The immune system

Question 1

What are the three main lines of immune defense in vertebrates?

Answer 1

Physical/chemical barriers, innate immunity (although, arguable, the physical and chemical barriers are part of innate immunity), and adaptive immunity.

Question 2

Name two physical barriers against infection.

Answer 2

Skin and mucous membranes.

Question 3

What is the function of lysozyme?

Answer 3

It is an enzyme that breaks down bacterial cell walls, found in tears, mucus and saliva.

Question 4

How does stomach acid contribute to immunity?

Answer 4

It kills ingested pathogens by creating a low pH environment

Question 5

What is the difference between innate and adaptive immunity?

Answer 5

Innate is fast and non-specific; adaptive is slow, specific, and has “memory” (responds more rapidly to previously encountered pathogens).

Question 6

Can the immune system distinguish between self and non-self?

Answer 6

Yes, especially the adaptive system via antigen recognition.

Question 7

Which cells act as the bridge between innate and adaptive immunity?

Answer 7

Antigen-presenting cells (e.g., dendritic cells).

Question 8

How do pathogens typically enter the body?

Answer 8

Through skin wounds, mucosal surfaces (airways, urinary and reproductive tracts), or ingestion (gastrointestinal tract).

Question 9

What does it mean for the immune system to be “self-tolerant”?

Answer 9

It avoids attacking the body’s own cells.

Question 10

What cells are involved in innate immunity?

Answer 10

Macrophages, neutrophils, dendritic cells, NK cells.

Question 11

Which immune system acts first?

Answer 11

Innate immunity.

Question 12

How does the innate immune system recognize pathogens?

Answer 12

Through conserved molecular patterns like PAMPs.

Question 13

What is a key feature of adaptive immunity?

Answer 13

Antigen specificity and memory.

Question 14

Which cells are central to adaptive immunity?

Answer 14

B lymphocytes and T lymphocytes (Helpers and cytotoxic).

Question 15

What do B cells produce?

Answer 15

Antibodies.

Question 16

What are the two main types of adaptive responses?

Answer 16

Humoral (antibody-mediated) and cell-mediated.

Question 17

Does the innate system improve with time?

Answer 17

No — it has no memory.

Question 18

What allows the adaptive system to improve?

Answer 18

Clonal selection and expansion and memory cell formation.

Question 19

Do innate and adaptive immunity interact?

Answer 19

Yes — innate responses activate and shape adaptive responses.

Question 20

What is the primary function of neutrophils?

Answer 20

Phagocytosis and rapid response to bacterial infection.

Question 20

What do macrophages do besides phagocytose?

Answer 20

Release cytokines and present antigens to T cells.

Question 21

What type of immune cell connects innate to adaptive immunity?

Answer 21

Dendritic cells, which present antigens to B cells in the thymus and lymph nodes.

Question 22

How do NK cells kill infected cells?

Answer 22

By releasing perforins and signaling molecules to induce apoptosis.

Question 23

What chemical do mast cells release during inflammation?

Answer 23

Histamines.

Question 24

What is a Pattern recognition receptor (PRR)?

Answer 24

A cell membrane receptor detects microbial molecules and activates immune cells.

Question 25

What are cytokines?

Answer 25

Signaling proteins that mediate immune responses.

Question 26

Which innate cells are professional antigen-presenting cells (APCs)?

Answer 26

Dendritic cells and macrophages.

Question 27

Why is innate immunity important even if we have adaptive immunity?

Answer 27

It provides rapid protection and activates adaptive responses.

Question 28

What triggers inflammation?

Answer 28

Infection or tissue injury.

Question 29

What causes redness and warmth during inflammation?

Answer 29

Vasodilation increases blood flow.

Question 30

What is histamine’s role?

Answer 30

Increases vascular permeability and recruits immune cells.

Question 31

What cells arrive first at the infection site?

Answer 31

Neutrophils.

Question 32

What do macrophages do in inflammation?

Answer 32

Clear pathogens and release cytokines to regulate the response.

Question 33

What are the five cardinal signs of inflammation?

Answer 33

Redness, heat, swelling, pain, loss of function.

Question 34

What is chemotaxis?

Answer 34

Directed movement of immune cells toward chemical signals.

Question 35

What happens if inflammation is not resolved?

Answer 35

It can become chronic and cause tissue damage.

Question 36

Is inflammation part of the adaptive immune response?

Answer 36

No — it’s part of the innate immune response.

Question 37

What are the two main lymphocyte types?

Answer 37

B cells and T cells.

Question 38

What is the primary function of B cells?

