L32&33 Immunity

Question 1

L32: Innate Immunity

What are the four main functions of the immune system?

Answer 1

1. Recognising threats – Differentiates between self and non-self.
2. Responding to threats – Utilises barriers, innate immunity, and adaptive immunity.
3. Resolving the response – Controls inflammation and prevents excessive damage.
4. Remembering the threat – Forms immune memory (adaptive immunity).

Question 2

L32: Innate Immunity

What are the three main types of barriers in the immune system?

Answer 2

1. Physical barriers – Skin, mucosal surfaces.
2. Chemical barriers – Antimicrobial secretions, low pH.
3. Biological barriers – Commensal bacteria competing with pathogens.

Question 3

L32: Innate Immunity

How does the skin act as a physical barrier to infection?

Answer 3

Thick and dead outer layer (keratin).

Dry surface (prevents microbial growth).

Impermeable to pathogens.

Antimicrobial secretions (e.g., defensins, lysozymes).

Question 4

L32: Innate Immunity

What role do mucosal surfaces play in immunity?

Answer 4

Thin single-cell layer allowing passage of molecules (e.g., O₂, CO₂, nutrients).

Mucociliary elevator in the lungs removes trapped microbes.

Antimicrobial peptides prevent infections.

Commensal bacteria prevent pathogen colonisation.

Question 5

L32: Innate Immunity

What are the six major types of pathogens?

Answer 5

1. Bacteria
2. Viruses
3. Fungi
4. Protozoa
5. Worms (Helminths)
6. Flukes

Question 6

L32: Innate Immunity

How many bacterial cells colonise the human body?

Answer 6

The human body contains 10¹⁴ human cells but is colonised by 10¹⁵ bacteria, meaning over 90% of cells in/on the body are non-human.

Question 7

L32: Innate Immunity

What are the three levels of immune defence?

Answer 7

1. Physical barriers – Skin, mucosa, antimicrobial secretions, commensal bacteria.
2. Innate immunity – Immediate, non-specific response with no memory.
3. Adaptive immunity – Specific, memory-based response taking 4-6 weeks to develop.

Question 8

L32: Innate Immunity

What are the main humoral (soluble) components of innate immunity?

Answer 8

1. Complement system – Plasma proteins (C1-C9) aiding pathogen destruction.
2. Acute phase proteins – Produced by the liver in response to infection (e.g., C-reactive protein (CRP), Mannose-binding lectin (MBL)).

Question 9

L32: Innate Immunity

What are the three complement activation pathways?

Answer 9

1. Lectin pathway – MBL binds to sugars on the microbe, activating the complement system.
2. Alternative pathway – C3b binds to the microbe, triggering complement activation.
3. Classical pathway – Antibodies bind to the microbe, initiating the pathway.

Question 10

L32: Innate Immunity

What does C3b do in the complement system?

Answer 10

Opsonisation – Tags microbes for phagocytosis.

Activates the alternative pathway.

C3a activates mast cells, leading to histamine release.

Question 11

L32: Innate Immunity

What is the function of the Membrane Attack Complex (MAC)?

Answer 11

Formed by C5-C9.

Creates pores in bacterial membranes.

Causes bacterial lysis by allowing water to rush in.

Question 12

L32: Innate Immunity

What are PRRs and what do they detect?

Answer 12

PRRs are receptors that detect Pathogen-Associated Molecular Patterns (PAMPs).

Toll-Like Receptors (TLRs) are key PRRs.

Question 13

L32: Innate Immunity

Where are Toll-Like Receptors (TLRs) found?

Answer 13

Surface TLRs detect bacterial cell wall components (LPS, peptidoglycan).

Endosomal TLRs detect viral nucleic acids (RNA/DNA).

Question 14

L32: Innate Immunity

What is the function of cytokines and chemokines?

Answer 14

Cytokines – Small proteins that mediate immune responses.

Chemokines – Attract immune cells to infection sites.

Question 15

L32: Innate Immunity

What are the four main steps in inflammation?

Answer 15

1. Sentinel Cells Detect Infection – Macrophages, dendritic cells, mast cells release cytokines and chemokines.
2. Blood Vessel Changes – Increased permeability allows immune cells to enter tissues.
3. Recruitment of Effector Cells – Neutrophils and monocytes migrate to the site.
4. Pathogen Elimination – Phagocytosis, complement activation, NK cell killing.

Question 16

L32: Innate Immunity

How does the interferon response protect against viruses?

Answer 16

Virus-infected cells produce interferons (IFN-α, IFN-β).

Interferons:

Activate antiviral genes in neighbouring cells.

