Lecture 02: Inflammation and Repair PDF

January 14, 2025 LECTURE 02: INFLAMMATION AND REPAIR I.​ OUTLINE Outline ​ Acute inflammation ○​ Up to 2 weeks (old classif...

January 14, 2025 LECTURE 02: INFLAMMATION AND REPAIR I.​ OUTLINE Outline ​ Acute inflammation ○​ Up to 2 weeks (old classification; general) ○​ Vascular ○​ Cellular ○​ Termination/Progression ​ Termination: Inflammation stops there because there is no more threat to the tissue ​ Progression → leads to Chronic Inflammation ​ Chronic inflammation ○​ 2 weeks or more (old classification; general) ​ Can happen without going through acute inflammation → if stimulus is very severe ○​ Much more specific ​ Analogy: War ​ Chemicals, complement proteins, molecules involved in inflammation = Traps ​ Epithelium (mechanical barrier) = Defense ​ Leukocytes = Soldiers ​ Specific to a certain offending agent ​ Major players are macrophages and lymphocytes ​ Can recruit cells from acute phase (neutrophils, eosinophils) depending on demand ​ Not exclusive to each other ○​ Initiation of healing ​ [a] Regeneration ​ Functional cells will regenerate to fix damage ​ Dependent on the availability of the stem cells that differentiate to specialized cells ​ Ex: skin will regenerate if the functional cells are still intact (less damage) ○​ Superficial = Only epithelium removed → Stem cells found in basal layer can proliferate and cover the defect again ​ [b] Repair ​ A plug/patch of connective tissue  ​ Ex: the skin will repair if there is no more functional cells and the fibroblasts will take over to fix extensive damage ○​ Extensive burn wound → No stem cells in the area = Connective tissue and fibroblasts take over the space left behind ​ Scarring II.​ INFLAMMATION Inflammation ​ Protective response to remove injurious cause and neutralize the sequelae of the injury (pathologic of misdirected or uncontrolled) ​ Can be pathologic ○​ Inflammatory cells attack the normal tissue (e.g. autoimmune diseases) ○​ There must be a balance: They can get rid of the offending agent without affecting the normal tissues ​ General steps [5 R’s]: ○​ Recognition ​ Identify the offending agent ​ Achieved by the different receptors on the surface of the cells ​ E.g., Epithelium can recognize offending agents and send signals to inflammatory cells underneath the epithelium ○​ Recruitment (of more inflammatory cells) ​ After they deem the specific agent as injurious ​ Through the use of different chemical mediators (amines, cytokines) ​ Leukocytes found within the blood vessels will be attracted to site of injury due to chemical mediators ​ Migrate through the ↑increase in the permeability of the vascular wall (vascular phase) → vasodilation ○​ Accommodates more blood cells → Slows down the flow → Leukocytes get more exposed to receptors on endothelium → Migrate to site of injury ○​ Removal ​ Remove or neutralize microbes causing injury in the area ○​ Regulation ​ Stop the inflammatory process then healing will start ○​ Repair  ​ If the cells in that area can still regenerate, then growth factors will induce regeneration/multiplication/division of these cells ​ If there are no source of new cells present, the fibroblasts will take over, proliferate, make ECM, and fill in the space left behind by the dead cells (repair) ​ Cardinal signs: ○​ Rubor (redness) ​ Due to the vasodilation ​ More red blood cells coming/increase blood flow ○​ Tumor (swelling) ​ Due to permeability ​ Fluids and smaller plasma proteins can go out of blood vessels and accumulate in interstitial tissue → Swelling ​ Accumulation of leukocytes = mass effect ○​ Calor (heat) ​ Due to the increase in blood flow/vasodilation ​ From local effects of cytokines/interleukines ​ Reset temperature and modify it locally ​ Others can affect CNS → affect body temperature ○​ Dolor (pain)​ ​ Due to irritation of nerve endings in specific area ​ A protective process ​ Tells that something is wrong and you have to do something abt it ​ Body’s reaction to avoid severe injury ○​ Functio laesa (loss of function) ​ Because of the injury to the specialized cells or parenchyma [A] Acute