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MAD Exam 2 > Immunoglobulins > Flashcards

Immunoglobulins Flashcards

1
Q

clones

A

individual B cells, with their unique B-cell receptors, are referred to as clones

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2
Q

clonal expansion

A

when a B cell is activated, ONLY the specific clone that matches the antigen is replicated

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3
Q

beneficial functions of immunoglobulins (antibodies)

A
  1. neutralize toxins or viruses (prevent it from binding to its receptor)
  2. aid in the uptake and clearance of bacteria (opsonization)
  3. facilitate complement activation
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4
Q

negative functions of immunoglobulins (antibodies)

A
  1. cause autoimmunity
  2. cause allergies and other hypersensitivity reactions
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5
Q

basic structure of an immunoglobulin

A

-composed of 2 IDENTICAL heavy chains (50 kDa) AND 2 identical light chains (25 kDa)
*joined by disulfide bonds (inter-chain and intra-chain)
-composed of a VARIABLE region and a CONSTANT region (Fc)
*sialylation (addition of sialic acid) of the constant region

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6
Q

variable region of an immunoglobulin

A

*antigen binding site (formed by both the heavy AND light chains)

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7
Q

Fc region of immunoglobulins

A

the four Cs:
Constant
Carboxy terminal
Complement binds here
Carbohydrate side chains

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8
Q

Fab region of immunoglobulins

A

*fragment antigen binding site; at N terminus of the immunoglobulin
*where unique immunoglobulin binds to an antigen
*each BCR has a unique Fab region
**antigen binding requires contact with BOTH the heavy and light chains

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9
Q

antibody

A

the secreted form of the B cell receptor (BCR), also referred to as an immunoglobulin
*recognize and bind specific antigens via Fab

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10
Q

antigen

A

the specific molecule(s) of a pathogen to which an immune response is directed

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11
Q

epitope

A

the specific part or feature of an antigen which is RECOGNIZED by an antibody

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12
Q

how do antigens and antibodies interact

A

all of the NON-covalent forces
[electrostatic, hydrogen bonds, van der waals, hydrophobic]

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13
Q

do antigens and antibodies use covalent bonds to interact

A

NO!!
just non-covalent bonds

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14
Q

linear epitope

A

a type of antigen:antibody interaction in which amino acid residues are ADJACENT in the polypeptide chain

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15
Q

discontinuous epitope

A

a type of antigen:antibody interaction created from amino acid residues located in DIFFERENT PARTS of the polypeptide chain
*antibodies responding to tertiary protein structure/folding

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16
Q

sources of generation of antibody diversity

A
  1. combinatorial diversity
    a) multiple germ line gene segments (V, D, J)
    b) multiple heavy and light chain pairings
  2. junctional diversity
  3. somatic hypermutation
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17
Q

combinatorial diversity: V(D)J recombination

A

-light chain: V and J segments
-heavy chain: V, D, and J segments
*RAG-1 and Rag-2 (components of VDJ recombinase) mediate gene rearrangements
*once the rearrangement occurs, it is permanent, and the DNA in that B cell is different than the DNA in other cells!!
*occurs during B cell development in the bone marrow

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18
Q

which chain (light or heavy) gets rearranged first during V(D)J recombination

A

heavy chain gets rearranged first

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19
Q

RAG-1 and RAG-2

A

components of the VDJ recombinase that are critical for rearrangement of genes in B cell development

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20
Q

combinatorial diversity: multiple heavy and light chain pairings

A

virtually any of the heavy chains can be paired with any of the light chains

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21
Q

junctional diversity

A

RANDOM addition of non-template nucleotides at the junctions between gene segments (V/D/J) upon gene rearrangement by terminal deoxynucleotidyl transferase (TdT)

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22
Q

terminal deoxynucleotidyl transferase (TdT)

A

the enzyme responsible for junctional diversity during B cell development
*TdT deficiency greatly reduces diversity of immunoglobulins

23
Q

where does somatic hypermutation occur

A

in the spleen or lymph nodes (NOT in the bone marrow) AFTER REARRANGEMENT has created a functional BCR

24
Q

activation induced cytidine deaminase (AID)

A

the enzyme that is critical for somatic hypermutation during B cell maturation

24
Q

somatic hypermutation

A

*within the V component of the Fab region of both light and heavy chains, there are 3 hypervariable regions [3 in each of the chains, so 6 total that antigen is contacted by], which undergo point mutations with high frequency
*requires activation induced cytidine deaminase (AID)
*continues to happen in subsequent generations when exposed to antigen, all in an effort to get a more tightly bound antigen-antibody complex

25
Q

hypervariable region 3 (HV3)

A

the most diversity is observed in this region because it is at the junction of V and J, so junctional diversity (by Tdt) can occur here in addition to somatic hypermutation

26
Q

hypervariable regions and affinity

A

PROPORTIONAL: the affinity of an immunoglobulin for an antigen will increase as the number of hypervariable regions that participate in epitope binding increases

27
Q

what part of the immunoglobulin determines its class (and subclass)

A

the heavy chain, specifically the Fc (constant) region; can be changed (class-switching)