Induce RNAse enzymes to degrade viral RNA.

Activate Protein Kinase-R, inhibiting viral replication.

Question 17

L32: Innate Immunity

How do Natural Killer (NK) cells kill virus-infected cells?

Answer 17

1. Recognise lack of MHC-I molecules.
2. Release perforin and granzyme to induce apoptosis.
3. Kill via Antibody-Dependent Cellular Cytotoxicity (ADCC).

Question 18

L32: Innate Immunity

What are the key characteristics of innate immunity?

Answer 18

Always present and responds immediately.

No memory, relies on Pattern Recognition Receptors (PRRs).

Clears most infections before adaptive immunity is needed.

Question 19

L32: Innate immunity

What are the three key mechanisms of innate immunity?

Answer 19

1. Barrier defences – Skin, mucosa, antimicrobial secretions.
2. Cellular defences – Neutrophils, macrophages, NK cells.
3. Humoral defences – Complement system, acute phase proteins.

Question 20

L32: Innate immunity

What are the three main roles of innate immunity?

Answer 20

1. Immediate response – Recognises PAMPs and activates defences.
2. Pathogen clearance – Phagocytosis, complement activation, NK cell killing.
3. Inflammation – Recruits immune cells and initiates adaptive immunity.

Question 21

L32: Innate immunity

What are the main innate immune cells and their functions?

Answer 21

• Neutrohils (60-70% WBCs) - Phagocytosis, oxidative burst, NETosis (trapping microbes in DNA nets)
• Monocytes/Macrophages (7%) - CIrculate in blood, differentiate into macrophages in tissues, phagocytosis, antigen presentation
• Natural killer cells (2%) - Recognise virus-infected/cancerous cells, release perforin and granzyme to induce apoptosis
• Mast cells - Release histamine, increase blood flow, recruit immune cells
• Dendritic cells - Bridge between innate and adaptive immunity, present antigens to T cells

Question 22

L32: Innate immunity

What are the key functions of neutrophils?

Answer 22

Phagocytosis – Engulfs and destroys microbes.

Oxidative burst – Produces reactive oxygen species to kill microbes.

NETosis – Releases DNA traps to catch and kill microbes.

Question 23

L32: Innate immunity

How do neutrophils find infection sites?

Answer 23

Follow chemokine signals (e.g., CXCL8/IL-8) to infection sites.

Recognise C3b-opsonised pathogens.

Question 24

L32: Innate immunity

How do NK cells identify and kill infected cells?

Answer 24

Detect cells lacking MHC-I molecules (which are often infected or cancerous).

Release perforin and granzyme to induce apoptosis.

Can kill via Antibody-Dependent Cellular Cytotoxicity (ADCC) by recognising Fc receptors.

Question 25

# L32: Innate immunity What are the two types of receptors NK cells use?

Answer 25

1. Activating receptors – Detect stress signals from infected cells. 2. Inhibitory receptors – Detect MHC-I; if absent, NK cells kill the target.

Question 26

# L32: Innate immunity What role do mast cells play in the immune response?

Answer 26

Act as sentinel cells in tissues. Release histamine, leading to vasodilation and increased permeability. Recruit immune cells via cytokine release.

Question 27

# L32: Innate immunity How does histamine contribute to inflammation?

Answer 27

Dilates blood vessels → increases blood flow. Increases permeability → immune cells and plasma proteins enter tissues. Causes swelling, redness, and heat at the infection site.

Question 28

# L32: Innate immunity What are the three main functions of the complement system?

Answer 28

1. Opsonisation – Coats microbes with C3b, making them easier to phagocytose. 2. Inflammation – C3a and C5a recruit immune cells and promote inflammation. 3. Lysis – C5-C9 form the Membrane Attack Complex (MAC), lysing bacteria.

Question 29

# L32: Innate immunity What triggers each complement pathway?

Answer 29

Lectin pathway – Mannose-binding lectin (MBL) binds to microbial sugars. Alternative pathway – C3b spontaneously binds to microbes. Classical pathway – Antibodies (IgG/IgM) bind to pathogens.

Question 30

# L32: Innate Immunity What are the five steps of phagocytosis?

Answer 30

1. Recognition & Attachment – PRRs (e.g., TLRs) recognise PAMPs or opsonised microbes. 2. Engulfment – Pseudopodia extend and enclose the microbe in a phagosome. 3. Lysosome Fusion – Phagosome fuses with a lysosome, forming a phagolysosome. 4. Microbe Killing – Enzymes, ROS, and antimicrobial peptides kill the microbe. 5. Antigen Presentation – Fragments of microbes are presented to T cells.