Inflammation ​ Onset: minutes or hours after stimulus ​ Duration: may last up to days (7 to 14 days); onset after around 2(?) hours ○​ Chronic inflammation can happen for 2 weeks or more ​ Can happen initially when stimulus is very severe ​ Happens after acute inflammation ​ Stages: ○​ Vascular ​ Histamine ​ Main chemical mediator ​ From amino acid histidine ​ Elimination of carboxyl group ○​ Functional groups contain N → why it’s an “-amine” ​ Promote vasodilation and increase in permeability ○​ Endothelium separates from each other ​ Allows the flow of fluids, water, or plasma proteins outside the blood vessels → accumulate in site of injury (i.e., interstitial tissue) ​ ​ Histologic slide showing the vascular phase (left) and temporal profile in days (right) ○​ Capillaries are filled with RBCs and some leukocytes → just the initial part (vasodilation) ​ Leukocytes will be seen lined up at the vascular walls ​ Edema sets in first and inflammatory cells will not be able to enter, but there are already fluids and plasma proteins going out (causes edema to the area of injury) ○​ Edema will then be filled with neutrophils, monocytes, and macrophages ○​ Cellular ​ Recruitment of leukocytes ​ Involve surface molecules from leukocytes and endothelium ○​ In endothelium, there are selectin molecules  ​ There is transient binding → there is lesser affinity; allows binding to be reversible ​ Due to blood flowing slower (because of vasodilation), leukocytes will go down ​ In normal blood flow, it is laminar (one direction flow) ○​ The tendency of the matter with a bigger mass (e.g., cells) are in the center while the smaller ones (e.g., plasma proteins, fluids) are in the periphery ​ Advantageous due to no interaction of surface molecules of leukocytes and the endothelium ​ When there is vasodilation, slows down the flow and makes it more turbulent ○​ Centrally located cells go to periphery exposing them to selectin molecules ​ Selectin molecules will interact with the surface glycoproteins of the leukocytes ○​ Transient binding: Leukocytes will roll down ○​ The selectins will slow down the momentum ​ Cellular adhesion molecules will have more strong affinity/binding ​ Will keep leukocytes in place and allow them to migrate to site of injury ○​ The leukocytes will be in place (comes intact will wall) then migrates ○​ Termination vs. Progression ​ Termination – eliminated the causative agent ​ Progression – the agent is not eliminated Vascular Stage ​ Vasodilation is immediately followed by increased permeability ○​ Increase in permeability ​ Achieved by contraction of endothelium to increase the space between ​ There is still basement membrane ​ Not allow all molecules to pass through ○​ E.g., RBCs → to make them stay inside the blood vessels ○​ Histamine, bradykinin, leukotrienes → main molecules involved and initiate vasodilation (esp. histamine) ​ Endothelial contraction ​ Short-lived (15 to 30 minutes) ○​ Kininase quickly inactivates bradykinin ​ Bradykinin ← Kininogen (through kallikrein enzyme) ​ Leukotriene ← 5,8,11,14-eicosatetraeonic acid ○​ Disturbs laminar flow → allows cells (RBCs and leukocytes) to go to the periphery ​ If there is laminar flow: ​ Those with less mass (fluids) → found on periphery  ​ Those with more mass (cells) → found at the center ​ RBCs do NOT have the receptors for selectin and cell adhesion molecules ○​ Will NOT make them adhere to epithelium ​ Origin of leukotriene come from the cell membrane of endothelium ​ The cell membrane will be broken down by phospholipase ○​ Once phospholipids are broken down to arachidonic acid, enzymes will further metabolize this to produce different cytokines/chemical mediators ​ We study these pathways to develop drugs that inhibit these different enzymes ​ COX-2 inhibitor → e.g., celecoxib (celebrix) and etoricoxib (arcoxia) ​ Leukotriene receptors → increase in vascular permeability and bronchospasm (in asthma) ○​ Montelukast → a drug that inhibits this receptor ​ Steroids → e.g., cortisone, hydrocortisone, histamine ○​ Diphenhydramine → an antihistamine but is more centrally active (also works