8 - Adaptive Immunity and Influenza

Question 1

Where do B cells mature and what happens to self-reactive B cells

Answer 1

In the bone marrow. B cells that bind self-antigens undergo apoptosis (negative selection)

Question 2

What do B cells have on their surface that allows them to recognise antigens

Answer 2

B cell receptors (BCRs) specific to particular antigens

Question 3

What do B cells differentiate into after activation

Answer 3

Plasma cells (secrete antibodies) and memory B cells (long-term immunity)

Question 4

Where do naive B cells encounter antigens

Answer 4

In secondary lymphoid organs (e.g. lymph nodes, spleen)

Question 5

What activates B cells

Answer 5

Binding of their BCR to a specific epitope on an antigen

Question 6

How do CD4+ helper T cells help B cells

Answer 6

They secrete cytokines to promote B cell differentiation

Question 7

What happens after B cell activation

Answer 7

Clonal expansion and differentiation into plasma and memory B cells

Question 8

What do plasma cells produce

Answer 8

Soluble antibodies specific to the antigen’s epitope

Question 9

What’s the role of the variable region in an antibody

Answer 9

It binds to antigens — different for each antibody; forms antigen-antibody complexes

Question 10

What does the constant region determine

Answer 10

The antibody class

IgM
IgD
IgG
IgA
IgE

(each with distinct functions)

Question 11

What are the main functions of antibodies

Answer 11

Neutralisation, opsonisation, and complement activation

Question 12

IgM

Answer 12

First antibody produced

Question 13

IgD

Answer 13

B cell activation

Question 14

IgG

Answer 14

Most abundant, long term immunity

Question 15

IgA

Answer 15

Mucosal secretions (tears, saliva)

Question 16

IGe

Answer 16

Allergies and parasitic responses

Question 17

What characterises the primary immune response

Answer 17

Slow (5–10 days)

Low levels of IgM first, followed by IgG

Memory cells are formed

Question 18

What characterises the secondary immune response

Answer 18

Faster (1–3 days), stronger

Mainly IgG

Memory B/T cells kick in hard

Question 19

How is antibody diversity generated

Answer 19

Random DNA rearrangement of V (variable), D (diversity), and J (joining) gene segments

Question 20

Steps of the humoral immune response

Answer 20

Antigen recognition
T cell help
Clonal expansion/differentiation
Antibody production + pathogen elimination

Question 21

What is an allergy

Answer 21

An overreaction to harmless substances (allergens), involving IgE and histamine release

Question 22

What is autoimmunity

Answer 22

Immune system attacks the body’s own cells due to failure of self-tolerance

Question 23

Give one example each of an allergy and an autoimmune disease

Answer 23

Allergy: Hay fever, asthma

Autoimmunity: Type I Diabetes, Rheumatoid Arthritis

Question 24

How does HIV evade the immune system

Answer 24

Infects CD4+ helper T cells by binding to CD4 proteins → endocytosis → T cell death → weakened immunity

Question 25

What defines AIDS in a patient

Answer 25

Severely reduced CD4+ T cell levels and high susceptibility to infections/cancers

Question 26

Which proteins are key for influenza entry and exit

Answer 26

Hemagglutinin (HA) → entry Neuraminidase (NA) → exit

Question 27

What does HA bind to

Answer 27

Sialic acid on respiratory epithelial cells

Question 28

How does NA assist viral exit

Answer 28

Cleaves sialic acid → allows virus to leave cell and spread

Question 29

What’s the role of ion channel M2

Answer 29

Promotes H⁺ influx into endosomes, aiding viral uncoating

Question 30

What is antigenic drift

Answer 30

Minor mutations in HA/NA genes → gradual changes → seasonal flu

Question 31

What is antigenic shift

Answer 31

Major reassortment from two viruses mixing in one host → new subtype → pandemic risk Example - H1N1 Swine Flu (2009)