MCQ 40 Set 3

Three Lines of Defense

• Physical and chemical barriers offer continuous protection.
• Innate immunity is rapid and nonspecific.
• Acquired immunity is slow, long lasting, and highly specific.

First Line of Defense: Physical Barriers

• Skin acts as a physical barrier, blocking pathogens.
• Epidermis consists of packed epithelial cells; the outer layer contains dead keratinocytes.
• Dermis is packed with immune cells.
• Skin is slightly acidic with a high concentration of NaCl, often dry, and utilizes antimicrobial peptides (AMPs).
• Skin varies in temperature, constantly sheds cells, and contains a thick layer of dead cells and resident immune cells.
• Epithelial lining acts as a barrier and signals the presence of pathogens.
• Mucus and cilia trap bacteria.
• Normal microflora compete with pathogens.
• Expulsive reflexes like coughing, sneezing, and vomiting help remove pathogens.

First Line of Defense: Chemical Barriers

• Stomach pH is high, while skin has high salt and acidic pH to prevent pathogen colonization.
• Saliva contains lysozymes that cleave glycosidic bonds between NAG and NAM, weakening bacterial cell walls, making them prone to lysis due to osmotic pressure.
• AMPs are antimicrobial peptides found in skin, saliva, and siderophores with cationic and hydrophobic properties, targeting bacteria, viruses, and fungi by disrupting bacterial membranes.
• Eukaryotic cells are less charged, and therefore less affected by AMPs.
• Psoriasin, produced by keratinocytes, disrupts bacterial membranes and binds to zinc to inhibit bacterial growth, specifically targeting Gram-negative bacteria while maintaining the skin barrier.
• Defensins are + charged peptides (30-45AA) of alpha (immune cells) & beta defensins (skin and saliva) that kill bacteria and viruses by creating pores in the membrane, leading to depolarization.
• Lactoferricin, found in saliva and breast milk, chelates iron, has antimicrobial properties and can be cleaved by enzymes into the AMP lactoferricin.

Phagocytosis

• Macrophages (resident in tissues) and neutrophils (recruited from the blood) carry out phagocytosis.
• Steps in phagocytosis:
  • Chemotaxis (attraction)
  • Attachment via receptor binding
  • Ingestion and phagosome formation
  • Lysosome fusion
  • Microbial killing and digestion
  • Release of waste.

Recognizing Microorganisms

• Macrophages recognize fungi/bacteria through Pattern Recognition Receptors (PRRs) that detect Pathogen Associated Molecular Patterns (PAMPS).
• Toll-like receptors (TLRs): different TLRs recognize different PAMPs like peptidoglycan (TLR2), lipopolysaccharide (LPS) (TLR4), flagellin (TLR5), ssRNA (TLR7), dsDNA (TLR9) and pili (TLR10)
• Microbes have Pathogen Associated Molecular Patterns (PAMPS) that are not easily mutated.
  • Nucleic acid: ddRNA and ssRNA in viruses.
  • Proteins: flagellin (bacterial flagella) and pilin (bacterial pilli).
  • Lipids: lipopolysaccharide (LPS) (G- cell wall) and lipotechoic acid (G+ cell wall).
  • Carbohydrate: mannan (fungi & bacterial cell wall), glucans (fungal cell wall), peptidoglycan (bacterial cell wall).

Opsonization

• Opsonization involves coating pathogens with opsonins (antibodies or complement proteins) to enhance phagocytosis.
• Tagging: Antibodies coat the pathogen.
• Recognition: Macrophages recognize the antibody's Fc region using their Fc receptors.
• Engulfing: The macrophage binds to the antibody and "eats" the pathogen.
• Killing: The pathogen is destroyed inside the macrophage.

