CH 24 ADAPTIVE IMMUNITY

What is the difference between adaptive and innate immunity?

• Innate immunity: first line of defense, works immediately, non-specific (doesn’t target a specific pathogen)

• Adaptive immunity: THIRD LINE. slower, develops after exposure, highly specific to the pathogen, creates memory for faster future response

👉 Innate = instant general defense; Adaptive = learned, specific defense.

Differentiate humoral from cell-mediated immunity.

• Humoral immunity: involves B cells → become plasma cells and memory cells → plasma cells make antibodies (IgA, IgG..)→ fight extracellular pathogens (outside cells)

• Cell-mediated immunity: involves T cells → become cytotoxic T cells (kill infected cells) or T helper cells(activate other immune cells) → fight intracellular pathogens (inside cells)

👉 B cells make antibodies; T cells kill infected cells and help other immune cells.

Which T helper cell recognizes APCs like macrophages and dendritic cells?

T helper 1

Which T helper cell recognizes B cells?

T helper 2

Define antigen. What type of molecules can they be?

- a molecule in the body that triggers the immune system
- can be a protein, lipid, nucleic acid, or complex carb

• cause antibodies to be made

a molecule that triggers the immune system to respond

• Can be: proteins, lipids, nucleic acids, or complex carbohydrates

👉 Antigen = anything the immune system can recognize as “foreign.”

Which molecule acts as the best antigen and why?

• Proteins → most diversity in shape → immune system can recognize many different ones

How do B cells and T cells interact with antigens?

• B cells: use antibodies on their surface to bind antigens directly

• T cells: use T cell receptors to bind antigens presented by MHC molecules

👉B cells grab antigens themselves; T cells need help from MHC “presentation.”

What is an epitope?

• epitopes on antigen

• The specific part of an antigen that an antibody or T cell receptor binds to

• can be made of: Proteins, Peptides (small pieces of proteins), Complex sugars (polysaccharides)

• When your immune system detects an epitope, it triggers an immune response.

👉 Epitope = “target spot” on an antigen.

What is the function of an antibody?

• Recognize antigens

• Trigger immune responses like phagocytosis, complement activation, and neutralization

👉 Antibodies = immune system’s “flags” to attack invaders.

Describe an antibody’s structure.

• Shape = Y

• Chains: 2 heavy (long, inside) + 2 light (short, outside)

• Variable region: top of Y, binds antigen

• Constant region: bottom of Y, binds host cell receptors

👉 Antibody = Y-shaped flag: top grabs invader, bottom signals immune cells.

Where is the antigen-binding site on an antibody?

• Located on variable regions (two tops of Y)

👉 Top tips of the Y = grab the target.

How do variable regions differ across antibodies?

• Different amino acid sequences → bind different epitopes/antigens

👉 Each antibody top is unique to its target.

Which part of the antibody binds to host cell receptors?

• Stem of heavy chain constant region (bottom of Y)

👉 Bottom of Y = connects to immune system.

Host cell receptors = proteins on your cells that pathogens can attach to in order to infect you. They act like "locks," and pathogens have the "keys."

What are the five classes of antibodies?

• IgG

• IgA

• IgM

• IgD

• IgE

Which three antibody classes are in a monomer form? Which two form polymers?

- IgG, IgD, and IgE are monomers form
- IgA and IgM form polymers (2 or more monomers)

What is an antibody isotype?

• Antibodies have a constant region on their heavy chains.

• If the amino acid sequence in this constant region is different, the antibody is a different class.

Isotype tells us:

➡ Which antibody class it is:

• IgG

• IgA

• IgM

• IgD

• IgE

Based on constant region differences.

What is an antibody idiotype?

Idiotype = what antigen the antibody binds.

What it means:

• Two antibodies can have the same constant region (so they are the same class).

• But if the antigen-binding sites (the variable regions) are different, they will bind different epitopes.

Based on variable region differences.

Tells you: what exact epitope the antibody binds.