Question 31

# L32: Innate Immunity What are Toll-Like Receptors (TLRs) and what do they detect?

Answer 31

TLRs are Pattern Recognition Receptors (PRRs) that detect PAMPs. Found on cell surfaces and endosomes.

Question 32

# L32: Innate Immunity What are acute phase proteins and where are they produced?

Answer 32

Produced by the liver in response to infection. Upregulated by IL-6, IL-1, TNF-α.

Question 33

# L32: Innate Immunity What are key acute phase proteins and their functions?

Answer 33

1. C-Reactive Protein (CRP) – Opsonises bacteria, activates the classical complement pathway. 2. Mannose-Binding Lectin (MBL) – Binds to microbial sugars and activates complement.

Question 34

# L32: Innate Immunity How do interferons protect against viruses?

Answer 34

Virus-infected cells release Type I Interferons (IFN-α, IFN-β). Interferons: Activate RNAse enzymes to degrade viral RNA. Induce Protein Kinase-R, blocking viral replication. Enhance NK cell and macrophage activity.

Question 35

# L32: Innate Immunity What are the key differences between innate and adaptive immunity?

Answer 35

Innate immunity is immediate, while adaptive immunity takes days to weeks to develop. Innate immunity is non-specific, recognising general pathogen patterns, while adaptive immunity is highly specific and recognises unique antigens. Innate immunity has no memory, whereas adaptive immunity forms memory, leading to a faster response upon re-exposure. Key innate cells include neutrophils, macrophages, dendritic cells, and NK cells, while adaptive immunity involves T cells and B cells. Innate immunity relies on the complement system and cytokines, whereas adaptive immunity relies on antibodies and T cell receptors.

Question 36

# L32: Innate Immunity What are the three main roles of innate immunity?

Answer 36

1. Immediate response – Recognises PAMPs and activates defences. 2. Pathogen clearance – Phagocytosis, complement activation, NK cell killing. 3. Inflammation – Recruits immune cells and initiates adaptive immunity.

Question 37

# L32: Innate Immunity What are the key functions of neutrophils?

Answer 37

Phagocytosis – Neutrophils engulf and digest microbes. Oxidative burst – They produce reactive oxygen species (ROS) to kill pathogens. NETosis – They release DNA strands to trap and kill microbes.

Question 38

# L32: Innate Immunity How do neutrophils find infection sites?

Answer 38

They follow chemokine signals like CXCL8 (IL-8) to infection sites. They recognise C3b-opsonised pathogens, allowing for easier phagocytosis.

Question 39

# L32: Innate Immunity How do NK cells identify and kill infected cells?

Answer 39

They detect cells lacking MHC-I molecules, which are often infected or cancerous. They release perforin and granzyme, inducing apoptosis (cell death). They kill via Antibody-Dependent Cellular Cytotoxicity (ADCC) by recognising Fc receptors on antibody-coated cells.

Question 40

# L32: Innate Immunity What are the two types of receptors NK cells use?

Answer 40

Activating receptors detect stress signals from infected cells. Inhibitory receptors detect MHC-I; if absent, NK cells kill the target.

Question 41

# L32: Innate Immunity What are the three main functions of the complement system?

Answer 41

1. Opsonisation – Coats microbes with C3b, making them easier to phagocytose. 2. Inflammation – C3a and C5a recruit immune cells and promote inflammation. 3. Lysis – C5-C9 form the Membrane Attack Complex (MAC), lysing bacteria.

Question 42

# L32: Innate Immunity What triggers each complement pathway?

Answer 42

The lectin pathway is triggered when mannose-binding lectin (MBL) binds to microbial sugars. The alternative pathway is activated when C3b spontaneously binds to microbes. The classical pathway is activated when antibodies (IgG or IgM) bind to pathogens.

Question 43

# L32: Innate Immunity What are the five steps of phagocytosis?

Answer 43

1. Recognition & Attachment – PRRs (e.g., TLRs) recognise PAMPs or opsonised microbes. 2. Engulfment – The pathogen is enclosed in a phagosome. 3. Lysosome Fusion – The phagosome fuses with a lysosome, forming a phagolysosome. 4. Microbe Killing – Enzymes, ROS, and antimicrobial peptides kill the microbe. 5. Antigen Presentation – Fragments of microbes are presented to T cells.

Question 44

# L32: Innate Immunity What are some key TLRs and their ligands?

Answer 44

TLR4 recognises Lipopolysaccharide (LPS) from Gram-negative bacteria. TLR2 recognises peptidoglycan and lipoproteins from Gram-positive bacteria and fungi. TLR3 recognises double-stranded RNA from viruses. TLR7 and TLR8 recognise single-stranded RNA from RNA viruses. TLR9 recognises unmethylated CpG DNA from bacteria and DNA viruses.