The Process of Phagocytosis and Cell Killing

• Recognition: PAMPs on microbe surface bind to PRRs on immune cell surface.
• Ingestion and phagosome formation: Receptor initiates phagocytosis via signal transduction, actin rearrangement forms pseudopodia around the target cell, forming a phagosome.
• Phagosome maturation:
  • Encapsulation: microbe is engulfed into phagosome inside the phagocyte,
  • Fusion with Early Endosomes: early endosomes deliver proteins that initiate the maturation process,
  • Fusion with Late Endosomes: late endosomes acidify the environment,
  • Fusion with Lysosomes: phagosome fuses with lysosomes, forming a phagolysosome in an acidic environment with enzymes.
• Microbial Killing and Digestion: Hydrolytic enzymes, ROS, and nitrogen intermediates kill and break down the microbe.
• Debris Clearance: Waste is released or processed for antigen presentation.

How Macrophages Kill Bacteria

• Acidification: Reduction of pH to 3.5-4 using H+ ATPase Pump.
• ROS species: Hypochlorite OCL- (containing bleach), nitric oxide, superoxide and peroxynitrite
• AMP: AMP: defensins (cationic peptides for ion pores in membrane)
• Enzymes: lysozymes that degrades peptidoglycan layer, Dases, RNses and Proteases
• Nutrient removal: Removal: siderophore and nutrient transporters

Cell Signaling and Immune Gene Expression

• Upon binding, TLRs combine, and the TIR domain signals the cell to express immune genes.
• Signal transduction ends on NF-kB -- a main shared transcription factor.
• NF-KB promotes AMP production, enhances phagocyte capacity in phagosome maturation, induces cytokine and inflammatory protein production.

The Inflammatory Response

• Cascade complex at the site of infection.
• Four cardinal signs: Redness, edema, swelling, pain, and heat.
• Mass recruiting of immune cells.
• Acute (short term) response to infection.
• Chronic (long term) response to cell damage (e.g., IBS and arthritis).

Types of Cells in Inflammatory Response

• Neutrophils: most abundant, circulate in blood (die after 8h) and are phagocytes.
• Macrophages: (i.e. Cooper cells) resident cells that are phagocytes and are first to encounter microbes, found in external barriers such as the gastrointestinal submucosal layer, skin, and alveoli of the lung.
• Monocytes: recruited to site to differentiate.
• Dendritic cells: sense danger, release cytokines and reside in tissue.
• Mast Cells: reside in skin and mucosal tissues, activated by PAMPS, cytokines, or antibodies and linked to allergic reactions. Release histamine and cytokines leading to vasodilation, increased capillary permeability and stimulation of inflammation.

Inflammatory Response Steps

• Before infection or injury, monocytes and neutrophils circulate, while resident macrophages, dendritic cells, and mast cells wait in tissues.
• Injury and infection results in localized tissue damage and bacterial entry.
• Activation of immune cells (PRR/PAMPS) induces innate immune cells and leads to cytokine release of cytokines, chemokines, histamine and bioactive lipids (TNF, IL-8, IL-1) is released by activated innate immune cells via PRR/PAMPS.
• Capillary alteration and vasodilation: mast cells release histamine, capillaries and venules increase in diameter, fluid and plasma proteins enter tissue. Inflammatory mediators esc into blood.
• Extravasation: endothelial cells are activated by TNF and express selectin, chemokines cause leukocytes to express high affinity integrin, junctions of endothelial cells are broken, leukocytes cross into tissues.
• Phagocytosis and wound clearance: Neutrophils arrive first, followed by monocytes (macrophages) and then DC/macrophages, travels to lymph nodes to present antigens and clotting occurs.

Inflammatory Mediators: Cytokines

• Leukocytes use cytokines to communicate.
• Cytokine binds to cytokine receptors on target cells, and affects cell adhesiveness, enzyme activity, cell death or survival, and gene expression.
• Communication: Inducing stimulus-> Cytokine gene activation -> Cytokine secretion-> Reaching cytokine receptor -> Gene/enzyme activation -> Biological effect.
• Cytokine family includes IL-1, IL-8, TNF, and Interferons.
  • IL-1: Release by macrophages and epithelial cells and Binds to IL-1 receptor that causes proinflammatory effects.
  • TNF Release by macrophages and neutrophils, binds to TNF receptor and causes proinflammatory effects.
  • IL-8 (CXCL8) recruits and activities neutrophils.

