ABO discrepancies pt1

ABO subgroups represent

Phenotypes that show weaker variable serologic reactivity with commonly used human polyclonal anti-a, anti-b and anti-a,b

Inheritance of ABO subgroups

Alternate allele at the A or B locus

_ subgroups are more common than B subgroups

A

Lectins

Seed extracts that agglutinate human cells with some degree of specificity

A1 lectin

Dolichos biflorus: agglutinates A1 and A1B

B lectin

Griffonia(banderiaea) simplicifolia: agglutinates B cells

H lectin

Ulex europaeus: agglutinates O cells (H specificity) and other ABO groups based on H antigen sites available

H lectin reacting strength

O>A2>B>A2b>A1>A1B

A subgroups are _% A1 or A1B

80

A subgroups are _% A2 or A2B

20

Quantitative difference between A1 and A2

Decreased # of antigen sites, lower amount of transferase enzyme, and lower amount of branching

Qualitative difference between A1 and A2

difference in precursor oligosaccharide chains, subtle difference in transferase enzyme, and formation of anti-a1 in some subgroups

Inheritance of the A1 gene elicits production of

High concentrations of 3-N-acetylgalactosaminyltransferase which converts all of the H precursor to A1 antigens

A1 antigen sites

810,000-1,170,000

A2 antigen sites

240,000-290,000

Immunodominant sugar for both A1 and A2

N-acetly-D-galactosamine

Difference between A1 and A2

Concentration of 3-N-acetylgalactosaminyltransferase

_% of A2 produce anti-A1

1-8%

_% of A2B produce Anti-A1

22-35%

How is human based Anti-A1 antisera made?

Group B plasma is mixed with A2 cells, anti-a is absorbed into the cells and anti-A1 stays in the serum. Centrifuge, remove the A2 cells, and anti-a1 is left

Anti-A1 lectin resembles

The action of a specific antibody but is not one, it only agglutinates with A1 cells but not A2 cells

Compatible units for an A2 subgroup

1st A2

2nd O

Compatible units for an A2B person

1st: A2 or A2B

2nd: B

3rd: O

Which A type would be more compatible with O platelet products and why?

A2 because they lack the A1 antigen that O makes an antibody to

Besides AB, what group is also considered universal platelet donors?

A2

Subgroups of B are

Very rare

Classifications of B subgroups are made by

Alternate alleles at the B locus

Criteria used to determine weak B phenotypes (5)

Strength of anti-b, anti-a,b, and anti-h

Presence or a sense of ABO isoagglutinins in serum (back typing)

Absorption in elution studies

B soluble substance in saliva

If galactose gene is present

Bombay genotype defect

Defect in FUT1 (H gene) and FUT2 (secretor gene)

Bombay inheritance

hh usually occurs in children of consanguineous marriages

Can be classic or para-bombay

Classic bombay

Can inherit ABO genes (written with superscripts)

Para-bombay

Rare; mutated FUT1 gene with or without FUT2

Mutation has the L-Fucose enzyme reduced that can have small traces of H, A, and B antigens (detected by elution)

Bombay red cell reactions

Fail to react with anti-a, anti-b, and anti-H

Bombay serum reactions

Contains anti-a, anti-b, anti-a,b , and anti-h (very potent and reacts at 37°)

Transfusion to Bombay individual

Normal O red cells would cause immediate lysis (IgM)

Only Bombay blood will be compatible

Bombay screening reactions

Screen and cross match: all reaction

Auto control: negative

A3 forward type reactions

Anti a: ++mf

Anti-b: 0

Anti-a,b: ++ mf

Anti-H: 3+

A3 reverse type reactions

Anti-A: no

Anti-B: yes

Anti-a1: sometimes

Substances present in saliva of A3

A,H

A3 number of antigen sites

35

Ax forward type reactions

Anti-a: wk/0

Anti-b: 0

Anti-a,b: 2+

Anti-h: 4+

Ax reverse type reactions

Anti-a: 0/wk

Anti-b: yes

Anti-a1: almost always

Substances in saliva of Ax

H

Ax antigen sites

5

Ay forward type reactions

Negative for all except anti-h

Ay reverse type reactions

Only anti-b +

Substances in saliva of Ay*

A and H*

Number of antigen sites in Ay

1

A(el) forward type

Same as Ay

A(el) reverse type

Anti-a: some

Anti-b: yes

Anti-a1: yes

Substances present in Ael saliva

H

Number of antigen sites for A(el)

0.7

B3 forward reaction

Anti-A: 0

Anti-b: ++mf

Anti-a,b: ++mf

Anti-h: 3+

B3 serum antibodies present

Anti-a

Substances present in saliva of B3

B and H