Humoral Immunity 1

Question 1

What are antibodies?

Answer 1

Y shaped molecules expressed by immune cells to target pathogens

Question 2

How do antibodies work?

Answer 2

Antibodies work by preventing bacteria entering by binding to the bacteria docking site or neutralising them

Question 3

Antibody structure?

Answer 3

2 heavy and 2 light chains

Question 4

How many classes does the heavy chain have and what are they divided into?

Answer 4

Heavy chain has 5 classes:γ, δ, α, μ and ε.
These are further divided into 4 subclasses: Y1, Y2, Y3 & Y4.
which can be further divided into alpha-1 or alpha-2

Question 5

How many domains, constant and variable regions does the heavy chain have?

Answer 5

Heavy chain has 4 domains, 3 constant and 1 variable

Question 6

Describe the variable region and its function?

Answer 6

The variable region is very specific and binds to specific epitopes of specific antigens.

Question 7

How many variables and constant regions does the light chain have?

Answer 7

1 variable and 1 constant

Question 8

How many classes does the light chain have?

Answer 8

kappa (κ) chain or lambda (λ) chain

Question 9

Describe the constant region?

Answer 9

The constant region is very responsible for biological activities.

Question 10

How many forms do antibodies have and what are they?

Answer 10

B cell receptor or secreted form.

Question 11

What is the final form and what is it used for?

Answer 11

The final form is the secreted form and is used to fight off pathogens

Question 12

What is the final form of antibody anchored to?

Answer 12

It is anchored to the plasma membrane of B cells

Question 13

What forms can the antibody be in when secreted?

Answer 13

When the antibody is secreted it can be in monomeric or pentameric forms.

Question 14

In which form are antibodies initially secreted as?

Answer 14

As a monomer and then combined to produce a multimeric form

Question 15

Where do B cells spend their life?

Answer 15

B cells spend their life in bone marrow, blood, spleen and secondary lymphoid organs.

Question 16

What can the life cycle of B cells be divided into?

Answer 16

The life cycle can be divided into antigen-dependent and independent stages.

Question 17

Describe the steps involved in the lifecycle of B cells?

8 Steps

Answer 17

1. Starts with Stem cell which differentiates into pro B cell
2. Pro B cells undergo VDJ (variable diversity joining) recombination which codes in the heavy chain- constant and variable regions and become a pre-B cell. It can only pre-b cell once it makes a functional heavy chain.
3. Then it undergoes another VDJ recombination to code in the light variable and heavy chain regions.
4. B cell continues to mature until it expresses IgM and IgD.
5. Becomes a mature circulating B cell and then becomes activated once it encounters a pathogen.
6. B cell migrates into the germinal centre (GC) and will undergo a special selection to hone its variable region to that particular pathogen.
7. Undergoes affinity maturation and class switching
8. Differentiates into plasma cells which secrete antibodies and memory B cells

Question 18

What are somatic recombinations and an example?

Answer 18

Any changes at the DNA level are called somatic recombination e.g. VDJ recombination

Question 19

What is differential splicing?

Answer 19

changes at the mRNA level are called differential splicing

Question 20

What is each chain of antibody made of?

Answer 20

Each chain is made of one single polypeptide

Question 21

What is the hinge region between in antibodies?

Answer 21

The hinge region is between CH1 and CH2

Question 22

What makes the antibody flex and so what does this expose?

Answer 22

These are a stretch of polypeptides that make the antibody flex so that the active site can be exposed

Question 23

What chain is the hinge region longer in?

Answer 23

Longer in the heavy chain

Question 24

What are the Fv regions?

Answer 24

Variable regions of light and heavy chains working together

Question 25

What are Fab regions?

Answer 25

Variable fragment and first constant domains

Question 26

What are the Fc regions?

Answer 26

Heavy chain CH2 and CH3 working together

Question 27

What does glycan form a part of and what does it attract?

Answer 27

Glycan (sugar group) forms part of the active site and forms a pocket where the receptors of the other immune cells will be attracted to.

Question 28

What stabilises the antibody structure?

Answer 28

Disulphide bonds stabilise the structure

Question 29

What are CDRs?

Answer 29

Protrusions that interact with the antigens

Question 30

Where are CDRs located in the antibody?

Answer 30

They are located in the variable light and variable heavy chains

Question 31

The lifecycle of B cells (Antigen independent stage)

Answer 31

1. Stem cell differentiates into Pro-B cell 2. Pro-B cell undergoes DNA recombination (First, the V region combines with the DJ region- this is VDJ recombination) 3. This codes for the heavy chain variable region. the heavy chain variable region is co-expressed with μ constant region- constant region for IgM antibody class (this is the default for all B cells before they encounter pathogens) 4. Pre B cell expresses valid functional chains 5. This pre B cell expresses a placeholder light chain to hold it in place as light chain is not generated yet. 6. Undergoes third recombination on the light chain- VJ recombination. codes in the variable and constant regions on light chain. 7. There are also additional processes such as junctional flexibility and P and N nucleotide addition. This contributes to the diversity of the antibody. 8. Once B cell can express IgM and IgD ( has capacity to alternatively splice mRNA), it becomes a mature/resting/naive B cell.

Question 32

How many loci are there that encode Ig?

Answer 32

There are three genetic loci encoding Ig - Two for the light chain: kappa and lambda locus - One for heavy chain

Question 33

What chromosome is the lambda and kappa chain found on?

Answer 33

In humans, the lambda chain is found on Chr22 and kappa on Chr2

Question 34

What chromosome is the heavy chain found on?

Answer 34

The heavy chain is on Chr14

Question 35

What genes regarding antibodies are inherited and not inherited?

Answer 35

No antibody genes are inherited and only gene segments are inherited

Question 36

What does arranging gene segments in different combinations generate?

Answer 36

Arranging these gene segments in different combinations generate many Ig sequences causing the B cell to be unique.

Question 37

What segments are there in the light chain?

Answer 37

In the light chain there is variable and J gene segments

Question 38

What regions are there in the heavy chain?

Answer 38

In the heavy, there are V, D and J regions,

Question 39

What do segments code for once they've been rearranged?

Answer 39

Once they are rearranged at the DNA level, they will code for the CDRs

Question 40

What do the J or DJ regions code for?

Answer 40

The J or DJ region codes for CDR3 (3RD CDR) region