Question 45

# L32: Innate ImmunityL32: Innate Immunity What are the main cytokines involved in inflammation?

Answer 45

IL-1 increases fever and activates endothelial cells. IL-6 stimulates the production of acute-phase proteins. TNF-α increases vascular permeability and recruits immune cells. IL-8 (CXCL8) recruits neutrophils to infection sites. IL-10 is anti-inflammatory and limits the immune response.

Question 46

# L32: Innate Immunity What is the difference between inflammation and fever?

Answer 46

Inflammation is a local response to infection or injury, involving redness, swelling, heat, and pain. Fever is a systemic response, raising body temperature to slow pathogen growth. Inflammation is driven by IL-1, IL-6, and TNF-α, while fever is triggered by IL-1, IL-6, and PGE₂.

Question 47

# L33: Adaptive Immunnity What are the main features of innate immunity?

Answer 47

Present at birth. Uses preformed pathogen recognition receptors. Rapid response but lacks specificity. Components: Barriers, phagocytes, NK cells, complement system.

Question 48

# L33: Adaptive Immunnity What are the main features of adaptive immunity?

Answer 48

Develops in response to infection or vaccination. Uses highly variable receptors. Stronger, antigen-specific response. Includes immunological memory. Components: B cells, T cells, and antibodies.

Question 49

# L33: Adaptive Immunnity What is the major disadvantage of adaptive immunity?

Answer 49

It is slower to respond compared to innate immunity.

Question 50

# L33: Adaptive Immunnity What is immunological memory?

Answer 50

The ability of the immune system to "remember" an antigen, leading to a faster and stronger response upon re-exposure.

Question 51

# L33: Adaptive Immunnity What are the key innate immune cells and their roles?

Answer 51

Neutrophils & Macrophages: Phagocytose pathogens. Eosinophils: Attack parasites. Natural Killer (NK) cells: Destroy infected cells. Mast Cells: Involved in allergic reactions. Dendritic Cells: Act as antigen-presenting cells (APCs).

Question 52

# L33: Adaptive Immunnity What are the two main types of adaptive immune cells?

Answer 52

B Lymphocytes: Produce antibodies. T Lymphocytes: Help other immune cells (T helper cells) or kill infected cells (Cytotoxic T cells).

Question 53

# L33: Adaptive Immunnity What do B cells do in the immune response?

Answer 53

They bind free antigens and differentiate into plasma cells that secrete antibodies.

Question 54

# L33: Adaptive Immunnity What is the structure of the B cell receptor (BCR)?

Answer 54

2 identical heavy chains. 2 identical light chains. Recognises 3D shapes of antigens.

Question 55

# L33: Adaptive Immunnity What happens when an antigen binds to a B cell receptor (BCR)?

Answer 55

The B cell is activated and begins producing antibodies.

Question 56

# L33: Adaptive Immunnity What are the five main antibody classes?

Answer 56

IgM: First antibody produced; low affinity but high avidity. IgG: Main antibody in circulation; crosses the placenta. IgA: Found in mucosal surfaces (e.g., gut, respiratory tract). IgE: Involved in allergic responses. IgD: Function not well understood, involved in B cell activation.

Question 57

# L33: Adaptive Immunnity What is class switching in antibodies?

Answer 57

A process where a B cell changes the class of antibody it produces while keeping the same antigen specificity.

Question 58

# L33: Adaptive Immunnity What is the function of T cells in adaptive immunity?

Answer 58

Cytotoxic T cells (CD8): Kill virus-infected and cancerous cells. T Helper cells (CD4): Activate B cells and other immune cells.

Question 59

# L33: Adaptive Immunnity Q: How do T cells recognise antigens?

Answer 59

They only recognise processed peptides presented by MHC molecules.

Question 60

# L33: Adaptive Immunnity What are the two types of MHC molecules and their roles?

Answer 60

MHC I: Present on most body cells, recognised by cytotoxic T cells (CD8). MHC II: Present on antigen-presenting cells (APCs), recognised by helper T cells (CD4).

Question 61

# L33: Adaptive Immunnity What are antigen-presenting cells (APCs)?

Answer 61

Dendritic cells, macrophages, and B cells—these present antigens to T cells.

Question 62

# L33: Adaptive Immunnity Where do B and T cells develop?

Answer 62

B cells: Bone marrow. T cells: Bone marrow → migrate to the thymus for maturation.

