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Blood Bank CCF > Lewis Blood Group > Flashcards

Lewis Blood Group Flashcards

Exam 1

1
Q

What is unique about the way Lewis antigens are formed on the red cell?

A

They are not manufactured by the red cell itself, but instead made by tissue cells which secrete them into body fluid. The antigens are then absorbed onto RBCs.

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2
Q

What is the purpose of the secretor gene and how does it differ from the H gene?

A

It adds the H antigen to the type 1 precursor chain, it differs from H in that it adds H antigen to the type 1 precursor chain whereas H adds to the type 2 precursor chain. They both add L-fucose to the chain.

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3
Q

What does the Lewis gene (Le) code for?

A

The enzyme a-4-L-fucosyltransferase which adds L-fucose to GlcNAc of the precursor chain

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4
Q

How is the Le(a) antigen formed?

A

When only the Lewis enzyme is able to act on the type 1 chain

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5
Q

How is the Le(b) antigen formed?

A

When both the Secretor and Lewis enzymes are able to act on the type 1 chain.

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6
Q

If both enzymes (Secretor and Lewis) are present, which will usually act on the type 1 chain first?

A

Secretor

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7
Q

If an individual inherits both the Lewis and Secretor genes, what will their Lewis phenotype be?

A

Le(a-b+)

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8
Q

Is an Le(a-b+) individual truly Le(a-)? Why?

A

No, there is a small undetectable amount of Le(a) antigen present. It is undetectable because the secretor enzyme is able to outcompete the Lewis enzyme most of the time converting most type 1 chains to the Le(b) antigen. However, a very small amount of type 1 chains get converted by the Lewis enzyme first creating Le(a) antigen.

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9
Q

If an individual only inherits the Lewis gene, what will their Lewis phenotype be?

A

Le(a+b-)

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10
Q

If an individual only inherits the Secretor gene, what will their Lewis phenotype be?

A

Le(a-b-)

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11
Q

How does the Secretor gene effect ABO antigens in secretions?

A

Inheriting the secretor gene is what allows individuals to express ABO antigens in secretions, without it, there are no expression of ABO antigens

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12
Q

How does the Secretor gene effect the presence of Lewis antigens in secretions?

A

Lewis antigens are present in secretions no matter what and therefore the secretor gene does not effect this. If the individual has no secretor gene, they will still secrete the Le(a) antigen. They will however be unable to create and secrete the Le(b) antigen.

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13
Q

Is the Le(a+b-) phenotype considered to be a secretor or nonsecretor?

A

Nonsecretor

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14
Q

Is the Le(a-b+) phenotype considered to be a secretor or nonsecretor?

A

Secretor

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15
Q

Is the Le(a-b-) phenotype considered to be a secretor or nonsecretor?

A

Can be either. Since they have no Lewis gene they cannot form any of the Lewis antigens, however they can form and secrete ABO antigens. If they inherit the Secretor gene they will be a secretor, if they do not, they will be a nonsecretor.

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16
Q

Describe the Lewis antigen development from birth to adulthood.

A

At birth: phenotype as Le(a-b-), At 10 days old: Lewis enzyme becomes active giving a phenotype of Le(a+b-) if Lewis gene is inherited, 1-6 years old: Secretor enzyme (if inherited) slowly becomes more active, during this time children may phenotype as Le(a+b+), 6 years old: Enzymes reach their normal level of activity, therefore if both were inherited, the individual will be Le(a-b+)

17
Q

At what temperature do Lewis antibodies react best?

A

Room temperature or colder

18
Q

Are Lewis antibodies naturally occurring or immune antibodies?

A

Naturally occurring

19
Q

Are Lewis antibodies usually IgM or IgG?

A

IgM, occasionally IgG

20
Q

Is Lewis reactivity increased or decreased by enzymes?

A

Increased

21
Q

Which phenotype is most likely to make anti-Le(a)?

A

Le(a-b-)

22
Q

Why is anti-Lea almost never seen in Le(a-b+) individuals?

A

Individuals with this phenotype still make a small amount of Le(a) that is undetectable therefore their bodies do not recognize the Le(a) antigen as foreign

23
Q

Describe the difference in reactivity between anti-LebH and anti-LebL.

A

Anti-LebH- reacts best with both Le(b) and H present on the RBC, Anti-LebL- reacts with Le(b) regardless of the amount of H antigen

24
Q

Which blood types react strongest with anti-LebH?

A

Group O or A2 (they have the highest amounts of H)

25
Q

What can happen to the mother’s Lewis antigens during pregnancy?

A

They can decrease in strength resulting in the phenotype Le(a-b-)

26
Q

Describe the neutralization technique.

A

Soluble Lewis antigen (usually from saliva) is mixed with the Lewis antibody in plasma, the antigen binds the antibody removing the antibody from the plasma, the plasma can then be mixed with reagent RBCs for normal testing without the Lewis antibody interfering with testing.

27
Q

Why are the Lewis antibodies not a concern in HDFN?

A

IgM molecules are too big to cross the placenta and even if some IgG do cross, babies do not express Lewis antigens

28
Q

Why are the Lewis antibodies not a concern for TRXNs?

A

Most do not react at 37C and even if a patient has a Lewis antibody and the donor cells the corresponding antigen, the Lewis antigens can disassociate just as easily from the RBCs. The released antigens can neutralize the patient’s antibody.

29
Q

How is it possible for an individual to have the Le(a+b+) phenotype?

A

They must inherit a gene that creates a weaker secretor enzyme. They can be either SewSew or Sewse. The Lewis enzyme in this situation can more easily competing causing Le(a) and Le(b) antigen to be formed in equal amounts.

30
Q

What ethnicity is most likely to have the Sew allele?

A

Asians

31
Q

Which Lewis phenotype is most common among Caucasians and African Americans?

A

Le(a-b+)

32
Q

Which phenotype is much more likely to be seen in African Americans than in Caucasians?

A

Le(a-b-)

33
Q

What percentage of individuals are ABH secretors?

A

0.8

34
Q

Individuals that have the Le(a-b+) phenotype are more susceptible to what illness?

A

Helicobacter pylori (stomach ulcers)

Blood Bank CCF (26 decks)

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