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Immunology > B Cells and Antibodies > Flashcards

B Cells and Antibodies Flashcards

1
Q

In the basic Ig, there are two heavy chains and two light chains linked by disulfide bonds. The heavy chains contribute to both the Fc and Fab fragments. True or false?

A

true

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2
Q

Light chains only contribute to the ___ fragment

A

Fab

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3
Q

Light chain isotopes are __ and __

A

kappa; lambda

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4
Q

The fab fragment contains what two things?

A

antigen binding site; complementarity determining region (CDR)

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5
Q

Hypervariable regions, or CDRs make physical contact with the antigen. True or false?

A

true

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6
Q

The Fc fragment = fragment constant. What makes up the constant region?

A

AA sequence with little variation within a class

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7
Q

What recognizes the Fc fragment?

A

phagocytes, NK cells, and granulocytes with Fc receptors

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8
Q

What does the Fc fragment bind to?

A

C1q and CRP (IgG and IgM)

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9
Q

What does the Fc fragment determine?

A

the classes of the antibody

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10
Q

IgG has the longest serum half-life. how long is it?

A

23 days

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11
Q

IgG is the major isotype in the serum. What percentage of total isotype does it take up?

A

70-80%

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12
Q

IgG is inovlved in complement activation and opsonization, toxin and virus neutralizaiton, and agglutination of particulate antigens. True or false?

A

true

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13
Q

IgG is the only class that crosses the ____

A

placenta

note: provides the fetus and newborn with passive protection; 100% of newborn’s IgG is of maternal origin; dissipates by age 5-6 months

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14
Q

IgG is the major isotype synthesized during the ____ immune response

A

secondary

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15
Q

In persons older than 6 months, elevated serum IgG indicates what?

A

past infection or the convalescence phase of a current infection, prior vaccination, or chronic infection

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16
Q

___ is the first class of antibody to be made in response to all antigens and is the major class of the primary immune response

A

IgM

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17
Q

This class have a valence of 2

A

IgG

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18
Q

IgM has a valence of ___

A

10

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19
Q

IgM comprises __% of the serum Ig pool

A

10

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20
Q

IgM activates the ___ complement pathway

A

classical

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21
Q

Elevated IgM to an infectious agent indicates what?

A

active infection of recent onset

hint: involved in the primary immune response

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22
Q

This is the only class to be produced by the fetus

A

IgM

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23
Q

IgA is found where?

A

mucus, saliva, colostrum, breast milk, sweat, GI secretions

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24
Q

IgA found in secretions is usually ____ (has a valence of 4)

A

dimeric

25
Q

Secretory components protects secretory IgA from ____

A

proteases

26
Q

sIgA protects the MALT from microbial invasion and certain toxins, mainly by interfering with what?

A

adherence to microbe/toxin host cells

27
Q

IgE binds to what?

A

basophils, mast cells, and eosinophils bearing FceR

28
Q

Cross-linking of FceR causes basophils and mast cells to degranulate, releasing ____ which contributes to inflammation

A

histamine

29
Q

IgE originally evolved to combat ___ infections

A

helminthic

30
Q

In developed countries, IgE is most often associated with what?

A

immediate hypersensitivity diseases such as asthma and hay fever

31
Q

IgD is found along with ___ on the surface of mature B cells

A

IgM

32
Q

Antigen binding to surface IgD triggers what?

A

B cell differentiation to plasma cells

33
Q

Which class i the best at agglunation?

A

IgM

34
Q

Which classes have the most antiviral acitivity?

A

IgG and IgA

35
Q

Even in the absence of antigen stimulation, a human can make more than ___ different antibody molecules

A

10^12

36
Q

The pre immune repertoire is large enough to ensure that there will be what?

A

an antigen-binding site to fit almost any potential antigenic determinant

37
Q

Kappa light chain DNA contains about __ variable region eons and ___ joining (J) regions

A

40; 5

note: any V region can join with any J region, all intervening introns and unused exons are looped out

38
Q

An enzyme complex called the VDJ recombinase is responsible for what?

A

looping out the DNA separating the V and J exons

39
Q

Two important components of the VDJ recombinase are the Rag-1 and Rag-2 enzymes. People who are deficient in Rag proteins cannot make functional antibodies (or TCR molecules) and suffer from what?

