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MCD- immunology > Antibodies > Flashcards

Antibodies Flashcards

1
Q

What family group are antibodies under?

A

Immunoglobulins- a large family of soluble glycoproteins

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2
Q

What are the three secondary effector functions of antibodies once bound to antigens?

A
  • Complement activation
  • Opsonisation ( promotion of phagocytosis)
  • cell activation via specific antibody-binding receptors (Fc receptors)
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3
Q

Which immunoglobulin category do antibodies fall into ?

A

Gamma immunoglobulins

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4
Q

What features of the antibodies helps its function?

A

Increased gamma globulin- strong antibody response
Diffuse band- large variety of antibodies
Small sharp band- monoclonal expansion of antibodies: indicative of myeloma.

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5
Q

Explain how the immunoglobulin molecule looks/

A

N,C= poylpeptide terminals
-4 polypeptide chains held together by disulphide bonds
-the 2 heavy chains are identical and the 2 light chains are identical
-it is symmetrical
(pg 86 immunology 4)
Light, heavy, heavy, light

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6
Q

What type of bond holds together the chains in the immunoglobulin?

A

Disulphide bonds

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7
Q

What is the purpose of the hinge regions of the antibody?

A

Makes it flexible which allows antibody Fabs to bind to the antigens as the antigens may be narrowly or widely spaced.

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8
Q

What is the Fab and Fc part of the antibody and what happens to the Fc part when antigen binds?

A

Variable region is where the antigen bind - Fab
Constant part- Fc (doesn’t have to change because doesn’t bind to antigens)
Fc changes conformation when the antigen bounds and can activate complement.

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9
Q

What does the antibody domain also contain?

A

Has an internal intrachain disulphide bond- these are immunoglobulin domains

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10
Q

What did scientists find when sequencing the amino acid sequence of the variable region on antibodies and where are they located?

A

There are three hypervariable regions called the complementarity determining regions.
Located: at loops which are at the end of protein and interact with antigens.

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11
Q

What shape does the constant region take

A

Has a barrel shaped-beta pleated sheet, which is held together by highly conserved internal disulphide bonds.

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12
Q

What part of the variable region of the antibody binds to the antigen?

A

The complementarity determining regions are found at the end of the variable regions and interact with antigens

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13
Q

What forces are involved in antibody-antigen binding?

A

THEY ARE ALL NON-COVALENT Hydrogen bonding, ionic bonding, van der waals, hydrophobic interactions

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14
Q

Define affinity.

A

The strength of the total non-covalent interactions between a single antigen-binding site and a single epitope.

Affinity is a measure of the strength of binding between a single binding site of an antibody and its antigen.

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15
Q

What equation shows affinity mathematically?

A

Ab + Ag Ab-Ag

K = [Ab-Ag:products]/[free Ab][free Ag]

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16
Q

Define avidity.

A

Avidity is the overall strength of binding between antibody and antigen, taking into account the number of binding sites on the antibody and the number of sites on the antigen (antigenic determinants or epitopes) that can be bound.

Generally, the more more binding sites that are bound to antigens, the higher the avidity

17
Q

What is antibody cross-reactivity? Give an example.

A

Antibodies that are produced in response to one antigen can cross-react and bind to a different antigen with a similar structure. E.g. cow pox vaccination induces antigen that are able to recognise small pox

18
Q

What are isotypes and allotypes of antibodies?

A

Isotypes: immunoglobulin structures that are present in all members of a species e.g. immunoglobulin sub classes
Allotypes – polymorphic variables – some people have them others don’t

19
Q

How do the different classes of antibodies differ?

A

(GAMED)

They vary in the constant region of their heavy chain.

20
Q

What are the two classes of light chain?

A

Kappa and lambda- only one type per antibody because they are symmetrical

21
Q

Which immunoglobulin classes have subclasses and how many subclasses do they have?

A 
IgG = 4 (in order of abundance – 1 is the most abundant) 
IgA = 2
22
Q

Describe the features of the IgG antibody

A
  • gamma heavy chain
  • most abundant immunoglobulin
  • occurs as a monomer : 4 subclasses,
  • move across the placenta
  • MAJOR activator of the classical complement pathway
  • variations in the hinge region.
23
Q

Describe the features for IgA?

A
  • alpha heavy chain
  • second most abundant immunoglobin
  • blood= monomer
  • secretions=dimer
  • preotects mucosal surfaces from bacteria, viruses and protozoa
24
Q

Describe the formation of secretory IgA.

A

-Process to get the dimeric IgA from below the epithelial layer into the lumen
IgA is produced by plasma cells
Dimeric IgA binds to the Poly-Ig receptor on the basolateral surface of the epithelia
This triggers endocytosis.
Once inside the cell, the poly-Ig receptor is cleaved and the dimeric IgA is secreted with the secretory component
The secretory component is derived from the poly-Ig receptor.

25
Q

Describe IgM featues?

A

Pentameric, 5 monomers joined by the J chain-10Fab
-mainly confined to blood
first Ig produced after exposure to antigen
-multiple binding sites compensates for low affinity (high avidity)
-efficient agglutination
-held together by disulphide bond

26
Q

Featured of IgD

A
  • Low serum concentrations

- surface IgD expressed early in B cell development, so involved in B cell development and activation

27
Q

Features of IgE?

A

Low concentration in blood

  • produced in response to parasitic infections and in allergic diseases.
  • binds to high affinity Fc receptors of mast cells and basophils.
28
Q

How can IgE activate cells?

A

It binds to the Fc (Fc-epsilon-RI) receptor on mast cells and basophils with high affinity .When antigens bind by cross linking to the IgE, which is attached to the mast cell, it stimulates degranulation and release of histamine.
OR
allergen will bind to IgE which re bound to the mast cell and cause release of histmaines.

29
Q

Which two Ig classes are mainly responsible for activating complement?

A

IgM and IgG

30
Q

What are each except for IgA and IgD of the immunoglobins classes good at?

A

IgG: neutralising, opsonisation,
good at binding to virus infected cells and NK cells can recognise cells coated in IgG leading to ADCC(Antibody Dependent Cell-mediate Cytotoxicity)
igM: agglutinating
igE: mast cell sensitisation

31
Q

where are all the immunoglobulins found?

A 
Blood= IgG IgM
Extracellular fluid= IgG
Secretions across epithelia= dimeric IgA
foetus= IgG
Mast cells below epithelia= IgE

MCD- immunology (10 decks)

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