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IMIN 371 > Intro to B cells, T cells. and Abs > Flashcards

Intro to B cells, T cells. and Abs Flashcards

1
Q

What is a B cell Ag?

A

A substance that binds to Ab, can be any organic molecule such as protein, carbohydrate or DNA

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2
Q

What is an epitope?

A

portion of Ag recognized by an Ab, mostly discontinous (can be linear or 3D)

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3
Q

What is a polyclonal antisera?

A

A collection of different Ab.s from serum that recognizes different epitopes of the same antigen

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4
Q

What is a mAb?

A

Ab dervied from a single B cell clone; has the same specificity/epitope; used as tools in research and therapies to treat disease

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5
Q

What are the different chains that compose an Ab, and how are these chains held together?

A
  • 2 identical heavy and light chains
  • held together by interchain and intrachain disulphide bonds
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6
Q

How many light and heavy chain genes do humans and mice have, and how many alleles are there for the light and heavy chain genes?

A

2 light chain genes:
- kappa and lamda (4 alleles)
1 heavy chain gene (2 alleles)

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7
Q

What are the five isotypes of heavy chain genes?

A

IgM, IgD, IgG, IgE, IgA

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8
Q

What is the function of the variable region of the light and heavy chain?

A

binds Ag

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9
Q

What is the function of the constant region of the light and heavy chain?

A

important for the structure of Ab, and C-term constant regions of heavy chain have effector functions

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10
Q

Each Vh/Vl and Ch/Cl region on an Ab form a conserved structure, what is this called?

A

immunoglobulin (Ig) domain

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11
Q

What are the functions of the hinge regions and carbohydrates on Ab.s?

A

Hinge:
- found on some isotypes
- gives flexibility
Carbohydrate:
- have effector functions
- e.g. attract complement

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12
Q

What does the Fab and Fc regions of Ab.s stand for and what do they encompass?

A

Fab:
- fragment Ag-binding
- Vh and Vl
- contains Ig domain
Fc:
- fragment crystallized
- carbohydrates (CHO)
- heavy constant region

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13
Q

Where are Ig domains found, besides Ab.s?

A
  • TCR a and b chains
  • CD4
  • CD8
  • MHC-I
  • MHC-II
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14
Q

What are some characteristics of the Ig domain?

A
  • 110 a.a. in size
  • each domain consists of two b sheets that form a B sandwich/barrel structure
  • B sandwhich is held together by a disulphide bond and hydrophobic interactions between the sheets
  • contain complementary determining regions (CDRs)
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15
Q

What are the CDRs on Ab.s and what is their function?

A

3 loops in the VL and VH that connects beta strands are highly variable between Ab.s of different specificities - form the Ag binding site

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16
Q

What are the CDRs of the TCR and what is their function?

A

CDRs of the alpha and beta chains of the TCR form the Ag binding site

17
Q

How are the BCR and TCR modular receptors?

A

contain Ag binding sites (BCR = Ig; TCR = alpha (gamma) and beta (delta)) and signaling subunits (BCR = Igalpha and Igbeta; TCR = CD3)

18
Q

What processes is BCR signaling critical for?

A
  1. B cell development
  2. mature and memory B cell activation
  3. survival of mature naive B cells
19
Q

What are the BCR signaling subunits and what are some of their characterisitcs?

A

subunits = Igalpha and Igbeta
characteristics:
- nonconvalently coupled to the light and heavy chains
- contain ITAMs in their cytoplasmic regions

20
Q

What are the Ag-binding subunits on a TCR, how are these similar to BCR subunits, and what do they bind?

A

subunits = alpha (gamma) (similar to Ab light chain), beta (delta) (similar to Ab heavy chain)

bind specific MHC + peptide combinations

21
Q

What are the signaling subunits of a TCR and what is an important characteristic of them?

A

subunits = collectively called CD3
important characteristic = contain ITAMs

22
Q

What is TCR singling critical for?

A
  1. T cell development
  2. activation of mature/memory T cells
  3. T effector cell function
  4. survival of mature, naive T cells
23
Q

What are the functions performed by Ab.s, and call all these functions be performed by Ab.’s with different isotypes?

A
  1. neutralization -> inactivates pathogens and toxins
  2. agglutination -> similar to neutralization -> pathogens stick together and cannot enter cells
  3. opsonization -> make a pathgoen tastey -> marks pathogen for phagocytoksis
  4. complement activation -> opsonization of Ag.s, and formation of MAC -> lysis of pathogen
  5. ADCC -> NK cells kill tumour and unhealthy cells via inducing apoptosis
  6. degranulation -> trigger mast cells, eonsinophils to degranulate (used for bigger pathogens)

not all isotypes perfom all these functions

24
Q

What is an Ab isotype?

A

Ab.’s with different CH regions

25
Q

How do Ab isotypes differ from one another?

A

with respect to sequence and number of Ig domains (4-5 domains/heavy chain). Different isotype constant (Fc) regions perform different functions

26
Q

Which Ab isotypes are secreted as monomers, dimers or pentamers? How are the polymers (dimers and pentamers held together)

A

monomers: IgD, IgG and IgE
dimer: IgA
pentamer: IgM

dimers and pentamers held together via a J chain

27
Q

Which Ab isotype is the most versitile?

A

IgM

28
Q

Which Ab isotypes highly activate the complement pathway?

A

IgG and IgM

29
Q

Which Ab isotypes crosses the placenta well?

A

IgG

30
Q

Which Ab isotypes are present on the surface of mature B cells?

A

IgM and IgD

31
Q

Which Ab isotypes bind to FcR of phagocytes well?

A

IgG (mostly), some IgM and IgA

32
Q

Which Ab isotypes mediate mucosal transport via poly-Ig R well?

A

IgA

33
Q

Which Ab isotype induces mast cell and/or basophil degranulation the best?

A

IgE and IgD

34
Q

What were the two puzzling questions to early immunologists?

A
  1. how can Ab.s be generated against almost any organic molecule?
  2. how does the body produce the appropriate Ab for an infection?
35
Q

What is the clonal selection theory?

A

a theoretical model to explain how pathogens select B cells to secrete Abs (also holds true for hot T cells are selected by Ag)

36
Q

What are the four tenets of clonal selection theory?

A
  1. each B cell expresses on its cell surface and Ab of one specificity
  2. Ags select specific B cells for activaiton
  3. effector B cells (plasma and memory) have the same Ag. specificity as the original B cell that was selected by Ag
  4. B cells that recognize self Ags are removed from the repertoire during development

IMIN 371 (20 decks)

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