Chemokines

• Chemokines are chemoattractants that affect cell mobilization and cell adhesiveness of immune cells
• Establish a concentration gradient and are released early by macrophages and damaged cells.
• Named for conserved cysteine (C) residues (CC or CXC).
  • CC attracts monocytes and macrophages.
  • CXC attracts neutrophils.

The Complement System

• Part of the innate system found in the blood plasma and produced in the liver.
• Three Roles:
  • Killing (lysis) of foreign cells
  • Tagging foreign material (opsonising)
  • Proinflammatory signalling and chemoattraction

Complement Pathways

• All pathways meet and make C3 convertase and form the MAC (membrane attack complex).
• Classical pathway: starts with antibody.
  • C1 Complex binds Fc region of antibody, activating C1r and C1s.
  • C1s cleaves C4 into C4a and C4b, C4b covalently attaching to bacteria and binds C2.
  • C1s cleaves C2 into C2a and C2b, C4b and C2a make active protease C4bC2A = classical C3 convertase.
• Lectin pathway: starts with lectin.
  • Mannose binding lectin (MBL) binds repeating mannose (bacteria and yeast).
  • MBL-associated serine protease (MASP) cleaves C2 and C4.
  • C4b attach to surface and combines with C2a giving C4bC2a = c3 convertase.
• Alternative pathway: Doesn’t need antibody/microbe to start.
  • C3 in blood is hydrolysed and binds to Factor B.
  • Factor B cleaved by Factor D into Bb and Ba.
  • Bb >> C3(H2O)Bb (initial C3 convertase).
  • Factor B binds with C3b Factor D cleave Factor B forming c3 convertase.
  • C3b bounded converted will convert C3 convertase to C3 convertase that amplifies itself creating an amplification loop.

Terminal Complement Pathway

• Formation of C5 Convertase:
  • The C3 convertase (C3bBb), generated in the alternative pathway, binds an additional C3b molecule to form the C5 convertase (C3bBbC3b).
  • C3a induces local inflammatory response
  • The C3 convertase (C4b2a) from the lectin (or classical) pathway similarly binds an additional C3b, forming the C5 convertase (C4b2aC3b)
• C3b has high reactive thioester bond that covalently attaches to microbial cell.
• The C5 convertase cleaves C5 into C5a (recruits and activates immune cells) and C5b: initiates MAC assembly.

MAC

• C6, 7, and 8 are recruited to the membrane.
• C8 inserts and C9 forms a cylindrical pore.
• Bacterial death (results of a hole under pressure): bores in outer membrane allows antimicrobial enzymes in, affects function of inner membrane, leads to cytosol leakage bacterial lysis and results to cell wall instability.

Completment Function

• Tag microbe via opsination using:
• C4b and C3b covalently attached to bacteria and acts as ligand for Complement Receptor.
• Alert immune system through inflammatory response.
• Lyse invaders.
• Cleaved ‘a’ products act as anaphylatoxins where it binds to specific receptors on immune cells.

Regulation of Complement

• Complement doesn't kill our own cells because mammalian cells have receptors (e.g., CD59) that inhibit the complement cascade.
• Patients lacking terminal complement proteins are susceptible to pathogen infections.

Antibodies and Adaptive Immunity: Recap

• All antibodies are produced in B cells made de novo in the bone marrow.
• Each B-cell clone produces a different antibody with a variable (v) region that differs as well and constant (c) region remains the same.
• Adaptive immune system is not inherited
• Antibody are located on segments within chromosome.
• 30-45 variable light chain gene segments.
• Heavy chain has Diversity gene segments.
• Each B-cell clone will have its own variable region for light and heavy chain generated through:
• Combinatorial diversity: Genetic recobintion between V+J+D [heavy] and V=J [light]
• Junctional diversity: Random mutations are generated at junctions of the segments.
• Somatic hypermutations: Mutation on an antibody while its created.
• B cells, while being binded to an antigen, clones itself and secreted within lymph nodes. Affiinity can be improved within B cells creating more mutations.