Characteristics of IgG antibody

• Monomer form (single Y)

• Most abundant in blood and tissues @ 75%

• Functions: opsonization (tagging), complement activation, virus neutralization

👉 IgG = main antibody in blood, tags invaders for attack.

Characteristics of IgA antibody

• Dimer form (two Ys joined) 15%

• Found in mucosal surfaces (saliva, mucus, breast milk)

• Functions: neutralize pathogens at surfaces and prevent pathogen attachment

👉 IgA = guards surfaces like mouth, nose, and gut.

Characteristics of IgM antibody

• Pentamer form (5 Ys linked) 10%

• Usually stays in blood vessels

• First antibody produced in immune response

• Effective at clumping pathogens (agglutination) and activating complement

👉 IgM = first responder, clumps germs together.

Characteristics of IgD antibody

• Monomer form (single Y) 0.2%

• Only binds antigen when attached to a B cell

• Found in blood and lymph

👉 IgD = antenna on B cells to detect invaders.

Characteristics of IgE antibody

• Monomer form (single Y) 0.2%

• Binds antigen when attached to mast cells or basophils

• Causes release of histamine → allergy symptoms

• Can attract complement proteins and phagocytes

👉 IgE = antenna on mast or basophil triggers allergies and fights parasites.

Five outcomes of antigen-antibody reaction

• Agglutination: clumps bacteria together, reduce number of infectious units

• Opsonization: coats pathogens to help phagocytes eat them, surrounds the bad

• Neutralization: covers pathogen so it can’t infect cells, makes it look spiky so can’t land

• Complement activation: triggers inflammation & lysis, drills hole then bursts

• ADCC (Antibody-Dependent Cell-Mediated Cytotoxicity): antibodies guide NK cells to kill big parasites, uses macrophage and eosinophils, and NK cells to target cell

Q: What is the humoral immune response and their B cells?

a part of the immune system where B cells make antibodies to fight germs outside cells

most effective against extracellular pathogens

because microbes have many small parts called epitopes, and each B cell recognizes only one epitope—B cells need the help of T helper cells (T dependent antigen)

→The B cell shows the germ piece to the T helper cell using MHC Class II, and the T cell gives the B cell a “go make antibodies!” signal.

Define clonal selection

• making B cell babies

• B cells that match a specific antigen multiply → make more identical B cells

• Some become memory cells (long-term)

• Some become plasma cells (antibody factories)

👉 Matching B cells make copies to fight the invader now and later.

with the perfect match, the b-cel will make babies that will then differeiate to plasma or memory

Describe the process of clonal selection.

1. when a B cell with an antibody binds to its matching antigen, this triggers clonal selection and expansion

2. this specific B cell and antibody combo will now go through lots of mitosis to make many clones of itself

3. some of these clones will differentiate into memory B cells and some will differentiate into plasma cells

Difference between plasma and memory B cells

• Plasma B cells: secrete antibodies during active infection

• Memory B cells: hang around for long-term immunity → respond quickly if antigen comes back

👉 Plasma = fights now; Memory = remembers for later.

Compare and contrast T-dependent and T-independent antigens.

T-dependent:

• binds to the B cell, required

• T helper 2 cell recognizes antigen on MHC II → activates B cell

• B cell goes through clonal selection → makes plasma & memory B cells

T-independent:

• not required by B cells

• large antigens cluster the B cell

Difference between primary and secondary immune response

Primary Response (first time you see the pathogen):

• Happens after the first infection or first vaccine

• Slow – antibodies take several days to appear

• Starts with IgM first, then switches to IgG

• B cells become:

  • Plasma cells (make antibodies)

  • Memory B cells (saved for next time)

Secondary Response (second exposure or booster shot):

• Triggered by memory B cells

• Very fast and much stronger

• Mostly IgG made

• This is the reason vaccines work (booster = bigger response)

Which MHC class do cytotoxic T cells recognize? Which co-receptor do they use (CD4 or CD8)?

MHC I

they use CD8

Which MHC class do helper T cells recognize? Which co-receptor do they use (CD4 or CD8)?

