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CMOD Week 1 > Immuno 2 > Flashcards

Immuno 2 Flashcards

1
Q

Antibodies are the effector molecules (globular proteins) produced in LARGE (not small) quantities by __ cells

A

B. Specifically plasma cells.

each antibody produced by a single B cell has the exact same specificity for antigen

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2
Q

What do antibodies do?

A

they simply bind to specific ligands on the surface of pathogens. These PROTEINS have no toxic properties and do not themselves destroy invading pathogens. Because antibodies also serve as ligands for receptors on phagocytic cells, when they bind to a pathogen they promote uptake and destruction of the pathogen by phagocytes (opsonization)

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3
Q

Additional roles of antibodies.

A

In addition, some isotypes of antibodies serve as ligands for the 1st component of the classical complement cascade (opsonization). Finally, in some cases binding of antibodies to a pathogen (or pathogen-derived toxin) prevents binding of the pathogen (or toxin) to its host ligand, thereby preventing infection or toxicity (neutralization).

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4
Q

Describe the structure of antibodies.

A

All antibody molecules have a common core structure that consists of two identical “light chains” (approx. 24kD), and two identical “heavy chains” (approx. 55 or 70kD). One of the two light chains is attached to each heavy chain, and the heavy chains are attached to each other; these attachments are formed by intrachain disulfide bonds.

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5
Q

T or F. heavy and light chains are encoded on the same genes

What are lg domains?

A

F. They are encoded on separate genes

heavy and light chains consist of a series of similar (not identical) sequences (domains); about 110 residues in length (Ig domains)

immunoglobulin (Ig) domains fold independently, interchain disulfide bonds help form the domains

the amino-terminal Ig domain of each chain (variable region) is highly variable between different Abs; the remaining domains are conserved (constant regions)

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6
Q

Note on domain structure.

A 
the constant (C) domains and variable (V) domains of all antibody molecules have a similar structure; it is important to
remember that Abs perform their functions in extracellular spaces in the presence of infection, where they encounter variations in pH, salt concentration, proteolytic enzymes, and other potential destabilizing factors; their unique tertiary structure enables them to withstand these environmental factors and maintain their functionality
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7
Q

Describe the shape of the C and V domains of antibodies.

A

both C and V domains are a roughly cylindrical shape and are formed by two adjacent β-sheet structures that are covalently linked by an intrachain disulfide bond

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8
Q

the adjacent β-sheets of C and V domains form structures known as a _____.

A

a β-barrel or β-sandwich (a β-barrel is a common secondary structural motif of proteins)

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9
Q

B-barrels formed in antibody molecules are called?

A

immunoglobulin folds

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10
Q

What is the primary difference between C and V domains?

A

V domains are larger and have extra loops of polypeptide chain

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11
Q

The extra loops of polypeptide chain in the V domains form what?

A

the flexible loops of V domains form the antigen-binding domains

ABDs are found in located regions on BOTH the heavy and light chains

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12
Q

A variability plot in which the amino acid sequences of the V domains of many heavy and light chains have been compared, revealed that sequence variability in confined to 3 distinct regions within these variable domains. What are they?

A
  1. hypervariable regions (HV) are designated HV1, HV2, and HV3 (or complementarity-determining regions CDR1-3).
  2. the low variability regions between these hypervariable regions are known as framework regions (FR1, FR2, FR3, and FR4)
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13
Q

What do the framework regions of the V domains (FR1-FR4) form? What about the hyper variable (HV) sequences

A

the B-sheets that provide the structural framework of the domains, while the hypervariable sequences correspond to the loops between the β-sheets

therefore, the hypervariable regions are localized to a particular surface of the immunoglobulin molecule

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14
Q

How do the HV regions of the light and heavy chains in an antibody interact?

A

when the heavy chains and the light chains are paired in an antibody molecule, their hypervariable regions are brought together, creating a single hypervariable site at the tip of each “arm” of the antibody molecule. This conjoined hyper variable site forms the antigen-binding site

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15
Q

The antigen binding regions of an antibody molecule are aka?

