaglandins following the initial release of IL-1β sets the stage for the initiation of acute inflammation and has multiple effects on the affected tissue. We will now discuss some of these effects. Tumor necrosis factor α and prostaglandin release by macrophages induce the vasodilation of postcapillary veinules; vasodilation is further enhanced by the release of histamine, prostaglandins, and more TNF-α by mast cells activated by IL-33, C3a, C5a, and/or PAMPs. With a similar blood volume passing through a vessel of greater diameter, blood flowing nearer the endothelial walls slows down (by some estimates, about 40 μm/s near the endothelial walls, as compared to the blood flow in the middle part of the vessel which remains greater at about 4,000 μm/s) and cells tend to slow down and marginate (further helped by erythrocyte margination of leukocytes). Rolling and tethering: At a distance, IL-1β, TNF-α, and histamine stimulate the expression of selectins and their ligands on endothelial cells and circulating leukocytes (e.g., s-Lex, P- & Eselectins on endothelial cells, & L-selectin, PSGL-1 & ESL-1 on leukocytes) thus begins the cell tethering and rolling process. Arrest, adhesion, and migration: In closer proximity, CXCL8 (via CXCR1 or CXCR2, the CXCL8 receptors on leukocytes) stimulates the expression of high-affinity integrins on circulating leukocytes (LFA-1, Mac-1, VLA-4, PECAM-1, & CD99) and their respective ligands on endothelial cells (ICAM-1, ICAM-2, VCAM-1, PECAM-1, & CD99), and leukocytes further slow down, stop rolling, and begin crawling on the surface of the endothelial wall. Vascular permeability: Leukocytes then begin breaching through endothelial cell borders by disrupting adherens junctions and tight junctions (although tight junctions are few and somewhat loose between endothelial cells, except for the blood-brain barrier…). Engagement of integrin receptors (ICAM-1 & VCAM-1), along with endothelial cell stimulation by TNF-α, histamine, bradykinin, and prostaglandins, induce signaling events that disrupt vascular endothelial specific cadherin (VE-cadherin) and opens up adherens junctions. There is also evidence that leukocytes can pass through endothelial cells directly (transcellular migration, especially at the blood-brain barrier – different mechanism, obviously, and possibly because blood-brain barrier endothelial cells contain more tight junctions). Either way, transmigration (syn. diapedesis or extravasation) is initiated. Top https://rossmed.instructure.com/courses/3318/pages/week-2-fusion-session-%7C-tbl-acute-inflammatory-response-and-complement 19/71 1/25/24, 12:55 AM Week 2: Fusion Session | TBL: Acute Inflammatory Response & Complement: Hemtlgy Onclgy Infectn Imm - January 2024 Transcript Leukocytes cross the vascular endothelium through a multistep process that includes rolling, adhesion, crawling, and transmigration, which enables them to leave the bloodstream and reach sites of infection or inflammation. Top Homing: Once transmigration has occurred, leukocytes migrate along the extracellular matrix by following the chemotactic gradients provided by CXCL8, C3a, C5a, TNF-α, and other chemotactic factors. https://rossmed.instructure.com/courses/3318/pages/week-2-fusion-session-%7C-tbl-acute-inflammatory-response-and-complement 20/71 1/25/24, 12:55 AM Week 2: Fusion Session | TBL: Acute Inflammatory Response & Complement: Hemtlgy Onclgy Infectn Imm - January 2024 Watch this video: Extravasation (https://www.youtube.com/watch? app=desktop&v=Sv66abGd6xA) Interplay Between the Acute Inflammatory Response and Coagulation Pathways There is a strong interrelationship between the acute inflammatory response and the extrinsic coagulation pathway you have seen in Biochemistry, whereby the acute inflammatory response activates the extrinsic coagulation pathway, and the extrinsic coagulation pathway enhances the acute inflammatory response. Tumor necrosis factor α and IL-1β stimulate the expression of tissue factor (TF) on the surface of endothelial cells, monocytes, and macrophages. Tissue factor interaction with factor VII leads to the activation of factor VII (factor VIIa) and, with factor X, stimulates protease-activated receptors (PARs) on the surface of platelets, endothelial cells, and leukocytes. Thrombin stimulation of platelets leads to platelet activation, which stimulates further TF