3.1 Antibody Structure and Function Flashcards

1
Q

What do B cells recognise?

A

Antigenic epitopes on the surface of pathogens

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2
Q

What is an antibody?

A

An antigen-binding protein

Soluble version of B cell surface antigen receptor

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3
Q

What secretes antibodies and where from/to?

A

Plasma cells in lymph nodes
Efferent lymph > blood > tissue (EXTRACELLULAR SPACE)

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4
Q

Where are soluble antibodies found?

A

Serum

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5
Q

Describe the structure of an antibody

A

Two heavy chains (protein domains) - constant regions

Two light chains - variable regions

Disulphide bridges and flexible hinge regions

Mirror image

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6
Q

What is the structural difference between a cell surface antibody and a soluble antibody?

A

Surface antibodies contain a transmembrane protein allowing it to attach to the cell surface, unlike soluble antibodies.

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7
Q

What are the three basic functions of antibody?

A

Neutralisation - prevents adhesion
Opsonisation - promotes phagocytosis
Complement activation - lyses bacteria

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8
Q

Describe neutralisation

A

Antibodies bind virus antigens to prevent them binding to cells

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9
Q

Describe opsonisation

A

Antibody coats pathogen to be phagocytosed by macrophage/neutrophil (Fc receptors)

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10
Q

Describe complement activation

A

Antibody binds antigen and intermediate molecule C1q allows antibody (adaptive) to link complement (innate) pathway

Leads to formation of Membrane-Attack Complex on surface of antigen

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11
Q

What determines the class/isotype of antibody?

A

Heavy chain gene determines class (Fc)

CH mu, delta, gamma, epsilon, alpha

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12
Q

What are the two types of light chain?

A

Light chain can be CL kappa or CL lambda

Random process and has little effect on biological function

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13
Q

How are the different heavy chains and light chains used to create the different classes/isotypes of immunoglobulins? (4)

A
  • Lymph dev., recombination of light and heavy chains estalishes variable region
  • B cell selects light chain constant gene (kappa/lambda) and leaves bone marrow
  • Default is delta/mu (IgD/IgM)
  • Activated by foreign antigen (in secondary lymphoid tissues) B cell can alter heavy chain gene to change class but keep same variable region and light chain (CLASS SWITCHING)
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14
Q

What is the function of IgD?

A

IgD(oorway)

  • On surface of niave B cells
  • Acts as membrane-bound antigen receptor
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15
Q

What s the function of IgM?

A

IgM (moneric or pentamic)

  • Moneric IgM expressed as membrane bound antigen receptor on naive B cells
  • Pentameric IgM - first antibody secreted in immune response
  • Acts as agglutinin
  • potent activator of compliment cascade
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16
Q

What is the function of IgG?

A

Ig
- Neutralisation
- Opsonisation
- Complement cascade

Can cross placenta in primates for neonatal protection

17
Q

What is the function of IgA?

A

IgAhhhhhh! (tears)

  • External secretions as diamer (with secretory component polypeptide chain)
  • Neutralising, barrier
18
Q

What is the function of IgE?

A

Ig(allerg)E

  • Anti-parasitic (helminths)
  • Binds Fc-epsilon receptors on mast cells
  • Cross linkage for degranulation