Immunoglobulins Flashcards
what is another word immunoglobulin
antibody
immunoglobulins are present where? 4
plasma, tissues, secretions and lymphatics
immunoglobulins are a product of which immune system?
humoral
immunoglobulins are secreted by what?
plasma cells - activated B cells
what are the 5 classes of immunoglobulins?
IgG
IgM
IgA
IgD
IgE
annotate this diagram of immunoglobulin structure with the following regions
- variable region
- constant region
- heavy chain
- light chain
-Fab
- Fc
- Hinge
- disulphide bonds
antibodies have dual function, what are the functions?
recognition function - Fab region binding to antigen
effector function - clearing mechanism - Fc region interacting with effector molecules
what are the two types of light chain that are used in all antibody classes?
lambda
kappa
in any individual antibody molecule, both light chains are?
the same
light chains fold up into 2 globular domains termed what?
VL - variable light domain
CL - constant light domain
what determines the class of antibody?
heavy chain
in IgG what is the type of heavy chain?
γ gamma
in IgA what is the type of heavy chain?
α alpha
in IgM what is the type of heavy chain?
μ mu
in IgD what is the type of heavy chain?
δ delta
in IgE what is the type of heavy chain?
ε epsilon
heavy chains fold up into 4 (or 5) globular domains, what are they starting from N terminus?
VH - variable heavy
CH1 - constant heavy 1
CH2
CH3
(CH4)
annotate this image with the domains
what holds the domains together in an immunoglobulin?
non-covalent interactions between: VL-VH, CL-CH1, CH3-CH3
oligosaccharides between CH2-CH2 (less closely linked)
in the VL and VH domain there are 3 parts in the amino acid sequence that determine the what antigen a specific antibody will bind to what are these areas called?
hypervariable loops 1,2, and 3
or
complementary determining regions CDR1,2, and 3
when the VH and VL domains are paired their 6 CDRs create what?
the antigen binding site
what does epitope mean?
actual structural part of the antigen that is recognised
what is the most abundant immunoglobulin in plasma?
IgG
what is the structure of IgG?
Shape, number of HC and LC and subclasses
Y shaped
2HC and 2LC
4 subclasses IgG1,2,3 and 4
IgG is very efficient at triggering ? and ? via ?
complement
phagocytosis
Fc receptors
what is the only Ig class to pass the placenta from mother to foetus? why is this important?
IgG
protects baby in the first months of life because there is a lag where the baby cant make its own IgG
IgG is the predominant antibody of the primary or secondary immune response?
secondary
IgM is found where?
only in plasma and secretions, its too large to enter tissues
what is the structure of IgM?
5 Y shaped units
joined by a joining chain (J chain- extra polypeptide) and disulphide bridges
heavy chain has 5 globular domains
how does the structure of IgM relate to its function?
10 binding sites mean that it is very good at linking onto numerous particles and clumping viruses together - agglutination
IgM is very efficient at activating what?
complement
IgM is the predominant antibody of the primary or secondary immune response?
primary
Human IgA is the major antibody in what?
seromucous secretions e.g. saliva, milk, colostrum, gut, tracheobronchial system and genito-urinary system
what is the class of antibody first encountered by many invading bacteria and viruses
Human IgA
what are the subclasses of IgA in humans?
IgA1 and IgA2
serum IgA is predominantly in monomeric or dimeric form?
monomeric 90% IgA1 10% IgA2
secretory IgA is predominantly monomeric or dimeric?
dimeric 40% IgA1 60% IgA2
in secretory IgA which is predominantly dimeric there is an additional polypeptide. what is it called and what does it do?
secretory component
helps protect the secretory IgA in the harsh environment of secretions e.g. extreme pH or proteolytic enzymes.
recognise this
recognise this
what is the structure of IgE
y shaped
5 globular domains in each heavy chain
lots of N linked oligosaccharides (sugars)
what does IgE do?
interacts with Fc receptor FcεR1 -> expressed on mast cells and basophils and is associated with the allergic response (due to high affinity)
important in protection against parasitic infections
where is IgD mostly found?
on the surface of lymphocytes
what is the function of IgD?
unclear - thought to be involved in the control of antibody response
what are the key effector molecules that immunoglobulins interact with?
Fc receptors
complement
what are Fc receptors?
receptors that bind specifically to the Fc region of immunoglobulins
what are the Fc receptors that are specific to IgG Fc region?
FcγRI, FcγRII, FcγRIII
what are the Fc receptors that are specific to IgA Fc region?
FcαR
what are the Fc receptors that are specific to IgE Fc region?
FcεRI , FcεII
what happens when an Fc receptor binds to the Fc region of an immunoglobulin
invading pathogen has many antibodies that bind to it resulting in multiple Fc receptors being engaged at the same time.
- phagocytosis
- release of activated oxygen species and enzymes
- release of inflammatory mediators e.g. histamine
- enhanced antigen presentation
- clearance of immune complexes
release of the inflammatory mediator histamine is triggered by what receptor? what releases it?
FcεRI
released from mast cells and basophils