expression, chemokine release, as well as endothelial and leukocyte adhesion molecules and vascular leakage, as discussed in the previous sections. Thrombin also stimulates further production of TNF-α, IL-1β, and IL-6, as well as C5a formation in a manner that is independent of the alternative, lectin, and classical complement activation pathways. Fibrin and fibrin/fibrinogen degradation products also stimulate leukocytes and endothelial cells to produce and release proinflammatory cytokines such as TNF-α, IL-1β, and IL-6. Finally, activation of the intrinsic coagulation pathway factor XII (Hageman factor) activates factor XI (intrinsic coagulation pathway) and prekallikrein (kallikrein-kinin system). Prekallikrein activation leads to the production of vasoactive peptides such as bradykinin, which is a strong vasodilator also capable of inducing vascular leakage. Bradykinin is also very important in the regulation of blood pressure as well as a host of diseases. The same processes occur during adaptive inflammatory responses that further recruit neutrophils, monocytes, lymphocytes, and eosinophils, but some of the chemotactic factors are expressed preferentially depending on the type of response and effector cells required. In addition to responses to infections, inflammation, and hemodynamic changes will be of particular relevance in numerous disease conditions such as sepsis, shock, atherosclerosis, disseminated intravascular coagulation Top (DIC), myocardial infarction, etc. Finally, the desired outcome of acute inflammation is resolution, regeneration, and return to homeostasis; this stage is characterized by a shift in the inflammatory response toward tissue https://rossmed.instructure.com/courses/3318/pages/week-2-fusion-session-%7C-tbl-acute-inflammatory-response-and-complement 21/71 1/25/24, 12:55 AM Week 2: Fusion Session | TBL: Acute Inflammatory Response & Complement: Hemtlgy Onclgy Infectn Imm - January 2024 repair, which will be addressed with your pathologists, as will other types of inflammation, such as chronic inflammation.  Macrophage Activation In response to an infection, another important event that occurs is macrophage activation. In and of themselves, macrophages are able to kill a variety of microorganisms, but killing effectiveness and efficiency are greatly enhanced following activation. Now, macrophages are plastic, and they can be activated for different purposes depending on the signals provided for their activation. For example, macrophage activation by InterFeroN gamma (IFN-γ) yields what is sometimes referred to as M1 macrophages or classically activated macrophages; these macrophage's function is mainly to kill microbes. On the other hand, macrophages stimulated with IL-4 become what is referred to as M2 macrophages, and their function mainly involves tissue repair. As previously mentioned, you will learn more about tissue repair in Pathology, so for now, we will focus on macrophage activation for the purpose of microbial killing. Top https://rossmed.instructure.com/courses/3318/pages/week-2-fusion-session-%7C-tbl-acute-inflammatory-response-and-complement 22/71 1/25/24, 12:55 AM Week 2: Fusion Session | TBL: Acute Inflammatory Response & Complement: Hemtlgy Onclgy Infectn Imm - January 2024 Transcript Classically activated macrophages (M1) are involved in pro-inflammatory responses and pathogen clearance, while alternatively activated macrophages (M2) participate in tissue repair and immune regulation, exhibiting an anti-inflammatory phenotype. Activation of macrophage microbicidal mechanisms requires at least two signals: 1. IFN-γ and 2. another signal (usually either TLRs or other signaling PRRs, or TNF-α) In this context, IFN-γ is absolutely necessary for macrophage activation, whereas the other signal may vary (TNF-α or other signals such as those elicited by signaling PRR engagement). Cellular sources of IFN-γ in the body are Natural Killer cells (NK cells), type 1 innate lymphoid cells (ILCs), CD4 T helper 1 lymphocytes (TH1 cells), and CD8 cytotoxic T lymphocytes (CTLs); the latter two (TH1 cells and CTLs) are products of adaptive immunity and will be developed further in the Antigen Presentation and T Cell Lymphocyte Biology lecture, so the only available sources of IFN-γ during the innate stage of the immune response are NK cells and type 1 ILCs. Our focus at this stage will be on