Question 63

# L33: Adaptive Immunnity What is clonal selection?

Answer 63

When a lymphocyte encounters its specific antigen, it rapidly proliferates, creating an army of antigen-specific cells.

Question 64

# L33: Adaptive Immunnity What is V-D-J recombination?

Answer 64

A random genetic recombination process in B and T cells that creates millions of different antigen receptor variants.

Question 65

# L33: Adaptive Immunnity What is the purpose of vaccination?

Answer 65

To stimulate the immune system to produce protective antibodies without causing the disease.

Question 66

# L33: Adaptive Immunnity What are the two types of vaccines?

Answer 66

Live attenuated vaccines: Contain a weakened form of the pathogen (e.g., MMR, Polio). Inactivated/component vaccines: Use dead pathogens or antigenic components (e.g., Hepatitis B, Influenza).

Question 67

# L33: Adaptive Immunnity What is passive immunisation?

Answer 67

Direct transfer of antibodies from another source (e.g., antivenom, monoclonal antibodies).

Question 68

# L33: Adaptive Immunnity What are the advantages and disadvantages of passive immunisation?

Answer 68

Advantage: Immediate protection. Disadvantage: Short-lived, does not generate memory.

Question 69

# L33: Adaptive Immunnity What are monoclonal antibodies?

Answer 69

Lab-engineered antibodies designed to target a specific antigen.

Question 70

# L33: Adaptive Immunnity How are monoclonal antibodies produced?

Answer 70

By fusing B cells with myeloma (cancer) cells to create hybridomas, which continuously produce antibodies.

Question 71

# L33: Adaptive Immunnity What are some uses of monoclonal antibody therapy?

Answer 71

Cancer treatment (e.g., HER2-targeted therapy). Autoimmune disease treatment (e.g., anti-TNF for rheumatoid arthritis). COVID-19 treatment (e.g., monoclonal antibodies against SARS-CoV-2).

Question 72

# L33: Adaptive Immunnity What is affinity vs. avidity in antibody binding?

Answer 72

Affinity: Strength of a single antigen-antibody bond. Avidity: Combined strength of all binding sites on a single antibody molecule.

Question 73

# L33: Adaptive Immunnity Why is IgM effective despite low affinity?

Answer 73

It is pentameric, meaning it has multiple binding sites, increasing avidity.

Question 74

# L33: Adaptive Immunnity What are the primary vs. secondary lymphoid organs?

Answer 74

Primary: Bone marrow & thymus (where lymphocytes develop). Secondary: Lymph nodes, spleen, tonsils, Peyer’s patches (where immune responses occur).

Question 75

# L33: Adaptive Immunnity How do lymphocytes travel through the body?

Answer 75

Circulate between blood, lymph, and secondary lymphoid organs to find antigens. Enter lymph nodes via high endothelial venules (HEVs).

Question 76

# L33: Adaptive Immunnity How do T cells get activated?

Answer 76

Antigen presentation by MHC molecules on APCs. Co-stimulatory signals (e.g., CD28 binding to B7). Cytokine signalling determines differentiation (e.g., into helper or cytotoxic T cells).

Question 77

# L33: Adaptive Immunnity How do B cells get activated?

Answer 77

Bind to free antigen using BCR. Require signals from T helper cells to fully activate.

Question 78

# L33: Adaptive Immunnity What are the three mechanisms cytotoxic T cells use to kill infected cells?

Answer 78

Perforin & Granzyme: Create holes in the target cell membrane and trigger apoptosis. Fas Ligand (FasL): Binds to death receptors, inducing cell death. Cytokine secretion: Activates other immune cells to help clear infection.

Question 79

# L33: Adaptive Immunnity What are cytokines?

Answer 79

Small proteins that act as immune messengers, regulating immune cell activity.

Question 80

# L33: Adaptive Immunnity Give examples of important cytokines and their roles.

Answer 80

IL-2: T cell proliferation. IL-4: B cell activation & class switching to IgE. IFN-γ: Activates macrophages & enhances MHC expression. TNF-α: Inflammatory response & fever.

Question 81

# L33: Adaptive Immunnity What is the complement system?

Answer 81

A series of proteins that enhance immune responses by opsonising pathogens, lysing cells, and promoting inflammation.

Question 82

# L33: Adaptive Immunnity What are the three pathways of complement activation?

Answer 82

Classical Pathway: Activated by antibodies binding to a pathogen. Alternative Pathway: Directly triggered by microbial surfaces. Lectin Pathway: Activated by mannose-binding lectin (MBL) binding to microbes.