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Book - Transfusion Medicine for Pathologists > Ch. 5 - Red cell antigens > Flashcards

Ch. 5 - Red cell antigens Flashcards

1
Q

How many blood group systems are there? How many blood group antigens?

A

At least 30 blood groups, with >284 blood group antigens.

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2
Q

What genes are responsible for the H-antigen on red cells? What about in secreted products?

A

FUT1: Encodes a fucosyltransferase that acts on type 2 carbohydrate precursor chains on cells.

FUT2 (Se): Encodes a fucosyltransferase that acts on type 1 carbohydrate precursor on secreted products.

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3
Q

What is the bombay phenotype?

Para-bombay?

A

Bombay: hhsese genotype, with no functional FUT1 or FUT2 resulting in no expression of H antigen.

Para-bombay: No functional FUT1 but may have FUT2. Lack H antigen on RBCs but possess them in secretions.

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4
Q

What is the association between leukocyte adhesion deficiency (LAD) and bombay phenotype?

A

A subtype of LAD with mutation in GDP-fucose transporter SLC35C1 results in a Bombay-like phenotype and loss of leukocyte CD15 & sialyl-LeX.

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5
Q

Recall the amount of H expression of different blood groups (list in highest to least expression)

A

O > A2 > B > A2B > A1 > A1B > H+ > null (Bombay)

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6
Q

What genes (and gene products) are responsible for the A/B blood antigens?

A

ABO*A&raquo_space; N-acetylgalactoseamine transferase

ABO*B&raquo_space; Galactose transferase

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7
Q

What causes acquired B antigen?

A

Bacterial infection and deacetylation of blood group A (terminal N-acetylgalactosamine) into blood group B (galactose).

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8
Q

What is the difference between A1 and A2 phenotypes?

A

A1 individuals have a more efficient N-acetylgalactosaminotransferase resulting in increased conversion of H to A. Qualitative differences also result in A1-lectin binding.

A2 individuals also will therefore have more H antigen.

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9
Q

What is the rate of A and B expression in whites, blacks, and asians?

A

Whites: 43% express A, 9% express B
Blacks: 27% express A, 20% express B
Asians: 27% express A, 27% express B

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10
Q

When are ABO antigens fully expressed in childhood?

A

Detectable as early as 5-6 weeks of gestation, reach adult levels of expression by 2-4yrs.

Antibodies:

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11
Q

What is the B(A) phenotype?

A

Weak expression of A antigen on group B cells. Results from a mutation in the B-galactosyltransferase that allows it to transfer N-acetylgalactoasamine.

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12
Q

What gene encodes the Lewis antigens (A and B?)

A

FUT3 (only one gene)

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13
Q

What is the difference between LeA and LeB?

A

LeA results from FUT3’s effects on type I chains (prior to the effect of FUT2). LeB results from FUT3’s effects AFTEr the effect of FUT2.

LeA cannot be changed to LeB, nor vice versa. Secretors (those with FUT2) will preferentially make LeB.

(both of these may be converted to A/B LeA/B)

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14
Q

What are the main three Lewis phenotypes?

A

Le(a+b-): Functional lewis gene (FUT3), no Se (FUT2)
Le(a-b+): Functional lewis gene (FUT3) and Se (FUT2)
Le(a-b-): No functional lewis gene (FUT3)

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15
Q

What is the prevalence of the LeA antigen in whites and blacks? LeB?

A

LeA: 22% in both caucasians and blacks.
LeB: 72% in caucasians, 55% in blacks.

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16
Q

What are some infectious associations regarding the Lewis antibodies?

A

H. Pylori attaches to gastric mucosa with Leb
Norwalk virus also has tropism for Leb

Le(a-b-) people are at risk for Candida and E. coli infection.

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17
Q

What happens to the Lewis antigens during pregnancy? In transfusion? In childhood?

A

Pregnant patients have decreasing Lewis antigen and may form transient antibodies against it.

Donated blood takes on the recipient’s Lewis phenotype due to passive transfer.

Children make more LeA initially, and so Le(a-b+) children may be briefly Le(a+b+)

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18
Q

Do Le(a-b+) individuals produce anti-Lea?

