5. ABO Blood Group System

Question 1

Genes control production of..

Answer 1

Glycosyltransferases - inherited glycotransferase results in addition or specific terminal sugar to an oligosaccharide chain containing L-fucose (H gene)

Question 2

H gene

Answer 2

• ABO system includes H gene with allele h
• Present as HH or Hh in 99.99%. of population
• hh genotype EXTREMELY rare Bombay phenotype Oh (types as “O”, anti-H antibody present)
  e. g. CAR ACCIDENT: give individual O blood despite the blood containing the H antigen

Question 3

Inheritance of H results in production of..

Answer 3

a-2-L-fucosyltransferase

** Adds L-fucose to terminal end of oligosaccharide chain bound to RBC membrane

Question 4

Blood Group A and B immunodominant sugars can only be added to structures with H sugar. Why?

Answer 4

Since H = precursor substance of A and B, Group A and B (and AB) people have less H than Group O people

Question 5

H - L-fucose (Blood type O = highest concentration of H)

Answer 5

Added by: α-2-L-fucosyl-transferase

Question 6

A - N-acetyl-D-galactosamine

Answer 6

Added by: N-acetylgalactosaminyltransferase

Question 7

B - D-galactose

Answer 7

Added by: D-galatosyltransferase

Question 8

Importance of ABO System

Answer 8

The ONLY blood group system in which reciprocal (or antithetical)
antibodies are consistently and predictably present in the serum of all* individuals

Question 9

Ag on RBCs

Answer 9

Group O – H
Group A – A, H
Group B – B, H
Group AB – A, B, H

Question 10

Ab in serum/plasma

Answer 10

Group O – anti-A, anti-B, anti-A,B
Group A – anti-B
Group B – anti-A
Group AB – none

Question 11

Natural formation of ABO antibodies is due to..

Answer 11

Immune stimulation (probably continual) by substances ubiquitous in nature (eg: bacteria, fungi, pollen)

Question 12

Problematic for transfusion IgM (complement activating)

Answer 12

ABO incompatible blood can result in immediate intravascular hemolysis that can result in death of the recipient

Question 13

IgM antibodies

Answer 13

• Pentamer
• Prefer cold temperatures (RT, 4 degrees celsius)
• Complement activating – RBC destruction

Question 14

MOST IMPORTANT

Answer 14

• Antigens present at birth
• Antibody titer increases after birth
• Mostly IgM Antibody (IgG component also present)
• ABO incompatibility is a major cause of death in BB (usually preventable if done accurately – try to avoid human error)

Question 15

Antigens: 3 Allelic genes determine 2 ags (present at birth)

Answer 15

Inherit one gene from each parent – codominant
Example AO x BO
Offspring can be
OO, AO, BO, AB
Exceptions - rare
Bombay Blood Type
hh - no H substance
Make an anti-H => reacts with all O, A, B, AB cells

Question 16

Antibodies

Answer 16

Mostly IgM with small amounts of IgG (naturally occurring)

• • Anti-A,B (not routinely used) – ABO confirmation of O units, working up ABO discrepancies
• • Anti-H – cold reactive

Question 17

Forward Blood Grouping

Answer 17

Known antisera (antibodies) to determine unknown antigens; tests red cells of unknown type with known reagent antisera

Question 18

Reverse Grouping

Answer 18

Known antigen to determine unknown antibodies; test plasma of unknown type with known reagent A1 and B cells

Question 19

Selecting RBCs for transfusion – Questions to ask:

Answer 19

What ABO antibodies are in the recipient’s plasma?
What ABO antigens are present on the donor’s RBCs?

Y = okay to transfuse
N = do not transfuse