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Foundations of health and disease > B cells and antibodies > Flashcards

B cells and antibodies Flashcards

1
Q

What is an antibody?

A

Antibodies are glycoproteins with a minimum molecular weight of around 150,000 Daltons that bind to specific antigens.

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2
Q

How does the specificity of antibodies work?

A

Each antibody binds to a single specific antigen.

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3
Q

What is the role of B lymphocytes in antibody production?

A

Each individual B lymphocyte produces antibodies that bind to the same antigen, but the structure of the antibody changes over time.

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4
Q

How many different B lymphocytes are there in the human body?

A

There are billions of different B lymphocytes in the human body, each capable of producing an antibody to a different antigen.

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5
Q

What is the term used for the part of an antigen to which the antibody binds?

A

The part of an antigen to which the antibody binds is known as the epitope.

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6
Q

What is the structure of an antibody in a naïve B cell?

A

In a naïve B cell, the antibody includes an additional transmembrane domain that anchors it on the surface of the B cell, where it is known as a B cell receptor (BCR).

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7
Q

What activates the B cell receptor (BCR)?

A

The BCR is activated by antigen cross-linking and additional cytokine-mediated stimulation by T helper cells.

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8
Q

What happens to a mature B cell after BCR activation?

A

After BCR activation, the mature B cell undergoes BCR gene rearrangements, which allow the secretion of a soluble antibody form of the BCR.

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9
Q

Does the structure of the antigen-binding site change during BCR activation?

A

No, the structure of the antigen-binding site remains identical throughout the activation process.

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10
Q

What is the name of the domain responsible for antigen binding in an antibody?

A

The domain responsible for antigen binding is called the Fv (variable fragment) domain.

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11
Q

What are the components of an antibody structure?

A

An antibody structure consists of heavy chains, light chains, variable regions (V), constant regions (C), disulfide bonds (SS), and an antigen-binding site.

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12
Q

What are the hypervariable regions in an antibody?

A

The hypervariable regions are parts of the antibody that differ between antibodies and contribute to their specificity for different antigens.

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13
Q

What determines the antibody classes?

A

The heavy chains of antibodies determine the antibody classes, including IgG, IgD, IgE, IgA, and IgM.

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14
Q

Which antibody class is primarily found as monomers and dimers?

A

IgG is primarily found as monomers and dimers.

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15
Q

Which antibody class is the majority of total serum immunoglobulins?

A

IgG is the majority of total serum immunoglobulins.

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16
Q

How many constant domains does each light chain and heavy chain have in an IgG antibody?

A

Each light chain has one constant domain, while each heavy chain has three constant domains in an IgG antibody.

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17
Q

What is the effect of affinity and avidity on antibody function?

A

Affinity and avidity impact antibody function by influencing the binding strength and multivalency of the antibody with its target.

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18
Q

What is the difference between univalent and bivalent antibodies?

A

Univalent antibodies have a single binding site, while bivalent antibodies have two binding sites.

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19
Q

What primarily determines the functional differences among human immunoglobulin isotypes?

A

The three-dimensional structure of the heavy chain constant region largely determines the functional variations among human immunoglobulin isotypes.

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20
Q

How do differences in the heavy chain constant region influence antibody function?

A

Differences in the heavy chain constant region impact antibody function by determining which immune system partner the antibody molecule interacts with, such as antibody receptors on macrophages or complement proteins.

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21
Q

Does the three-dimensional structure of the heavy chain constant region affect the antigen-binding capability of the antibody?

A

No, the three-dimensional structure of the heavy chain constant region does not directly affect the antigen-binding capability of the antibody. It primarily influences the interaction with immune system partners.

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22
Q

How does IgM exist in terms of its structure?

A

IgM exists in a pentameric form, where five individual antibody molecules are linked together by the J chain.

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23
Q

How many antigen binding sites does IgM have?

A

IgM has 10 antigen binding sites due to its pentameric structure.

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24
Q

How does the pentameric structure of IgM compensate for its affinity for antigens?

