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Immunology > Lecture 3 - Immunoglobulins/Antibodies > Flashcards

Lecture 3 - Immunoglobulins/Antibodies Flashcards

1
Q

What is the composition of the antibody?

What holds together the 2 chains to the constant region?

A

2 light chains
2 heavy chains
- identical to one another (both light same, and both heavy are the same)

  • held together by disulfide bond
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2
Q

Where is the variable region of the antibody and where is the constant region?

A

Variable is the end of the light chain (N terminus)

Constant = C terminus

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3
Q

Where does an antigen bind?

How many epitopes does it bind?

A

ANTIGEN binds to variable region

  • VL and VH (light & heavy)
    antibody molecule can bind 2 antibodies (one on ach side, but the SAME since the sequences are identical)
  • epitope is the antigenic determinant –> binds 1 epitope on each side
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4
Q

What are the 5 classes of Immunoglobulins?

What are their heavy chains?

A

IgM –> mu

IgG –> gamma

IgE –> epsilon

IgA –> alpha

IgD –> delta

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5
Q

Where do the isotopes of the immunoglobulins differ?

A

Constant region of the heavy chain!

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6
Q

What are the 2 types of light chains?

A

Kappa
Lambda

-One immunoglobulin will either be KAPPA or LAMBDA (not one kappa one lambda on an immunoglobulin molecule)
similar structural, functionally we do not know how different they are

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7
Q

What is Fab? What is Fc?

Where can proteases cleave the antibody? What bonds are present here?

A

Fab = fragment antibody

Fc = (can crystalize) in the constant region

  1. HINGE region (offers flexibility for antigen interaction)
    - DISULFIDE BONDS will be cleaved
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8
Q

How can the isotopes differ?

A
  1. Carbohydrate
  2. Based on constant region (heavy chain)
  3. Length of heavy chain
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9
Q

What is unique about IgM?

What is its structure in Serum or blood?

How many antigen molecules can it bind?

A
  1. Polymorphic structure
  2. PENTAMER when in serum or blood
  3. Can bind 10 antigen molecules
    - held together by a J chain(when pentamer)
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10
Q

What is unique about IgA?

When is it a dimer?
When is it a monomer?

What is the function of the secretory component?

A

Polymorphic

  1. Dimer = SECRETORY IgA
    - (mucosal)
  2. Monomer = BLOOD
    - held together by a J chain (like IgM)
  3. Secretory component protects the hinge region from proteolytic degradation
    (ex: in the gut, there are many microbes)
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11
Q

There are 4 kinds of IgG heavy chains. True or False

A

TRUE

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12
Q

Where is IgD usually found? Is it ever found in serum?

A

IgD –> found on the SURFACE of a B cell

NEVER found in serum

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13
Q

What is the major immunoglobulin in blood?

A

IgG

HALF-LIFE for IgG is 3 weeks!
- about 100 mg/mL

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14
Q

What are the 5 main functions of Immunoglobulins?

A
  1. Neutralizes the toxin that is made by bacteria, neutralizes viruses
  2. OPSONIZATION when antibody attaches to the bacteria
    - it allows it to be taken up by cells easily

3.Sensitization for killing by NK cells

  • Natural Killer Cells
    Antibody bound to bacteria & recognized by NK cell
  • NK cell will take it up & degrade it
  1. Activates the complement system
    Complement:
    -series of enzymatic reactions that occur once an antibody binds something
  2. Sensitization of mast cells
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15
Q

Where is IgA distributed?

IgG?

A
  1. IgA - mucosal epithelium
    = DIMERIC IgA
  2. Across placenta
    (baby is morn with maternal IgG)
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16
Q

Cross-linking of IgE on mast cells leads to what?

A

DEGRANULATION

-IgE: antibody responsible for ALLERGIES
present in VERY small quantities (nano gram/micro gram per mL)
very affective in an allergic response

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17
Q

Describe what occurs in IgE and allergies.

A
  • if no antigen is present, no reaction occurs
  • but if an antigen is present, the antibody CROSS LINKS
  • antigen binds 2 antibody molecules
  • sends a signal to the mast cell to DEGRANULATE

** IgE and FC receptor mediated reaction = CROSS – LINKING IgE

  • when they cross-link they AGGREGATE BY THE PRESENCE OF THE ANTIGEN
  • and the result is degranulation
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18
Q

What distinguish Ig Isotypes?

