Module 9 - Immunology

• Immunology = study of immune system and immunity

• Immunity is the ability of an organism to resist infections

• 2 branches

  • Innate immunity is multifaceted system of defences targeting invading pathogens in nonspecific manner

  • Adaptive immunity is multifactored system of defences that specifically  target invading pathogens and that develop memory to invading pathogens

• Reaction to microbes

  1. Tolerate - microbes are friendly or harmless

  2. Segregate - keep microbes out of places where they shouldn’t be

  3. Defend - mount immediate and aggressive defense response if microbes are causing damage

• Human immune system involves all 3

• Innate immunity

  • Non inducible

  • Non specific

  • Quick response (hours)

  • No previous exposure required

  • Physical and chemical barriers

  • Phagocytes

    • Neutrophils, macrophages, dendritic cells and eosinophiles

  • Inflammation

    • Mast cells and basophils

• Adaptive immunology

  • Activated when innate fails

  • Specific recognition of pathogens

  • Slow process

    • Multi steps to process antigen/epitopes

  • Develop memory

  • T cells and B cells

  • Antibodies

Q: The innate immune system is composed of…

A: several non specific mechanisms that include barrier defences like phagocytes and complement system, inflammatory and fever

Physical defences

• Innate immunity

  • Cellular barriers deny entry

    • Skin, mucous membrane, endothelial cells

    • Breaks in these barriers can lead to bacteria entering

  • Mechanical defences remove potential threats

    • Shedding of skin cells, mucociliary sweeping, peristalsis, flushing action of urine and tears

  • Microbiome

    • Compete with pathogens for cellular binding sites and nutrients

Chemical defences

• Innate immunity

  • Body fluids

    • Chemicals that regulate pH

    • Inhibit microbial growth

    • Enzymes (lysozymes break walls in bacteria)

    • Nutritional immunity makes nutrients unavailable

  • Antimicrobial components

    • Antimicrobial peptides (AMPs)

    • Bile acids

  • Complement systems

  • Cytokines

  • Mediators of inflammation

Q: A fish cutter develops fish tank granuloma (skin infection) why?

A: cuts on the skin remove layers of the innate protection and allow entry of bacteria pathogens

Innate protection

• Compliment system (innate)

  • Plasma proteins

    • Sequential interaction

    • Cascade: complement activation

  • Enzymes

  • Membrane Attack Complex (MAC)

    • Pore makes hole in membrane in bacteria to shrink and explode it

  • Boost innate and adaptive response

  • Designation ex

    • C# or C#a

    • C= complement

    • # = order of discovery

    • a= anaphylatoxin = inflammation

    • B = opsonization

  • Classical pathway = antibody antigen complex at C1

  • Lectin pathway = mannrose binding lectin at C4

  • Alternative pathway at C3

  • Membrane attack complex at C6

• Cytokines and chemokines (innate)

  • Molecular messenger of immune system

    • Cytokines binds to receptors

      • Signalling cascade leads to transcription activator

      • Autocrine = same cell secretes and receives cytokine signal

      • Paracrine = cytokine signal secreted to a nearby cell

      • Endocrine = cytokine signal secreted to circulatory system and travels to distant cells

    • Chemokines are sub class of cytokines

      • Recruit circulating immune cells to site of injury

    • Interferons sub class of cytokines

      • Activate anti-viral response of nearby cells

      • Self defence against viruses

Q: compared to other antiviral drugs a chemical called interferon is unusual because

A: it doesn’t have any direct antiviral action by itself but instead secreted by virus infected cells and signals other cells to begin making anti viral factors

Immunity: organs

• Blood and lymphatic systems

  • Allow circulation and distribution of immune cells

  • Lymph dumps antibodies and immune cells into blood

• Secondary lymphoid organs

  • Lymph nodes

  • Leukocytes to detect antigens or pathogens circulating in lymph system

• Mucosa associated lymphoid tissue (MALT)

• Spleen

Cellular players

• Derived from pluripotent hematopoietic stem cells (HSCs)

  • Erythocytes (RBS)

