BIO 669 Innate Immunity: Inflammation and Wound Healing Latest updated 2022/2023
Immunity
• First line of defense: barriers that are occurring to
... [Show More] prevent penetration of pathogens in the body, we have bacteria in our body and gut but that is not an issue. This bacterium prevents pathogens from
proliferating and becoming an issue. First line defense is skin, secreted chemicals such as acidic sweats, movement of fluid over the surface as pathogens start to attach
o Innate (natural) (native) immunity
▪ Physical, mechanical, biochemical barriers
• Second line of defense
o Inflammation
• Third line of defense (if the first two cannot clear infection in timely manner)
o Adaptive (acquired) (specific) immunity
First Line of Defense
• Physical barriers:
o Skin, sloughing off layers continuously
o Linings of the gastrointestinal, genitourinary, and respiratory tracts
o Sloughing off of cells
o Coughing and sneezing
o Flushing—urine
o Vomiting- reverse peristalsis to clear out problems
o Mucus and cilia used in the airway to trap particles and move mucous up to the esophagus and sent through the GI tract broken down by digestion
First Line of Defense (Cont.)
• Epithelial cell-derived chemical barriers:
o Secrete saliva, tears, earwax, sweat, and mucus
o Antimicrobial peptides
▪ Cathelicidins, defensins, collectins, and mannose-binding lectin (part of the complement system)
• Normal microbiome (beneficial to our health)
o Each surface colonized by bacteria and fungi that is unique to the location and individual
Second Line of Defense
• Inflammatory response (first immune response to injury)
o Nonspecific, works the same way no matter due to what reason
o Caused by a variety of materials
▪ Infection, tissue necrosis, trauma, physical or chemical injury, foreign bodies, immune reaction, ischemia, etc.
• Local manifestations
o Redness (rubor), heat (calor), swelling (tumor), pain (dubor), loss of function
Second Line of Defense (Cont.)
• Inflammatory response
o Vascular responses:
▪ Blood vessel dilation due to inflammatory mediators (histamine, serotonin, bradykinin) increase vascular permeability
▪ Increased vascular permeability and leakage, proteins leak into the tissue allowing for swelling, heat, increase blood flow (redness), serving the purpose of increasing the
Inflammation
• Goals:
temperature for enzyme function of healing fighting pathogens, dilutes toxins, brings oxygen, increases lymphatic drainage
▪ White blood cell adherence to the inner walls of the vessels and migration through the vessels
o Hypercoagulability, vessels start clotting off to wall off damaged area and prevent extension or growing
o Prevent and limit infection and further damage
o Initiate adaptive immune response and create WBC
o Initiate healing
o Limit and control the inflammatory process, bring in macrophages that engulf the damaged tissues and allows for initiation of new blood vessels to provide new nutrition for the healing process
o This must be self-limiting or it will be a chronic inflammatory condition which is recurring inflammatory mediators constantly keeping the area inflammed which is not good, mediators must be released to limit the inflammation
Plasma Protein Systems
• Protein systems: 3 diff protein systems to help the inflammatory process work well, part of the innate response, made in bulk, in the plasma and are ready if needed. They require activation, they are pro- enzymes that are not active.
o Complement system: complements antibodies, clears them out, identifies pathogens, stimulates further inflammation and drawing WBC to the damaged area
o Clotting system limits the spread of infection and bleeding associated w trauma
o Kinin system helps ramp up inflammation even further as bradykinin increases permeability of the vasculature allowing for more fluid and cells enter into the affected tissue
Plasma Protein Systems (Cont.)
• All contain inactive enzymes (proenzymes)
o Sequentially activated
▪ First proenzyme is converted to an active enzyme
▪ Substrate of the activated enzyme becomes the next component in the series (cascade)
Plasma Protein Systems (Cont.)
