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An Sc 411 > Lec 4: Antibodies > Flashcards

Lec 4: Antibodies Flashcards

1
Q

Describe the push for an adaptive immune system.

A
  • pathogens have devised a number of clever mechanisms to evade the innate immune response
  • the body needed to devise defence mechanisms that could adapt to each of these organisms no matter how diverse they were
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2
Q

Describe the adaptive mechanisms of immunity.

A
  • necessary if pathogenic organisms breach innate defences and spread through host
  • specificity
  • adaptable
  • systemic
  • includes antibodies, antigen presentation, recognition of self/nonself
  • forms basis of memory
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3
Q

What are the 2 main regions of an antibody?

A
  • recognition function

- biological function

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4
Q

What is the recognition function?

A
  • specifically binds to individual microorganisms (variable, complementary in shape to specific microorganisms)
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5
Q

What is the biological function?

A
  • communicate with complement and phagocytes

- constant

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6
Q

What is an antigen?

A

a macromolecule that induced specific antibody formation

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7
Q

What is an antibody?

A

a protein or glycoprotein that binds antigen

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8
Q

Describe the molecular structure of antibodies.

A
  • composed of 2 identical heavy chains and 2 identical light chains
  • generates 2 discrete regions for binding antigen
  • held together by disulphide bonds
  • certain segments of the variable region are hyper variable providing a mechanism for increased affinity
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9
Q

What is the role of the hinge region?

A
  • increases the efficiency of binding
  • neutralization reactions in viruses (agglutinating the virus particles to form a clump of viruses to make it difficult to enter host cells)
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10
Q

What region of the antibody is the major determinant of antibody functional properties?

A
  • the Fc region
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11
Q

What is ADCC?

A
  • antibody dependent cellular cytotoxicity
  • FcR mediated
  • mast cells, basophils and eosinophils degranulate, NK cells secrete perforin and granzymes which induce apoptosis of target cells
  • macrophages can also do it through other mechanisms
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12
Q

Is there antibody diversity across species?

A
  • yes
  • different species have different antibodies differentiated by Fc region
  • cannot expect them to respond same way to pathogenic challenge; depends on what kind of antibodies they can produce
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13
Q

What are the 2 ways that phagocytosis can occur?

A
  • conventional direct recognition: phagocyte recognizes conserved surface components on bacterium
  • antibodies recognize variable component on bacterium. Constant region of Ab then detected by FcRs on phagocyte linking innate and adaptive responses
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14
Q

What is the complement system?

A
  • made up of 25 plasma proteins that react with one another to opsonize pathogens and induce a series of inflammatory responses to help fight infection
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15
Q

What are the functional outcomes of the complement system?

A
  • trigger inflammatory responses
  • attract phagocytes
  • promote phagocytosis by opsonization
  • directly attack membrane of microbe
  • stimulation of Ab production
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16
Q

Describe the activation of complement by IgG and IgM.

A
  • both can do it but with different efficiencies
  • IgM greater efficiency because more binding sites
  • It takes two units of IgG or one unit of IgM to trigger complement activation
17
Q

Describe the cellular basis of antibody production.

A
  • antibodies are produced by B cells
  • B cell mediated responses through antibodies are systemic (T cell response is local because cell-cell interaction)
  • Abs carried rapidly through blood or lymph or secreted through epithelial layers to protect interface between animal and environment
  • Abs are the secreted form of B cell antigen receptor (immunoglobulins)
18
Q

Describe the clonal selection theory.

A
  • antibodies are formed before antigens are ever seen by the body and they are selected by the antigen
  • selection: antigen binds lymphocyte bearing a complementary receptor
  • activation: activated B cell then forms an expanded clonal pool
  • provides a cellular basis for the generation of effector and memory cells
19
Q

Describe a primary response.

A
  • occurs when a B cell is first activated by an antigen
  • B cell proliferates and differentiates to form plasma cells and memory B cells
  • plasma cells produce antibodies
  • memory cells: differentiated B cells capable of rapid conversion to plasma cell upon subsequent stimulation with same antigen
20
Q

Describe a secondary response

A
  • another exposure to the same antigen
  • memory B cells rapidly form plasma cells and additional memory cells
  • faster and produces more antibodies than the primary response
21
Q

What is affinity maturation?

A
  • mutations of B cell immunoglobulin genes which affect the antigen binding regions and result in higher affinity for antigen
22
Q

What is isotype switch?

A
  • mutations of B cell immunoglobulin genes which results in changes in the effector functions of antibodies secreted from germinal centre B cells
  • changes in antibody class/ isotope
23
Q

Describe how affinity maturation provides specificity upon reimmunization

A
  • initial exposure to an antigen results in low affinity antibodies (IgM) but continued exposure leads to high affinity antibodies
  • peak of IgM is reached in 10-14 days
  • antibodies then fall to pre immunization levels
  • upon reimmunization, many undergo isotope switch to produce IgG
  • as a result, following reimmunization, serum antibodies are primarily IgG and have a greater affinity for antigens; also antibody titres are higher and persist for longer
24
Q

Describe a primary response.

A
  • occurs when a B cell is first activated by an antigen
  • B cell proliferates and differentiates to form plasma cells and memory B cells
  • plasma cells produce antibodies
  • memory cells: differentiated B cells capable of rapid conversion to plasma cell upon subsequent stimulation with same antigen
25
Q

Describe a secondary response

A
  • another exposure to the same antigen
  • memory B cells rapidly form plasma cells and additional memory cells
  • faster and produces more antibodies than the primary response
26
Q

What is affinity maturation?

A
  • mutations of B cell immunoglobulin genes which affect the antigen binding regions and result in higher affinity for antigen
27
Q

What is isotype switch?

A
  • mutations of B cell immunoglobulin genes which results in changes in the effector functions of antibodies secreted from germinal centre B cells
  • changes in antibody class/ isotope
28
Q

Describe how affinity maturation provides specificity upon reimmunization

A
  • initial exposure to an antigen results in low affinity antibodies (IgM) but continued exposure leads to high affinity antibodies
  • peak of IgM is reached in 10-14 days
  • antibodies then fall to pre immunization levels
  • upon reimmunization, many undergo isotope switch to produce IgG
  • as a result, following reimmunization, serum antibodies are primarily IgG and have a greater affinity for antigens; also antibody titres are higher and persist for longer

An Sc 411 (21 decks)

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