MHC II
they use CD4

Where does the cell-mediated immunity happen?

it uses T cells, recognizing antigens infected with intercellular pathogens

What is the function of T helper cells?

• Activate macrophages, dendritic cells, and B cells.

• Cause release of cytokines to direct immune response.
  👉 T helpers are “immune coaches,” telling cells how to fight.

What is the function of cytotoxic T cells?

Recognize intracellular antigens (from viruses, bacteria inside cells, or cancer cells).

Via MHC I and CD8 co receptor

• Kill these infected or abnormal cells by releasing:

  • Perforins → make holes in the target cell’s membrane.

  • Granzymes → enter cell and trigger apoptosis (programmed cell death).

• Result: the infected cell is destroyed, stopping the infection.
  👉Cytotoxic T cells = “cell assassins,” killing infected cells.

What is the function of T helper 1 cells?

Recognize antigens presented by dendritic cells and macrophages (APCs).

Via MHC II and CD4 co recep

• Release cytokines to:

  • Activate these APCs

  • Promote complement activation

  • Stimulate inflammation

  • Help opsonization

  • Help cytotoxic T cell differentiation

👉 boosts attack on infected cells and inflammation.

What is the function of T helper 2 cells?

Recognize antigens presented by B cells.

Via MHC II and CD4 co recep

• Release cytokines to:

  • Stimulate B cells to make antibodies

• Focuses on humoral (antibody) immunity, especially against extracellular pathogens.
  👉helps B cells make antibodies

How are T helper cells and cytotoxic T cells different from each other?

• T helper cells: do not kill. They activate other immune cells like B cells, macrophages, and dendritic cells.

• Cytotoxic T cells: can kill infected or cancerous cells directly to cause lysis or apoptosis.

Define antigen-presenting cell (APC).

• Immune cell that processes antigens and displays them on MHC II molecules.

• Purpose: activates T helper cells to start the adaptive immune response.

• Examples: macrophages, dendritic cells, B cells.
  👉 APC = “flag bearer” showing antigens to T helper cells.

What is the role of natural killer (NK) cells in antibody-dependent cell-mediated cytotoxicity (ADCC)?

• Bind to antibody-coated target cells.

• Release cytotoxic granules containing:

  • Perforins → make holes in target cell membrane

  • Granzymes → trigger apoptosis

• Purpose: destroy large targets (like virus-infected cells or parasites) flagged by antibodies.

List and describe the four types of adaptive immunity.

• Active natural: body encounters antigen naturally → makes antibodies

  • Ex: getting COVID

• Passive natural: antibodies pass from mother to child

  • Ex: through placenta or breastfeeding

• Active artificial: vaccines give antigens → body makes antibodies

  • Ex: flu shot

• Passive artificial: inject pre-made antibodies

  • Ex: antivenom or immunoglobulin therapy
    👉 Super simple: Active = body makes antibodies; Passive = gets antibodies from outside.

Do vaccines provoke a primary or secondary immune response?

• Vaccines cause a primary immune response first (slow, initial antibody production).

• Memory B cells are formed → next exposure triggers secondary response (faster, stronger, mostly IgG).

Define herd immunity

• Most of a population is immune, so disease spreads slowly or not at all.
  👉 Herd immunity = “group protection.”

Define R0 value.

Average number of people one sick person infects in a susceptible population.
👉 R0 = “contagion score.”

Why are disease outbreaks sporadic?

Not everyone is susceptible, so outbreaks stop when few susceptible hosts remain.

⭐ Front: Define and describe live attenuated vaccines.
Back:

• Vaccine uses a weakened pathogen (virus or bacteria)

  • Still has antigens and can replicate a little in the host

• Weakened by:

  • Mutating virulence genes

  • Growing in cell culture or non-human host

• Advantages:

  • Mimics natural infection closely

  • Strong, long-lasting immunity (both cellular and humoral)

• Example: Measles, Mumps, Rubella (MMR)
  👉 Super simple: Live vaccine = “tiny live germ” that trains immune system.