on CNS, makes you feel groggy) ○​ Cetirizine → an antihistamine that also acts on CNS (makes you feel sleepy) ○​ Levocetirizine → Does not affect CNS compared to diphenhydramine Cellular Stage [MRAMC - kamag-anak ni Gordon Ramsay] ​ Phases: ○​ [2.1] Margination ​ Happens because of turbulence in the blood flow ​ The leukocytes and blood cells will marginate in the periphery ○​ [2.2] Rolling ​ Because of effect of interaction between selectin molecules and glycoproteins ​ Transient binding → just slows down the momentum or the flow of WBCs ○​ [2.3] Adhesion ​ Via cellular adhesion molecules ​ The ligand (integrin), when intact, there will be a stronger binding and keep the leukocytes in place ○​ [2.4] Migration ​ Transmigration/Diapedesis (movement through an intact endothelium (not destroyed but just contracted)) ○​ [2.5] Chemotaxis ​ Chemokines (IL-8, C5a, LTB4) ​ Chemical mediators that attracts the migrating leukocytes to the site of injury [What Happens When Cells Reach the Site of Injury?] Phagocytosis ​ Neutrophils and macrophages ○​ Need to have molecule that recognizes surface molecules on the microbes or substance for them to phagocytose ​ Phagocytic receptors ○​ Mannose receptor: mannose, fucose residues ​ Aka carbohydrate residues ○​ Scavenger receptor: modified (oxidized or acetylated) LDL → surface molecules found in microbes ​ Modified: due to acetylation or oxidation of lipoproteins ○​ Once invagination happens, it will now enclose microbe ​ Will then detach to form vesicle (called phagosome) → fuse with lysosomes ○​ Break down offending agent ○​ Comes in contact with lysosome, ​ Contains lots of reactive molecules → to destroy and break down offensive agent ○​ In nature, it will always prefer a reaction that will utilize a low energy level ​ Why free radicals are very reactive ​ Enhanced when particles to be phagocytosed are coated with opsonins (Ig, C3b, mannose-binding lectin) ○​ Opsonin: General term for molecules that surround the surface of the microbe/substance that needs to be phagocytosed ○​ It can be immunoglobulin (Ig), which will surround and attach to the surface → more attachment sites → enhance phagocytosis  ✊🍆💦 😤 Phagocytosis ​ Granule contents can be released during “frustrated phagocytosis” ○​ Contents of granules will be released ​ Different chemicals found within the specific granules ○​ Azurophilic granules ​ Present in all WBCs that came from lineage of myeloid stem cells ​ [a] Myeloperoxidase (H2O2+ Cl- HOCl ) ​ [b] Lysozyme (degrades cell wall) ​ [c] Defensin (cysteine-rich proteins → disrupt cell membranes) ○​ Specific granules ​ Only found in certain population of cells ​ [a] Neutrophils = collagenase ​ Can degrade collagen ​ Neutral color; neither too red or too blue ○​ There is a mix of enzymes that are both positive and negative ​ [b] Eosinophils = major basic protein (arginine-rich) ​ Positively charged arginine takes up negatively charged eosin → make it more red ​ [c] Basophil = heparin, histamine, PLA2 (more negatively charged molecules) ​ Loves the basic stain ​ Neutrophil extracellular trap (NET) ○​ Viscous meshwork of nuclear chromatin (via citrulline, converted by arginine deaminase in the presence of ROS) ○​ Traps microbes ○​ Postulated to be a source of antigen in SLE ○​ Cell “kills” itself → Releases nucleus ○​ [Hypothesized] that it can induce systemic lupus erythematosus  Termination vs. Progression Stage ​ Lipoxin → can halt inflammatory process ​ Macrophage and dendritic cells will take up some of the debris and present it to phagocytes (if agent is still not eliminated ○​ Where it can progress to a chronic inflammation ​ The antigen-presenting cells (dendrites, macrophages, etc.) [B] Chronic Inflammation ​ Have more specific response ○​ The lymphocytes are able to know this specific agent (i.e., the broken down molecules) is causing this specific injury ​ Will generate an appropriate response for it ​ infiltration with mononuclear cells ○​ Macrophage ○​ Lymphocytes ○​ Upper image: acute inflammation of lung ​ Presence of Vasodilation (representing vascular phase) ​ Presence of migration of