  • Leukocytes (WBC)

  • Platelets

• Monocytes - immature

  • Mature differentiate

• Granulocytes

  • Granules can be stained

  • Toxins and enzymes

  • Destroy targets

Innate immune system

Cell types and roles

• Dendric cells

  • Antigenic presenting (APCs) residing in skin and mucous membranes

• Macrophages

  • APC residing in tissues and organs (spleen, lymph nodes and MALT)

  • Role in adaptive immunity

• Neutrophils

  • Elimination and destruction of extracellular bacteria

  • Blood and bone marrow

• Eosinophiles

  • Protection against protozoa and helminths and role in allergies

• Basophils

  • Role in inflammation and allergic reactions in blood

• Mast cells

  • Inflammation and allergic reaction in tissues

• Natural killer cells

  • Kill virus infected cells and cancerous cells

Q: What kind of lymphocytes would you expect to be over represented at site of viral infection?

A: natural killer cells

Phagocytosis of pathogens

• Uptake of extracellular pathogen

  • Phagosome

• Purpose is to destroy

• Membrane bound inclusions: lysosomes

  • Bacterial substances

  • Reactive oxygen species

  • Enzymes: lysozymes, proteases

• Lysosomes fuse w phagosome: phagolysosome

• Some pathogens can avoid, neutralize or kill phagocytes

• PAM on bacterium

• PARR receptor on cell

Recognizing pathogens

• Recognize pathogen associates molecular pattern (PAMS)

  • Unique microbe structures

• Pattern recognition receptors

  • Toll like receptors (TLRs)

  • NOD like receptors (NDRs)

    • Repeated patterns to bind

• Signal transduction

• Phagocytosis

  • Engulfment of pathogens

Killing microbes without phagocytosis

1. Killing something bigger than you (parasites)

   • Extracellular killing by Eosinophils

   • Secretes toxic protein that perforate parasite wall

2. Killing something hiding within a cell

   • Extracellular killing by natural killer cells (NK)

     • Seek and destroy virus infected host cell

     • Secretion of degrading enzymes

Q: how can the immune response recognize pathogens during their first encounter?

A: pathogen associated molecular patterns recognized by pattern recognition receptors

Inflammation

• Normal biological response

  • Promotes healing

• Redness (erythema), swelling (edema), pain, heat

• Production of activators

  • Pro-inflammatory molecules

    • Ex histamine - induce inflammation

  • Phagocytes and lymphocytes

    • Clean up and monitor danger

    • Induce vasodilation

    • Increased vascular permeability

  • Influx of phagocytes

    • Increase inflammation

Fever

• Inflammatory response - normal

  • Not localized

• LPS will induce fever

  • Exogenous pyrogen

• Cytokines will induce fever

  • Endogenous pyrogens

• Act on prostaglandins

  • Act on hypothalamus

• Limit growth of pathogen

• Uncontrolled inflammation

  • Toxic/septic shock

• 37 is normal body temp

  • Most pathogens like that temp, so increase body temp slows bac growth

  • Make sure control on fever - end up in toxic of septic shock if uncontrolled

• Slows growth of temp sensitive microbes

• Reduce availability of nutrients used by microbes

  • Iron, zinc, copper conc decrease in serum

• Increase metabolic activity of phagocytic cells

• Stimulate acute inflammation

• Low grade fever is beneficial but high grade (above 40 degrees) can be dangerous and must be controlled

• Medical drugs are antipyretic (ibuprofen, aspirin)

Q: why would a fishmonger develop granuloma in response to Mycobacterium marinum infection?