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⭐ Front: Define and describe inactivated (killed) vaccines.
Back:

• Vaccine uses dead pathogen

  • Cannot replicate in host

• Safer than live vaccines

• Usually requires booster shots to maintain immunity

• Mainly stimulates humoral (B cell/antibody) response

• Example: Inactivated polio vaccine (IPV)
  👉 Super simple: Dead vaccine = “non-living germ” teaches antibodies.

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⭐ Front: Define toxoids.
Back:

• Inactivated toxins produced by pathogens

• Cannot cause disease, but still trains immune system to fight the toxin

• Example: Tetanus vaccine
  👉 Super simple: Toxoid = “neutralized poison” for immunity.

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⭐ Front: Define subunit vaccines.
Back:

• Use only pieces of the pathogen (antigens)

• Stimulate immune response without whole germ

• Example: Hepatitis B vaccine
  👉 Super simple: Subunit = “just part of germ” trains immunity.

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⭐ Front: Define recombinant vaccines.
Back:

• Subunit vaccine made by genetic engineering

• Antigens are produced by modifying DNA in lab organisms

• Example: Hepatitis B recombinant vaccine
  👉 Super simple: Recombinant = “lab-made germ pieces.”

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⭐ Front: Define and describe virus-like particle (VLP) vaccines.
Back:

• Mimic whole virus shape but no viral genome

• Cannot infect cells

• Present antigens to immune system

• Stimulate B cells for antibody production

• Example: HPV vaccine
  👉 Super simple: VLP = “fake virus shell” that teaches immune system.

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⭐ Front: Define and describe outer membrane vesicle (OMV) vaccines.
Back:

• Made from outer membrane of bacteria

• Contain pathogen antigens to stimulate immune system

• Mimics the natural pathogen without causing infection

• Example: Some meningococcal vaccines
  👉 Super simple: OMV = “bacterial pieces” for safe training.

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⭐ Front: Define and describe polysaccharide vaccines.
Back:

• Made from sugar capsule of bacteria

• Stimulates immune response poorly in children

• Not very immunogenic by itself

• Example: Pneumococcal polysaccharide vaccine
  👉 Super simple: Polysaccharide = “sugar coat” of bacteria.

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⭐ Front: Define and describe protein-polysaccharide conjugated vaccines.
Back:

• Polysaccharide linked to a protein

• Produces stronger immune response, especially in children

• Example: Haemophilus influenzae type b (Hib) vaccine
  👉 Super simple: Conjugate = “sugar + protein” = stronger vaccine.

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⭐ Front: Define and describe nucleic acid vaccines.
Back:

• DNA vaccines: inject naked DNA plasmid encoding viral antigen → host makes antigen → stimulates immune response

• RNA vaccines: inject naked mRNA encoding viral antigen → host makes antigen → stimulates immune response

• Stimulates both humoral (B cells) and cell-mediated (T cells) immunity

• Example: Pfizer/Moderna COVID vaccines (RNA)
  👉 Super simple: Nucleic acid = “DNA/RNA instructions” → body makes viral protein → trains immune system.

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⭐ Front: Define and describe viral vectored/recombinant vector vaccines.
Back:

• Use harmless virus or bacteria as a delivery vehicle

• Carries genes that encode pathogen antigens

• Vectors are genetically modified

• Example: Johnson & Johnson COVID vaccine
  👉 Super simple: Viral vector = “delivery truck carrying antigen genes.”

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⭐ Front: What type of vaccine is Pfizer/Moderna COVID vaccine?
Back:

• Nucleic acid vaccine (RNA)

• RNA instructs cells to make viral spike protein

• Trains immune system without infecting cells
  👉 Super simple: Pfizer/Moderna = “mRNA instructions” → body makes harmless spike → immunity.

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⭐ Front: What type of vaccine is Johnson & Johnson COVID vaccine?
Back:

• Viral vector vaccine

• Harmless virus carries gene for spike protein

• Trains immune system to recognize SARS-CoV-2
  👉 Super simple: J&J = “virus delivery truck” → teaches immune system.