A

Even if the affinity for antigen is not fully developed, the pentameric structure of IgM provides an avidity effect by having multiple antigen binding sites.

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25
Q

What is the structure of secretory IgA (sIgA)?

A

Secretory IgA (sIgA) exists as a dimer, where two individual antibody molecules are linked together by a J chain and a secretory piece.

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26
Q

What is the function of the secretory piece in sIgA?

A

The secretory piece protects sIgA from proteolysis and facilitates its secretion across mucus membranes.

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27
Q

How many antigen binding arms does sIgA have?

A

sIgA has four antigen binding arms, which contribute to increased avidity for binding to extracellular pathogens.

28
Q

How are the chains of an antibody molecule assembled?

A

The chains of the antibody molecule are assembled by splicing together variable (V), diversity (D), joining (J), and constant (C) gene segments.

29
Q

Which chains involve the V, D, J, and C gene segments in antibody assembly?

A

The heavy (H) chain is formed from V, D, J, and C gene segments, while the light (L) chain lacks the D gene segment.

30
Q

What is required for somatic recombination to occur in antibody assembly?

A

Somatic recombination requires recombination signal sequences, recombination activation enzymes (such as RAG-1/2), and epigenetic changes to the DNA structure, including modifications to methylation and acetylation.

31
Q

What is the outcome of somatic recombination in terms of antibody repertoire?

A

Somatic recombination generates a vast repertoire of available antibodies, allowing the immune system to respond to the numerous pathogenic threats encountered throughout a lifetime.

32
Q

What are epigenetic changes in the context of somatic recombination?

A

Epigenetic changes refer to modifications to the structure of DNA that do not affect the nucleotide sequence but play a role in regulating gene expression and somatic recombination.

33
Q

How does somatic recombination contribute to antibody diversity?

A

Somatic recombination, specifically V(D)J recombination, generates diverse antibody sequences by recombining variable (V), diversity (D), and joining (J) gene segments during the assembly of the heavy chain variable region.

34
Q

Which gene segments are involved in somatic recombination for the heavy chain?

A

Somatic recombination involves recombination between the V, D, and J gene segments to produce the sequence of the heavy chain variable region.

35
Q

What is referred to as class switch recombination?

A

Class switch recombination is a process separate from V(D)J recombination and refers to the rearrangement of the constant (C) gene segments, resulting in the switch of antibody isotypes or classes.

36
Q

Which region of the antibody is affected by V(D)J recombination?

A

V(D)J recombination influences the variable region of both the heavy and light chains, contributing to the diversity of the antigen-binding sites.

37
Q

What is the significance of somatic recombination in antibody production?

A

Somatic recombination plays a crucial role in generating a vast repertoire of diverse antibodies, allowing the immune system to recognize and respond to a wide range of antigens.

38
Q

What does the constant region of an antibody determine?

A

The constant region (Fc) of an antibody defines its antibody class or isotype.

39
Q

What is the role of the Fc region?

A

The Fc region of an antibody is recognized by specific receptors called Fc receptors.

40
Q

Where are Fc receptors found?

A

Fc receptors can be found on leukocytes, including phagocytes.

41
Q

How do Fc receptors assist phagocytes?

A

Fc receptors help phagocytes identify pathogens that have been targeted by antibodies and facilitate the process of phagocytosis to eliminate those pathogens.

42
Q

What is the significance of Fc receptors in the immune response?

A

Fc receptors play a crucial role in linking the effector functions of antibodies, such as opsonization and activation of immune cells, leading to the elimination of pathogens.

43
Q

Where do B cell progenitors emerge and differentiate?

A

B cell progenitors emerge in the bone marrow, where they also undergo further differentiation before entering the bloodstream as committed B cells with synthesized immunoglobulins following somatic recombination

44
Q

What is somatic (V(D)J) recombination?

A

Somatic recombination, specifically V(D)J recombination, is the process by which gene segments encoding the variable regions of the immunoglobulin genes are rearranged to generate diverse antibody sequences in developing B cells.