• Complement system
o Produces biologically active fragments that recruit phagocytes, activate mast cells, and destroy
pathogens, can be activated in one of three ways
o Activation of C3 and C5
▪ Opsonin: stimulates receptors on immune cells to stimulate phagocytosis which identifies the pathogen or damaged cell as marked for phagocytosis
▪ Chemotactic factors: help guide specific WBC to the area of damage
▪ Anaphylatoxins: stimulates inflammation
o Pathways: 3 diff ways of activating the compliment system
▪ Classical: antibody binding to a pathogen
▪ Lectin: mannose binding lectin or a carbohydrate binding protein able to identify a pattern that’s not typically found on our cells but typically found on pathogen cells and it
acts a lot like an antibody
▪ Alternative: activating the complement system by binding by an antibody or mannose binding lectin, a way of enhancing the other two pathways of their stimulation of complement
Plasma Protein Systems (Cont.)
• Coagulation (clotting) system: another cascade with multiple factors that affect downstream factors leading to the formation of fibrin from fibrinogen starting to form a web that collect platelets forming a clot. 2 diff ways of getting this system started.
o Forms a fibrinous meshwork at an injured or inflamed site
▪ Prevents the spread of infection
▪ Localizes microorganisms and foreign bodies
▪ Forms a clot that stops bleeding
▪ Provides a framework for repair and healing
o Main substance is an insoluble protein called fibrin
o Extrinsic pathway: most common, found inside the blood that signal for increased clotting
o Intrinsic pathway: responds to endothelial cell damage or the lining of the blood vessels
Plasma Protein Systems (Cont.)
• Kinin system
o Functions to activate and assist inflammatory cells
o Primary kinin is bradykinin, acts like histamine
o Causes dilation of blood vessels, pain, and smooth muscle contraction; increases vascular permeability, leads to inflammation, limits bleeding in damaged area and starts coagulation pathway to stimulate clotting
Plasma Protein Systems (Cont.)
• Control and interaction of plasma protein systems
• Tight regulation is essential, guns at your house to protect yourself, still must be locked away
• Multiple mechanisms are available to either activate or inactivate (regulate) these plasma protein systems to prevent unwanted actions with our cells and they use different activation pathways to prevent
unwanted activation unless there is a stimulus to cause activation
Cellular Components of Inflammation
• Cellular components:
o Erythrocytes (RBC)
o Platelets
o Leukocytes
▪ Granulocytes (phils)
▪ Monocytes (in the plasma, once it crosses into the interstitial it differentiates and doesn’t reproduce it changes into a macrophage)
▪ Lymphocytes (B and T cells)
Cellular Components of Inflammation (Cont.)
• Cellular receptors: looking for certain receptors found on pathogens that are not on our cells
o Pattern recognition receptors (PRRs)
o Pathogen-associated molecular patterns (PAMPs) (mannose, we don’t have these in our cells)
o Damage-associated molecular patterns (RBCs signal that they’ve been damaged)
o Toll-like receptors (looking for patterns that aren’t associated in our DNA such as double stranded RNA)
o Complement receptors (found on WBC that undergo phagocytosis and can engulf and get stimulated to begin phagocytosis)
o Scavenger receptors (same as above)
o NOD-like receptors (stimulate recognition of things not in the cell such as viral proteins as viruses invade and reproduce)
Cytokines
• Signaling molecules that can help to stimulate response to different stimuli such as infection or damage, guides lymphocytes and leukocytes to the area of damage. Responsible for activating other cells and regulating inflammatory response. Can stimulate inflammation or decrease inflammation.
o Chemokines
▪ Synthesized by many cells (macrophages, fibroblasts, endothelial cells) in response to proinflammatory cytokines
▪ Induce chemotaxis to promote phagocytosis and wound healing
▪ Examples:
• Monocyte/macrophage chemotactic proteins
• Macrophage inflammatory proteins
• Neutrophils
Cytokines (Cont.)
• Interleukins (IL), type of cytokine that are made by WBC
• Produced primarily by macrophages and lymphocytes in response to stimulation of PRRs or by other cytokines
• Many types
o Examples:
o IL-1 is proinflammatory, stimulates fever causing the hypothalamus to set the body temp
o IL-10 is anti-inflammatory
Cytokines (Cont.)