A

the idotype of the antibody

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16
Q

What is idiotype?

A

term to describe the 3D or tertiary structure of the antigen binding site of an antibody. The idiotype is essentially the shape of the antigen-binding site that accommodates the shape of a particular antigen

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17
Q

T or F. Each antibody molecule has only a single idiotype. Why or why not?

A

T. because both of the antigen-binding sites of any antibody monomer are identical, and therefore, they have an identical shape.

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18
Q

The region of the antigen on an invading micro-organism that is recognized by the antibody by its HV regions is called?

A

an antigenic determinant or EPITOPE

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19
Q

Again, what is the function of antibodies?

A

the function of antibodies is to bind to microorganisms and to facilitate their destruction and removal from the body

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20
Q

Antibodies produced during INFECTION usually have specificity for what kinds of epitopes?

A

those that are composed of either
carbohydrate or protein (remember, the surface of pathogens typically are composed of glycoproteins, polysaccharides, glycolipids, and proteoglycans)

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21
Q

What are multivalent antigens?

A

Antibodies typically have specificity for epitopes that are composed of carbs or proteins. Complex macromolecules like these typically have multiple epitopes, each of which can be bound by a separate antibody molecule (but those antibodies don’t necessarily have to be distinct)

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22
Q

T or F. a multivalent antigen can have a single epitope that is repeated many times, or it can have a number of distinct epitopes

A

T. Repeat: a multivalent antigen can have a single epitope that is repeated many times, or it can have a number of distinct epitopes. What is the significance of this?

Most pathogens are multivalent

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23
Q

Can antibodies be produced that have specificity for epitopes that care composed of things other than carbs or proteins? If so, what are they typically used for?

A

Yes. Such antibodies are involved in allergic reactions and autoimmune diseases and are not involved in defense against infection (e.g. antibodies specific for DNA are characteristic of systemic lupus erythematosus)

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24
Q

The binding of ABs to antigens (via what regions on each?) is based solely on what kinds of forces?

A

non-covalent forces (electrostatic forces, hydrogen-bonding, van der Waals forces, and hydrophobic interactions)

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25
Q

How are van der Waals and hydrophobic interactions between ABs and antigens produced? In other words, what characteristic of ABs allows for this to occur?

A

the antigen-binding regions of antibody molecules are typically rich in aromatic amino acids which can participate in many van der Waals and hydrophobic interactions

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26
Q

How do the HV regions of light and heavy chains come together? What do they form to facilitate antigen binding?

A

the hyper variable regions (orcomplementarity-determining regions or CDRs) of the variable Ig domain of the light and heavy chains come together to form a unique shape that, together with the amino acid side chains that reside in these regions, allows the antibody to bind to a specific epitope; The HV regions of the heavy and light chain come together to form pockets, grooves, or extended surfaces that allow them to bind to their specific antigen.

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27
Q

T or F. it is possible that there could be several structurally distinct antibodies that could bind to the exact same epitope

A

T; however, each of these antibodies could bind to the epitope with different binding strengths

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28
Q

The binding strength of any antibody to its particular antigenic determinant is known as?

A

the binding affinity.

NOTE: it is important for you to remember that all non-covalent protein:protein interactions are reversible; an antibody that has high affinity for an antigen stays bound longer than an antibody that has low affinity

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29
Q

What is avidity?

A

the combined binding strength of all antigen-binding domains of an antibody bound to the antibody’s cognate antigen simultaneously

When an antibody is bound to a multivalent antigen via each of its antigen-binding regions, for the antibody to release from the antigen, both of the binding regions would have to release at the same time. Because antibodies typically bind with high affinity to their antigen, the binding equilibrium for each antigen- binding region of the antibody for antigen is shifted strongly to the bound state for both of the antigen-binding regions. The higher the affinity, the less likely that both binding regions will release at the same time.

Since IgM has 10 antigen-binding regions (because it is a pentameric), it has the highest potential avidity of any of the antibody isotypes (by far).

30
Q

Antibodies can bind to what two types of antigenic determinants of proteins?

