Week 3: Innate Immunity

2 Soluble mediators of innate immunity

• cytokines

• Complement

Pathogen breakers barrier, what occurs next

• four steps

• Releases PAMPs (pathogen-associated molecular patterns)

• Detected by PRR (pattern recognition receptor)

• Activates signal transduction

• Activates NFκB

  • Controls the production of soluble mediators of innate immunity (among other things!)

What are cytokines?

• what are they a category of

• What does it behave (2 things)

• What type of molecule are they? - + an additional role

• 
  

• category of signalling molecules used in cellular communication

• helps enhance the cell’s ability to rid of pathogens and promote healing

• A soluble protein that moderate cell behaviour at small concentrations

• Acts locally and systematically to the same producing cells or other cells

• Biological activities

Cytokines: pro vs anti-inflammatory

• pro-inflammatory cytokines

  • Things that induce sickness

  • IL-1B, IL-6, tumour necrosis factor (TNF)

• Anti-inflammatory cytokines

  • IL-10, IL-4, transforming growth factor b (TGFb)

What are complements?

• what is it made out of

• What does it operate similarity to?

• What is a zymogens

• What are triggers for activating it?

• a complex network of plasma and cell surface proteins

• Operates similarly to a blood clotting casade

• Known as a zymogens

  • A pro-enzyme that requires a biochemical change to become active - amplification Of an active factor activating the next, then the next, then the next

• Triggers for activating the first factor

  • Microbial patterns (PAMPS)

  • Immune complexes (between antibody and non-self proteins)

Different complement effector mechanisms

• just list them

• The membrane attack complex (MAC)

• Opsonization

• Enhance inflammation

The membrane attack complex

• What does the MAC consist of?

• Why doesn’t this form on human cells?

• MAC is located on the cell surface (appears like tubes)

• Components C5-C9 creates the complex that perforates (creates opening in) the cell membrane

• On a separate cell, the human cell, has a specific component CD59 that binds on to a complex (C5b,6,7,8) and prevents the recruitment of C9 to form the pore

• Therefore only can form pores in the microbes to kill them, rather than the human cell due to having CD59 to prevent forming the MAC

Opsonization

• what are opsonins? What proteins are opsonins (2)?

• What are they recognized by

• opsonin: coat bacteria - very important, making microbes more palatable/digestible

  • C3b, and iC3b - both gets bind index to the complement receptors CR3 and CR1

• Recognized by complement receptors expressed on phagocytes

Enhance Inflammation

• explain the process

• Four main steps

• the complement’s C3b receptor binds to the microbe

• Release of both C3b and C5a

  • C5 needs to under proteolytic first in order for C5a to be released

• Leukocytes are recruits and activation by C3a and C5a binding to the corresponding C3a and C5a receptors on the cells

• Leukocytes then destroy the microbes

Three important mechanisms that inhibit complement

• C1 INH

• Factor H

• Protectin (CD59)

Main roles of each (only one sentence)

• C1 INH: shuts down the classical and lectin pathways

• Factor H: binds to C3b and targets factor I to cleave the protein

• Protectin (CD59): integers with the assembly of the complement attack complex by binding to C7 and C8

C1-inhibitor deficiency

• what type of disease

  • What is the cause of the disease (What encodes for it)

• Prevalence ratio

• Symptom (main name + definition)

  • Also explain when it happens and that are some links with family human life

• Common affected areas (4)

• an autosomal dominant disease

  • Lack of the C1-inhibitor

    • Encoded by SERPING1

  • Not proper functioning of inhibitor protein

• Likelihood 1:50,000

• Characterized by recurrent episodes of swelling (angioedema)

  • Lasts 2-5days

  • Links with trauma, infection, stress

• Infected organs: limbs, face, intestinal tract, airway

Three main types of phagocytes

• monocytes/macrophages

• Neutrophils

• Dendritic cells

Monocytes/Macrophages

• monocytes: when found in the blood

• Macrophages: differentiated once travelled to the tissue

  • Structure: have many protrusions to seek pathogens

• Main role: phagocytose (to eat) pathogens and kill,

Types of macrophages and their definitions

Resident macrophages

• live in tissues

  • Have unique gene expression depending on their microenvironment

    • Liver - Kupffer cells

    • Brain - microglial cells

    • Lung: - alveolar macrophage

    • Bone - osteoclast

Neutrophils

• a.k.a polymorphonuclear leukocytes (PMNs)

