Adaptive Immune System

Question 1

Discuss recognition of antigens by immune system

Answer 1

PRRs- cell surface, cytoplasmic, secreted

MHC-cell surface

T cell receptor(TCR)- cell surface

Antibody (BCR)- cell surface, secreted

Question 2

Where does B cell develop and what are it’s stages?

Answer 2

In the bone marrow

Stem cell —> Pro-B —> Pre-B —> Immature B —> Mature B

Question 3

What are the types of B cells and their features?

Answer 3

B1 and B2

B1

• derives from fetal liver
• self renewing
• in peritoneal and pleural cavities
• T independent response
• low affinity for IgM

B2

• conventional B cells
• replenished from bone marrow
• present in secondary lymphoid tissues
• T dependent
• high affinity for IgG, IgA, IgE

Question 4

At which stage of B cell maturation does VDJ recombination finish?

Answer 4

Pre-B

Question 5

What does recombination allow B cells to do?

Answer 5

Create antigen receptors that can recognize each individual antigen in a specific way (only 1 antigen specificity expressed per B cell)

Question 6

What is ITAM? What is it required for?

Answer 6

Immunoreceptor Tyrosine based Activation Motif

Required for B cell to send signal to nucleus that an antigen has been detected.

Question 7

What is the variable region that is expressed as a protein after recombination contains CDR segments referred to as?

Answer 7

Hypervariable regions

Question 8

What is an antibody?

Answer 8

Also known as immunoglobulin.

A fragment, antigen binding, Y shaped protein consisting of light and heavy chains that recognize antigens

Question 9

What are two different forms of light chain immunoglobulins?

Answer 9

Kappa and lambda

Question 10

What is the main difference between the gene segments of the immunoglobulin light chain and heavy chain?

Answer 10

The light chain gene segment does not have a diversity segment

Question 11

Genetic recombination of the immunoglobulin heavy and light chains occur in a specific sequence? What is the sequence?

Answer 11

2 attempts at recombination of the heavy chain
2 attempts at recombination of the kappa light chain
2 attempts at recombination of the lambda light chain

Question 12

If allelic exclusion were to malfunction during an immunoglobulin recombination, what may occur?

Answer 12

a B cell that expresses different light and heavy chains on it IgM and IgD

Question 13

What causes the generation of antibody diversity? (Antigen independent)

Answer 13

• random recombinations of VJ and VDJ genes
• random addition of nucleotides to DNA during recombination by TdT
• random combination of heavy chains with light chains

Question 14

What causes the generation of antibody diversity? (Antigen dependent)

Answer 14

• somatic hypermutation and affinity maturation (variable region)
• isotype switching (constant region)

Question 16

How are heavy chain and light chain recombination mediated?

Answer 16

Recombinase enzymes RAG-1 and RAG-2 (recombination activating gene) that recognize recombination signal sequence (RSS) nucleotides flanking V, D and J gene segments

Question 17

What are the types of T cells?

Answer 17

Th: helper T cell

Tc/CTL: cytotoxic T cell/cytotoxic T lymphocyte

Treg: naturally occurring regulatory T cell

Question 18

Where do T cells develop?

Answer 18

They travel from the bone marrow as T cell precursor and enter and develop in the thymus and later enter the secondary lymphoid tissues

Question 20

What occurs in the thymus?

Answer 20

Thymic education. T cells learn to recognize “self” and where any reactivity again self antigens are eliminated

Question 21

Where do T cells pass through and what do they interact with?

Answer 21

Within the thymus:
The cortex: interact with thymic epithelial cells
The medulla: interact with dendritic cells and macrophages

Question 22

What is positive selection and where does it occur?

Answer 22

T cells expressing TCRs (T cell Receptors) capable of binding self-MHC on cortical epithelial cells survive. Occurs in the thymic cortex

Question 23

What is negative selection and where does it occur?

Answer 23

T cells expressing TCRs with high affinity for self undergo apoptosis or become Treg. Occurs in the medulla

Question 24

What does the B cell costimulation complex consist of?

Answer 24

Leu13, CR2, CD19 with ITAM attached and CD81

Question 25

Why is the co stimulatory complex needed?

Answer 25

Along with the transmembrane version of the antibody and the Ig-alpha and Ig-beta molecules are needed for B cell activation

Question 26

What do CD4+ T cells recognize? What do CD8+ T cells recognize?

Answer 26

CD4+ T cells recognize MHC class 2 molecules

CD8+ T cells recognize MHC class 1 molecules

Question 27

What are the two pathways a B cell could differentiate into?

Answer 27

Naive B cell —> Activated B cell —> proliferation —> 1 of 2 pathways

1. Plasma cells —> antibody
   Antibody secreting version of B cell
2. Memory B cell
   Important in developing secondary immune response

Question 28

What does clonal selection allow the immune system to do?

Answer 28

Recognize a wide variety of antigens and produce a tailored response to that antigen

Question 29

What does the activation of Naive T cells require?

Answer 29

Dendritic cells are a requirement.

Question 30

What occurs during T cell differentiation?

Answer 30

Naive T cell —> Activated T cell —> proliferation —> effector T cell or Memory T cell

Question 31

Which molecules are unregulated on the surface of a dendritic cell to convert it from phagocytic to antigen presenting?

Answer 31

MHC Class 2, B7 (CD80, CD86)

Question 32

How many signals does lymphocyte activation require?

Answer 32

2 signals.

Signal 1- from specific interaction of TCR with peptide-MHC complex on an APC

Signal 2- binding of costimulator receptor such as CD28with its ligand (CD80)