A
  1. continuous epitopes (linear)

2. discontinuous epitopes (non-linear)

31
Q

What are continuous epitopes?

A

a linear or continuous epitope is formed by a linear stretch of amino acids

32
Q

What are discontinuous epitopes?

A

a non-linear or discontinuous epitope is formed by portions of an antigen that are
brought together due to the arrangement of the antigen; for example: amino acids from different parts of a polypeptide that are brought together when the protein is in its native form (its normal tertiary structure); if that tertiary structure is disrupted, the epitope no longer exists because the antibody contact points are no longer together in a discreet formation

33
Q

antibody molecules can be subdivided into five different isotypes based on the type of heavy chain that is found in the antibody. What are they?

A 
IgA: alpha (α), 
IgD: delta (δ), 
IgE: epsilon (ε), 
IgG: gamma (γ), and 
IgM: mu (μ).
34
Q

T or F. light chains have a single variable region and a single constant region

A

T

35
Q

How many V and C regions do heavy chains have?

A

heavy chains have one variable (V) region and either three (IgG, IgD, and IgA) or four (IgM and IgE) constant (C) regions

36
Q

Which antibodies types have heavy chains with 3 constant regions? 4 constant regions?

A

3- A, D, G

4- E, M

37
Q

What is a hinge region?

A

rich in proline residues, the hinge region allows flexibility of the Ab molecule that enables it to more easily bind to antigenic determinants
and/or immune components (FcR). These are found only in ABs IgA, D, and G.

NOTE: the hinge region of IgG and IgA is sensitive to proteolytic cleavage

38
Q

What are the two types of light chains?

A

kappa and lamda

these different light chains types can be present in any of the five AB types, BUT only one of these types is found in an individual Ab molecules because each antibody molecule is composed of 2 identical light chains (and two identical heavy chains)

39
Q

What kinds of light chains are IgG Abs composed?

A

In humans, approx. 60% contain kappa light chains, while 40% contain lama light chains

40
Q

What are the subtypes of IgA Abs?

A

IgA1 and IgA2

41
Q

What are the subtypes of IgG Abs?

A

IgG1, IgG2, IgG3, and IgG4. These differ in the structure of the hinge

42
Q

Which Ab isotopes can exist as multimeric structures of Ab molecules?

A

IgM and IgA

43
Q

What facilitates IgM and IgA Abs being able to exist as multimers (IgM typically as pentameric and IgA typically as dimeric)?

A

the joining or J chain

44
Q

What is the J chain?

A

The J chain is a 15 kD polypeptide that
is disulfide linked to the tail-pieces (extensions at the carboxyterminal region of the alpha and mu heavy chains). It functions to stabilize IgA and IgM multimers

45
Q

What are secretory components? Where are they produced?

A

In mucosal secretions, another polypeptide called the secretory component is attached to the IgA dimer non-covalently. The secretory component of IgA is produced by epithelial cells that line the luminal surface of mucosal tissues. Secretory component on the surface of the cells combines with IgA produced locally by lymphocytes and transports the IgA through epithelial cells (lining mucosal surfaces) into secretions

46
Q

IgA composes what percent of serum immunoglobulin?

What is its half-life?

A

5-15%
6 days

can occur are monodic, dimeric, or trimeric structures (multimerized by J chains)

47
Q

Where can the dimeric form of IgA by found in the body?

A

colostrum/breast milk, intestinal and respiratory secretions, saliva, tears, and other
secretions

48
Q

IgA-deficient individuals experience increased incidence of what?

A

respiratory and some gastrointestinal infections

49
Q

IgD composes what percent of serum immunoglobulin?

A

less than 1%. Not secreted in appreciable amounts and has no known effector role in a humoral immune response

50
Q

What is the primary role of IgD?

A

exists primarily as membrane IgD; serves with IgM as an antigen receptor on early B cell membranes to help initiate Ab
responses by activating B cell growth

51
Q

IgD composes what percent of serum immunoglobulin?

A

less than 1%.

52
Q

Where is most IgE found?