• High number in the blood (50-70%)

• Main role: get to the site of the infection, enter tissues, use PRR (pattern recognition receptors) to bind to PAMPs, and ingest and kill microorganisms

• The cytoplasms: full of granules containing toxic products for killing

• After ingesting, they release their granules from the cytoplasms, killing the pathogens

• Cause collateral damage

NETs

• full name

• Why is it used in neutophils

• used to trap pathogens

• NET: neutrophil extracellular traps

  • Neutrophil will die, releasing it’s DNA

  • DNA sticky and traps bacteria

  • Macrophages come clean up the mess

Dendritic Cells

• resident cells in mucosal tissues that look around for pathogens

• Look like dendrites with huge extensions

• Main roles: survey the mucosal sites, sample bacteria, chew them up to present to T cells

• DC considered pro antigen presentation cells (presenting antigen to T cells)

Granulocytes

• characteristics

• Types

• multi-lobular nuclei and cytoplasm filled with granules; names derived from the appearance of their granules in stain

• Types

  • Eosinophils

  • Basophils

  • Neutrophils (already discussed)

Eosinophils And Basophils

• different characteristics

• Same characteristics

• Eosinophils are infrequent cells (1-6% of leukocytes) while basophils are the least common (0.01-0.3%)

• Stains with Eosin for eosinophils and basic dyes for basophils

Similar (both…)

• Degranulating cells

• Often associated with parasite killing

• Mediators of allergic reactions/asthma

Natural killer (NK) cells

• classification

• Part of which immune system

• Main roles

• Similar to

• non-T, non-Blymphocytes

• Part of the innate immune system

• Recognizes and kills abnormal cells (e.g. tumor and virally-infected cells)

• Similar cytolytic mechanisms to cytotoxic T lymphocytes (CTL)

Phagocytosis Process

• Chemotaxic and adherence of microbe to phagocyte

• Ingestion of microbe by phagocyte

• Formation of a phagosome

• Fusion of the phagosome with a lysosome to form a phagolysosome

• Enzymes digest and kill through oxidative burst

• Formation of a residual body containing indigestible material

• Discharge of waste materials

Summary

Microbe → phagocyte → phagosome vesicle (phagocyte + microbe) → +lysosome = phagolysosome → enzyme digest → residual body with waste → dischargex$

Oxidative burst (respiratory burst)

• What is produced (another name for it), mediate by what?

• How is it produced?

• the production of o2-based toxic molecules (reactive oxygen species (ROS)) mediated by the NADPH oxidase complex

• ROS formed from o2 to form intermediate o2 products (like H2O2) that are indirectly toxic to bacteria

How does neutrophils kills microbes

• several mechanisms

• ROS: respiratory burst/oxidative burst

• Lysozyme: an enzyme that breaks bacterial cell walls

• Antimicrobial peptides

• Formation of NETS, serving to trap, therefore killing bacteria

Defects in killing bacteria: Chronic granulomatous disease (CGD)

• explain the case study

• 4 year-old boy is investigated because of repeated episodes of ear infections and pneumonia

• Examination: underweight boi, fluid coming out of right ear, scars formed from healed abscesses (weird acne like thing). Other family members who are males has same symptoms

• Observation: increase number of neutrophils in the blood - defect suspected

  • Reason: his neutrophils weren’t able to generate an oxidative burst = no toxic o2 molecules and phagocytes could not kill the ingested microbes

• Final diagnosis: CGD

  • More details: a mutation affected the NADPH oxidase and prevent generation of ROS requires for oxidative burst and therefore no microbes gets killed through this process

• Common symptoms with similar patients: patients have re-current infections and ‘granuloma’ a tumor like formation of immune cells surrounding in-digested microbes

CGD genetics

• a deficiency in NADPH oxidase and its inability to make ROS

• 60% of these case: mutation in gp91^phox (encoded by the gene CYBB)