• Tumor necrosis factor-alpha, not an interleukin but seen as a key regulator for inflammation
o Secreted by macrophages in response to PAMP and toll-like receptor recognition
o Induces fever by acting as an endogenous pyrogen, inducing IL1 and IL6 which cause fever
o A strong inflammatory mediator causing granuloma formation attracting lymphocytes causing clotting and get the area walled off recruiting WBC to the area
o Increases synthesis of inflammatory serum proteins
o Causes muscle wasting (cachexia) and intravascular thrombosis if found in the muscle
o High levels can be lethal
o Target of biologic agents to try to diminish the immune response when over expressed for what we consider a normal response, for example autoimmune conditions such as RA Crohns this factor can be used to ramp down the immune response which can lead to progression of the disease.
Cytokines (Cont.)
• Interferon (IFN)
o Protects against viral infections
o Produced and released by virally infected host cells in response to viral double-stranded RNA, can stimulate other cells to protect themselves before they are infected
▪ Protects neighboring healthy cells
• Types:
o IFN-α and IFN-β
▪ Induce production of antiviral proteins
o IFN-
▪ Increases microbiocidal activity of macrophages
Mast Cells and Basophils
• Mast cells are cellular bags of granules located in the loose connective tissues close to blood vessels
• Skin, digestive lining, and respiratory tract
• Contain histamine, cytokines, and chemotaxis (attracting immune cells) factors that can lead to vascular permeability
• Basophils are found in blood and probably function in same way as mast cells
Mast Cells and Basophils (Cont.)
• Chemical release in two ways
o Degranulation
▪ The release of the contents of mast cell granules
▪ A receptor was engaged to release the cell granules causing a strong immediate acute response
▪ The receptor can be an antibody acting as a receptor
▪ Antibody IgE can bind to the mast cell not causing it to engage but sticking out and acting as a surrogate receptor for the mass cell and then degranulate (seen in allergic
responses)
o Synthesis
▪ The new production and release of mediators in response to a stimulus
Mast Cell Degranulation
• Histamine
o Vasoactive amine that causes temporary, rapid constriction of the large blood vessels and the
dilation of the postcapillary venules, allows for leakage of fluid into the tissues causing the edema and pain and redness that come with inflammation
o Retraction of endothelial cells lining the capillaries Mast Cell Degranulation (Cont.)
Histamine
• Receptors:
o H1 receptor (hayfever, causing inflammatory responses)
▪ Proinflammatory
▪ Present in smooth muscle cells of the bronchi
▪ Antihistamines can make you feel better and breathe better as blocking the H1 receptor can help cause vasodilaton of the bronchi smooth muscle
o H2 receptor
▪ Anti-inflammatory
▪ Present on parietal cells of the stomach mucosa
• Induces the secretion of gastric acid
• As histamine binds to this receptor, it stimulates digestion
• Antagonists include antacid to block acid production
Degranulation
• Chemotactic factors:
• Neutrophil chemotactic factor
• Attracts neutrophils and eosinophils to the area
• Eosinophil chemotactic factor of anaphylaxis (ECF-A)
• Attracts eosinophils
Synthesis of Mediators
• Leukotrienes
o Product of arachidonic acid from mast cell membranes
o Similar effects to histamine in later stages
• Prostaglandins
o Similar effects to leukotrienes; they also induce pain
o Aspirin and some other nonsteroidal anti-inflammatory drugs (NSAIDs) block the synthesis of prostaglandins, thereby inhibiting inflammation and pain
• Platelet-activating factor
o Similar effect to leukotrienes and platelet activation
Endothelium
• Endothelial cells adhere to underlying connective tissue matrix
o Help to direct and Interact with this inflammation circulating cells, platelets, plasma proteins
o wall off area of spread of the damage from trauma
o Regulate circulating inflammatory components
o Damage to these initiates platelet adherence, can interact with platelets to form clots
Platelets
• Activated by tissue destruction and inflammation
• Activation leads to interaction with coagulation cascade to stop bleeding
• Degranulation with serotonin release (acts like histamine but is a neurotransmitter)
• From the platelets serotonin acts like histamine so it will cause vasodilation causing an increase in blood flow but slowing it down due to an increase in permeability allowing for leukocytes to get a better
attachment to the cell well starting to migrate into the tissue
Phagocytes
• Neutrophils, main responder in early inflammatory response, large % in plasma
• Phagocytic, can engulf and phagocyte the pathogens or debry in the damaged area
• Also referred to as polymorphonuclear neutrophils (PMNs)
• Predominate in early inflammatory responses
• Ingest bacteria, dead cells, and cellular debris
• Cells are short lived and become a component of the purulent exudate
Phagocytes (Cont.) these are less frequently found
• Eosinophils
o Mildly phagocytic
o Defense against parasites (large worms, WBC can’t deal with) and regulation of vascular mediators they have neurotoxin agents that can kill off the worms. They are linked to hypersensitivity reactions such as allergies
• Basophils
o Similar to tissue mass cells
o Least prevalent granulocytes
o Primary role unknown
Phagocytes (Cont.)