A: Aggregation of macrophages and other immune cells formed in response to chronic inflammation

• Mycobacterium hard to kill bc of mycolic acid layer

Q: the acquired immune system is characterized by

A: 2 diff branches humoral immunity and cell mediated immunity, memory to previous threats, discriminate banger and non danger, recognize diff types of danger

Adaptive immunity

• Adaptive and specific

  • Discriminate - distinguish between specific foreign molecules

  • Diversify - recognize many possible foreign molecules

  • Memorize - remember foreign molecules after first exposure

• 2 components

  1. Humoral immunity

  • Antibodies produced by B cells (Bone marrow lymphocytes) in response to antigens

  1. Cell mediated immunity

  • Activation of T cells (thymus lymphocytes) to control intracellular microbes (virus, bac, parasites)

• Rapid response on second exposure

Antigens and immunogens

• Antigen = molecule/substance that interacts w antibodies or T receptor (TRC)

  • Not all antigens induce immune Reponses

• Immunogen = induce immune response

  • Conjugate vaccines

• Hapten = small molecules that binds to antibody

  • No immune response

  • Needs a carrier to be a immunogen

• Immunogenicity is dependent on

  • Complexity

  • Physical form and structural form

  • Dose

Epitopes

• Only sections or specific regions of antigen are recognized

  • Epitope or antigenic determinant

  • Binds

  • Multiple sites per antigen

• Antibodies can bind to full form of an antigen

• TRC needs the antigen to be process

  • 20 aa or less

Q: which of the statements about antigens is true

A: antigens can have more than 1 epitope

Incorrect: our own proteins are never recognized as antigens, an allergen is not an antigen (allergens are always antigens), antigen is always a threat for the host

Antibodies

• Immunoglobin

  • Glycoproteins

  • Blood and tissue fluids

• Monomer

  • 4 protein chains heldc by disulfide bonds

• Y shaped

  • 2 heavy chains + 2 light chains

• Fragment of antigen binding

  • FAB region

  • Variable - diversity and specify

  • Provide function

• Fragment of crystallization

  • Fc region

  • Binds to complement and phagocytes

• Antigen binding site only recognizes 1 antigen

Functions

• Opsonin's - opsonization

  • Flag attached to microbes

  • Macrophage kills

• Agglutination - clumps easier to clear

• Neutralization - no longer functional

• Cell mediated cytotoxicity

• Immune activation - complement activation

Immunoglobin classes

• IgA - neutralization, secreted in blood

• IgG -major circulating (want this one)

Q: what is the role of antibodies against spike proteins of covid if the antibodies block viral attachment?
A: neutralization

Major Histocompatibility Complex (MHC)

• Important for antigen presentation

• Surface expose glycoprotein

  • Dimers

• 2 classes MHC I and MCH II

  • MHC I

    • Found on all nucleated cells

    • Present self antigens

    • Present non self antigens

  • MCH II

    • Found on macrophages, dendritic cells and B cells

    • Present non self antigens

Antigen presentation

• Antigen presenting cells (APCs)

  • Process and present antigens

  • Macrophages, dendritic cells and B cells

  • Recognize and process antigen differently

• MCH II processing and presentation

  • B cells vs phagocytes

  • Antigen processing occurs in the phagloysome

  • Not all antigen presented

  • Immunogenic and dominant

• Any cells

  • MHC1 processing and presentation

  • Self regulation

  • Intracellular pathogens

  • Change normal processing

  • Non self presentation

Q: when comparing MHC I and II which statement is false?

A: MHC class I is found only on RBC whereas MHC II is only found on antigen presenting cells

True: I presents self and non self, II presents only non self, I interacts with CD8 and II interacts with CD4

Cell mediated immunity

• CMI driven by T-cells

  • Eliminate cells infected w microbe

  • Antibodies don’t enter cells

• Eliminate abnormal abnormal or cancer + non self tissues (transplant tissues)

• Regulate function of cells involved w innate immunity (macrophage) and humoral immunity (B cells)

  • RBC have no nucleus

T cell selection

• Differentiate btw host antigens and danger antigens

• Selection against T cells reacting to self antigens

  • Each T cell receptor binds a diff antigen

  • Selection occurs in thymus

  • Failure leads to autoimmunity (immune system attacks body)

  • Positive selection: TCR w weak interaction divide and grow

  • Negative selection: TCR w strong interaction die

• Interacts = kept, doesn’t interact = destroyed

• Classes

  • CD4 - regulatory T cells, coreceptor (helper)

