Download clinical significance of rc antibodies

Faculty of Allied Medical
Science
Blood Banking (MLBB 201)
CLINICAL
SIGNIFICANCE OF RC
ANTIBODIES
Prof. Dr. Nadia Aly Sadek
Director of Blood Bank Centre
Prof. in Haematology
MRI- University of Alexandria
Outcomes
By the end of this lecture, the students will
be able to:
 Clinical significance of rc antibodies.
 Factors affecting the clinical significance of
antibodies.
RC antibodies may be:
- Naturally occurring: not ellicited by any
stimulus
- Immune-induced: ellicited by blood
transfusion pregnancy, malignancy.
Thay are classified into:
- Alloantibodies: in response to an antigen
lacking on the individual RCs.
- Auto antibodies having specificity against
an antigen present on the individual’s own
RCs.
They are responsible for :1- Haemolytic Transfusion Reaction (HTR):
the antibody destroys antigen-positive
transfused RCs.
They are directed to ABO system, they are
IgM in nature hence, they can activate the
complement cascade causing intravascular
hemolysis.
2- Haemolytic disease of the fetus
and newborn (HDFN)

IgG maternally derived antibody is
directed against a paternally derivedantigen on the fetal or neonatal red cells,
crosses the placenta and destroys the fetal
RCs.
3- Hemolytic anaemia (HA)

An autoantibody against “ self “ antigens is
produced and causes increased red cell
destruction. These antibodies may be
warm reactive or react optimally in the
cold.
Factors affecting the clinical
significance of AbS
All antibodies bind to the appropriate
antigen. They are clinically significant
when they have the potential to initiate
accelerated destruction of RCs carrying
the cognate antigen whether it is immune,
naturally occurring or auto antibody.
Several factors play a role:
1- Antibody specificity
2- Concentration and avidity
3- Thermal amplitude: below 30 degrees, it
is not important.
4- IgG class/subclass (IgG1, IgG3)
5- Activity of of the mononuclear phagocytic
system
6- Antigen site density and mobility of the
antigen in the membrane.
7- Volume of RCs administered
8- Soluble blood group substances may
neutralize the Ab (Lewis substance).
Mechanisms of RC destruction
1- By Ab-dependent cytotoxic mechanism
2- Lysosomal enzymes released by
mononuclear cells effect the destruction,
however, both phagocytosis and
cytotoxicity may occur at the same time.
Antigen loss
This occurs when the Ab induces the loss of
its target Ag without significant damage to
the cells themselves.
This is also known as “depressed Ag”, “Ag
suppression” and “ antigenic modulation”.
This phenomenon has been observed for
multiple blood groups as well as Ags on
leukocytes, platelets and neoplastic cells.
Antigen loss is most often observed in the
Kell system, the Rh system may be also
involved. The DAT may be negative for
few days and then becomes weakly
positive.
Viral infection may decrease Kell synthesis
during erythropoiesis.
The spleen may participate in Ag loss.
Acquired changes in blood groups
1- Group A individuals may acquire a B Ag
and become AB. The B Ag is generally
weak and the A Ag is weakened.
This occurs in patients with GIT diseases,
especially cancer colon.
Bacterial enzymes in the blood remove the
acetyl group from D-acetyl galactosamine
(Group A Ag) to produce alpha galactose
(similar to blood group B Ag).
2- Weakening of A Ag is common in group A
patients with acute myeloid leukaemia
(AML). Sometimes 2 populations of cells
are present (A and …)
3- Modifications of ABH antigens are
manifest before the diagnosis of
malignancy and therefore indicate a preleukaemic state.
4- A or B Ags on RBCs can be abolished in
vitro by converting them back to H Ag by
enzymes such as chryseobacrterium
(A-zyme) or green coffeee beans (B-zyme).
This is the basis of the universal blood
group
Blood groups and diseases
- Group A individuals are more susceptible
to cancer stomach and colon. They have
hypoacidity, normally and need orange
juice and Vit B12 regularly.
- Group O individuals are more susceptible
to gastric and duodenal ulcers
(hyperacidity).
Study question
Write a short note about the Mechanisms of
RC destruction.
Assignments

Changes that occur in a blood bag
‫ايمن السعيد‬
Thank You