Interferons, antibodies and T-cell development

Question 1

What are toll like receptors? Innate immune system

Answer 1

Proteins found on the cell membrane or in vesicles that respond to foreign pathogens.

Question 2

What are interferons?

Answer 2

Signalling molecules that alert other host cells there is a foreign pathogen and synthesise antipeptides and also instruct macrophages and NK cells to begin to become activate and proliferate.

Question 3

How are interferons produced?

Answer 3

Virus enters the cell and migrates to the nucleus in attempt to intergrate itself into the host cell’s genome. When the host genome is damaged this secretes the transcription factor IRF which activates a gene which is converted into mRNA and translated into proteins and interferons are produced.

Question 4

What are the three types of interferons?

Answer 4

Alpha, beta and gamma

Question 5

Which cells secrete IFN-Y?

Answer 5

Lymphocytes or other immune system cells

Question 6

How is protein kinase R produced?

Answer 6

Alpha and beta interferons diffuse into adjacent tissue cell and activate a specific gene which produces protein kinase R (antiviral peptide).

Question 7

What is the function of protein kinase R?

Answer 7

Inhibits virus replicating in cell

Question 8

What is the function of IFN-Y?

Answer 8

Released from the infected cell and binds to IFN-Y receptors on nearby macrophages and induces a signalling cascade instructing the macrophage to proliferate, becomes bigger and increases expression of MHC-1 and MHC-2.

Question 9

How are natural killer cells activated?

Answer 9

By alpha and beta interferon

Question 10

Which type of cell secretes antibodies?

Answer 10

Plasma cells

Question 11

What are the role of IgG antibodies?

Answer 11

Initiates the complement system via the classical pathway when binding to an antigen resulting in cell lysis (MAC), oponisation by production of C3b and pro-inflammatory chemotaxic agents.
Also causes neutralisation by preventing the virus or bacterium attaching to host cell and phagocytosis and precipitation.

Question 12

What form are IgA antibodies produced in?

Answer 12

As a dimer

Question 13

Where are IgA antibodies found?

Answer 13

In the skin, saliva, mucosa lining

Question 14

Which antibodies have a role in passive immunity?

Answer 14

IgA antibodies are found in breast milk and IgG antibodies are passed through the placenta especially in the third trimester.

Question 15

When are IgM antibodies usually secreted?

Answer 15

In primary response to the pathogen, therefore a good indicator for early diagnosis.

Question 16

What is the role in of IgM antibodies in type 2 hypersensitivity?

Answer 16

Can bind to multiple antigen binding sites when in the monomeric form causing glucination.

Question 17

Can IgM also induce the complement system?

Answer 17

Yes, it can initiate causing a downstream pathway of MAC, opsonisation and pro-inflammatory chemotactic agents.

Question 18

Where is the monomeric form of IgE antibodies found?

Answer 18

In the respiratory tract mucosa
Urogenital structures
Lamina propria
Lymphatic tissue

Question 19

Describe the role of IgE antibodies.

Answer 19

IL-4 activates and causes proliferation of plasma cells which produces IgE which binds to the allergen. Together with the allergen they bind to the FcER1 receptors on mast cells and continued binding of the antigen-antibody complex causes degranulation of the mast cell releasing leukotrienes, histamines and prostaglandins. Histamines bind to the H1 receptors on vascular smooth muscle causing vasodilation and for the blood vessels to become leaky causing oedema. It also causes contraction of bronchial smooth muscle which causes wheezing and difficulty breathing.

Question 20

What is the role of IgD antibodies?

Answer 20

Acts as a B cell receptor

Question 21

How does plasma undergo changes from producing IgM to IgG antibodies?

Answer 21

Due to somatic hypermutation where different cyotkines activate different genes which causes different production of antibodies.

Question 22

Does IgM or IgG production change in the secondary infection?

Answer 22

IgG massively increases.

Question 23

Explain the two types of immunity.

Answer 23

Passive immunity: antibodies didn’t have to be produced by fighting off an infection, was given them.
Active immunity: antibodies acquired by fighting off the infection.

Question 24

What are some examples of naturally acquired passive immunity?

Answer 24

IgG antibodies through the placenta or IgA antibodies in Mother’s milk.

Question 25

What are some examples of naturally acquired active immunity?

Answer 25

Being infected with the pathogen

Question 26

What are some examples of artificially acquired passive immunity?

Answer 26

Anti-venom

Question 27

What are some examples of artificially acquired active immunity?

Answer 27

Vaccines

Question 28

Describe the antibody structure.

Answer 28

Two variable light chains either side parallel to two variable heavy chains connected by disulfide bonds to the heavy chain constant. The variable region is specific to the antigen (due to recombination). Fc region at the bottom of the heavy chain constant where complement binding occurs.

Question 29

Where are T cells produced?

Answer 29

In the bone marrow which then travel to the thymus for maturation and selection due to chemotactic agents such as thymosin, thymotoxin, thymopoetin, thymic factors.

Question 30

What is the role of thymosin, thymotoxin, thymopoetin, thymic factors?

Answer 30

They activate a certain set of genes in the T cell and secrete RAG 1 and RAG 2, which shuffles the DNA and lead to the production of a TCR (T cell receptor).
They also activate genes to produce CD8 and CD4.

Question 31

Explain thymus positive selection.

Answer 31

The thymus cell expresses both MHC-1 and MHC-2 on its cell surface binding specifically to the T cell with CD4 and CD8 expressed on its cell surface. CD4 binds to MHC-2 and CD8 binds to MHC-1, if they bind selectively= positive selection.

Question 32

What happens if the T cell doesn’t bind to the MHC ?

Answer 32

Undergoes apoptosis by thymus glands secreting FAS which triggers genes to undergo apotosis.

Question 33

What happens if the TCR recognises self antigens?

Answer 33

FOS is secreted by the thymus cells which triggers genes to undergo apotosis.

Question 34

Describe the last step in T cell development?

Answer 34

The T cell either interacts with the MHC-2 through the CD4 complex causing up-regulation of CD4 genes and down-regulation of CD8 genes. Or it interacts with the MHC-1 thymus cell through the CD8 complex and up-regulates the CD8 genes and down-regulates the CD4 genes.

Question 35

What are T regulatory cells?

Answer 35

Have either CD4 and TCR or CD8 and TCR on cell surface differentiated from T helper or T cytotoxic cells through CD25/IL-2 interaction.

Question 36

Where do the T cells go after they have developed?

Answer 36

White pulp in blood vessels around the spleen or the lymph nodes and park in the cortex.

Question 37

Where do T regulatory cells go?

Answer 37

Hassal’s corpusles