Immunoglobulins Flashcards
Antigen definition
any substance which elicits an immune response
which portion of an antigen is recognised by antibodies
epitopes (antigenic determinant)
each antigen can have many epitopes
where are immunoglobulins present
what type of cells secrete them
plasma, tissues, secretions and lymphatic system
activated B cells
what are the five classes of immunoglobulins
IgG - gamma
IgA - alpha
IgM - mew
IgE - epsilon
IgD - delta
“gamed”
what are the chains of an immunoglobulin?
variable heavy
variable light
constant heavy
constant light
what are the two fragments of an immunoglobulin and their functions
Fragment antigen binding (Fab) - responsible for recognising and binding antigens
Fragment crystallisable (Fc) - responsible for effector function/interacts with effector molecules
which enzyme cleaves
papain
what are the two types of light chains in immunoglobulins
lambda
kappa
where and by what are immunoglobulins glycosylated
in the gap in the CH2 domain of the Fc region
by n-linked oligosaccharides attached to asparagine (Asn) residues
how can millions of different antigens have a small number of effector molecules
antibodies work as adapter molecules
i.e. unique Fab region but Fc region interacts with the same effector molecules as other antibodies
how does the antigen system recognise millions of different antigens?
three hypervariable loops or CDRs in each variable domain
CDR = complementarity determining region
how do hypervariable loops or CDRs form the antigen-binding site
CDRs are found on the loops between beta-sheets
when the VH and VL chains come together their 6 CDRs lie close together in 3D space
what type of chemical interactions do antibodies bind antigens with
non-covalent
which Ig subclass is most abundant in plasma (10 mg/ml)
IgG
which Ig subclasses trigger complement
IgG and IgM
which Ig subclass crosses the placenta
IgG
“goo goo gaga”
which Ig subclass forms a pentamer
what are they joined together by
IgM - five points on a capital M
joined together by joining (J) chain and disulphide bridges
why is IgM only present in plasma and secretions
too large to enter tissues
how many Fab sites does IgM have
10 (5x2)
which Ig subclasses primarily make the first and second degree responses
1st - IgM
2nd - IgG
which Ig has two subclasses (one and two)
IgA
what is the function and origin of IgA secretory component (SC)
protects against harsh conditions of secretions
derived from the receptor mediating export
what joins secretory IgA into a dimer
J chain
major function of IgA
Major Ig present in seromucous secretions
prevents bacteria and viruses from binding mucosal surfaces
major function of IgM
agglutinating (clumping together) particles (e.g. viruses)
which Ig subclass is associated with the allergic response
IgE
“allergEEE”
which Ig subclass has extra C domains in the Fc region
IgE
IgD role
antigen receptor on the surface of B-cells
involved in B cell differentiation
what are the protective functions of Igs
blocking the entry of pathogens into host cells
neutralisation of toxins
what are Fc receptors
effector molecules
what does activation of complement eventually lead to
opsonisation and lysis
what is opsonisation
coating something to make it more susceptible to phagocytosis