• Monocytes and macrophages as they enter into the tissue they engage and change into macrophage
• Monocytes are produced in the bone marrow, enter the circulation, and migrate to the inflammatory site, where they develop into macrophages
• Macrophages typically arrive at the inflammatory site 24 hours or later after neutrophils
Phagocytes (Cont.)
• Dendritic cells, don’t fight the infection but detect signs of infection and after detection dislodge and make their way to lymphocytes in the lymph nodes to help activate those respond
• In peripheral organs and skin
• Migrate through lymph vessels to lymph tissue and interact with T lymphocytes to generate an acquired immune response
Phagocytosis
• Process by which a cell ingests and disposes of foreign material
• Production of adhesion molecules that help WBC stick to the cell wall to be stopped in the area they need to be
• Margination (pavementing)
o Adherence of leukocytes to endothelial cells
• Diapedesis
o Emigration of cells through the endothelial junctions
Phagocytosis (Cont.)
Phagocytosis (Cont.)
• Steps:
o Adherence: if you lose this ability, you won’t have any cells making their way into the tissue
causing impaired immune response
o Engulfment
o Phagosome formation
o Fusion with lysosomal granules
o Digestion/Destruction of the target
o Tuberculosis subverts this process allowing the organism to live within the phagosome and never merge with the lysosome unless activated by immune cells, allowing itself to be phagocytized but secretes molecules that prevent it from merging with the lysosome so it stays alive and live in the phagosome undigested because it prevented merging of the lysosome
Natural Killer Cells
• Unique, don’t look for specific peptides like lymphocytes would, don’t have the same receptors that neutrophils and macrophages have. Recognize and eliminate cells infected with viruses
• Also, able to recognize and eliminate cancerous cells
• Therefore, immunocompromised patients have higher rates of cancer
• Inhibitory and activating receptors to allow differentiation between normal and abnormal cells
• Produce cytokines and toxic molecules
• Only type of cell that will kill on a contact basis causing cell suicide (apoptosis)
Acute and Chronic Inflammation
• Acute
o Self-limiting, brief, localized, should resolve and if not it will form a lot of dead debris
o Local manifestations—result from vascular changes and corresponding leakage of circulating components into the tissue
▪ Heat, swelling, redness, pain
▪ Exudative fluids
Exudative Fluids
• Serous exudate
o Watery exudate: indicates early inflammation
• Fibrinous exudate
o Thick from proteins, clotted exudate indicates more advanced inflammation
• Purulent exudate (suppurative)
o Pus: indicates a bacterial infection from neutrophils and macrophage from phagocytic debris and
death
• Hemorrhagic exudate
o Exudate contains blood indicates bleeding
Systemic Manifestations of Acute Inflammation
• Fever
o Caused by exogenous and endogenous pyrogens (IL1, IL6, TNF Alpha)
▪ Act directly on the hypothalamus, cause a higher set point of body temp
• Leukocytosis
o Increased numbers of circulating leukocytes
▪ Left shift; increase in number of immature leukocytes because of more rapid production and release into circulation.
▪ Immature lymphocyte production indicates acute change or a left shift
Systemic Manifestations of Acute Inflammation (Cont.)