neutrophils/phagocytes ○​ Lower image: Chronic inflammation of lung ​ Collection of lymphocytes ​ With germinal centers ​ Alveolar space with type 2 pneumocytes ​ type I are flattened ​ Has thick walls due to fibrosis ​ When chronic inflammation sets in, it sends signals of either repair and/or regeneration to proceed → accumulation of fibroblasts and ECM → lead to thickening of walls ​ Tissue destruction ○​ Either by offending agent or by inflammatory cells (“frustrated phagocytosis”)  ○​ Normal tissues surrounding area of injury is also affected ​ Attempts at healing ○​ Granulation tissue formation ○​ Regeneration and repair Macrophage ​ Bridges acute and chronic inflammation ​ Can present antigen if acute inflammation cannot control the initial injury ​ Either: ○​ Derived from monocyte (postnatal, half-life of ~1 day); or ○​ From progenitor cells in yolk sac (fetal, lifespan = months to years) ​ Present at birth ​ Has longer life span (present for months or years) ​ Morphology ○​ Monocyte: abundant cytoplasm with single, indented nucleus ○​ Macrophage: Cytoplasm takes majority; Nucleus in the periphery ​ Monocyte that migrated and differentiated ​ Increase in cytoplasm will accommodate phagocytosis ​ May have different names in different organs ○​ Liver = Kupffer cells ○​ Lymph node = sinus histiocytes ○​ CNS = microglial cells ○​ Lungs = alveolar macrophages/dust cells ​ Its like a cycle ○​ Initially, the macrophage will present antigen to lymphocytes → lymphocytes will be activated → T cells or B cells ​ If B cells → antibody (specific for offending agent) ​ T cells differentiate depending on type of infection ​ T helper (Th1, Th2, Th17) ○​ Th1 → enhance activity of macrophage and turn it into M1 macrophage (pro-inflammatory) ○​ Th2 → induce other macrophages to differentiate into M2 macrophage (anti-inflammatory → promotes repair/regeneration/healing)  ​ T cytotoxic ​ Natural killer cells Lymphocytes ​ Classified into B and T lymphocytes ​ T lymphocytes ○​ CD4+ (T-helper) ​ Th1 ​ Th2 ​ Th17 ○​ CD8+ (T-cytotoxic) ○​ NK cells (Natural Killer) ​ Based on protein expression ​ B lymphocytes ○​ B-memory ​ Due to presence of memory, in the event of same injury, there is faster response ○​ Plasma cells ​ Antibody synthesizing cells ​ Both T and B lymphocytes originated from the bone marrow ​ Diagram: How lymphocytes differentiate ○​ B cells ​ Originate from bone marrow ​ Immature B cells migrate to different lymphoid tissues ​ Mucosa-associated lymphoid tissue → found in submucosa ​ Lymph nodes → Distributed throughout the body ○​ Connected by lymphatic vessels ​ Spleen ​ Thymus → Predominant T cells ​ Stay in lymphoid tissues until antigen is presented ​ Dendritic cell: presenting molecule found on cytoplasmic extensions ​ Rich in the presenting molecules ​ Once presenting the antigen, the B lymphocytes will activated → plasma cells or memory B cells  ​ If you have a lymphoma (malignant process), monoclonal proliferation ​ Originates from one type of cell population ​ The only way to identify them is to identify their protein expressions → via immunohistochemical staining ○​ T cells ​ Originated from the bone marrow ​ Immediately migrate to the thymus ​ Thymus → the site for their differentiation ○​ CD8+ → MHC I ​ T-cytotoxic ​ Kills the cell that presents MHC I ​ Virtually present in all nucleated cells ​ Antigens that bind to MHC I are synthesized intracellularly ○​ E.g.., viral proteins, proteins from malignant cells ○​ CD4+ → MHC II (surface receptors/molecules that present antigen from outside the cell) ​ T-helper ​ Present in phagocytes (macrophage, neutrophils, dendritic cells) or endothelial cells ​ APCs (antigen-presenting cells) ○​ NK (natural killer) cells ​ Do not differentiate in thymus, differentiate from bone marrow straight to the other ​ Innate immunity ​ Reaction is NOT specific unlike other T cells [Importance of Histochemical Stains] Lymphocytes ​ B cells → populate lymphoid follicles ​ T cells → found in paracortex ​ ○​ CD20 → B cells ​ Highlight lymphoid follicles ○​ CD3 → T cells ​ Highlights the paracortical area ○​ bcl-2 → Anti-apoptotic ​ Increase in expression of bcl-2 → those cells are resistant or do not somewhat undergo apoptosis ○​ Validates that the specific molecules are present in all phenotypes of the cells ​ ○​ Intestinal ​ Can see surface epithelium (simple columnar) with goblet cells ○​ Submucosa: collection of lymphocytes ○​ To determine if normal inflammatory reaction or malignant/lymphoma , use specific biomarkers or histochemical stains ​ CD20 → highlights malignant cells  ​ CD3 → highlight some; polyclonal (not monoclonal) → likely not a lymphoma and most likely an inflammatory reaction [Basis for the process of immunohistochemical staining] ​ CD20 ○​ B cells have Ig and coreceptors ​ Coreceptors: CD20 and CD21 ​ Why CD20 is present in ALL B cells → coreceptor for IgM found on surface of lymphocytes ​ CD3 ○​ Coreceptor of either CD8 or CD4 ​ A coreceptor for T cell receptor → why it is present in ALL T cells ​ bcl-2 ○​ Regulators of apoptosis ​ Immunohistochemical process ○​ Isolate the specific protein (e.g., CD3) ○​ Inject in animal (e.g., mouse) ○​ animals will develop antibody against these proteins ○​ We aspirate/isolate those antibodies ○​ Conjugate collected antibodies with chromogen ○​ If the Ab w/ chromogen is applied to a tissue, these Ab will bind to the specific cells expressing the protein ​ Once it binds, collection of the chromogen can be observed under the microscope (e.g., the brown pigment areas in the pictures) CD4+ T lymphocytes / T-helper cells ​ Subsets: ​ Th1 ○​ IFN-γ → M1 macrophage (pro-inflammatory) ​ Induce differentiation of macrophage to M1 ​ Th2 ○​ IL-4, IL-13 → M2 macrophage (anti-inflammatory, but pro-healing) ​ Interleukin: Induce macrophages to differentiate to M2 ​ Anti-inflammatory ​ pro-healing ○​ IL-5 → eosinophil ​ Th17 ○​ IL-17 → neutrophils, monocytes ​ Recruits more neutrophils and monocytes to become macrophages CD8+ T lymphocytes / Cytotoxic T-cells ​ Recognizes foreign molecules produced intracellularly, which are presented by MHC Class I (found in all nucleated cells) ​ Kills cells presenting the foreign molecules through perforins and granzymes ○​ Granzymes → induces apoptosis; cleaves caspases ○​ Perforins → Induce necrosis Natural Killer Cells (NK Cells) ​ Expresses CD3 (may have arisen from the T-cell precursor) ​ Appear to target virus-infected Co-receptor of CD8 or CD4 cells that are not attacked by cytotoxic T cells ​ Expresses Fc portion of IgG → participates in antibody-dependent cell lysis ​ Part of acute inflammatory response ○​ First line of defense against virus-infected cells ​ Do NOT express CD8 or CD4 ​ Can be recruited ○​ Participate in antibody lysis B lymphocytes ​ Plasma cell → antibody-producing ​ Play a role in adaptive immunity ​ When they are stimulated/activated, they can be differentiated into two : Plasma cells or Memory B cells ○​ Plasma cells ​ Anti-body producing ​ Abundant cytoplasm ​ Eccentrically located nuclei with hista??? Pattern ​ Perinuclear clearing (halo) represent well-developed golgi apparatus ​ Synthesizing many antibodies thus further modifying GA ○​ Memory B cells ​ Retain information ​ When attacking agent is encountered again, they can perform according mechanism ○​ Take note of Germline DNA configuration (V, D J, C) ​ Specificity committed - ​ Isotope committed - ​ Antibodies are widely diverse due to different genes responsible for different segments ○​ Combination somehow puts indiv at risk by developing self-targeting antibody (autoimmune disease) ​ Autoimmune disease is hereditary because you’re genetically pre-disposed to have such antigens  Other cells ​ Eosinophils ○​ IgE-mediated ○​ Parasitic infections ​ Recruited via immunoglobulin E plasma cells ○​ Major basic proteins in specific granules → toxic to parasites ​ Mast cells ○​ aka basophils (when differentiated) ○​ Binds Fc portion of IgE ○​ Histamine, prostaglandins in specific granules ​ Neutrophils ○​ Recruited by IL-17 in chronic inflammation ​ Produced by T helper 17 Granulomatous Inflammation ​ Attempt to contain an agent difficult to eradicate ​ Prevalent in the Philippines due to tuberculosis ​ Cause is usually fungal infection ​ Two types: ○​ Foreign body granuloma ​ Sutures, talc, crystals ​ Absorbable sutures = degraded by granuloma ​ In reactions of our immune system to foreign bodies ○​ Immune granuloma ​ Persistent T cell-mediated immune response usually infectious in nature (fungal, tuberculosis) ​ Related to CD4+ (Th1) III.