NK cells. Top https://rossmed.instructure.com/courses/3318/pages/week-2-fusion-session-%7C-tbl-acute-inflammatory-response-and-complement 23/71 1/25/24, 12:55 AM Week 2: Fusion Session | TBL: Acute Inflammatory Response & Complement: Hemtlgy Onclgy Infectn Imm - January 2024 Macrophage activation during the innate phase of the immune response results from a collaboration between macrophages and NK cells. Macrophages having detected microbes or microbial products, e.g., through TLR engagement, synthesize and release IL-12. The IL-12 then engages its receptor on the surface of NK cells, and the NK cells respond to this signal by synthesizing and releasing IFN-γ. IFN-γ released by the NK cells can now stimulate macrophages. The concomitant stimulation of macrophages with 1. IFN-γ and Top 2. TNF-α and/or TLR engagement signals macrophages to increase microbicidal killing through many different mechanisms: induction of inducible nitric oxide synthase for the production of microbicidal (or bacteriostatic) reactive nitrogen intermediates such as nitric oxide (•NO), nitrite (NO2-), nitrogen dioxide (•NO2), nitrate (NO3-) and nitrogen oxide https://rossmed.instructure.com/courses/3318/pages/week-2-fusion-session-%7C-tbl-acute-inflammatory-response-and-complement 24/71 1/25/24, 12:55 AM Week 2: Fusion Session | TBL: Acute Inflammatory Response & Complement: Hemtlgy Onclgy Infectn Imm - January 2024 (N2O3), [increased respiratory burst efficiency [increased superoxide (O2•-), hydrogen peroxide (H2O2), the hydroxyl radical (OH•) and, sometimes, hypochlorous acid (HOCl) production], as well as oxygen-independent mechanisms such as increases in the expression of a number of granule-associated proteins such as elastases, collagenases, lipases, deoxyribonucleases, polysaccharidases, sulfatases, phosphatases, and defensins, as well as restriction of nutrients such as iron chelation and tryptophan starvation from pathogen-containing vacuoles. Note As you may have noticed already, and this will become a recurrent theme in Immunology as we progress through the material, cellular immune responses will almost always require two or more signals to be enacted upon, i.e., ‘immune cells usually need two or more permissions’ to respond in a certain way. This likely ensures that 1. cells are not ‘accidentally’ responding to a marginal event, and 2. cells can be more fine-tuned in their response(s). One way of seeing things is Top that an immune cell will respond to stimuli when signal 2 confirms signal 1. For example, IFN-γ alone cannot activate macrophages; macrophages are activated when stimulated with IFN-γ and a second signal, such as TNF-α or PRR engagement, or both. Similarly, as we will see later for T lymphocytes, antigen presentation alone cannot activate T cells (in fact, antigen presentation in the https://rossmed.instructure.com/courses/3318/pages/week-2-fusion-session-%7C-tbl-acute-inflammatory-response-and-complement 25/71 1/25/24, 12:55 AM Week 2: Fusion Session | TBL: Acute Inflammatory Response & Complement: Hemtlgy Onclgy Infectn Imm - January 2024 absence of co-stimulatory signals will render T cells anergic, potentially leading to T cell death); for activation, T lymphocytes require two separate signals: 1. antigen presentation to their T cell receptor and 2. separate so-called co-stimulatory signals that will bind a different receptor, namely CD28, but we will develop this in detail later in the Antigen Presentation and T Lymphocyte Biology lecture.  Important Soluble Mediators of Inflammation Mediators and their functions that are bolded and highlighted are the ones you need to know at this point. IL-1ß (cytokine): initiation of inflammatory response, induction of other proinflammatory cytokine synthesis and secretion (IL-1β, TNF-α, IL-6, & CXCL8) as well as other inflammatory mediators (LTs, prostaglandins) and adhesion molecules (endothelial cell activation & transendothelial migration (i.e., expression of selectins and integrins); IL-18 (cytokine): induction of antiviral mediators; TNF-α (cytokine): vasodilation, chemotaxis, endothelial cell activation, transendothelial migration, and activation of neutrophils; CXCL8 (IL-8; chemokine): chemotaxis and activation of leukocyte/endothelial cell firm adhesion; IL-12 (cytokine): activation of Natural Killer cells (NK cells) for the synthesis and release of InterFeroN-gamma (IFN-γ); IFN-γ (cytokine): activation of macrophage microbicidal functions; IFN-α (cytokine): induction of antiviral mediators; IL-33 (cytokine): nuclear alarmin cytokine released during tissue injury and involved in the control of the immune system; also involved in different pathological processes such as asthma, allergy, etc. C5a (complement fragment; further Top developed in the Complement System lecture…): activation of mast cells (degranulation) and chemotaxis; C3a (complement fragment; further developed in the Complement System lecture…): activation of mast cells (degranulation) and chemotaxis; https://rossmed.instructure.com/courses/3318/pages/week-2-fusion-session-%7C-tbl-acute-inflammatory-response-and-complement 26/71 1/25/24, 12:55 AM Week 2: Fusion Session | TBL: Acute Inflammatory Response & Complement: Hemtlgy Onclgy Infectn Imm - January 2024 Histamine (vasoactive amine): vasodilation, vascular permeability, and constriction of smooth muscle cells; pruritus (itching); Leukotrienes (arachidonic acid-derived lipids; LTB4, LTC4, LTD4, & LTE4): constriction of smooth muscle cells; Prostaglandins (arachidonic acid-derived lipids): pain, vascular permeability, vascular smooth muscle regulation, chemotaxis; Bradykinin (peptide): vasodilation and vascular permeability; burning pain and itching.  Important Cellular Mediators of Inflammation Mediators and their functions that are bolded and highlighted are the ones you need to know at this point. Macrophages: phagocytosis, synthesis and release of proinflammatory cytokines, microbial killing; Neutrophils: phagocytosis, release of DAMPs, microbial killing; Mast cells: release of soluble inflammatory mediators; Endothelial cells: release of proinflammatory mediators and infiltration of plasma and leukocytes.  Systemic Inflammation Mediators & their functions that are bolded and highlighted are the ones you need to know at this point. When proinflammatory cytokines are released systemically (i.e., through the whole body), they induce non-specific signs and symptoms such as fever (the pyrogenic cytokines are IL-1ß, TNFα, IL-6, & IFN-α), malaise, myalgia (muscle ache), arthralgia (joint pain), cephalgia (headache), anorexia (loss of appetite), skin allodynia, bone marrow leukocyte production (IL-6, IL-1ß, & Top TNF-α), as well as synthesis and release of acute-phase reactants by the liver (IL-6 & IL-1ß): IL-1ß (cytokine): fever, synthesis of acute-phase reactants (or acute-phase proteins) by the liver; https://rossmed.instructure.com/courses/3318/pages/week-2-fusion-session-%7C-tbl-acute-inflammatory-response-and-complement 27/71 1/25/24, 12:55 AM Week 2: Fusion Session | TBL: Acute Inflammatory Response & Complement: Hemtlgy Onclgy Infectn Imm - January 2024 TNF-α (cytokine): fever, vasodilation, increased muscle and fat catabolism (cachexia); IL-6 (cytokine): fever, synthesis of acute-phase reactants by the liver (e.g., C-reactive protein (CRP), D-dimer protein, mannose-binding lectin (MBL or mannose-binding protein (MBP)), alpha-1 antitrypsin, alpha-1 antichymotrypsin, alpha-2 macroglobulin, alpha-1-acid glycoprotein (AGP), fibrinogen, prothrombin, factor VIII, von Willebrand factor, plasminogen, complement factors, ferritin, serum amyloid A (SAA), serum amyloid P component (SAP), procalcitonin (pCT), ceruloplasmin (Cp), haptoglobin (Hp), procalcitonin (pCT), among others). A few useful clinical correlations: Terminology: Acute inflammation: rapid onset lasting a few hours to a couple of weeks. Chronic inflammation: insidious onset or following acute inflammation, lasting for weeks to years. Inflammatory conditions are usually followed by the suffix ‘itis,’ such as pneumonitis, dermatitis, vasculitis, hepatitis, pancreatitis, etc. Fever: Elevation of body temperature above the normal range Caused by IL-1ß, TNF-α, IL-6, and IFN-α systemic release, which stimulates the production of prostaglandin E2 (PGE2), which is, in turn, responsible for raising the hypothalamic body core temperature set-point (this will be further developed in the Temperature Regulation lecture given in Physiology, as well as in Clinical Medicine lectures and other activities, e.g., Patient with Fever); Causes peripheral vasoconstriction responsible for cold sensation and chills; Above 37°C, there is a 13% increase in oxygen consumption for every 1°C increase in body temperature; consequently, the