How do we recognize the various isotopes?

A

H chains!

  • we make an antibody to react with the constant region
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19
Q

What are 3 ways that antibodies mediate humoral immunity?

A
  1. Neutralization
  2. Opsonization
    -antibody promotes phagocytosis
    - FC gamma receptor on the phagocytic cell
    FC receptor will recognize antibody coated on the bacteria & will phagocytose it
  3. Complement system
    - enhances opsonization and lyses some bacteria
20
Q

What is required for the activated of Fc-receptor Mediated Killing?

A

Requires aggregated Ig

  • aggregations occur & Fc receptor cross-link
  • activation of macrophage leads to phagocytosis and destruction of bacterium
21
Q

When are Ig levels most important?

How do levels of IgG change in the baby? IgM, IgA?

When is the critical point for maternal IgG in the baby and why?

A

During gestation

1.just before the baby is born = it has relatively high levels of maternal antibody IgG
(half life of antibodies is 3 weeks/21 days)

  1. when the baby is born - every 21 days/3 weeks the amount of maternal antibody if HALF

baby begins to make IgM, makes almost NO

IgG until about 6 months or 9 months

I gA is made even later

6-9 months is when maternal antibody goes down, and its not making its own antibody at this point
- become sick at this point **

22
Q

What do titers show?

A

Titer - show how much antibody is there

23
Q

In the example with measles, why does getting the disease create more antibodies against measles than getting the vaccine?

A

ANTIBODY MEMORY

  • vaccine is not as good as getting the disease
  • antibody level does not decline! about 3,000 years = half life
24
Q

What is the difference between polyclonal and monoclonal antibodies?

A

Monoclonal
- take all the B cells from 1 clone

Polyclonal:
- many different B cells making antibodies to different epitopes (separate clones of B cells)
- Ab from multiple clones of B cells is
polyclonal Ab

25
Q

What is IVIG?

What is its clinical use?

A

Intravenous Immunoglobulin

  • polyclonal Ab used to treat many immune deficiencies and inflammatory diseases

take blood from 10,000 people and pool it
cell the blood to physicians to treat many immune deficiencies and inflammatory diseases
many antibodies to many diseases
& prevent inflammation!

26
Q

What are tumor-specific monoclonal antibodies?

A

specific to certain antibody of a tumor ***

  • Tumor specific antibody recognizes a tumor antigen
  • antibody binds to the antigen on the tumor cell
  • NK cells have FC receptors that are activated
  • kill the tumor cells

DRUG ending with “mab” is a monoclonal antibody

27
Q

How are immunoglobulin Classes or ISOTOPES identified?

A

By the constant region of H chains

28
Q

Which is the variable region?
N terminal or C terminal region?

H or L chains?

A

Nterminal region is variable

- BOTH H and L in the Variable region of N terminus

29
Q

Which immunoglobulins are responsible for the following:

  1. Predominant Ab in the SECONDARY response
  2. Predominant Ig in EXTERNAL secretions
  3. Predominant Ab in the PRIMARY response
  4. Found mainly on the surface of B cells
  5. Involved in Allergic Hypersensitivities
A
  1. Predominant Ab in the SECONDARY response = IgG
  2. Predominant Ig in EXTERNAL secretions = IgA
  3. Predominant Ab in the PRIMARY response = IgM
  4. Found mainly on the surface of B cells - IgD
  5. Involved in Allergic Hypersensitivities - IgE
30
Q

What is the structure of IgM in its secreted form?

How is it expressed on the surface of B cells? (which form)

Does it cross the placenta?

Serum Concentration?

A

What is the structure of IgM in its secreted form?
- PENTAMER

How is it expressed on the surface of B cells? (which form)
- MONOMERIC form

Does it cross the placenta?
- NO

Serum Concentration? –> 100mg/dl

31
Q

What is the form of IgG in its secreted and membrane form?

Does it cross the placenta?

A
  1. Monomeric
  2. Does cross the placenta

Serum Concentration = 1200mg/dl

32
Q

Which immunoglobulin functions as a B cell Ag receptor along with IgM?

