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SEM 4: Immunology > Humoural Immunity - Part 1 > Flashcards

Humoural Immunity - Part 1 Flashcards

1
Q

What are antibodies?

A
  • Y-shaped molecules made by plasma cells
  • Fight foreign molecules and cancerous cells
  • Work by blocking pathogens from entering or by tagging them for removal by other immmune cells.
  • Also called immunoglobulins
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2
Q

What is the basic structure of antibodies?

A
  • Have 2 heavy chains and 2 light chains.
  • Heavy chains have 4 domains with 5 different classes: mu, delta, gamma, alpha and epsilon.
  • There are 9 different heavy chains.
  • Light chains have 2 domains: kappa and lambda
  • The first domain of the heavy and light chain form the variable region.
  • The rest of the antibody is the constant region.
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3
Q

What are the subclasses of gamma and alpha?

A

Gamma: y1, y2, y3, y4
Alpha: a1 and a2

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4
Q

What is the function of the variable region?

A
  • It is the targeting system of the antibodies.
  • Different antibodies = different variable regions that bind on pathogen only.
  • 2 antibodies can recognise different parts of a pathogen.
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5
Q

What is the unique about the constant region?

A
  • Same in every antibody of the same class e.g. All IgM have a Mu heavy chain; IgG has a gamma chain
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6
Q

What are the two versions of antibodies?

A

Membrane bound B-cell receptor

Secreted antibody

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7
Q

What is the secreted antibody form?

A

The final version of the Ab secreted by mature plasma cells. However, before it is anchored to B cells membrane for weapon development.

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8
Q

What are the 4 domains of the heavy chain?

A

Variable heavy domain (Vh)
Ch1 (constant region)
Ch2 (constant region)
Ch3 (constant region)

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9
Q

What are the 2 light chain domains?

A

variable light domain

constant light region

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10
Q

What makes up the antigen binding region of the antibody?

A

The variable region of the light and heavy chain. They are different between antibodies secreted from different B cells.

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11
Q

What is the function of the constant region?

A

It plays a part in the biological activity of the antibody and is the same for all antibodies of the same class.

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12
Q

What is each chain made of (genetically)?

A

A string of amino acids with a NH3+ amine group start and a COO- carboxyl group end.

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13
Q

What holds the heavy and light chain together?

A

Held together by disulphide bonds between the cysteine amino acid residues in the chains.

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14
Q

What is the function of the intramolecular disulphide bonds?

A

Used to stabilise each domain

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15
Q

Where is the hinge region and what is its function?

A

It is between Ch1 and Ch2 domains to provide flexibility to the molecule. It flexes and bends like the opening of the thumb, index and middle finger.

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16
Q

What is the function of the carbohydrate glycusylations on the Ch2 region near the effector region active site?

A

They promote interaction between the antibodies and other immune cells it recruits.

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17
Q

What is the function of the ribbon structure of antibodies?

A

Can be traced from the beginning of the domain and followed along. It helps identify the differences between the domains. It also clearly shows the glycosylations protruding out of the Ch2 domains.

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18
Q

What is the function of the space-filled structure of antibodies?

A

It is the closest to what an antibody would look like in real life.

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19
Q

What is Fv?

A

Variable fragment made up of light and heavy variable regions (2 domains)

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20
Q

What is Fab?

A

Fragment made up of Fv and the first constant regions.

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21
Q

What is Fc?

A

Fragment made up of Ch2 and Ch3 domains

22
Q

What is important to remember about fragments?

A

They are not the same as domains.

23
Q

What are complementarity determining regions (CDR)?

A

Located on the variable region where the antibody interacts with antigens that are on the surface of pathogens or cancer cells.

24
Q

What is different about the CDRs on each variable region?

A

They are different in regards to shape and structure on the light chain and heavy chain variable regions.

25
Q

What are the four antibody functions to combat pathogens?

A
  1. Bind to the part where the pathogen docks to host cells and prevent them from entering.
  2. Bind to the active sites of toxins produced by pathogens and neutralise them
  3. Opsonisation of pathogens so they are more visible to other immune cells.
  4. Form immune complexes that will remove other cells or involve complement to promote inflammation, phagocytosis and MACs.
26
Q

Describe the role of antibodies in opsonisation (function three) in detail

A

Antibodies are involved in tagging pathogens so they are more visible to other immune cells such as macrophages and NK cells. The variable regions will bind to the pathogen whilst the constant region will interact with the Fc receptor of macrophages to perfom antibody dependent cellular phagocytosis (ADCP) or NK cells to perform antibody dependent cellular cytotoxicity (ADCC).

27
Q

What is the function of antibody dependent cellular phagocytosis?

A

Performed by macrophages to engulf smaller pathogens

28
Q

What is the function of antibody dependent cellular cytotoxicity?

A

Performed by NK cells which releases chemicals to induce apoptosis and used generally for infected or cancerous cells.