  • CD8 - helps interactions

T cell receptors

• Binds antigens

• In thymus

• Initiate activation

• T cell co receptors

  • Strengthens interaction btw TCR and MHC

  • CD4 binds MHC II (only antigen)

  • CD8 binds MHC I (only nuclear)

    • CD4 and 8 are coreceptors

• Helper T cells

  • Only APC activate

    • MHC II presenting antigen to TCR

    • CD4 interaction w MCH II

    • Secretion of cytokines leading to activation, proliferation and differentiation

  • Ex. Helper T cell interacts w MHC II w CD4 antigen extracted from pathogen

    • Memory helper T cell important, Th1 cells stimulate cytotoxic T cells (cells that kill), Th2 antibodies (cell mediated response)

• Cytotoxic T cells

  • MHC I presenting to TCR (CD8 interaction)

  • Cytokines activate

    • Co-stimulation w TH1

    • Without co stimulation not as effective or long lasting

    • Effector cytotoxic T cells - kills infected cells

    • Memory cytotoxic T cells

B cell selection

• BCR recognize 1 antigen

• Produce antibodies

• Diversity by diff process - recombination and hypermutation

• Selection in bone marrow

  • Positive selection -working receptor

  • Negative receptor - eliminate strong interaction w self

• Don’t want self interaction

B cell stimulation

• Activated by antigen interaction w BCR

• T cell independent

  • Repeating epitopes

  • 2nd signal: PAMP interact w TLR

  • Proliferation and differentiation into plasma cells

  • IgM response -

• Helper T cells - stronger

  • B cells activated by T cells

  • Stronger and induce memory

  • Internalization of antigen

  • Presentation using MHC II to TH2 cells

  • Cytokine activate - memory and switch antibody class

    • IgA, IgM - something other than primary antibody response

Q: designing a vaccine and want a strong antibody response, what type of T cells would you target to ensure strong B cell activation?

A: TH2 cells (antibody)

• TH1 (stimulate cytotoxic T cells)

• Cytotoxic T cells (destroy)

  • Know ones above

Q: when comparing innate and adaptive immunity which statement is true?

A: innate immunity is first and second line of defense that prevents entry and spread of dangers, whereas adaptive is third line of defense with specific response to dangers

Immunization

• Vaccine - name of virus from cowpox

• Immunity from vaccines (adaptive immunity)

  • Passive + natural acquired

    • acquired from antibodies passed through breastmilk or placenta

  • Passive + Artificial

    • Antibodies harvested from one person

  • Active + natural acquired

    • Gained through illness and recovery

  • Active and artificial

    • Vaccine (protective)

    • Doesn’t induce illness - induce immune response against specific antigen

• Many types of vaccines

  • Live attenuated

    • Non pathogenic viable microbe

    • Mimic real infection

    • Not safe for immunocompromised

  • Whole inactivated

    • Pathogen is dead

    • Entire microbe no risk of infection

    • Weaker immunity - stronger dose and booster

  • Sub unit

    • Immunogenic piece of microbe

    • Limited side effects

    • Booster needed

  • Toxoid

    • Inactivated toxin

    • Antibodies neutralize toxin

    • Doesn’t prevent infection

  • Conjugated

    • Low immunogenic antigen attached to immunogen

    • Effective in younger kids

    • Costly and may interfere w other vaccines

  • Viral like

    • Proteins that assemble as capsid

    • Mimic virus

    • Low immunogenically

  • RNA

    • RNA strand can be translated

    • Highly adaptable

    • Costly

Q: major disadvantage to toxoid vaccines?
A: doesn’t protect against infection

Boosters

• Antibodies produced during secondary response

  • More effective

  • Bind w higher affinity

• Plasma produced during secondary response

  • Live longer

  • Levels of antibody remain elevated for longer

• No cervical cancer in women with vaccine = 100% effective (scotland)

Factors that effect efficiency

• Intrinsic host factors

• Parrinatal host factors

• Extrinsic host factors

• Behavioral factors

• Nutritional factors

• Enviro

• Vaccine

• Admin