45
Q

What is negative selection in B cell development?

A

Negative selection is a process in B cell development that eliminates B cells with high affinity for self-antigens to prevent the production of autoantibodies.

46
Q

What is the difference between immature and mature B cells?

A

Immature B cells are B cells that have undergone somatic recombination but have not yet completed their maturation process. Mature B cells have successfully matured and are ready to respond to antigens.

47
Q

Where does the maturation of immature B cells into plasma cells occur?

A

In the spleen, immature B cells come into contact with antigens and undergo maturation to become plasma cells, which are antibody-secreting cells.

48
Q

What does the B cell receptor resemble?

A

The B cell receptor resembles a membrane-bound antibody.

49
Q

How do B cell receptors function?

A

B cell receptors cooperate with co-receptor molecules and receptor-associated molecules to facilitate signaling and immune responses.

50
Q

What happens after antigen binding to the B cell receptor?

A

After antigen binding, a phosphorylation step occurs, initiating a signaling cascade within the B cell.

51
Q

What is the outcome of the signaling cascade initiated by the B cell receptor?

A

The signaling cascade leads to altered gene expression, which contributes to changes in cell proliferation and cell survival.

52
Q

How does altered gene expression affect B cells?

A

Altered gene expression influences B cell proliferation, leading to their expansion, and influences cell survival, promoting their long-term survival.

53
Q

What happens when B cell number 2 encounters an antigen on the target pathogen?

A

B cell number 2 expresses a receptor that binds to the antigen on the target pathogen, initiating a response.

54
Q

What is the outcome of antigen binding to B cell number 2?

A

Binding to antigen eventually leads to the secretion of soluble antibody by B cell number 2, which neutralizes the pathogen.

55
Q

What else is produced during B cell maturation?

A

Memory cells are also produced during B cell maturation, and they have long lifespans and can quickly respond if the pathogen is encountered again.

56
Q

What is affinity maturation?

A

Affinity maturation involves minor changes in the amino acid sequence of the variable domain in the mature B cell after it encounters antigen for the first time.

57
Q

What is the significance of affinity maturation?

A

Affinity maturation improves the binding strength (affinity) of antibodies to their target antigens, enhancing the immune response over time.

58
Q

What happens during clonal expansion?

A

Each B cell (and T cell) expresses its own unique antigen receptor, and activation of a specific cell leads to the production of clones with the same antigen-binding capability.

59
Q

What is required for the activation of B cells?

A

B cell activation requires not only the binding of antigen to the receptor but also stimulation by growth factors such as interleukin-2.

60
Q

What can happen if a B cell is unable to be activated?

A

If a B cell is unable to be activated, either due to an inability to bind antigen or receive the necessary growth factor stimulation, it can become functionally inactive (anergy) or undergo cell death by apoptosis.

61
Q

What is anergy?

A

Anergy refers to a state of functional inactivity in a B cell that is unable to respond to activation signals.

62
Q

What is apoptosis?

A

Apoptosis is a programmed cell death that can occur in B cells as a result of failed activation or other cellular processes.

63
Q

How do primary and secondary immune responses differ?

A

In the primary immune response, the first isotypes produced by a B cell are IgD and IgM. During class switching, IgG is generated, which becomes the main mature antibody form. However, there is no switch back from IgG to IgM.

64
Q

What is the main antibody form generated during the primary immune response?

A

IgG is the main mature antibody form generated during the primary immune response.

65
Q

What does class switching affect in antibodies?

A

Class switching affects the constant domain of antibodies, allowing them to interact with different effector molecules while retaining affinity for the same antigen.

66
Q

How does the time after antigen exposure affect the immune response?

A

During the first antigen exposure, the primary immune response occurs. During subsequent antigen exposures (second exposure and onwards), the secondary immune response occurs, which is faster and more robust than the primary response.

67
Q

What can cause antigen exposure?

A

Antigen exposure can result from a pathogen infection or vaccination.

Foundations of health and disease (45 decks)

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