Immune Wokshop W3

Question 1

What is the difference between helper T cells and cytotoxic T cells?

Answer 1

Helper
- help activate macrophages and B cells
- They are CD4+ T cells
- They secrete cytokines
- They recognise antigens presented by MHC2
- They require co-stimulation by APC’s
- They secrete cytokines such as IFN-y, IL-2, IL-4
- They are immune coordinators

Cytotoxic
- They kill infected cells
- They are CD8+ T cells
- They release cytokines such as granzyme, performing and or FasL
- They recognise MHC1
- They require help from CD4+ and APC’s for full activation
- They are immune assassins

Question 2

Explain why CD4T cells are important for your immune system

Answer 2

• CD4 T cells help activate other immune cells
• If we dont have CD4 we cannot activate macrophages or dendritic cells or B cells
• without B cells there is no antibody production so no IL-4 or IL-5 being secreted
• memory CD4+ T cells
• HIV affects CD4+

Question 3

Explain what positive and negative selection means for T cells

Answer 3

T Cell Selection (in the Thymus)
Positive Selection:

• Location: Takes place in the thymic cortex.
• Process: Immature T cells (thymocytes) express both CD4+ and CD8+ receptors
• Outcome: T cells become either CD4+ (helper T cells) or CD8+ (cytotoxic T cells).

Negative Selection:
- Purpose: Eliminates T cells that bind too strongly to self-antigens presented on MHC molecules, which could cause autoimmunity.
- Location: Occurs in the thymic medulla.
- Process: T cells that bind strongly to these self-antigens undergo apoptosis.
- Outcome: Only T cells with moderate binding to self-MHC survive and enter the peripheral immune system.

Question 4

How do antibodies work?

Answer 4

• Has a Y shaped structure
• Produced by B cells
• Neutralisation = antibody binds to antigens on pathogen and blocks pathogen ability to infect
• oposonization = antibody Coates the pathogen and is so marked for destruction, the phagocyte recognises it and engulf it
• aggulitination = antibody binds to multiple antigens - clumping

Question 5

How is the antibody diversity in our body created?

Answer 5

• somatic recombination / VDJ rejoining for heavy chain
• For light chain it is just VJ
• - V - D - J - -> - V - DJ - -> - VDJ -
• We can add or remove nucleotides which cause a frame shift
• Somatic hypermutation

Question 6

What happens in your body when you become infected with bacterium

Answer 6

The immune system becomes defensive to eliminate pathogen and prevent spread

Innate : non-specific response first line defence
- Mucus straps bacteria
- cilia Sweep bacteria away away from respiratory tract
- Stomach acid kills bacteria
-Macrophages and neutrophils detect the bacteria and engulf
-Tissue damage triggers release of inflammatory mediators
-Blood vessels dilate which increases blood flow
-Increased permeability results in immune cells going into tissues equals swelling
-Chemotaxis

If innate can’t clear, then adaptive is activated
- Activation of APC’s equals CD4+ helper cells activated
- Help a cell release cytokines equals activation of B cells to make antibodies

Question 7

Explain what happens in your body for you to experience an allergic reaction to pollen

Answer 7

• Pollen enters the body and is recognised by the immune system
• Dendritic cells or other antigen-presenting cells detect the pollen and process them as antigens
• They are presented to naive T helper cells in the lymph nodes
• The immune system mistakenly interprets the pollen as a threat and the TH2 cells release cytokines that drive an IgE mediated immune response
• B cells are stimulated by IL-4 to produce IgE antibody specific to pollen
• These antibodies bind to mass cells and basophiles arming them for future encounters with pollen

When exposed to pollen again, the allergic reaction is triggered and the pollen binds to the IgE antibodies and cross-linking causes more cells and base fuels to release histamine which produce the symptoms of an allergic reaction

Question 8

What are the main differences between first and second generation antihistamine?

Answer 8

1st
• lipophilic - cross blood brain barrier
• Sedating
• Not selective for histamine receptors
• Act on muscarinic receptors
• Anti colonergic effect
• Motion sickness

2nd
• cannot cross
• Non sedating
• more selective
• One a day

Question 9

Explain the difference between a type one and a type four hypersensitivity reaction

Answer 9

1
• activated by antibodies
• faster
• anaphylactic
• mast cells involved to release histamine
• IgE antibody
• chemotaxis

4
• cell mediated by T
• Slower - delayed onset

Question 10

Explain the pharmacology action of antihistamine that prevent motion sickness

Answer 10

• anti cholenergic effect

Substances that block the action of a Sarcoline at muscarinic receptors in the parasympathetic nervous system

Question 11

Explain what positive and negative selection means for B cells

Answer 11

B Cell Selection (in the Bone Marrow)
Positive Selection:
- Purpose: Ensures that B cells produce functional B-cell receptors (BCRs) capable of recognizing antigens.
- Process: Immature B cells that successfully rearrange their immunoglobulin genes to produce a functional BCR (antibody) survive. B cells that fail to produce functional BCRs undergo apoptosis.
- Outcome: B cells with functional receptors continue to develop.

Negative Selection:
- Purpose: Prevents the survival of B cells that bind strongly to self-antigens, reducing the risk of autoimmunity.
- Process: Immature B cells are exposed to self-antigens in the bone marrow.
B cells that bind strongly to self-antigens undergo a fate ie apoptosis
- Outcome: Only B cells that do not strongly recognize self-antigens are allowed to mature and leave the bone marrow