• Increased plasma protein synthesis, the liver will make these acute phase reactants
o Acute-phase reactants:
▪ C-reactive protein (CRP)
▪ Fibrinogen: clotting cascade, complement system can be enhanced through production
▪ Haptoglobin: a molecule that binds any free Hgb, if the infection caused hemolysis or damage to the erythrocytes, they will spill Hgb out into the plasma which is damaging to
the kidneys because toxic substances are released onto the kidney cells causing oxidation.
Haptoglobin is a way of blocking this oxidation and binding to the Hgb and marking for recycling elsewhere
▪ Amyloid
▪ Ceruloplasmin, etc.
▪ Measure by increased sedimentation rate (ESR) or CRP levels
Chronic Inflammation
• Other causes of chronic inflammation:
• High lipid and wax content of a microorganism
• Ability to survive inside the macrophage
• Toxins
• Chemicals, particulate matter, or physical irritants
• Inflammation lasting 2 weeks or longer
• Often related to an unsuccessful acute inflammatory response, lack of ability to fully clear infection
• Something to help sustain inflammatory response such as lack of resolution of cause or maintain of inflammatory response
• Can enter a repeating cycle where leukocytes are activated and lead to cell damage causing chemotaxis and recruitment of more leukocytes keeping the inflammatory process going. This is a reason why the adaptive immune response has a way of ramping down and turning off. You do not want to get into a
chronic inflammatory situation.
• Characterized by pus formation, suppuration, and incomplete wound healing
• If there is a high lipid or wax content in the pathogens it is difficult for the phagocytes to phagocytose, so you need more cells to clear the infection
• Also, other intracellular pathogens such as TB, leprosy, listeria all can end up making it harder to clear infection if they are hiding in the cell.
Chronic Inflammation (Cont.)
Chronic Inflammation (Cont.)
• Characteristics: Chronic/Long term
o Excessive healing can lead to dense infiltration of lymphocytes and macrophages
o Granuloma formation, circumscribed area of dense infiltrate activated cells and connective tissue
o Scar formation, calcification.
o Epithelioid cell formation
o Giant cell formation
Wound Healing
• Simply trying to regenerate new cells to replace damaged or lost cells
• Regeneration
• Resolution
o Clear out the debris. Returning injured tissue to the original structure and function, the connective tissue is not going to lay in a specific way but overtime as stress is laid on it it will lay in a certain way
• Repair
o Replacement of destroyed tissue with scar tissue
o Scar tissue
▪ Composed primarily of collagen to restore the strength of the tissue but not its function
Wound Healing (Cont.)
• Healing
• Filling in the wound
• Sealing the wound to prevent further infection and loss of fluid (epithelialization)
• Shrinking the wound caused by connective tissue being pulled together (contraction)
Wound Healing (Cont.)
• Primary intention
o Wounds that heal under conditions of minimal tissue loss
o Surgical site and putting the tissue sites back together, healing through primary intention
• Secondary intention
o Wounds that require a great deal more tissue replacement
o A lot of tissue loss creating a deficit loss
o Open wound
Wound Healing (Cont.)
• Wound healing there are 3 phases
• Inflammation phase
o Coagulation
o Infiltration of wound-healing cells dealing with infection or trauma
o Angiogenesis is the supplying of new vessels, the metabolic need
Wound Healing (Cont.)
• Proliferative phase
o Granulation: new blood vessels, new cells, a healing and red response
o Epithelialization: overgrow and seal the wound
o Requires fibroblast proliferation, collagen formation, wound contraction
Wound Healing (Cont.)
• Remodeling and maturation phase
o Continuation of cellular differentiation with previous tissue
o Scar tissue formation following lines of stress
o Scar remodeling once initially healed
Wound Healing (Cont.)
Dysfunctional Wound Healing
• May occur during any phase of wound healing
o Ischemia
o Excessive bleeding could cause hematomas
o Excessive fibrin deposition creates fibrinous exudate making it hard for the cells to populate the area because it is populated with proteins
o Predisposing disorders
▪ Diabetes causing delayed in poor healing and decreased angiogenesis, diminished nervous system function so not proper responses, leads to multi organism infections versus single infection in those that are not diabetic
▪ Obesity
▪ Wound infection
▪ Inadequate nutrients
▪ Numerous drugs
▪ Tobacco smoke, nicotine causes vasoconstriction causing ischemia of the surgical site etc delaying wound healing and maybe stop wound healing
Dysfunctional Wound Healing (Cont.)
