Grouping of
blood on the basis of nature of proteins present on the surface of RBC is called
as blood group. The protein on the surface of RBC is called as antigen. With
respect to the antigen present on the surface of RBC compatible protein is
found in plasma. The protein in plasma is called as antibody. The antigens are
denoted by capital alphabets while antibodies are denoted by small alphabets.
There are many systems of blood grouping as more than 40 different types of
antigens are found on the surface of RBC. However, ABO – system and Rh- system of grouping are
of great importance for blood transfusion.
The ABO-
system of blood grouping was first introduced by Karl Landsteiner in 1900 AD and
introduced three blood groups A, B and O. Later in 1902 AD Decastello and sturlii introduced another group AB. In 1930 AD Karl Landsteiner was awarded Nobel Prize for his discovery.
introduced three blood groups A, B and O. Later in 1902 AD Decastello and sturlii introduced another group AB. In 1930 AD Karl Landsteiner was awarded Nobel Prize for his discovery.
If antigen A
is on the surface of RBC blood group is A, if antigen B is on the surface of
RBC blood group is B, if both antigen A & B are on the surface of RBC the
blood group is AB and if both antigen A & B are not present on the surface
of RBC the blood group is O.
Table blood group, showing antigen and antibody
Blood group
|
Antigen on the surface of RBC
|
Antibody in Plasma
|
A
|
A
|
b
|
B
|
B
|
a
|
AB
|
A & B
|
X
|
O
|
X
|
a & b
|
Blood transfusion: - During blood transfusion the antigens of donors must be compatible with the antibodies of recipients. If they are not compatible with each other the RBC of donors agglutinate and it may results in the death of the person. The blood transfusion can be done as in the table listed below:
Donors(
antigens)
|
|||||
Group-A
( A)
|
Group-B
(B)
|
Group-AB
(A & B)
|
Group-O
(X)
|
||
Recipients(antibodies)
|
Group-A
(b)
|
Yes
|
No
|
No
|
Yes
|
Group-B
(a)
|
No
|
Yes
|
No
|
Yes
|
|
Group-AB
(X)
|
Yes
|
Yes
|
Yes
|
Yes
|
|
Group-O
(a & b)
|
No
|
No
|
No
|
Yes
|
|
From this table, we came to know that O group blood can be
given to any blood group as it has no antigens on the surface of RBC. Thus, it
is called as universal donor. The AB group blood can receive any blood group as
it has no antibody in plasma. Thus, it is called as universal recipient.
Identification of blood group:
To identify blood group the blood is mixed in serum of
antibody-a and antibody-b separately. If
the blood agglutinates with antibody-a and does not agglutinate with antibody-b
then the blood is of group-A. If the blood agglutinates with antibody-b and
does not agglutinate with antibody-a then the blood is of group-B. If the blood
agglutinates with both antibody-a and antibody-b then the blood is of group-AB.
If the blood does not agglutinate with both antibody-a and antibody-b then the
blood is of group-O. This can be summarized as in the following table:
Blood group
|
Antibody-a
|
Antibody-b
|
A
|
Agglutinated
|
Non-agglutinated
|
B
|
Non-agglutinated
|
Agglutinated
|
AB
|
Agglutinated
|
Agglutinated
|
O
|
Non-agglutinated
|
Non-agglutinated
|
Inheritance of blood group: Human blood group
is represented by gene I which stands for Iso-haemoagglutinogene and it
has three alleles which are IA, IB and IO. The
IA is for blood group-A, The IB is for blood group-B
while IO is for blood group-O. The alleles IA and IB
are co-dominant with each other while both are dominant over IO.
From these three alleles following six different allelic pairs can be formed
and they represent for different blood groups as in the table.
Allelic pairs
|
Condition
|
Blood group
|
IAIA
|
Homozygous
|
A
|
IAIO
|
Heterozygous
|
A
|
IBIB
|
Homozygous
|
B
|
IBIO
|
Heterozygous
|
B
|
IAIB
|
Co-dominance
|
AB
|
IOIO
|
Homozygous
|
O
|
Example:- When a man with blood group heterozygous A
get married with a woman of blood group heterozygous B, what are the probable
blood groups in children?
Parents: Heterozygous-A Heterozygous-B
Allels: IAIO IBIO
Gametes: IA IO IB IO
Children: IAIB IAIO IBIO IOIO
Blood group: AB A B O
Thus,
the probable blood groups are AB, heterozygous-A, heterozygous-B and O.
Rh- Factor: - In 1940 AD, Karl Landsteiner and Weiner identified a new
antigen on the surface of RBC of Rhesus monkey ( Macca rhesus) and named it as
Rhesus antigen or Rh- antigen or Rh- factor. This antigen is also found on the
surface of human RBC. About 85% human are with Rh- antigen on their RBC. Persons
with Rh-antigen are called as Rh-positive (Rh+) while without
Rh-antigen are called as Rh-negative (Rh-). The Rh+ and Rh- blood
are incompatible with each other and cannot be mixed with each other. The
Rh-antigen has great importance during blood transfusion and pregnancy.
Erythroblastosis foetalis:- The Rh- factor is also inheritable and creates
serious problem when a Rh-negative woman get married with a Rh-positive man. If
the woman conceives a Rh-positive foetus, the Rh-factorwill pass into mother's
circulation through placenta and stimulates Rh-antibodies formation in mother's
body. As the number of Rh-antibodies produced during first pregnancy is less,
the first Rh-positive child becomes normal.
If
the woman again conceives with a Rh-positive child, the results may be
dangerous. When the Rh-positive blood passes into mother's circulation, more
Rh-antibodies are formed and some Rh-antibodies will pass into foetus through
placenta. The Rh-antibodies react with Rh-antigen and it causes agglutination
of RBC which may results into the death of the developing foetus. This is
called as erythroblastosis foetalis.