Blood group antigens Flashcards
1
Q
Carbohydrate antigens
A
- ABO, Lewis, H, I, i, M, N, P1
- affected by genes that encode enzymes (genes for protein antigens encode structural proteins)
- glycosyltransferases catalyze transfer of saccharides to carbohydrate precursor chains
- naturally occuring antibodies
- antibodies are usually IgM
- antibodies are usually reactive at room temperature
- “agglutinating” antibodies (not coating antibodies)
- react at IS
2
Q
H antigen
A
- made from type 1 (in serum and secretions) and type 2 (RBCs) carbohydrate chains by the enzyme products of the H (FUT1) and Se (FUT2) genes
- in secretions and in plasma, type 1 chains are converted into H antigen (1H) by enzymatic reaction (fucosylation) of the Se gene product (Fut2)
- on the surfaces of red cells, type 2 chains are converted to H antigen (2H) by fucosylation of H gene product (Fut1)
3
Q
Lewis antigens
A
- made from type 1 precursor by the enzyme product of Le (FUT3) gene
- secreted Leb and Lec are receptors for Norwalk virus and H pylori
- Lea is the Ca 19-9 epitope
4
Q
A and B antigens
A
- made from H antigen by the enzyme products of ABO gene
- the A allele encodes N-acetyl-galactosaminyl transferase that adds N-acetyl galactosamine (NAG) to H, resulting in A antigen
- the B allele encodes galactosyl transferase that adds D-galactose to H, resulting in B antigen
- the O allele does not encode a functional enzyme, and group O red cells contain abundant unaltered H antigen
5
Q
I and i antigens
A
- epitopes within the ABH antigens
- unbranched type 1 and type 2 oligosaccharides represent i antigen
- branched type 1 and 2 oligosaccharides are I antigens
- branched oligosaccharides (I) increase with age
- in neonates and cord blood, i antigen predominates
- in high red cell turnover states, a resurgence of i is sometimes observed
- increased postnatal i antigen expression is characteristic of
- congenital dyserythropoietic anemia (CDA) type II
- Blackfan-Diamond syndrome
6
Q
Protein antigens
A
- all the non-carbohydrate antigens, including Rh, Kidd, Kell, S, s, Duffy
- antibodies acquired only after exposure to products containing antigen
- antibodies are usually IgG
- reactive at 37 degrees
- “coating” not agglutinating antibodies
- react at AHG phase
7
Q
O blood group produce what antibodies
A
- produce naturally occuring anti A and anti B IgM
- also produce IgG anti AB, which can cause ABO related hemolytic disease of newborn, which is typically mild
8
Q
A blood group
A
- results from AA or AO genotype
- 2 principal subgroups are A1 and A2
- A1 cells express more A substance than A2 cells
- 80% of blood group A people have A1 phenotype
- A1 and A2 cells can be distinguished by strength of reaction with
- anti A1 reagent from serum of blood group B people
- Dolichos biflorus lectin, which has anti A1 activity
- Ulex europaeus, which has anti H activity (reacts with A2 more than A1)
- anti A1 can be found in serum of 5% of blood group A2 and 35% of A2B people
- anti A1 is usually clinically insignificant
9
Q
Bombay phenotype
A
- very rare
- has been seen in all populations
- no H produced in blood
- H produced in secretions if the Se gene is present
- the H deficient secretor is often called the para-Bombay phenotype
- these people produce a dangerous anti H
10
Q
Type 1 and 2 oligosaccharides
A
- Type 1 is unbound and found in secretions and in plasma
- Type 2 is found only on red cell surface
- unbranched type 1 and 2 oligosaccharides represent i antigen
- branched type 1 and 2 oligosaccharides are I antigens
11
Q
The H (FUT1) gene
- product
- relative amount of H antigen in different blood groups
A
- encodes fucosyl transferase; substrate is type 2 precursor, product is H (2H)
- when A gene product acts on H antigen, adding NAG, the A antigen results
- when B gene product acts on H antigen, adding GAL, the B antigen results
- relative amount of H antigen is as follows:
- O >> A2 > B > A2B >A1> A1B
12
Q
The Se (FUT2) gene
A
- encodes a fucosyl transferase: substrate is type 1 precursor, product is H (1H)
- it produces the secretion and plasma equivalent of H substance and is responsible for appearance of A, B, and H substances in secretions
- the Se gene is an amorph
- 80% of population has the Se allele and are secretors