29
Q

Describe the function of antibodies in complement and immune complexes (function 4)

A

Ab will form immune complexes that are made up of antibodies and the pathogen. It will agglutinate and be removed by other cells. The immune complex can also involve complement molecuels such as C1q, C1s and C1r. It fixes complement that leads to a series of events which promotes inflammation, phagocytosis and formation of membrane attack complexes (MAC). These punch holes in the cell-membrane causing cell lysis.

30
Q

What are the 5 antibody classes?

A

IgG, IgD, IgA, IgE and IgM.

31
Q

Structure and function of IgG

A
  • Conical antibody structure with 4 domains in gamma chain
  • Main antibody in the serum followed by IgA
  • Only forms after affinity maturation that is later in the secondary response.
  • Mainly stays in the blood stream
32
Q

Structure and function of IgD

A
  • A longer hinge region and delta chain
  • Only antibody not secreted as it does not fight against pathogens, cancers or parasites
  • Indicates mature B cells
  • BCR
33
Q

Structure and function of IgE

A
  • Has 5 domains
  • Epsilon chain
  • Involved in allergy and is good in recruiting basophils for fighting off larger parasitic infections that cannot be phagocytosed by macrophages
34
Q

Structure and function of IgA

A
  • Alpha chain is similar to Mu chain in IgM and similar to IgG but have places where the J chain can interact
  • Second main antibody in serum
  • Late in the secondary response as forms after affinity maturation
35
Q

What is sIgA?

A

Secretory IgA is a two monomeric IgA joined by a J chain with a secretory component wrapped around it. This enables it to be secreted into the mucus and is good for respiratory infections

36
Q

Structure and function of IgM

A
  • Made up of 5 monomeric IgM molecules joined by a J chain
  • Heaviest antibody
  • Main Ab of primary response
  • Best at foriming immune complexes and fixing complement
  • Monomer is a BCR
37
Q

Which region undergoes class switching mostly?

A

Often affects the heavy chain constant region

- The other regions remain the same

38
Q

What is the function of class switching?

A

Enables the body to be more versatile when dealing with different pathogens

39
Q

What are the two types of class switching?

A 
Minor class switching 
Major class switching
40
Q

What is minor class switching?

A

Occurs between IgM and IgD. This occurs at the RNA level and does not affect the DNA of the B-cell itself. It is called differential splicing.

41
Q

What is major class switching?

A

Occurs at the DNA level: DNA recombination and is a permanent change e.g. IgM to IgG, IgA or IgE.

42
Q

How does the antibody know which class to switch to?

A

It knows by sensing chemicals e.g. cytokines around produced by Thelper cells to indicate which type of pathogen is being dealt with.

43
Q

What is the mechanism that occurs in major class switching?

A

Class switch recombinaiton (CSR)

44
Q

What does CSR require?

A

It requires cytokine signals, switch regions (in front of constant gene segments), AID and DSB repair proteins. With the help of AID and other enzymes, recombination can occur between switch regions.

45
Q

Which antibodies can switch?

A

Switching only occurs downstream so IgM to IgG, IgA and IgE. This is because the Mu region is before gamma, alpha and epsilon.

46
Q

Why can a class switch not be reverted?

A

Because when a switch occurs, all of the previous parts are removed and cannot be reverted back.

47
Q

Describe an example of class switchin

A
  1. First, a heavy chain has undergone VDJ recombination and affinity maturation
  2. The B-cell with this genome will be expressing the gene in two forms: IgM and IgD through differential splicing of mRNA. However, it receives signals to switch to IgA1.
  3. AID and DSB repair proteins allow the two switch regions in front of the Mu segment and the alpha segment to be pulled together.
  4. Then, this part is cleaved and joined into a switch DNA circle while the heavy chain low side will be rejoined.
  5. The VDJ region plus the first constant gene segment (alpha 1 in this case) will be transcribed and translated. These cells will now express IgA1.
48
Q

What is the structural difference between membrane and secreted Ig?

A

The difference is the secreted version has a tail piece whilst the membrane bound version has a hydrophobic transmembrane region and a cytoplasmic tail which acts as an anchor.

49
Q

What is the Cmu region made up of?

A

Made up of Mu1, Mu2, Mu3 and Mu4 with the tail piece located at Mu4. There is a stop codon and a polyA tail after the genes coding for the tail piece.This is then followed by M1 and M2 coding for the transmembrane region and the cytoplasmic tail.

50
Q

How are secreted antibodies differentially spliced for?

A

The whole region is transcribed into mRNA and the transmembrane and cytoplasmic tail are spliced out leaving the mRNA (stop codon and polyA tail) to code for secreted antibodies.

51
Q

How are membrane bound antibodies differentially spliced for?

A

The whole region up to the second polyA tail will be transcribed and 8 regions including the genes coding for the tail piece and the stop signal will be spliced out.

SEM 4: Immunology (15 decks)

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