Answer 38

To produce antibodies that neutralize antigens.

Question 39

What do cytotoxic T cells do?

Answer 39

Kill infected or abnormal cells directly.

Question 39

What do helper T cells do?

Answer 39

Activate B cells and other T cells using cytokines.

Question 40

What does “specificity” mean in adaptive immunity?

Answer 40

Each lymphocyte targets one specific antigen (Because of highly specific receptors).

Question 41

What is immune “memory”?

Answer 41

The capacity to respond more rapidly and strongly upon second exposure.

Question 42

What ensures self-tolerance?

Answer 42

Lymphocyte maturation in the thymus (T cells) and bone marrow (B cells), where self-reactive cells are eliminated.

Question 43

Why is diversity important in the immune system?

Answer 43

It allows recognition of virtually any pathogen.

Question 44

How long does it take to activate adaptive immunity?

Answer 44

Several days after initial exposure.

Question 45

Do T cells produce antibodies?

Answer 45

No — only B cells do.

Question 46

What are memory cells?

Answer 46

Long-lived B and T cells that “remember” an antigen.

Question 47

What is the primary immune response?

Answer 47

The initial response to a first-time antigen exposure.

Question 48

How do vaccines work?

Answer 48

By simulating an infection to create memory cells without causing disease.

Question 48

Which has higher antibody levels: primary or secondary response?

Answer 48

Secondary.

Question 48

How long does the primary response take to develop?

Answer 48

5 to 10 days.

Question 48

What is the secondary immune response?

Answer 48

The rapid, stronger response upon second exposure to the same antigen.

Question 49

Do memory T cells also respond faster during secondary exposure?

Answer 49

Yes, alongside memory B cells.

Question 50

What is clonal selection?

Answer 50

The activation and replication of a lymphocyte that recognizes a specific antigen.

Question 51

What is required for T cell activation?

Answer 51

Antigen presentation and costimulatory signals.

Question 52

What does clonal expansion mean?

Answer 52

The rapid division of activated lymphocytes into identical clones.

Question 53

What are effector cells?

Answer 53

Activated lymphocytes that fight the current infection.

Question 54

What are memory cells?

Answer 54

Long-lived cells that respond quickly to future exposures.

Question 55

What type of cell presents antigen to T cells?

Answer 55

Antigen-presenting cells (e.g., dendritic cells, macrophages).

Question 56

What is the role of MHC molecules?

Answer 56

To display antigens to T cells.

Question 57

Which MHC class do helper T cells recognize?

Answer 57

MHC class II.

Question 58

Which MHC class do cytotoxic T cells recognize?

Answer 58

MHC class I.

Question 59

What signals are required to fully activate T cells?

Answer 59

Antigen recognition + costimulation + cytokines

Question 60

What type of immunity do B cells mediate?

Answer 60

Humoral immunity.

Question 61

What is the main product of B cells?

Answer 61

Antibodies.

Question 62

What type of pathogens are targeted by humoral immunity?

Answer 62

Extracellular pathogens (e.g., bacteria, viruses in blood).

Question 63

What cells mediate cell-mediated immunity?

Answer 63

Cytotoxic T cells (CD8⁺).

Question 64

What type of pathogens are targeted by cell-mediated immunity?

Answer 64

Intracellular pathogens (e.g., viruses, cancer cells).

Question 65

What cell type helps both B and T cells activate?

Answer 65

Helper T cells (CD4⁺).

Question 66

What MHC class is used in humoral response initiation?

Answer 66

MHC class II (to activate helper T cells).

Question 67

What MHC class is involved in cytotoxic responses?

Answer 67

MHC class I (activates CD8⁺ T cells).

Question 68

Can one infection activate both branches?

Answer 68

Yes — most do.

Question 69

Which immunity involves antibodies?

Answer 69

Humoral immunity.

Question 70

What causes autoimmune disease?

Answer 70

Breakdown of self-tolerance, possibly triggered by genetic or environmental factors.

Question 70

What is an autoimmune disease?

Answer 70

A condition in which the immune system attacks the body’s own cells or tissues.

Question 71

Which immune cells are often involved in autoimmunity?

Answer 71

Both autoreactive T cells and B cells producing self-targeting antibodies.

Question 72

What is the role of self-tolerance?

Answer 72

To eliminate or inactivate immune cells that react to self-antigens.

Question 73

What is an allergy?

Answer 73

A hypersensitive immune reaction to a normally harmless substance.

Question 74

What is anaphylactic shock?

Answer 74

A severe, life-threatening allergic reaction that causes airway constriction and drop in blood pressure.