A1 and A2 subgroups

The distinction between the A1 and A2 subgroups is usually made by using anti-A1, which will agglutinate A1, but not A2, red cells. Anti-Al can be obtained in several ways: (i) it can be made by absorbing anti-A (from group B people) with A2 red cells; (ii)

Table 15.3 ABO grouping.

Agglutination of test cells with

Agglutination by test serum of

ABO group of test sample

Possible genotype

Anti-A Anti-Al Anti-B

Anti-A,B*

A cells B cells O cells

_ _ _

_

+ + -

O

O/O

+ + _

++

- + -t

Ai

Al/Al, A1/O, A1/A2

+ _ _

+

-/+* + -

A2

A2/A2, A2/O

_ _ +

+

+ - -

B

B/B, B/O

+ + +

+

- - -t

AiB

A1/B

+ _ +

+

_/+* - -

a2b

A2/B

*Anti-A,B (group O serum) is not generally used in routine laboratories.

fSome group A1 and AjB individuals may have weak anti-H in their plasma.

*Serum from a proportion of A2 (1-8%) and A2B (22-35%) individuals will contain anti-AJ.

*Anti-A,B (group O serum) is not generally used in routine laboratories.

fSome group A1 and AjB individuals may have weak anti-H in their plasma.

*Serum from a proportion of A2 (1-8%) and A2B (22-35%) individuals will contain anti-AJ.

it is found in the serum of some A2 and A2B persons (Table 15.3); (iii) it can be made from a saline extract of the seeds of the hyacinth bean, Dolichos biflorus; and (iv) mouse monoclonal anti-A1. Anti-A1 is not used routinely as it is not necessary to distinguish group A1 from group A2 blood for most transfusion recipients. There is no specific antibody for A2 red cells; if anti-A is absorbed with A1 cells, all the antibody is removed. Group B serum can therefore be thought of as containing two antibodies: anti-A, which agglutinates both A1 and A2 red cells, and anti-A1, which agglutinates only A1 red cells. The anti-A component of group O serum also has both antibodies.

The presence of the A2 allele in the presence of A1 cannot be determined by serology. Among people who are genotypically A/O or A/B, approximately three possess the A1 gene for every one who possesses A2 (Table 15.2).

The difference between the A1 and A2 subgroups is partly quantitative: the red cells of A1 and A1B subjects have more A antigen sites than A2 and A2B subjects respectively (Table 15.4). There is also good evidence for a qualitative difference between

A1 and A2. Relatively low abundance A-active oligosaccharide structures, called repetitive type 3A and type 4A (see p. 230) are present on A1, but not A2 red cells. This qualitative difference must be very subtle, because A2 red cells can absorb all the anti-A from group B serum if the absorption is carried out at 0-4°C for sufficient time.

For practical purposes, A2 can be regarded as a weaker form of A. Table 15.4 shows quantitative differences in the number of A antigen sites on A1 and A2 red cells. The table also shows that when both the A and B antigens are present, there are less sites for each than when either is present alone. The practical importance of this lies in the fact that the A antigen of A2B red cells may give an extremely weak reaction with anti-A, which could be missed in routine grouping tests if reagents of inadequate potency are used. Moreover, if the same person's serum contains anti-A1 and is tested in the reverse grouping only with A1 and not A2 red cells, they will be grouped as B. For this reason, potent anti-A reagents reacting with A2B cells should be used in routine blood grouping.

Table 15.4 Numbers of A and B antigen sites on red cells of various ABO groups.

Blood group of red cell Approx. no. of Approx. no. of

A antigen sites B antigen sites

Table 15.4 Numbers of A and B antigen sites on red cells of various ABO groups.

Blood group of red cell Approx. no. of Approx. no. of

A antigen sites B antigen sites

A1 adult

1 000 000

-

A1 cord

300 000

-

A1B adult

500 000

-

A1B cord

220 000

-

A2 adult

250 000

-

A2 cord

140 000

-

A2B adult

120 000

400 000

B adult

-

700 000

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Responses

  • marta folliero
    Why is anti h present in a1 and a1b?
    3 years ago
  • EVELYN
    Why is there no specifiC antibody for a2 red cElls?
    3 years ago
  • Hilda Hogpen
    Who discover in sub group a1 or a2?
    3 years ago
  • celedor
    What is different btween antigen a1 and a2?
    2 years ago
  • senay
    Why are A1 and A2 quantitively and qualitatively different?
    2 years ago
  • seija
    HOW TO RESOLVE A1 A2 SUBGROUP?
    1 year ago
  • Cipriano
    How to resolve antia1 antibody?
    7 months ago
  • neive
    What should the subgroup of a lectin and a2 be?
    30 days ago

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