The Adaptive Immune Response

• The immune system "remembers" due to the adaptive immune response. This is why vaccine are effective.
• Two Types:
  • Humoral: (antibodies)
  • Cell-mediated:
• When injury occurs: Macrophages, neutrophils, and complement help.
• Dendritic cells in epithelial tissues: Present in external-facing tissue, PRR, activated by microbes migrates to lymph nodes to present to antigen.

Lymphatic System and Lymph Nodes

• Lymph fluid travels driven by muscle movement and.
• Antigens are presented to B and T cells in lymph nodes.
• Pathway: External facing barriers breaches-> Microbes enters-> DC engulfs and displays the antigens -> Antigens presented in lymph nodes and Native B cells bind to antigen.

B-cells and T-cells (Lymphocytes)

• B cells produces and secrete antibodies for humoral immunity that mature in bone marrow.
• T cells detects and kill infected cells to mediate cellular immunity and mature in the thymus
• Both originate from stem cells in bone marrow and migrate to lymph nodes waiting to be activated.
• Receptors define each B-cell and T-cell.

B-cell Receptors (BCR)

• Has 42Y, two heavy chains and two light chains through disulide bridge.
• A pair of light chain and heavy chain make one antigen binding found at variable region site (x2).
• BCR are membrane bound antibodies (IgD)
• Recognizes antigens like carbs, lipids, DNA and proteins
• T-cell Receptor (TCR) are similar but has 1 binding. Ssite.
• T cell recognized proteins on surface of infected cells.
• 2L chain [L-Shape]-> Has alpha chain and beta chain joined via disulfide bridge

B Cell Activation, Clonal Selection and Secretion of Antibodies

• Antigens delivered into lymph nodes are then recognizes the naive b-cells that are then activated and creates clones that are differentiated.
• plasma cell: producing ranges antibodies recognising original antigen and have a life span of 5-6 days.
• Memory cells: have have same membrane bound antibody as activated parent b0-cell
• Responds quickly to infections.

T cells

• Mature in the thymus.
• TCR (t-cell receptor on its surface): each t-cell recognize different cells presented by infected cells effective against viruses or intracellular pathogens.
• Types:
  • Cytotoxic T cells (CD8 / Tc cells): Kills cancerous/infected cells
  • Helper T cells (CD4 / Th cells): activates Immune system using cytokines
• T cells can recognise antigens presented on MHC (major histocompatibility complex).
  • MHC1: Nucleated cells that are recognized by Cytotoxic T cells.
  • MHCII: macrophages and trigger and dendritic (survellance).

MHC1

• Infected cell presents antigen on MHC1 (presentation)
• T-cell recognizes it in infected tissue by T cell receptor and destroys antigens. (recognition)
• Tc cell kills infected cells (granenzyke and perforin). MHC1.

MHCII

• DC presents antigen on MHCII in lymph nodes (presentation)
• Th recognizes the T cell. (recognition)
• Releasing immune cells via (cytokines).

Clonal Expansion of T Cells

• Effector cells proliferate and become activated by DC in 1-2 days. (Th CD4 / Tc CD8). and released large amount of cytokines
• Allows B-cells to turn into plasma as well stimualting proliferation of Tc
• HIV targets CD4 cells = no effective immune system

B-Cell and T-Cell Activation

• After making new B cells, these newly created cells will migrate to spleen/lymph nodes.
• Antigens could be detected from lymph nodes using antigens via DC.
• Free antigens will be detected within spleen on detection. Activation.
• B-cells look for free antigen in lymph nodes based on molecular size (viruses and large antigens)
• T cell scan the APC within Lymph Node

B Cell Activation

• If the antigen is detected, B cells will remain lymph node and replicate themsel, causing th cloning.
• 5000 plasma can be created within clonse to product (GAMED) classes of antibodies with TCD or TCH.

