6. Adaptive Immune Response

Question 1

When can naive T cells trigger an immune response?

Answer 1

After they have been activated by antigen presenting cells

Question 2

What does the antigen presenting cell do?

Answer 2

Senses the pathogen
Captures the pathogen
Processes the pathogen (degrading protein from virus/bacteria)
Presents the pathogen

Question 3

What do dendritic cells and langerhans cells present the pathogen to?

Answer 3

Naive T cells

Question 4

What are naive T cells?

Answer 4

Tc ell that have not previously encountered the antigen

Question 5

What do macrophages and B cells present pathogen to?

Answer 5

Effector T cells

Question 6

What is the function of effector T cells with macrophages?

Answer 6

Phagocytic activities - enhance processes

Question 7

What are effector T cells?

Answer 7

T cells that have previously encountered the antigen and are capable of performing effector functions during an immune response

Question 8

What is the function of B cells and effector T cells?

Answer 8

T cells when presented with pathogens from B cells produce a different antibody
It is IgM in host cell, if cell is seeing antigen for second time the IgM changed to IgG by T cells

Question 9

What are the features of antigen presenting cells?

Answer 9

Strategic location
Diversity in pathogen sensors (PRRs)
Diversity in pathogen capture mechanisms

Question 10

What are the strategic locations of antigen presenting cells?

Answer 10

Mucosal membranes
Skin 
Blood
Lymph nodes
Spleen

Question 11

Describe the diversity in pathogen sensors (PRRs)

Answer 11

Extracellular pathogens (bacteria, fungi, Protozoa)
Intracellular pathogens (viruses)

Question 12

What is the diversity in pathogen capture mechanisms of antigen presenting cells?

Answer 12

Phagocytosis

Macropinocytosis

Question 13

Which PRRs can sense extracellular pathogens?

Answer 13

TLR1
TLR2
TLR6
TLR4 - important in sepsis
TLR5
TLR11

Question 14

What do TLR1 and TLR2 detect?

Answer 14

Gram positive: staphylocccus aureus, streptococcus pneumoniae

Question 15

What do TLR4 and TLR5 detect?

Answer 15

Gram negative: neisseria meningitidis, E. coli

Question 16

What are the PRRs that can sense intracellular pathogens?

Answer 16

TLR3
TLR7
TLR8
TLR9

Question 17

What can TLR9 detect?

Answer 17

Adenovirus

Question 18

What can TLR8 detect?

Answer 18

Norovirus

Question 19

What happens when a pathogen enters the body through a breach of innate barriers?

Answer 19

Macrophage starts engulfing pathogen, pathogen enters blood stream
Antigen presenting cells capture the pathogen
Antigen presenting cells move into the lymphatics to the lymphoid tissues
Moves into mucosal associated lymphoid tissues (MALT), lymph nodes and spleen
Antigen presenting cells present microbial antigen to the right T cell

Question 20

What type of immunity are extracellular microbes?

Answer 20

Humoral immunity

Question 21

What type of immunity is intracellular microbes?

Answer 21

Cell mediated immunity

Question 22

What are pathogens presented by?

Answer 22

Major histocompatibility complex (MHC) molecules

Question 23

What are the differences in classes of MHC?

Answer 23

MHC class 1 molecules - expressed on all nucleated cells (including macrophages)
MHC class 2 molecules - expressed on antigen-presenting cells, dendritic cells, macrophages, B cells

Question 24

What is a haplotype?

Answer 24

Set of MHC alleles that are inherited together from one parent and present on chromosome

Question 25

What a the key features of MHC class 1 and class 2 molecules?

Answer 25

Co-dominant expression
Polymorphic genes
Presentation of microbial peptides

Question 26

How does the presentation of microbial peptides change?

Answer 26

Antigen presenting cells present intracellular microbes via MHC class 1 molecules
Antigen presenting cells present extracellular microbes via MHC class 2 molecules

Question 27

Describe the endogenous processing of intracellular microbes

Answer 27

Viral protein present in cytosol
Marked for destruction by proteasome
Proteasome-generated viral peptide transported ER by TAP proteins
Formation of viral peptide-MHC class 1 complex if right match
APCs and non-APCs present peptides from intracellular pathogens to CD8+ T cells

Question 28

What is a disadvantage of endogenous pathway processing intracellular microbes?

Answer 28

Have to have correct MHC molecule

Question 29

What happens after a viral peptide-MHC class 1 complex is made?

Answer 29

Antigen-presenting cell will express viral peptides on MHC class 1 molecules
Activation of naive CD8+ T cells in lymphoid tissues
Search and kill all infected cells by activated CD8+ T cells
Any infected target cell will express viral peptides on MHC class 1 molecules

Question 30

Describe the exogenous processing of extracellular microbes

Answer 30

Microbes captured by phagocytosis or micropinocytosis
Degradation in small peptides in the endosome
Peptide-rich vesicles fuse with vesicles containing MHC class 2 molecules
Formation of peptide-MHC class 2 complex if right match
O
APCs presents peptides extracellular pathogens to CD4+ T cells

Question 31

Describe the features of peptide presentation by MHC class 1 and class 2 molecules

Answer 31

Peptide binding cleft - variable region with highly polymorphic residues
Broad specificity - many peptides presented by the same MHC molecule
Responsive T cells - MHC class 1 recognised by CD8+ molecules on T cells, MHC class 2 recognised by CD4+ molecules on T cells

Question 32

What is the clinical importance of MHC molecules?

Answer 32

• Host can deal with a variety of microbes
• No 2 individuals have the same set of MHC molecules (not being wiped out by a single microbe)
• Different susceptibilities to infections
• Major causes for organ transplant rejection
• HLA association with autoimmune disease