• Dysfunction during reconstructive phase
o Dysfunctional collagen synthesis
▪ Keloid scar: excessive collagen synthesis extends well beyond the area of the wound
▪ Hypertrophic scar: excessive collagen that stays within the bounds of the wound
o Wound disruption
▪ Dehiscence (increases risk of infection)
o Impaired contraction
▪ Contracture
Adaptive Immunity
• Purposes:
o Like the innate response in that they both work together. The adaptive response recruits the
innate response for help. Destruction of infectious microorganisms that are resistant to inflammation
o Long-term, highly effective protection against future exposure to the same microorganism
• Inducible, not always present, it is made to order
• Specific. It is looking for a small peptide or protein and not a pattern
• Long-lived, protection for a very long time due to the existence of B and T cells that have memory and have memory of a certain pathogen
• Has memory: B and T cells have memory have pathogens so they can respond quickly
Adaptive Immunity (Cont.)
• Elements:
o Antigens/immunogens
o Lymphocytes (T cells, B cells) these respond to antigens
o All immunogens are antigens but not all antigens are immunogens so they will not all start and cause an immune response
o Two different types of T cells, CD8 T cells are cytotoxic cells that kill and target the cell directly it is contact directed it must be touching the cell directly to recognize and kill it. The other type of T cell helps to stimulate and direct the CD8 T cell and the B cell named a CD4 or T helper cell to produce antibodies. The CD4 or T helper cell is what is targeted by HIV, so once HIV cells damage the T helper cells it also causes loss of activation and help to the other cells losing much adaptive response. This is different than B cells, they typically release antibody into the plasma
and where the antibodies engage, they can help through a process destroy the cell. B cells don’t need to be in contact with the antigen for it to be effective.
o Once these cells identify their target they undergo clonal production and form many clones of themself to deal with the pathogen and once it is dealt with some of these cells will become long lived memory cells
• Components:
o Humoral—immunoglobulins (antibodies)
o Bind to antigens on bacteria and viruses
o Cellular—T cells
▪ Subpopulations (effector T cells)
▪ Kill target directly
▪ Stimulate other leukocytes
• Both produce memory cells
• Interact
Adaptive Immunity (Cont.) (2 diff types)
• Active immunity (our immune system acted and responded, went through the process to respond to the infection) ex: getting chicken pox, an adaptive active process because you have T and B cells that recognize that antigen and upon exposure the second time it reacts so quickly you won’t get infected the
second time
o Exposure to antigen
o Immunization
• Passive immunity (body did nothing to stimulate create that immune response, given the immune response)
o Breastmilk antibodies to the child of pathogens that the mother has been exposed to
o Intravenous immunoglobulins IVIG
o Preformed antibodies or T cells are administered
Antigens and Immunogens
• Antigens
o Bind with antibodies, receptors on T and B cells but won’t always do so because they are not
recognized in their current form
o Not necessarily immunogens which are those that are able to produce production of antbodies in T and B cell activation. These things cause activation
• Immunogens
o Induce production of antibodies, T and B cells
o All immunogens are antigens but not all antigens are immunogens
• Haptens
o Too small to be immunogens by themselves but become immunogenic after combining with
larger molecules that function as carriers for the hatpens, need to bind with a carrier
Antibodies
Immunoglobulins (antibodies): diff reasons why the immune system favors one antibody over another, usually signaled by the cytokines that come into contact with the B cell during the class switching
Classes:
IgG: class G antibodies are most common, main source of antibodies
IgA: if pathogen coming in through mucousal areas because IgA can be secreted out onto mucosal surfaces IgM: all antibodies start as IgM, over the course of infection the B cell will switch frequently to another antibiotic class, typically IgG
IgE: dealing with parasites IgD
Characterized by differences in structure and function
Antibodies (Cont.) [Show Less]