ABO Blood Groups

Question 1

Name and construct antigens on the RBC in the ABO system: A, B, and H antigens

Answer 1

See pic

Question 1

Given phenotypic expression of ABO antigens, predict ABO blood types of offspring from various mating combos.

Answer 1

See pic

Question 2

Forward typing

Answer 2

Use commercial anti-sera (Ab) against patients RBCs to detect blood group antigen

Question 3

Reverse typing

Answer 3

Use patient sera against commercial RBCs (A1 and B cells) to see which Ab the patient produces

Question 4

Word of the day

Bombay

Answer 4

• Rare phenotype first described in Bombay, India where pt does not express A, B, or H antigen
• These pt still have ABO genes that can be transferred to offspring but just can’t express them on RBC bc no H antigen to lock onto

Question 5

Parabombay

Answer 5

• These pt have no H Ag on RBCs but may express small amounts of A or B Ag on RBC surface bc FUT2 generates small amounts of secrete A or B Ag that can absorb onto RBC (type I chain)
• Or caused by FUT1 that makes fucosyltransferase with very low activity

Question 6

Type I substances

Answer 6

Secretions, can be absorbed onto RBCs, FUT2

Question 7

Type II substances

Answer 7

Directly linked to RBC, FUT1

Question 8

On which chromosome is the ABO gene found?

Answer 8

Chromosome 9

Question 9

What does the ABO gene encode?

Answer 9

Encodes a glycosyltransferase that adds an N-terminal sugar to the end of H Ag attached to RBC

Question 10

A transferase adds which sugar to H Ag?

Answer 10

N-acetyl-galactosamine (GalNAc)

Question 11

B transferase adds which sugar to H Ag?

Answer 11

Galactose

Question 12

If a stop codon is within the ABO gene, what does this imply?

Answer 12

• No transferase is created, thus no sugar added to Type II substance
• Patient is Type O

Question 13

The H gene is found on which chromosome?

Answer 13

Chromosome 19

Question 14

What does the H gene encode?

Answer 14

Fucosyltransferase that adds a fucose to outer-most sugar of a Type I or Type 2 precursor chain

Question 15

T/F
The more H substance transferred to an A or B antigen, less detectible the H Ag

Answer 15

True

Question 16

List the H Ag detectability in each blood type from greatest to lowest detectability

Answer 16

O > A2 > B > A2B > A1 > A1B

Question 17

Why is H Ag not easily detectable in A1 or A1B patients?

Answer 17

• Because almost all H Ag sites are converted to A1 or B, thus serologically masking H Ag
• A1 and H have an inverse reciprocal relationship (more A1, less H)

Question 18

T/F
Type 2 chain precursor can express A or B without conversion to H Ag

Answer 18

False
Must convert to H Ag before A or B can be expressed

Question 19

T/F
As patients mature, Type 2 substance can become more branchy

Answer 19

True

Question 20

Subgroup

Answer 20

When a pt may appear a weaker version of the blood type due to fewer branchy H Ag transferred to A or B

Question 21

What would cause a patient to form an antibody against anti-branchy H?

Answer 21

If only linear H Ag is transferred to A or B, then the branchy H may appear foreign if introduced through transfusion

Question 22

List the 2 most common A phenotypes

Answer 22

• A1 = 80-90%
• A2

Question 23

Describe the A1 phenotype

Answer 23

• Branched A Ag (means that A attached to branched H Ag)
• More A1/RBC than A2/RBC
• Positive with anti-A Ab
• Positive with anti-A1 lectin
• Highly functioning A transferase transfers N-terminal sugar to branchy or linear H Ag no problem
• Most common Ag expression of A

Question 24

Describe the A2 phenotype

Answer 24

- Linear A antigens (means that A attached to linear H Ag) - Fewer A2/RBC than A1/RBC - Positive with anti-A Ab - Negative with anti-A1 lectin - Weaker A transferase only transfers N-terminal sugar to linear H Ag - Second most common expression of A

Question 25

anti-A1 lectin

Answer 25

- Plant-derived compound with the purpose of distinguishing between A1 and A2 blood types - Positively reacts with A1 and negatively reacts with A2 bc it detects branchy substances

Question 26

**T/F** B subgroups are more common than A subgroups

Answer 26

False A subgroups (20% of time) are more common than B subgroups

Question 27

Which A subgroups weakly agglutinate with anti-A and/or anti-A,B?