A

most IgE is bound to Fc receptors on mast cells where it serves as a receptor for allergens and parasite antigens; if sufficient
Ag binds to IgE on mast cells, the mast cells degranulate, releasing histamine, prostaglandins, platelet-activating factor, and
cytokines

53
Q

IgE is important for protection against ____ and is responsible for ____

A

parasitic infection

anaphylactic hypersensitivity

54
Q

IgG composes what percent of serum immunoglobulin?

half-life?

A 
85% in adults
23 days (longest of any isotype)
55
Q

What are the roles of IgG?

A
  • fixes complement (requires multiple IgG molecules)
  • stimulates chemotaxis
  • acts as an opsonin, therefore, facilitates phagocytosis
  • principle antibody isotype in anemnestic (memory) immune responses
  • crosses the placental barrier
56
Q

IgM composes what percent of serum immunoglobulin?

How does it exist?

A
  • comprises 5-10% of total Ig in adults
  • is secreted as a pentameric molecule (10 heavy chains and 10 light chains) stabilized by a J chain (has 10 antigen-binding domains)
57
Q

Notes about IgM.

A

is the most efficient Ig for fixing (binding to) complement; a single pentamer can activate the classical complement pathway;

promotes phagocytosis and bacteriolysis through complement fixing activity

58
Q

Where is monomeric IgM found?

A

monomeric IgM is found (along with IgD) on the surface of all naïve B cells; serves as a receptor for antigen

59
Q

Can IgM cross into tissue? Why?

A

cannot cross efficiently into tissue because of large size

60
Q

IgM are particularly important for immunity to what kinds of antigens?

A

particularly important for immunity to polysaccharide antigens (cell wall components of bacterial pathogens; T-independent
antigens)

61
Q

Each monomeric Ab has how many antigen-combining sites/variable regions (the regions of the Ab which interact with the epitope of the antigen)?

A

2

62
Q

The stem portion of an antibody is termed the ___ of an Ab?

A

Fc portion

63
Q

What is the Fc region of an antibody?

A

the Fc region interacts with complement components and with macrophages and NK cells to promote clearance of antigen and activation of subsequent immune responses.

64
Q

The hinge region of which Abs are susceptible to proteolytic cleavage?

A

IgG and IgA

65
Q

What does papain do?

A

enzyme through which cleavage of an IgG or IgA yields a single Fc fragment and two Fab fragments. Each Fab fragment contains a single antigen-binding site

66
Q

The Fc portion of IgG1 and IgG3 Ab are recognized by Fc receptors on what kinds of cells?

A

macrophages and neutrophils. these cells can therefore bind to and engulf opsonized pathogens

67
Q

The Fc portion of IgE binds to Fc receptors on what kinds of effector cells?

A

mast cells, basophils, and activated eosinophils. This enables these cells to respond by releasing inflammatory mediators

68
Q

the Fc portions of antibody:antigen complexes can bind to complement, initiating the complement cascade (IgG1, IgG2, IgG3, and IgM)

A

the Fc portions of antibody:antigen complexes can bind to complement, initiating the complement cascade (IgG1, IgG2, IgG3, and IgM)

69
Q

The Fc portion can facilitate delivery of antibody to sites they would not reach without active transport. Name some examples.

A

these sites include mucous, tears, and milk (IgA) and fetal blood circulation (IgG1, IgG2, and IgG3)

70
Q

What is the Clonal hypothesis?

A

During development, progenitor cells give rise to a large number of lymphocytes, each with a unique specificity.

During infection, lymphocytes with receptors that recognize pathogens are activated

B cells that make pathogen-specific antibodies can clonally expand and produce pathogen-specific antibodies that can mediate clearance of the infection

71
Q

When are plasma cells made?

A

A resting B cell (made in bone marrow) with a specific membrane bound Ig will recognize a pathogen initially. The stimulated B cell will then give rise to plasma cells which produce free floating/secreted antibodies

72
Q

What is Isotope switching?

A

B cells can be signaled to produce antibody of a different isotype. Only the constant region of the heavy chain is altered. Differences in the constant chains of Ab isotypes allows maximum versatility of antibody-mediated immune responses

CMOD Week 1 (18 decks)

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