Basic Mucosal Immune System (MIS) Information

• Protects toxic element that enters via mucus membranes
• largest immune system with single layer covered my mucus or microbial protein and reinforces the internal immune.
• Mircobiota can be within gut, in skin with sympotic or pathogin functions
• Divided between the 2 via anatomical or functional property, ie. gut.

Immunity withing the Guts/Microbes

• The microbines gut immunity that is within the mucosal help sustain internal homeostasis and protect the internal environment
• key components:
• Providing protection against pathogenic bacteria in the gut and Nutritional roles of the gut
• The DC sample the cells and have the ability to produce antigen to start certain immune response.

Regulatroy Control in Mucous

• Deletion of autoreactive T-cells and induction of regulatory is criticial
• 2 typees. foreign and naatural antigens to help immune system
• immune can be affected by T cells or IBD

organization of gut IS

• Villli help ahsofrion nutrient and helps immune cell function.
• peyers path
• Removing pathogens and allow tolerance between commenal microbs.

Pathogenic infection basics

• The disfunction within the regulation homeostasis
• Releasing IIl which will trigger the immune cell activation.
• IIl will cause cells to damage but it allows the activation with innate system for homeostasis.

DC/ Macrophage

• DC/activated cells which affect inflammation by secreting key inflammation to activate the immune response. neutrophills: Helps clears with cell death but tissue can be damanged.

Mucosal Immunity in Disease

• Disrefualition will cause disease in autoimmune system sucha s IBD, allergies of MIS, and infections Used to developed Key :
• DC activate antigen that are trnasffered to presented CDs or Ds.

Allergen Information

• Pollen

• Funguy

• insects

• animals

• indication with allergic effect. . aerodynamic properties of allergens grass pollen= hay fever for airborne. . animal allergen- cats- IgE with D 1

Sensitization

Immunization will NOT induce persistant . troublr breathing sneeing headach red/ watery eyes hives

Grass pollen

Properties of wil help releaes protien -Ige igA igg. NEUTRALIZERS. COMPLEMENT ACTIVATORS= ENGAGE IK Cell

Dust Mites

Main Allergens are Fecal matter Activated the TLR for inflamation

Cat dander.

Maon allgern is D 1= when inhales

Anaphylasixis

allergen and release NEI Blood oressure airwao Treatment is Injections

sublinguall

Sensitization

• manifestation of immune process that is mediated to path Helps secret with Th2 to help imflammatory cell recruitment
• ll4 induced key role is switching ALlergen is to help recognise cell function Lps doses effect outcomes = Th2 can reduce

Genomic imnfluence.

• protein seequence and influence to TH@ with cell function allgren influence doseage pathway

#######Th!# pathway 17-microbios 2 anaphylaxis. L5. esophlic diseases

tregs. 1 increase 1 L 2. reduce

Site -Dose with T cell medicated DO disorder dependaent to allergy affecrs the site

Immunity Disorders

• Initial/ 2end Transmissison type food contact bite air bone

Blood Centrifuge.

Hematacrit FBC TPPTl HBANC BLOOD SMEAR

WBC blood

T cell function issue. di Georges syndrome Chromosome

Blood Diagnostic

blood tests X ray ECHO Cardiographs Calcium suplmemtn

Thumis gland

Lack of t cells infection Brotons aGa

immunovirus disorder

B cells not producting antibodes male chronic damage lung s increases risjk

severe treatments: rest

Immujn system DO

weak immune system Aquired alergic reacftion too active Aout immune

SCID.

Rare and Inherited that causes mjor abnormalies with T and B cells

Treatments SCId

stem transplant enzym replace genes

HIV aids moncite retovirus = T CELL REDUCTIONS

HIV invasions

Infectisns cell helped by cell celector on T-cells

INATe Respose to HIV

D and A will preent it and key cell help NK: lylicit avtitivty

Humornal in HIP

Ocffyr later and neautrallizing

Why does immujne fail is hip inactivted cell latent infections peptide lack MHC to cell

Transplant DO

General.transplant Donor/HOST Tissue regeneration can helps Allo = ind to other Xneo is aniimal DO not work -rejectins