28
Q

isotypes

A

immunoglobulins of each class (IgG, IgM, etc)

29
Q

which immunoglobulin classes are monomeric

A

IgG, IgD, and IgE
(IgM = pentameric)
(IgA = dimeric)

30
Q

functions & characteristics of IgM

A

*produced in the immediate response to an antigen (FIRST antibody produced)
*pentameric when secreted to enable avid binding
*fixes complement
*does NOT cross the placenta
*found on surface of naive B cells

31
Q

functions & characteristics of IgD

A

*found on surface of naive B cells and in serum
*unclear function

32
Q

functions & characteristics of IgG

A

*main antibody in secondary response to an antigen
*MOST ABUNDANT ISOTYPE IN SERUM
*fixes complement
*opsonizes bacteria
*neutralizes bacterial toxins and viruses
*ONLY ISOTYPE THAT CROSSES THE PLACENTA

33
Q

functions & characteristics of IgE

A

*binds mast cells and basophils
*cross-links when exposed to allergen, mediating immediate HYPERSENSITIVITY through release of inflammatory mediators (like histamine)
*contributes to immunity to PARASITES by activating eosinophils
*LOWEST CONCENTRATION IN SERUM

34
Q

functions & characteristics of IgA

A

*prevents attachment of bacteria/viruses to MUCOUS MEMBRANES
*dimer when secreted
*released into SECRETIONS (tears, saliva, mucus) and breast milk

35
Q

which immunoglobulin(s) enhance phagocytosis via opsonization

A

IgG

36
Q

which immunoglobulin(s) neutralize toxins

A

IgM, IgG, IgA

37
Q

which immunoglobulin(s) prevent adherence of pathogens

A

IgM, IgG, IgA

38
Q

which immunoglobulin(s) activate CLASSIC complement system

A

IgM**, IgG

39
Q

which immunoglobulin(s) transport across placenta

A

IgG

40
Q

which immunoglobulin(s) cause sensitization of mast cells (allergic responses)

A

IgE

41
Q

which immunoglobulin(s) are active at mucosal surfaces

A

IgA**, IgG

42
Q

which immunoglobulin(s) are antigen receptors on naive B cells

A

IgM, IgD

43
Q

isotype switching - overview

A
  1. initial phase: naive mature B cells is activated & predominant circulating antibody is IgM
  2. B cells switch to producing other isotypes, with IgG being the predominant circulating antibody
  3. during secondary responses, rapidly activated memory B cells secrete isotypes OTHER THAN IgM
44
Q

the change from IgM to IgG or other isotypes does NOT

A

-involve additional heavy chain V/D/J or light chain V/J rearrangements
-change the heavy chain variable region or the light chain
-change the antigen specificity

45
Q

class switching - detailed

A
  1. B cell as antigen-presenting cell:
    a. receptor-mediated endocytosis
    b. antigen presentation on MHC II and recognized by TCR on helper T (Th) cell
  2. CD40 receptor on B cell binds CD40 ligand (CD40L) on Th cell
  3. Th cell secretes CYTOKINES that determine Ig class switching of B cell
46
Q

where does class switching of B cells occur

A

in the GERMINAL CENTERS of lymph nodes or spleen (pale areas within lymph node follicles)

47
Q

which happens first: class switching or somatic hypermutation?

A

class switching occurs prior to somatic hypermutation

48
Q

is the production of IgD from IgM dependent on class-switching?

A

NO; alternative splicing of a single primary transcript encoding the mu or delta constant regions is responsible for the appearance of IgD

49
Q

anti-isotypic antibodies

A

antibodies against the constant regions of heavy chains
*can be used to distinguish different classes of immunoglobulins

50
Q

enzyme-linked immunosorbent assay (ELISA)

A

used to identify SPECIFIC PROTIENS in a solution
1. antigen (pathogen or protein) binds to plastic plate; excess washed off
2. test antibody is added and plate washed
3. ligand to test the antibody is added
4. substrate is added and a colored product is produced by enzyme reaction; amount of color is proportional to the amt of antibody bound to antigen

51
Q

monoclonal vs. polyclonal antibodies

A

*most antibody responses are polyclonal (a range of B cells will make different antibodies against various epitopes of a given antigen
*a monoclonal antibody represents one unique immunoglobulin produced by a single B cell clone

52
Q

monoclonal antibody production

A
  1. immunize a mouse with antigen of choice; remove the spleen when the mouse is making an antibody response
  2. fuse the immune spleen cells with a myeloma tumor cells
  3. culture the cells in selective medium so only fused cells survive
  4. grow cells in individual culture plate wells
  5. the clones (hybridomas) are immortal producers of the desired monoclonal antibody that can be used as a therapeutic agent
53
Q

hyper-IgM syndrome

A

-due to mutated CD40 ligand on helper T cells (leading to lack of class-switching)
-X-linked recessive
-presents as severe pyogenic (pus-forming) infections in early life
-labs show normal or increased IgM with severely decreased IgG, IgA, and IgE and absence of germinal centers in lymph nodes

MAD Exam 2 (37 decks)

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