Answer 27

- A3 - Aend - Ax

Question 28

Which A subgroups show no agglutination and must be detected by elution testing?

Answer 28

- Am - Ay - Ael

Question 29

A3 subgroup

Answer 29

- Mixed-field appearance (some parts agglutinate and some do not, appearing smoky) - 35k Ag - May make anti-A1 and secrete A Ag

Question 30

Aend subgroup

Answer 30

- 10% RBCs hav enough A Ag to agglutinate serologically - About 3,500 Ag

Question 31

Ax subgroup

Answer 31

- **Does not** agglutinate with anti-A - **Does** agglutinate with anti-A,B - 4k Ag - Almost always have anti-A1 in serum

Question 32

Am

Answer 32

- Do not react strongly serologically - No anti-A1 in serum - Have detectable amounts of A enzyme in serum - 200-300 Ag

Question 33

Ay

Answer 33

- **Does not** agglutinate serologically with anti-A - **Does** secrete A Ag in saliva - Recessive - No anti-A1

Question 34

Ael

Answer 34

- Ag presence only detectible by adsorption/elution procedures - Have Ab that reacts with A1 and sometimes A2 cells - Only H substance in secretors and no A Ag in saliva

Question 35

B subgroup

Answer 35

- Very efficient transferase activity - Strong serological activity - Detected by bandeirea simplicifolia lectin - 600k-800k Ag on RBC

Question 36

B3 subgroup

Answer 36

- Mixed field agglutination with anti-B and anti-A,B - Weak transferase - Does not make anti-B

Question 37

Bx subgroup

Answer 37

- Reacts weakly with anti-B and anti-A,B - NO detectible amounts of transferase - Makes weakly reactive anti-B Ab

Question 38

Bm subgroup

Answer 38

- Detectible transferase but does not work well - Normal amount of B Ag on secretions - No anti-B detected (more freq in Japan)

Question 39

Bel subgroup

Answer 39

- Must be detected by adsorption and elution studies - Weak anti-B may be present - B Ag not in secretions

Question 40

Why is there no B2 subgroup?

Answer 40

Bc no anti-B2 lectin exists to detect B attached to branchy H Ag

Question 41

Which lectin detects A1?

Answer 41

Dolichos biflorus

Question 42

Which lectin detects B?

Answer 42

Bandeiraea simplicifolia

Question 43

Which lectin detects H?

Answer 43

Ulex europaeus

Question 44

Describe Cis-AB anomaly

Answer 44

- Rare splicing anomaly - A and B transferases are inherited on the same chromosome - Can pass AB blood type with O mate and can possibly produce type O children

Question 45

Describe B(A) pt anomaly

Answer 45

- Mainly B antigen with some A present - Transferase prefers to transfer galactose but can also transfer GalNAc - Genetic variant of B gene - Polyclonal anti-sera

Question 46

Describe acquired B pt anomaly

Answer 46

- If patient is originally A1 but has colon/rectal cancer, intestinal obstruction, gram-neg septicemia, then this can cause breakage of Ag to look like B Ag in a few RBCs - Mostly apparant with acified anti-sera

Question 47

Give example of acquired B anomaly

Answer 47

If pt is infected with E.coli, the bacteria have a deacetylating enzyme that removes the acetyl group from the A sugar, leaving a sugar that resembles D-galactose (appearance B)

Question 48

What does acquired B anomaly look like serologically?

Answer 48

- anti-A: 4+ - anti-B: 1+ - anti-A, B: 4+

Question 49

Why is the ABO system important?

Answer 49

- ABO system is the ONLY system where reciprocal (antithetical) Ab are consistent and predictable - Ab present in human plasma that have not been exposed to other human Ag (naturally occurring)