What is the serum concentration?

A
  1. IgD

2. 3mg/dl

33
Q

How does IgE fix to mast cells and basophils?

How is it secreted? Which form?

What is the concentration in serum?

A

Via FC receptor on cells

MONOMER in secreted form

VERY LOW in serum - 30 ug/dl

34
Q

Which immunoglobulin is predominant in EXTERNAL secretions? Which form of this dimer?

A

IgA

DIMER!

35
Q

IgA

  1. What is the function of the J chain?
  2. What form is it in serum?
  3. Does it cross the placenta?
  4. Serum Concentration?
  5. Primary ROLE?
A

IgA

  1. What is the function of the J chain?
    - joins the two subunits together
  2. What form is it in serum?
    - in its MONOMERIC form (dimer in external secretions)
  3. Does it cross the placenta?
    NO
  4. Serum Concentration? 300mg/dl
  5. Primary ROLE? Mucosal Immunity
36
Q

Which cells have Fc receptors on their surface? Aggregation of these receptors (via cross-linking) results in what?

A
  1. Phagocytic cells (macrophages, neutrophils)
  2. NK cells
  3. Eosinophils
  4. Basophils
  5. Mast Cells

Cross-linking and aggregation of FC receptors results in Ingestion and destruction of pathogens

37
Q

What is the half life for tetanus as compared for measles?

A

tetanus - 11 years

Measles - 3014

38
Q
  1. What is found at the 5’ end of each Ig locus?, what are they separated by?
    (300 bp long)
  2. What are found downstream to these genes (30-50bp long)?
  3. What is the name of the segment found ONLY in the H chain locus (heavy chain only)?
A
  1. 5’ end = V Region Exons ( 300BP)
    - separated by non-coding DNA
  2. Downstream to V region = Joining (J) Segments - 30/50 bp
  3. the Diversity (D) Segment is ONLY found in the H chain locus
39
Q

What is the the Light chain (Kappa and lambda) ENCODED by?

the Heavy chain?

In your answer, include a description of how the C regions are encoded (are they the same or different for light and heavy chains?)

A
  1. V and J exons and a constant region by a C exon (Ig light chain protein)
  2. V, D, J exons and the constant region of the protein is derived from multiple C eons
    - for transmembrane associated heavy chains –> exons encode transmembrane and cytoplasmic domains
40
Q

Ig cells are expressed only in cells of which lineage?

What is the essential first step for the production of antibodies?

A

B cell lineage!

Essential first step is the REARRANGEMENT of Ig genes

41
Q

True or false:
1. DNA rearrangements occur in a precise order

  1. Occur INDEPENDENT of antigen stimulation
A

TRUE for both!

42
Q

What is the first Ig rearrangement? What segments join? What happens to the intervening DNA?

What occurs next?

A

First Ig rearranged = HEAVY CHAIN DJ
- joins one D and one J segment, intervening DNA is deleted

After DJ rearrangement, V is joined to the DJ complex = VDJ gene

  • all D upstream (5’ of the rearranged D gene) are deleted
43
Q

What are the only type of cells in which VDJ recombination occurs?

What happens to the C region once the VDJ complex is formed

A

Only in cells committed to become B Lymphocytes

  • ** CRITICAL CONTROL STEP in Ig expression**
  • only rearranged V gene is transcribed

C region is separated from VDJ by an intron

44
Q

What does the 3rd somatic DNA recombination involve?

How is it different from the Heavy Chain DJ and VDJ formation?

A

Involves a light chain locus!

  • V segment is joined to J segment
  • C region separated from VJ by an INTRON
45
Q

How is the C region joined to the VJ region in Light Chain?

A

Splicing of the primary RNA transcript joins he C gene to the VJ complex
- forms mRNA that is translated to produce the K protein

  • light chain assembles with the previously synthesized Meu (u) to form the complete membrane IgM molecule
  • this is expressed on the cell surface and the cell is not the immature B lymphocyte
46
Q

What is the final step in Ig Gene rearrangement that determines if a cell is an immature B lymphocyte?

A

meu (closest to the VJ region) assembles with the light chain to form the complete membrane IgM molecule

  • expressed on the CELL SURFACE = immature B cell

Immunology (26 decks)

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