heart and respiratory rates tend to increase (tachycardia & tachypnea, respectively) with fever; the relationship between fever and blood pressure is complicated and depends on context (e.g., low in patients with sepsis, and elevated in patients with a mild viral infection). Malaise/myalgia/arthralgia: Caused by peripheral increase in PGE2. Top Anorexia: TNF-α and IL-1ß mediate appetite loss through hypothalamic anorexigenic signaling. https://rossmed.instructure.com/courses/3318/pages/week-2-fusion-session-%7C-tbl-acute-inflammatory-response-and-complement 28/71 1/25/24, 12:55 AM Week 2: Fusion Session | TBL: Acute Inflammatory Response & Complement: Hemtlgy Onclgy Infectn Imm - January 2024 Clinically, the measurement of acute-phase reactants in serum is an indication that there is an ongoing inflammatory process; however, it is non-specific and could be the result of an infection, an injury, an autoimmune disease, or even exercise, etc.  Clinical Markers of Inflammation As a result of IL-6 stimulation, and to a lesser extent IL-1ß, the liver generates an abundance of acute-phase reactants. Following phlebotomy (blood draw), some of these acute-phase reactants can readily be measured from the patient’s serum and provide the physician with information concerning the inflammatory status of the patient. Furthermore, inflammatory status can be measured by determining leukocyte counts (white blood cell (WBC) counts). Here, we will focus on the most important acute-phase reactants and cells commonly measured in the clinical setting. Biochemistry Erythrocyte sedimentation rate (ESR – elevated during inflammation): increased fibrinogen in the blood causes erythrocytes to bind one another and form stacks of red blood cells called rouleaux; as a result, erythrocytes sediment faster C-reactive protein (CRP): CRP is an opsonin that activates the complement system Serum amyloid A (SAA): SAA binds pathogen lipopolysaccharides akin to lipopolysaccharide binding protein (LBP); in tissue, SAA is chemotactic Mannose-binding lectin (MBL): MBL is an opsonin that activates complement Alpha-1 antitrypsin (and alpha-1 antichymotrypsin): alpha-1 antitrypsin is a serine protease inhibitor (serpin) that limits host damage by inhibiting leukocyte and lysosomal proteolytic enzymes Haptoglobin (Hp): Hp binds free hemoglobin (Hb), Hb-Hp complexes are internalized by monocytes/macrophages (through a scavenger receptor (CD163), and Hb is degraded – this prevents the loss of iron and kidney damage (free hemoglobin damages the liver); Hp also binds to CD11b/CD18 integrins to limit leukocyte damage Ceruloplasmin (Cp): Cp contains copper and scavenges iron (which many pathogens need) and limits host damage by scavenging free radicals as well as inactivating histamine (diamine oxidase activity) Top Ferritin: ferritin stores iron and restricts its utilization by pathogens Alpha-2 macroglobulin: alpha-2 macroglobulin is a protease inhibitor that limits host damage by neutralizing proteolytic enzymes; alpha-2 macroglobulin also inhibits fibrinolysis https://rossmed.instructure.com/courses/3318/pages/week-2-fusion-session-%7C-tbl-acute-inflammatory-response-and-complement 29/71 1/25/24, 12:55 AM Week 2: Fusion Session | TBL: Acute Inflammatory Response & Complement: Hemtlgy Onclgy Infectn Imm - January 2024 Fibrinogen: fibrinogen limits host damage by promoting coagulation D-dimer protein: D-dimer is a degradation product of fibrin and indicates fibrinolysis, a protective mechanism to avoid problematic blood clots Alpha-1-acid glycoprotein (AGP): immunomodulator, and inhibits platelet aggregation Procalcitonin (pCT): elevated during bacterial infections, particularly Cellular Leukocytosis: leukocyte count above normal range Neutrophilia: neutrophil count above normal range; general, but also suggestive of a bacterial infection or an infection with an extracellular microorganism Left shift (bandemia): increase in number of immature cells in blood, e.g., segmented bands (immature neutrophils) Lymphocytosis: lymphocyte count above normal range; suggestive of viral infection, or infection by an intracellular organism Eosinophilia: eosinophil count above normal range; suggestive of parasitic infection, allergy, or asthma Top https://rossmed.instructure.com/courses/3318/pages/week-2-fusion-session-%7C-tbl-acute-inflammatory-response-and-complement 30/71