• CYBB “x-linked”: affecting mainly males

Inflammatory response

• general steps

• Pathogens with PAMPs break through epithelium to get through the epithelium barrier

• The epithelial cells are activated upon contact, PRRs are triggered by any tissue-resident phagocytes, NFkB is activated by those phagocytes

• Soluble mediators (cytokines) of the innate immune defense produced by the activated cells

• Cells of the innate system recruited to the site

Local inflammation

• use the general steps (but instead be more specific to local inflammations)

• Healthy skin gets infected

• The epithelial and other resident effector cells gets recruited through PRRs to secret the cytokines

• Vasodilation (widening of the blood vessels) and increased vascular permeability allow the movement of fluid, protein, inflammatory cells to leave the blood and enter the tissue

• Infected tissue gets inflamed, causing redness, heat swelling and pain

Local inflammation - vascular changes

• Explain how it changes

• The purpose of the change

• The cytokines and complement factors will act on the vascular endothelial cells, resulting in vasodilation and the slowing the blood cells (the separation of endothelial cells and breaking of tight junctions)

• Cytokines help increase

  • Dilation of vessels

  • Permeability

  • Expression of adhesions molecules that trap white blood cells to the site

• Result: the movement of WBC to migrate to the injured or infected site

Cell migration process

• explain the extravisation process

• tethering and rolling

• The cytokines express more adhesion molecules that tethering and roll the white blood cells, mediated by SELECTINS

Extravisation process

• selectin will grab onto passing WBC

• The adhesion flattens the cell and allows for migration

• Innate effect cells (WBC and other things) migrate towards the site of infection out of the vessel by following the gradient of cytokines produced by infected epithelial cell

which pathogen will go to the site of infection?

• neutrophil

The effects of inflammation on other parts of the body

• how do they affect the feelings of the person (what type of feeling)

• How do they affect the other organs in the body (which ones and for all of them, how does it work)

• Cytokines makes you feel bad

• Cells from inflamed tissue will releases proinflammatory mediators into the blood

  • Brain = fever, malaise, loss of appetite

  • Liver: more synthesis of defense-related proteins like complement protein

  • Bone marrow: release of stored leukocytes and increase production in stem cells

  • Muscle and adipose tissue: increase catabolism to generate energy

    • Why is this important: increase by 1 degrees Celsius =33.8 Fahrenheit walking 35-40 km

Explain septic shock compared to local infection

• explain the local infection first if it is easier

Local infection (Gram-negative bacteria)

• LPS induces local macrophages to produce inflammatory mediators like these cytokines (TNFa, IL-1, IL-6)

• Local vessels dilate to recruit the cellular and humoral mediators of innate immunity and healing)

• Results

  • Phagocytosis

  • Tissue repair Through local clotting

  • Drainage of bacteria to local lymph nodes

  • Containment of infection

Systemic infection

• a systematic infection in that presence of e.g. gram-negative bacteria

• Cytokine storm: High levels of cytokines released by many immune cells (not just the local macrophages in the tissue)

• All blood vessel dilate and Edna occurs (fluid buildup trapped in the tissues) as protein and cellular fluid escapes into the tissues during cytokines work

• Result

  • Drop in blood volume (vasodilation) and pressure

  • Elevated heartbeat (like in fevers)

  • Disseminated intravascular coagulation (DIC): systemic clotting of small vessels

  • Blocks blood flow leading to organ failure and death

Why do people die

• cytokine production leads of a massive production of endogenous vasodilators

• a structural change in the endothelium might results in leakage of the fluid, causing tissue edema (inflammation)

• Plugging of select microvascular beds with neutrophils and clotting factors will block blood flow to organs

• Organ/lung-specific ‘ischemia’ restriction in blood supply

• Organ failure

How to treat a septic shock?

• cytokine storm dampening with steroid (anti-inflammatory effects)

• Activate protein C to remove the clotting

• Vasopressors to constrict blood vessel, stopping dilation

Mortality of septic shock

• leaderboard in leading deaths in the US

• mortality rate = 25-50%

• 13th leading cause of death in the US, most frequency case of deaths in intensive care units