Adaptive Immunity

Question 1

What is adaptive immunity?

Answer 1

A highly specific arm of the immune system that recognises antigens and generates immunological memory.

Question 2

What are the defining features of adaptive immunity?

Answer 2

Antigen specificity, immunological memory, and clonal expansion.

Question 3

In which organisms did adaptive immunity first appear?

Answer 3

Jawed vertebrates.

Question 4

Approximately when did adaptive immunity evolve?

Answer 4

Around 500 million years ago.

Question 5

What three biological features define adaptive immunity in vertebrates?

Answer 5

Organised lymphoid tissues, specific antibodies, and specific T cell receptors (TCRs).

Question 6

Where do B cells develop and mature?

Answer 6

In the bone marrow.

Question 7

Where do T cells develop and mature?

Answer 7

Originate in bone marrow, mature in the thymus.

Question 8

What is positive selection of T cells?

Answer 8

Selection for T cells that can recognise self MHC molecules.

Question 9

What is negative selection of T cells?

Answer 9

Elimination of T cells that strongly recognise self antigens.

Question 10

Why is T cell selection important?

Answer 10

To ensure functional immunity while preventing autoimmunity.

Question 11

What is an antigen?

Answer 11

A molecule that can be specifically recognised by the adaptive immune system.

Question 12

What types of molecules can act as antigens?

Answer 12

Proteins, polysaccharides, lipids (often protein-associated).

Question 13

How do B cells recognise antigens?

Answer 13

By binding intact, native antigens directly.

Question 14

How do T cells recognise antigens?

Answer 14

By recognising processed peptide fragments presented on MHC molecules.

Question 15

What is MHC restriction?

Answer 15

The requirement for T cells to recognise antigen only when presented by self MHC.

Question 16

Which cells express MHC class I molecules?

Answer 16

All nucleated cells.

Question 17

Which cells express MHC class II molecules?

Answer 17

Professional antigen-presenting cells (APCs).

Question 18

Name the professional antigen-presenting cells.

Answer 18

Dendritic cells, macrophages, B cells.

Question 19

What is the key virulence factor of Streptococcus pneumoniae?

Answer 19

Its polysaccharide capsule.

Question 20

Why is the capsule antigenically important?

Answer 20

Different capsule structures elicit different antibody responses.

Question 21

What is a serotype?

Answer 21

A variant of a microorganism defined by distinct antigenic structures.

Question 22

Why does immunity to one S. pneumoniae serotype not protect against others?

Answer 22

Because antibodies are specific to the capsule structure.

Question 23

What is antigenic variation?

Answer 23

The ability of pathogens to alter their surface antigens to evade immune recognition.

Question 24

Why is antigenic variation effective against adaptive immunity?

Answer 24

Because adaptive immunity relies on antigen specificity and memory.

Question 25

Name three mechanisms of antigenic variation.

Answer 25

Gene switching, genetic recombination, point mutation.

Question 26

How does Trypanosoma evade the immune system?

Answer 26

By switching Variant Surface Glycoprotein (VSG) expression.

Question 27

How many VSGs are expressed at one time in Trypanosoma?

Answer 27

Only one.

Question 28

Why does Trypanosoma infection cause waves of parasitaemia?

Answer 28

Repeated VSG switching allows immune evasion.

Question 29

Does Trypanosoma use antigenic shift?

Answer 29

No — it uses antigenic variation via gene switching.

Question 30

What two surface proteins of influenza undergo antigenic change?

Answer 30

Haemagglutinin (HA) and neuraminidase (NA).

Question 31

What is antigenic drift?

Answer 31

Gradual accumulation of point mutations in viral antigens.

Question 32

What does antigenic drift cause?

Answer 32

Seasonal influenza epidemics.

Question 33

What is antigenic shift?

Answer 33

Reassortment of genome segments producing a novel virus subtype.

Question 34

Which influenza viruses can undergo antigenic shift?

Answer 34

Influenza A only.

Question 35

Why does antigenic shift cause pandemics?

Answer 35

Because the population lacks pre-existing immunity.

Question 36

What is an antibody also known as?

Answer 36

An immunoglobulin (Ig).

Question 37

What is the basic structure of an antibody?

Answer 37

Two identical heavy chains and two identical light chains.

Question 38

What bonds hold antibody chains together?

Answer 38

Disulfide bonds.

Question 39

What determines antibody specificity?

Answer 39

The variable regions of the heavy and light chains.

Question 40

What is the function of the constant region?

Answer 40

Determines antibody class and mediates effector functions.

Question 41

How do innate immune cells recognise pathogens?

Answer 41

Using pattern recognition receptors (PRRs).

Question 42

What are PAMPs?

Answer 42

Pathogen-associated molecular patterns.

Question 43

Why are PAMPs ideal targets for innate immunity?

Answer 43

They are conserved, essential for pathogens, and absent from host cells.

Question 44

Name cells that express PRRs.

Answer 44

Macrophages, dendritic cells, neutrophils.

Question 45

What happens after PRR activation?

Answer 45

Cytokine release, inflammation, phagocytosis, and adaptive immune activation.

Question 46

What are cytokines?

Answer 46

Small soluble proteins that mediate immune cell communication.

Question 47

How do cytokines act on cells?

Answer 47

By binding specific high-affinity receptors.

Question 48

Why can cytokines act at very low concentrations?

Answer 48

Signal amplification through intracellular pathways.

Question 49

Why do leukocytes need cytokines?

Answer 49

To coordinate activation, proliferation, differentiation, and migration.

Question 50

How can cytokines regulate enzyme activity?

Answer 50

By up-regulating or down-regulating enzymes within target cells.

Question 51

How do cytokines affect gene expression?

Answer 51

By altering transcription of specific genes.

Question 52

How do cytokines regulate cell survival?

Answer 52

By promoting survival or inducing apoptosis.

Question 53

Why is cytokine-induced apoptosis important?

Answer 53

To terminate immune responses and prevent tissue damage.

Question 54

What is a chemokine?

Answer 54

A subclass of cytokine that induces leukocyte migration.

Question 55

What is chemotaxis?

Answer 55

Directed movement of cells up a concentration gradient.

Question 56

Approximately how many chemokines exist in humans?

Answer 56

Around 50.

Question 57

Name the two major chemokine families.

Answer 57

CC and CXC.

Question 58

How fast can leukocytes migrate in response to chemokines?

Answer 58

Up to 30 μm per minute.

Question 59

Why do only activated leukocytes migrate to infected tissue?

Answer 59

Because activation induces expression of specific chemokine receptors.

Question 60

What is cytokine pleiotropy?

Answer 60

One cytokine producing multiple effects on different cell types.

Question 61

Why does pleiotropy occur?

Answer 61

Different cells express different receptors and signalling pathways.

Question 62

What is cytokine redundancy?

Answer 62

Multiple cytokines producing the same biological effect.

Question 63

Why is redundancy beneficial?

Answer 63

Ensures immune responses occur even if one cytokine is absent.

Question 64

Explain how cytokines and chemokines together coordinate immune responses.

Answer 64

Cytokines regulate immune cell activation, differentiation, and survival, while chemokines direct the migration of activated leukocytes to sites of infection, ensuring coordinated and targeted immune responses.