Red cell Antibodies and their Role in Immune Haemolysis Flashcards
an Immunogen is anything that
stimulates a specific immune response ie see as ‘foreign’
an Antigen may be comprised of several
epitopes
each specific Antibody will bind to a particular epitope on a
antigen
Immunogenicity is a measure of the ability of an antigen too
to provoke an immune response
degree of polymorphism
determines
foreignness
Immunogenicity is dependant on what features of an antigen
degree of polymorphism molecular shape, charge, size and complexity accessibility number of copies homozygous versus heterozygous
Primary Immune Response
occurs when antigen is first encountered. Antibody production follows in 4 phases
lag phase
log phase
plateau phase
decline phase
Immunoglobulin class switch
from IgM to …..
and is what cell dependant
IgG
t cell dependant
class-switch gene recombination occurs during
B cell maturation
secondary immune response occurs
second exposure to antigen
in secondary immune response is lag time reduced or increased
reduced
In secondary immune response antibody titre rises .. . . .. and reaches a ……….
more quickly and reach’s a higher plateau of antibody levels
In secondary immune response memory B cells …..
Respond in a T cell independant way resulting in an immediate IgG response
in secondary response antibodys produced have improve …. and .,….
affinity and avidity
affinity is the strength of the bond between an individual antibody and antigen
avidity is the overall strength of the bond between a multi - epitope antigen and its respective polyclonal antibody
Red cell membrane structures are composed of …. and how immunogenic are they
Proteins: very strongly immunogenic
carbohydrates: not always immunogenic
Glycoproteins: carbohydrate chains linked to a protein backbone
often strongly immunogenic
Lipids: Poorly immunogenic
Glycolipids: Carbohydrate chains linked to lipid
moderately immunogenic
What is the immunological response to Protein antigens Rh
T cell dependant response
predominately IgG antibodies
What is the immunological response to Carbohydrate antigens ABO
Mostly T cell independent response
predominantly IgM antibodies
what is the immunological response to glycoprotein K, Fy
mostly t cell dependant response
predominately IgG antibodies
what is the immunological response to glycolipid P1
mostly T cell independent response predominantly IgM antibodies
Antibodies are …. found in
glycoprotein molecules
found in all body fluids
IgM and IgG function as
blood group antibodies
IgM reacts to what antigens and are ….
carbohydrate / glycolipid antigens and are mostly t cell dependant
IgG reacts to what antigens and are
protein / glycoprotein antigens and mostly T cell dependent response
interchain disulphide bonds link
both heavy and light chains together and link the two heavy chains together in the ‘Hinge ‘ region
light and heavy chains have distinct
regions characterised by either the similarity (Constant Section) or the heterogeneity (Variable Section) of the amino acid structure
five types of heavy chains which determines the
Ig class
each light chain has one variable (VL) and one constant
(CL) domain
each heavy chain has one variable (VH) and either
3 or 4 constant (CH) domains
each variable domain has three
hypervariable regions
hypervariable regions
are orientated together to form a
3-D shape which is complementary to the specific epitope
what is the Antibody binding site
(Fab region)
heavy chain constant domains are involved in the
effector functions of the Ig (Fc region)
proteolytic enzymes (at appropriate conc.) cleave the
basic Ig structure into distinct regions
Papain produces
two separate Fab fragments
one Fc fragment
Pepsin produces
Fc fragments one F(ab´)2 fragment
Haemolytic Transfusion Reactions
antibody mediated removal of…….
IgM or IgG alloantibodies may cause significant levels of…..
transfused ‘foreign’ red cells
of red cell destruction
Haemolytic Disease of the Foetus and Newborn (HDFN)
IgG alloantibodies may cause
foetal/newborn morbidity & mortality
Autoimmune Haemolytic Anaemias (AIHA)
IgM or IgG auto-antibodies mediate removal of
‘self’ red cells
Structure of IgM and held together by
pentameric structure consisting of five linked basic Ig units
held together by disulphide bonds and a separate J chain
IgM characterises what response
primary
IGM cannot cross the
placenta
Igm is optimal at what temp
4.c
What does IgM activate
complement
clinically significant IgM is still reactive at/near
37oC
IgM can cause ….
which involve
cause intravascular haemolysis….