A

SCID leaving them susceptible to all kinds of infections

40
Q

After the VJ construct is formed, the B cell transcribes an exact copy of the rearranged DNA yielding a primary RNA transcript. The unused exons and introns are spliced out of this RNA transcript to generate ____

A

mRNA

41
Q

During splicing of the RNA transcript, the ___ ___ region exon is brought adjacent to the VJ construct. The mRNA is then translated into a complete kappa light chain protein

A

kappa constant

note: primary RNA transcript -> mRNA -> kappa chain polypeptide

42
Q

The variable region of the antibody heavy chain is encoded. However, the heavy chain contains an additional set of exons that encode the ___ region between the variable and joining regions

A

diversity (D)

43
Q

The VDJ recombinase with its Rag-1 and Rag-2 enzymes is required for heavy chain DNA rearrangement. The rearrangement takes place in two steps. What are they?

A

formation of the DJ construct , followed by formation of VDJ construct

44
Q

In regards to heavy chain rearrangement, after the VDJ construct is formed, the B cell transcribes an exact copy of the rearranged DNA yielding a primary RNA transcript. The primary RNA transcript can undergo ____ RNA splicing which brings either ___ or ___ constant region exon adjacent to the VDJ construct adjacent to the VDJ construct in mRNA

A

alternative; delta; mu

45
Q

If the mu exon is placed next to VDJ, the antibody will be ___. If the delta exon is placed next to the VDJ, the antibody will be ___.

A

IgM; IgD

note: alternative splicing enables B cell to express both IgM and IgD on its surface at the same time

46
Q

Imprecision in joining the V, D, and J exons can lead to loss or gain of nucleotides, which in turn may result in AA sequence changes at the junction sites. This leads to ___ diversity and contributes to the overall variability in ____ specificity displayed by antibody molecules

A

junctional; antigen

47
Q

Small sets of nucleotides not encoded by the DNA template can be inserted at the V-J or V-D-J junctions by the enzyme ___ _____ transferase

A

terminal deoxynucleotidyl

note: this is called N-region diversity

48
Q

/when does the antibody become complete?

A

when two heavy chains combine with two light chains

49
Q

The antibody molecule is attached to the surface of the B cell via a ___-terminal polypeptide tail inserted in the B cell membrane. When the B cell differentiates into plasma cell, the polypeptide tail is not translated, and so the antibody is ___

A

C; secreted

50
Q

For the B cell to switch to the additional antibody classes (IgG, IgA, or IgE) an enzyme called ___-____ ___ ___ is required. This enzyme recognizes “switch” regions that precede all the heavy chain constant regions except Cdelta.

A

activation-induced cytidine deaminanse (AID)

51
Q

How does the AID enzyme work?

A

causes unused constant region exons and intervening introns to loop out and be excised from the DNA.

52
Q

Once a B cell has class-switched from IgM to one of the down-stream heavy chain isotopes, it can never again synthesize IgM because the mu constant region exon has been lost. This phenomenon explains what?

A

Why IgM is synthesized ruing the primary immune response but other classes such as IgG predominate during the secondary response

53
Q

The AID enzyme is activated when B cell receives what?

A

“help” from Thelper cells in the form of receptor-ligand interactions and cytokines

54
Q

What is the most important receptor-ligand interaction for class-switching?

A

CD40 on the B cell and CD40L on the Thelper cell

55
Q

The cytokines produced by the Thelper cell will determine which class of antibody the B cell will synthesize. True or false?

A

true

56
Q

Persons who lack functional AID, enzyme, CD40, or CD40L cannot class switch from IgM to other isotopes. These individuals suffer from what syndrome?

A

hyper-IgM syndrome

note: they are prone to certain infections and autoimmune diseases

57
Q

Somatic hypermutation is marked by point mutations in the ___ region exon that lead to the production of ___ ____ antibodies as the immune response progresses

A

point; higher affinity

58
Q

Antibody diversity derives five sources. What are they?

A
  1. random recombination of VJ (light chain) exons or VDJ (heavy chain) exons
  2. random combination of heavy chains with light chains
  3. somatic hypermutation mediated by the AID enzyme
  4. junctional diversity
  5. N-region diversity by terminal deoxynucleotidyl tranferase

Immunology (12 decks)

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