A

No, they still express LeA in small quantities.

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19
Q

What is the genetic basis of the I/i blood group system?

A

GCNT2, which encodes 6-b-N-acetylgalactosaminyltransferase. The action of this single protein on type 2 chains generates both I and i.

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20
Q

What are the possible I/i phenotypes?

A

I (I+), normally seen in adults (or by 2yrs of age).

i (I-), normally seen in children but can be seen in adults (known as iadult).

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21
Q

What are the two types of i(adult) phenotype?

A

With cataracts: Due to exon 2/3 mutation, results in loss of I in all tissues. More common in asians.

WIthout cataracts: Due to exon 1c mutation, only loss of I in RBCs.

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22
Q

Recall the major associations of Auto-anti-I and auto-anti-i.

A

Auto-anti-I: Cold agglutinin disease, mycoplasma pneumonia infection

Auto-anti-i: Infectious mononucleosis.

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23
Q

Describe the genetics underlying the P1PK blood group system.

A

A4GALT encodes one polymorphic (P1), one high-prevalence (Pk), and one low-prevalence (NOR) gene.

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24
Q

What are the infectious associations of the P1PK blood group system?

A

All three antigens act as receptors for UTEC.
P1 and Pk are receptors for streptococcus suis
Pk is a receptor for shiga toxin (but may be HIV-protective)
P antigen is a receptor for Parvovirus B19

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25
Q

What are the most common P1PK phenotypes?

A

P1 (P+, P1+, Pk+): 80%

P2 (P+, P1-, Pk+): 20%

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26
Q

In who are anti-P1 antibodies elevated?

In what context are auto-anti-P antibodies seen?

A

Those with hydatid cyst disease and bird handlers (bird feces contains a P1-like substance).

Auto-anti-P is seen in paroxysmal cold hemoglobinuria (Donath-Landsteiner antibodies bind at cold temperature, then hemolyze at warm temperature).

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27
Q

How many antigens are within the Rh system?

A

52 antigens (14 polymorphic, 26 low prevalence, 12 high prevalence)

28
Q

What is RhAG?

A

RH-associated blood group, AKA CD241, which is important for expression of Rh antigens.

29
Q

Describe the genes that encode the Rh complex.

A

RHD and RHCE genes are found on chromosome 1 and encode two homologous multipass membrane proteins.

30
Q

What is the function of Rh and RhAG?

A

They complex and interact with band 3, GPA, GPB, LW, CD47, ankyrin, and protein 4.2 to promote erythrocyte membrane integrity.

31
Q

What does the presence of stomatocytes suggest on a peripheral blood smear with respect to blood group antigen polymorphisms?

A

Rh(null) phenotype

32
Q

What is the prevalence of the D antigen in whites, blacks, and asians?

A

Caucasians: 85%
Blacks: 92%
Asians: 99%

33
Q

What is weak D?

A

Reduced expression of D antigen which may type as D- but should be treated as D+ from donors.

34
Q

What is partial D?

A

D is missing some epitopes relative to the reference D antigen. They may type as D but can form anti-D when exposed to the reference D antigen.

35
Q

What is D(el)?

A

A rare extremely weak phenotype which cannot be detected by serology. Seen in asians (30% of asians that type D-).

36
Q

What is nonfunctional RHD?

A

A condition (in whites, due to a deleted RHD;in asians, due to inactivation of RHD; in blacks, due to a pseudogene stop codon) where there is no D expression?

37
Q

What is elevated D?

A

Enhanced expression due to partial replacement of RHCE by the RHD gene. As such, many will express reduced C/e and E/e.

38
Q

Recall the big four Wiener’s haplotypes by race.

A

Whites: R1 > r > R2 > R0
Blacks: R0 > r > R1 > R2
Asian: R1 > R2 > r > R0

39
Q

What causes the Rh(null) phenotype?

A

Changes in RhAG affect trafficking of RhD and RhCE to the membrane.

40
Q

What is the order of immunogenicity of the Rh antigens?

A

D > c > E > C > e

41
Q

What Rh antibodies are most often implicated in HDFN?

A

Anti-D and Anti-c

42
Q

Describe the genetic basis for the Kidd blood group. What antigens are there?