‘Immediate-type’ transfusion reactions
cold-type autoimmune haemolytic anaemia
IgM very efficient as a ….
and detected in,,,…
agglutinating agent due to polyvalent structure
vitro by direct ‘saline’ methods
four IgG subclasses
(IgG1, IgG2, IgG3, IgG4
IgG1 & IgG3 are most significant as
Blood Group Antibodies
Production of IgG
predominant Ig in the secondary immune response
usually seen as Immune Antibodies
result of Pregnancy or Transfusion
usual antibody response to ‘protein antigens’
can all IgG classes cross placenta
yes
macrophages carrying …. bind to cells coated with …. results in …..
FcyR
IgG
extravascular haemolysis
this all activates complement
What two pathways mediate immune haemolysis
classical
- mediated by red cell antibody bound to Antigen
Alternative
- independent of antibody
The classical pathway is initiated by
Ag/Ab reaction on a cell surface
Destruction of antibody coated in red cells by
Haemolysis
- cascade completion results in ‘doughnut-like’ lesions in red cell membrane
- this haemolysis is Intravascular
Immune adherence (opsonization)
- sequence stops at intermediate (C3b) stage
- red cells destroyed phagocytic cells carrying complement and IgG receptors
- haemolysis is Extravascular haemolysis
what are the four stages of classical pathway
attachment or complement binding
Activation
Amplification
Membrane Attack phase (this is common for both alternative and common pathway)
what is the aim of stage 1 in complement pathway
binding of C1 complex
What is C1 composed of …. and dependant on ….
C1q: C1r2: C1s2 complex
and dependant Ca2+
what does C1 require
two Fc regions to lie in close proximity so C1q can then bind to the adjacent Fc sections via receptors on globular head regions
What happens when C1r is bound to Fc sections on antigen
C1r becomes an active enzyme
Stage 2 C1r then cleaves to
C1s
In stage 2 (activation) C1 interacts with C2 but how
C4 is first cleaved into the C4b (largest fragment) and C4a
C4b binds covalently to the cell surface
C2 then binds to the C4b
C2 is then cleaved by C1s to produce C2b
the resulting C4b2a complex is the C3 convertase of the classical pathway
In stage 3 (amplification phase) C4b2b does what
and what else happens
cleaves C3 into C3a and C3b
there is a major amplification as the large fragment C3b binds covalently to the cell surface
C3b is quickly inactivated in the plasma phase
bound C3b has immune adherence properties
the smaller C3a fragment is released into the fluid phase where it acts as an anaphylatoxin
a small amount of C3b binds to form C4b2bc3b complex
which is known as C5 convertase
Stage 4 part 1. what does C5 do and then what happens
C5 binds to the C3b component of the C5 convertase
the serine protease activity of C2b then cleaves C5 into C5b and C5a
the smaller C5a is released into the fluid phase
this is both has anaphylatoxic and chemotactic properties
C5b then binds C6 and C7
membrane attack phase 2 what does C5b67 do and what happens next
the trimolecular complex of C5b67 then binds to the cell membrane
C7 inserts into the lipid bilayer
C8 and then 10-16 molecules of C9 bind to create a membrane lesion
this membrane lesion is know as the membrane attack complex (MAC)
What are the properties of MAC
pore is hydrophobic externally but hydrophilic internally
allows influx of solutes and water across lipid bilayer
results in cell lysis
Antibody complement activation
Igm > IgG3> IgG1> IgG2: IgG 4 does not bind
regulation occurs in what stages of the classical pathway
AMPLIFICATION
MAC
ACTIVATION
how is the classical pathway regulated
by inhibitors that act directly on activated complement components
by rapid disassociation of newly formed complement complexes
by transient binding sites of activated components
what inhibitor affects the Activation complex amd regulates it
C1 inhibitor; short life span of C2b ; transient binding site of C4b
Amplification stage what regulates it
action of factor I; short life span of C3b
cell surface inhibitors eg decay accelerating factors (DAF) prevents assembly and promotes dissociation of the C3 convertase components
what regulates the membrane attack complex
action of plasma and membrane bound inhibitors
