Infectious Diseases Part I: The Immune System

Question 1

What is the immune system?

Answer 1

The immune system is a host defence system comprising many cells and processes to protect the body against diseases.

Question 2

What are the functions of the immune system?

Answer 2

• Detect a wide variety of pathogens that cause diseases.
• Distinguish pathogens from body’s own healthy cells.
• Destroy and remove pathogens.

Question 3

What are the types of immune system?

Answer 3

• Innate immune system
• Adaptive immune system

Question 4

Name the cells involved in the innate immune system.

Answer 4

• Neutrophils
• Basophils / Mast cells
• Eosinophils
• Monocytes / Macrophages
• Dendritic cells
• Natural killer cells

Question 5

How many gene clusters code for light chains of antibodies?

Answer 5

2.

Question 6

Which chromosome numbers are the gene clusters that code for light chains in antibodies found in?

Answer 6

Chromosomes 2 and 22.

Question 7

What does each light chain gene cluster have?

Answer 7

• Series of variable (V) genes
• Series of joining (J) genes
• One or more constant (C) genes

Question 8

How many gene clusters code for heavy chains of antibodies?

Answer 8

1.

Question 9

Which chromosome numbers are the gene clusters that code for heavy chains in antibodies found in?

Answer 9

Chromosome 14.

Question 10

What does each heavy chain gene cluster have?

Answer 10

• Series of variable (V) genes
• Series of diversity (D) genes
• Series of joining (J) genes
• Series of constant (C) genes

Question 11

How many gene clusters are expressed in an individual B cell?

Answer 11

1.

Recall that the 2 light chains in an antibody are identical!

Question 12

How do light chain gene clusters undergo rearrangement of genes?

Answer 12

Via somatic recombination:
* 1 of V gene recombines with 1 J gene to create VJ pair, catalysed by recombinase
* Transcription begins at L exon, finishes at C segment.
* Light chain pre-mRNA is spliced, joining VJ segment to C exon, forming mature mRNA
* Translation of mature mRNA occurs at rough ER.

Question 13

How do heavy chain gene clusters undergo rearrangement of genes?

Answer 13

Via somatic recombination:
* 1 D gene joins to J gene to form random combination of DJ pair.
* 1 V gene joins to rearranged DJ gene segment to form VDJ gene segment.
* pre-mRNA undergoes transcription.
* Splicing occurs to join VDJ gene segment to C exons, forming mature mRNA.
* Translation occurs to form polypeptide.

Question 14

What are the different classes of antibodies?

Answer 14

• IgM
• IgG
• IgA
• IgE
• IgD

Question 15

What classes of antibodies do naïve B cells express as B cell receptors?

Answer 15

IgM and IgD.

Question 16

Where does class switching occur?

Answer 16

It occurs in the nucleus of the B cells.

Question 17

What is class switching?

Answer 17

It involves change of amino acid sequence in the constant region of the heavy chain.

Question 18

How can B cells benefit from class switching?

Answer 18

It allows for more efficient humoral response.

Question 19

How does class switching occur?

Answer 19

Class switching occurs in individual B cells by further excision of DNA in the heavy chain gene cluster, resulting in the same VDJ segment to lie next to a different C gene, retaining the same epitope specificity in the antibody but with a different constant region.

Question 20

What is class switching dependent on?

Answer 20

It is dependent on the cytokines released by helper T cells that trigger class switching.

Question 21

What catalyses somatic hyper-mutation?

Answer 21

Cytidine deaminase.

Question 22

How do B cells benefit from somatic hyper-mutation?

Answer 22

The mutations may increase binding affinity of the antibody for its epitope.