A

SLC14A1 encodes a protein with the codominant and antithetical antigens Jka and Jkb as well as a high prevalence antigen Jk3.

43
Q

What are the antigenic frequencies of Jka, Jkb, and Jk3? By race, of course.

A

Jka: 77% caucasians, 92% blacks, 72% asians
Jkb: 74% caucasians, 49% blacks, 76% asians
Jk3: Nearly 100%, only rare polynesians are negative.

44
Q

What is the function of the Kidd blood group?

A

It is a urea transporter (absence of Kidd results in resistance to lysis in 2M urea, with decreased ability to concentrate urea in urine).

45
Q

Describe the genetic basis for the MNS blood group system. What are the antigens?

A

GYPA and GYPB genes encode glycophorin A (which carries the M and N antigens) and glycophorin B (which carries the S/s and U antigens).

46
Q

What is the function of the MNS blood group? What disease associations does it have?

A

It provides the majority of negative electrostatic charge on RBCs. It is also a receptor for Plasmodium falciparum.

47
Q

What lectin acts against the N antigen?

What is the U antigen?

A

Vicia graminea

U is an almost universally expressed antigen and is only lost in those who also have no S/s.

48
Q

What MNS phenotype is most common in caucasians? In blacks?

A

Caucasians: M+N+S+s+
Blacks: M+N+S-s+

49
Q

What kinds of antibodies are directed against M/N? Against S/s/U?

A

M/N: Naturally occurring, IgM and IgG, insignificant.

S/s/U: IgG, significant.

50
Q

What kinds of antibodies are directed against Kidd?

A

IgG, often also IgM (can bind complement). Note that they frequently display anamnestic response.

51
Q

Describe the genetic basis of the Duffy blood group antigen. What is its function?

A

DARC gene encodes for two forms of a transmembrane chemokine receptor.

52
Q

What disease is associated with the Duffy blood group?

A

DARC is a receptor for Plasmodium. It may also effect susceptibility to HIV and risk of prostate cancer.

53
Q

What are the relative frequencies of the duffy phenotypes? For caucasians and blacks.

A

Fy(a+b+): Caucasians 49%, Blacks 1%
Fy(a-b+): Caucasians 34%, Blacks 22%
Fy(a+b-): Caucasians 17%, Blacks 9%
Fy(a-b-): Caucasians very rare, Blacks 68%

54
Q

What kinds of antibodies are directed against Duffy?

A

IgG and IgM (rare). Note that Fyb is much, much less immunogenic than Fya.

55
Q

What are the minor duffy antigens?

A

Fy3, Fy5, Fy6

56
Q

Kell blood group: How many antigens, what CD designation, and what gene?

A

34 antigens
CD238
KEL gene

57
Q

What is the function of the Kell blood group?

A

It is thought to play a role in cell signaling and impact red cell maturation and differentiation. Note that it is expressed in erythroid precursors.

58
Q

What are the features and cause of McLeod syndrome?

A

Hemolytic anemia, myopathy, acanthocytosis, and chorea, resulting from a mutation of the XK (Kx) anchor.

59
Q

What are the frequencies of the K and k antigens?

A

K: 9% in caucasians, 2% in blacks
k: 99.8% in caucasians, 100% in blacks

60
Q

What are the minor Kell antigens?

A

Kpa (low-frequency antigen)
Kpb (reference high-frequency antigen)
Kpc (low-frequency antigen)

Ku (universal antigen)

Jsa (low-frequency antigen)
Jsb (high-frequency reference)

61
Q

What is the K0 phenotype?

A

Loss of the Kell glycoprotein (K-, k-) but markedly increased anchor Kx.

62
Q

What kinds of antibodies are directed against Kell?

A

IgG, extremely immunogenic and drastically responsible for HDFN.

63
Q

For each phenotype, give the equivalent Fisher-Race / Wiener:

DCE
R1
r^y

A

DCE: Rz
R1: DCe
ry: dCE

64
Q

What four Wiener haplotypes are very low prevalence?

A

Rz
r’
r’’
ry

65
Q

What is the Kmod phenotype?

A

Markedly decreased Kell antigens (K, k) and moderately increased Kx

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