​ HEALING (REPAIR & REGENERATION) Tissue Repair ​ Repair = parenchyma + connective tissue ○​ Connective tissue deposition? ○​ Fibroblast ??? ○​ If severe ○​ Occupy space left behind by dead tissues ​ Healing = superficial epithelium ○​ Regeneration ○​ Mild, superficial Regeneration ​ Dependent on the ability of the tissue to proliferate and on the preservation of stem cell niche ○​ [a] Labile or stable cells ​ Can undergo regeneration ONLY if there are still stem cells available ○​ Myocardial cells and nerve tissues are [b] permanent cells so dead cells will be replaced by scar formation ​ Cardiomyocytes will be replaced by ??? ​ Driven by the signals from macrophages and extracellular matrix ○​ Growth factor → DNA replication ​ Stored in the connective tissue (ground substance) ​ When there’s a break, it’ll take long if you synthesize the molecules unlike when there’s precursor molecules in ground substance so when there’s a break, regeneration and repair can easily be stimulated ​ Stem cells undergo cell cycle → Mitosis → Replication ○​ Ex. macrophages ​ Especially when induced by Th2 cells Regeneration ​ Liver ○​ Sources of regeneration: ​ Remaining hepatocytes ​ Priming (IL-6) → Growth factor → Enters the cell cycle (parenchymal then nonparenchymal) → Termination (poorly understood, TGF-beta may play a role) ​ Progenitor cells ​ Aka stem cells ​ When proliferative capacity of existing hepatocytes is compromised (chronic injury, inflammation) ​ Found in canals of Hering ○​ Located between hepatocyte places ○​ Left image: regenerating liver ​ Normally 1-2 hepatocytes ​ Here, plates are thickened ​ Lymphocytes (Th2): Responsible for activating macrophages (Kupffer cells) and turn them to M2 macrophages that favor stopping the inflammation and inducing regeneration Regeneration ​ Extent of damage? ○​ Remaining cells with capacity to proliferation (existing differentiated and/or precursor) ​ Patent blood vessels? ○​ Supply of nutrients and building blocks ​ Building blocks can be lipids, carbohydrates, nucleic acids etc ​ Pathways that convert one to another Angiogenesis ​ Development of new blood vessels ​ Steps: ○​ Vasodilation ​ Via action of nitric oxide (NO) >:( ○​ Breakdown of basement membrane and separation of pericytes ​ Basement membrane limits endothelium ​ Allow endothelium to proliferate towards the side that needs more BV ○​ Migration of endothelial cells towards site of injury ​ VEGF-A → Notch signaling pathway (regulation of branching) ​ VEGF – Vascular endothelial growth factor ​ Notch signaling → migration signaling molecule ○​ Receptor and ligand are found on 2 adjacent cells ○​ Proliferation ​ Induced by FGF-2 ○​ Remodeling into capillary tubes ​ MMP ​ MMP – matrix metalloproteinase ○​ Recruitment of pericytes or smooth muscle cells ​ PDGF (platelet derived growth factor) ○​ Suppression ​ TGF-B (transforming growth factor) ​ Regulates all signaling Repair by Scar Formation (Connective Tissue Deposition) ​ Patch rather than restore ​ Sequence of events: ○​ Hemostatic plug (minutes) ​ Presence of BV, plasma proteins and platelets leak out and plug defect ○​ Inflammation (6 to 48 hours) ​ Inflammatory cells go to site of defect ​ M2 macrophage differentiation induce cell proliferation ○​ Cell proliferation (up to 10 days) ​ Epithelial cells ​ Endothelial cells and pericytes ​ Fibroblasts ○​ Granulation tissue formation (pink, soft, granular appearance of scab) ​ Granulation tissue = “crust” over new scar ​ Why new scars bleed after scratching ​ Supports proliferation of either epithelial cells or connective tissue (deposition?) ○​ Progressive replacement of granulation tissue by collagen (TGF-B) Transforming Growth Factor B (TGF-B) ​ Has both promoting and regulatory functions ○​ Promoting = MAPK signaling ○​ Inhibitory = p15 ​ Mutual dependency of dimerization and transphosphorylation ○​ Dimerization: 2 TGF-B needed ○​ Cytoplasmic serine/threonine domains ○​ Phosphorylation of SMAD ​ Vertebrate homologue of mothers against Dpp (MAD) in Drosophila and small-sized (sma) in Caenorhabdtis elegans Remodeling of Connective Tissue ​ Connective tissue deposits collagen “haphazardly”, not strategically ​ Deposited extracellular matrix (ECM) components are degraded by matrix metalloproteinases ​ (MMPs) and stromelysins to rearrange their orientation (remodel) ○​ Rapidly inhibited by tissue inhibitors of metalloproteinases (TIMP) ​ Regulate MMPs (?) ​ Blue stain represents the collagen Clinical Application ​ Extent of damage can be reduced ○​ That’s why we suture to reduce extent of damage so it will heal via regeneration rather than scar formation ​ Two types of Healing in Surgery ○​ First intention ​ Small defect; can regenerate and restore normal architecture of tissue ○​ Secondary Intention ​ Defect is so wide that initially there’s CT deposition although cells migrated to CT deposition, there’s still defect ​ Defect prevented by suturing Healing by Primary Intention ​ Small cut ○​ Heal and restore without intervention ​ Day 1 to 2 = epithelial cells migrate and proliferate ​ Day 3 = neutrophils are largely replaced by macrophages ​ Day 5 = neovascularization peak ​ Week 2 = continued collagen deposition and fibroblasts proliferation ​ Month 1 = essentially normal epidermis Healing by Secondary Intention (Secondary Union) ​ Undergoes same processes as primary intention ​ Week 2 = provisional matrix of fibrin, fibronectin, and type III collagen is replaced by a matrix of collagen type I ○​ Involves CT deposition ○​ There would be remodeling ​ Month 2 = Myofibroblasts decrease wound size to 10 % ○​ Myofibroblasts ​ Fibroblasts with contractile function to try and reduce the defect ​ Proliferation is also the basis of ??? nde nea tinuloy dafok ​ Malamig, sumasakit sugat even after months because of contractile function Wound Suture ​ Involve granuloma formation ​ Apposes wound edge to mimic healing by 1st intention ​ Suture recovers 70% of the normal skin strength ​ 3 months = wound strength normally reaches 70% to 80% When is the healing pathologic? ​ Keloid ○​ Overdeposition/overproduction of CT during healing ○​ Elevated lesions = CT underneath the skin ○​ Myofibroblasts will just accumulate without regulation if there’s no necessary genes ​ Contracture ○​ Not that dysfunctional unless located in mobile areas (i.e., joints) ​ E.g., neck ​ Wound is pulling on mandible/mentum ​ Chronic wound ○​ Underproduction of necessary molecules ○​ E.g., diabetes ​ Difficulty in healing beacuse toxins produced by elevated blood sugar is preventing angiogenesis Summary: Acute Inflammation ​ Phagocytes ○​ Derived from monocytes ○​ Migrate to _____ (site of injury?) ​ Granulocytes ○​ Neutrophils, Eosinophils (eosin loving), Basophils (base loving) ○​ Have specific granules (also present in macrophages) ​ Dendritic cells ○​ Part of antigen presenting cells ○​ Lot of MHC II ○​ Between keratinocytes (cytoplasmic extensions between them) ​ NK Cells ○​ Main role is acute inflammation or innate immunity despite being lymphocytes ​ Not mainly involved in chronic (?) ○​ Kill viral infected cells initially ○​ When it can’t control, chronic inflammation comes in ​ Complement system ○​ Just complement proteins that forms a pore-forming molecule via cleavage ○​ Byproduct can act as opsonins Chronic Inflammation: Summary ​ Phagocytes and dendritic cells present foreign molecules to lymphocytes ​ B cells ○​ memory B cells ○​ plasma cells ​ T Lymphocytes ○​ T helper cells: CD4+ ​ Th1 → M1 macrophage (pro-inflammatory) ​ Th2 → M2 macrophages (anti-inflammatory ​ Th17 → neutrophils and more macrophages ​ ○​ Cytotoxic cells: CD8+ ​ Recognized virally infected cells ​ Induce destruction either via apoptosis or necrosis via perforin Healing & Repair: Summary ​ T helper 2 cells favor formation of M2 macrophages which is antiinflammatory ​ Either through regeneration or scar formation/repair ​ A