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Immunology > B and T cells > Flashcards

B and T cells Flashcards

1
Q

Where do B and T cells attack?

A

B cells attack outside the cells- recognise pathogen directly.
T cells attack inside the cells- antigen has to be presented to it.

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2
Q

How are antibodies produced and where are they found?

A

Antibodies are produced by B cells and are either found of B cell surface or secreted.

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3
Q

Antibody functions

A
  • Bind foreign antigens encountered by host

- Mediate effector functions to neutralise or eliminate foreign invaders.

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4
Q

Antibody structure

A

Antibodies are heterodimers: two light chains and two heavy chains bound by sulfide bonds and non-covalent forces.
Antibodies contain constant and variable regions.

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5
Q

Draw an antibody including: heavy and light chains, constant and variable regions, Fc and Fab and the antigen binding site.

A

…….

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6
Q

What are antigenic epitopes?

A

The parts of antigens recognised by antibodies

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7
Q

Different types of antigenic epitopes

A

Conformational epitope- structural- detect amino acids which are not next to each other.
Linear epitope- continuous sequence of aa- detect aa which are next to each other.

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8
Q

What are the forces involved in antibody binding?

A

hydrogen bonds
electrostatic interaction
van der Waals
hydrophobic interactions

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9
Q

Non- covalent bonds are weak. How are they made to be stronger?

A

The epitope and antibody binding site have to fit perfectly to create a stronger bond.

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10
Q

What is avidity?

A

When an antibody is using both binding sites to bind to two epitopes on the same particle- increase the strength of the bond.

Total binding on all antigen binding sites.

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11
Q

What are the antibody effector functions?

A
  • Neutralisation- antibody binds directly to pathogen to prevent attachment and entry into the cell.
  • Opsinisation- phagocytosed more easily
  • Complement activation- enhances opsonisation and lyses some bacteria.
  • Agglutination-clumping of particles-more likely to be phagocytosed.
  • Antibody-dependent cytotoxicity- mediated extracellular killing by NK cell. Antibody forms bridge to immune cells.
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12
Q

What’s the difference between antibody classes?

A

Antibody=immunoglobulin

Have different amounts of constant domains.

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13
Q

Where are B cells and antibodies made?

A

Bone marrow then move to secondary lymphoid tissue.

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14
Q

What is another site of B cell activity and antibody production?

A

Mucosal associated lymphoid tissue- MALT

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15
Q

Where is IgA generally found?

A

external secretions: saliva, tears, mucus

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16
Q

How does IgA get into the gut?

A
  • A poly Ig receptor is found of the basolateral side of intestinal cells. This attaches Ig and is internalised into the cell.
  • Part of the receptor is cleaved and the remaining part (secretory component) allows Ig A to be transported to the gut.
  • SC helps protect IgA from destruction.
17
Q

What are the two types of T-lymphocytes?

A

CD4 T-cells (T helper)

CD8 T-cells (cytotoxic)

18
Q

Where are T-cells made, where do they mature and where do they migrate to?

A

Made in the bone marrow, differentiate to mature cells (CD4, CD8) in the thymus and migrate to lymphoid tissue such as the lymph nodes.

19
Q

What did Jacques Miller find when he thymectomised a mouse?

A
  • They were susceptible to viral infection.
  • They had reduced lymphocytes.
  • They were immunodeficient.
20
Q

What happens to our thymus as we age?

A 
It involutes (shrinks)
Thymic function declines
21
Q

What immunoglobulins do B cell receptors express?

A

IgM and IgD

Different B cells express different Vh and Vl regions.

22
Q

What do different TCR Va and Vb domain contain and what does that result in?

A

Contain hyper variable regions which result in different Complementarity Determining Regions (CDRs) on different T cells, specific for different antigen epitopes.

23
Q

What does CD3 do?

A
  • Not involved in antigen recognition

- Interacts with TCR to mediate intracellular signalling.

24
Q

How do TCR recognise antigen?

A
  • TCRs do NOT recognise antigen directly.

- Antigen has to be processed and presented to them via the MHC.

25
Q

MHC class I: What are they, what do they do and what are they encoded by?

A
  • Cell surface glycoproteins expressed on all nucleated cells.
  • Involved in T cell (cytotoxic) recognition of an antigen.
  • Encoded by the A, B and C loci in humans.
26
Q

MHC class II: What are they, what do they do and what are they encoded by?

A
  • Cell surface glycoproteins expressed on antigen presenting cells (macrophages, dendritic cells, B cells)
  • Involved in T cell (helper) recognition of an antigen.
  • Encoded by the DP, DQ and DR regions in humans.
27
Q

MHC class III: What are they, what do they do and what are they encoded by?

A
  • Various protein with or without immune function including:
  • -components of complement
  • -tumour necrosis factor
  • -heat shock proteins
28
Q

Which two MHC classes are involved in antigen presenting to T cells?

A

Class 1 and 2

29
Q

Structure of Class I MHC

A

3 alpha chains, 1 beta loop- non-covalently linked.

Bound to membrane at 1 point

30
Q

Structure of Class II MHC

A

2 alpha chains, 2 beta chains
Both chains have transmembrane and cytoplasmic domains.
Bound to membrane at 2 points

31
Q

How are MHC genes expressed?

A

Co-dominantly

32
Q

What antigens does MHC class I present?

A

intracellular antigens (viral)

33
Q

What antigens does MHC class II present?

A

extracellular (worm, some bacteria)

34
Q

Processing of exogenous antigen to MHC class II.

A
  1. Antigen taken up by endocytosis.
  2. Endosome and lysosome fuse-endolysosome.
  3. Enzymes in endolysosome degrade antigen.
  4. Class II MHC synthesised in RER with associated peptide-invariant chain.
  5. Class II MHC transported to compartment for peptide loading. CPL and endolysosome fuse.
  6. Invariant chain degraded and is displaced by antigen peptides of the right size.
  7. MHC/peptide complex transported to cell surface and present peptide.
35
Q

Processing of endogenous antigen to class I MHC.

A
  1. Antigen in cytoplasm.
  2. Antigen degraded in proteosome.
  3. Antigen peptides transported by TAP to RER.
  4. p88 dissociates from MHC I in RER when peptide is bound.
36
Q

What happens once the antigen is in the MHC?

A

TCR binds to both antigen peptide and MHC.

37
Q

To which T cells do Class I and II present their antigens to?

A

MHC1=CD8 T cells

MHC2=CD4 T cells

38
Q

Advantages of MHC-associated recognition.

A
  • Extra recognition mechanism for pathogens to try to evade.
  • Recognising different parts of pathogen from antibody.
  • Some peptides are from functional parts of protein.
  • Can detect antigen that is inside cells.
  • Less scope for mutations in pathogens to avoid recognition.

Immunology (11 decks)

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