######Accept Graft AA B accept 4 combination

Transplants cell Mediations

Foreign identified and helps all LHA

LHA HLA HA

HLA human antigen = help reduce rejectiON Chromosome 1HLA-B Genes inheritensce

DNA test = high transplsnt, low is to find anti gen for vaccination Low to high to all HLA test

Autoimmunity

Failure if cell reaction to T cell DO, not seeins cell Pathop = B reaction

disorder

Cellia DO diebetes. Organ speific reactiond

#####Rejection Hyper. first hour accelorated is weekafrterDO

CD4 CD.8 NK macrphjae are reactions to cellular reactions and immune

Cellular immune react DO after few dars is transplant around injflamed cell = WBC antibodes occlusions blood will scab

Chronic Reject

cel and antibodes attacks and DO not ceasing functikning Months to yeah for organ normal functions. = vary from sites,

1Cell foreign peptide, 2.cell for anti preentcell. Precess for damage/ and MHC-

###Medicaafter transplammt prevent infections all youor life INFLMATOOR Y Immun MHRC

3- Sterids cytosine

####Bone marrow. Stem Cells = infusion and health auato= tranps plant your cell expect

After transplante - blood test, monitor, prevention of rejection.

##Risk Depends on many factor. allograft stem, cell, health rejection. transplant

organ dimage, infectins, cancer

• not rejections. progestone hormone cell, facail barrrier

Infection.

Anithy is neved Antobodes T cell Immune reposne antibodes taqrt Vacinness - generate antibotdes orrect Saftety protecrt.chepa.

vacucated Program

herdimmunify. transssion will reduced in a number people getring infection.

Infection. bacteria anti .capsule has problem child not make T cell independent response = so no vaccine until SOulotions .Chemaicall convert bacrgerial

• Addujants. substance enchaninge of immugen Tetenus tot not Has cells of bateria Freund complet addujcacnt in vivo to hcnage adntoddy

Acion on DC. = Detcing pathogens on dcc Recogntizon is activater throguh direct interaction of procuts

Peptide.

protecitve anti gen eliciting. immutnity Another. Sytnhesiy Over la poeotwides Rev immunogentic Test Poulstuon: assocstred to Resisitnce celel Lmimtatjns

Pepeitds high polympohich, Sol: enginneer in carrier pRO/

• Lipiad carriers adfujants. = minimal toxin LOss peotdios and protein to ell cyotlsma

pepided s can delivers to lyto for acotvasrtuon for CDs.

LIve are are more ptenteiot, elicitiion,

Live Aterated Virs.

Cystolic to stop t cells. Atteanutrad for measles for covid = inducing but not dissease.

Risks

Toxin behavio as virulent is ealy infect Genetic technolgig

• ISloalte and vitro New reconsitruted

• advanatgs. not bewt or mutageneitic.

• Atterntrd Vacies = tagetne engynesr mutated

• Grout will depend on Targernt the genes that encode as auxotropic organism

Grow poor. But long.

• Routwe of vaccinantion = injectinos
• dlsaddanvtaiges pain
• not mimic patgoen

New = thourgh mucoasl syrfrt.e neeed to understan orgsin

Case stusy

Effectievnes opf live atterted polio Sabina opes has 3 attenuaters Posetuve. able tro trangmiited to feacsl .pol

• Proteviity can imduce dna encoding migcrbioal and humsnm cyctokineint muslce / dna vafssinsut

PRO> NOt damage or ONE SINGLE micfrobal gnee

Bacterail palasaimd.

Therapecticlly to Contril existrign chronicu

2types.

immuned frkialry pathogeic efescrts

TH2 type is the the harm of fiberi

Th1 to contain but cause Granular form

Thz

Sextull transmuted

• protrin beign to TAP, and STUP petpided trans[irtted tp the Er IN INEFCECTED celss.

2 immunolff

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Explore the body's defenses. Learn about skin's barrier function, lysozymes in saliva, and antimicrobial peptides (AMPs). Includes mechanisms of Psoriasin, defensins, and lactoferricin.