- 20% are homozygous for se/se and are nonsecretors
13
Q
The Le (FUT3) gene
- how are Lea and Leb made
- Le(a-b+)
- expression on red cells
- expression changes with
- frequency of Le(a-b-) and Le(a+b+)
A
Encodes a fucosyl transferase: substrate is type 1 precursor and 1H, product is Lea and Leb
- Le fucosyl transferase adds fucose to type 1 precursor (in a different linkage than that catalyzed by Se) to make Lea
- the Le fucosyl transferase also can add fucose to 1H antigen to make Leb
- Thus
- Lea can be made if Le is present
- Leb is made only if both Se and Le are present
- in Le (a-b+) people, a minute amount of Lea is still made, such that anti Lea antibodies do not form
- though Lewis antigen is synthesized on free type 1 precursor substance, it becomes passively absorbed onto red cell surfaces
-
Le gene expression increases with age
- Lewis type cannot be reliably determined until 2nd birthday
- persons destined to be Le(a-b+) are as neonates Le(a-b-) then Le(a+b-) then Le(a+b+) and finally Le(a-b+)
- Lewis antigen expression is decreased during pregnancy and the Le(a-b-) phenotype is transiently expressed
- Le(a-b-) is present in blacks mainly
- Le(a+b+) is very rare
14
Q
Frequency of blood groups by ethnicity
A
- O > A > B > AB and D+ in all groups
- O
- hispanic > black > white
- A
- white > black > hispanic
- B
- black > white and hispanic
- AB
- white and black > hispanic
15
Q
ABO antibodies
A
- ABO antibodies are naturally occuring
- detectable in infants by 3-6 months, but may not reach adult titers until 2 years
- ABO incompatibility results in complement activation and brisk intravascular hemolysis
- reactions can accompany transfusion of incompatible red cells (i.e., major incompatibility) and transfusion of incompatible plasma (minor incompatibility)
16
Q
Lewis antibodies
A
- Lewis antibodies are naturally occuring
- found almost exclusively in Le(a-b-) people are commonly black
- Le(a-b+) people do not make anti Lea antibodies
- Lewis antibodies are nearly always IgM and insignificant
- during pregnancy, women can acquire Le(a-b-) phenotype, and they can develop Lea Leb antibodies, which cannot harm the baby since fetal cells do not express Le antigens
- rare significant Lewis antibody is anti Lea which are usually inconsequential because
- transfused red cells shed their Lewis antigens and acquire the Lewis phenotype of the recipient
- Lewis antibodies are quickly absorbed by free serum Lewis antigens
17
Q
Anti I and Anti i antibodies
A
- These are autoantibodies that are usually clinically insignificant
- anti I Ab is associated with mycoplasma pneumoniae and lymphoma
- anti i AB is associated with EBV
18
Q
P/GLOB antigens and phenotype
A
- P1, P, and Pk are 3 different carbohydrate antigens
- P1 is the only one of the above that belongs to the P blood group system
- Pk and P do not belong to P, but instead belong to GLOB system
- P antigen is the receptor for parvovirus B19 (fifth disease)
- P antigen is target of antibodies in paroxysmal cold hemoglobinuria (PCH)
- P group phenotypes are defined by reactivity with the antibodies anti P1, anti Pk, anti P, and anti PP1Pk
- 80% of whites and 95% of blacks have the P1 phenotype (P1+, P+, Pk-, PP1Pk+)
- the rare p phenotype is characterized by absence of P antigens
19
Q
Antibodies to P/GLOB blood groups
A
- people with p phenotype make potent anti PP1Pk
- anti PP1Pk is associated with delayed hemolytic transfusion reaction, HDFN, and first trimester spontaneous abortion
- people with P2 may make anti P1
- these are usually IgM, reactive at 4 degrees and not clinically significant
- anti P1 can be agglutinated by
- hydatid cyst fluid
- egg whites from pigeon eggs and turtledove eggs
- anti P1 titers may be elevated in
- echinococcal infection (hydatid cyst)
- bird handlers
- anti P1 associated with
- PCH
- viral infections in kids
- syphilis
20
Q
Rh antigens and phenotypes
- genes
- chromosome #
- other associated proteins
- variants
- Rh null associated with
A
- Rh antigens are polypeptide antigens encoded by closely linked gene loci RHD and RHCE
- genes found on chromosome 1
- products of RHD and RHCE genes form large complex on red cells
- additional proteins associated with Rh complex, including LW and duffy (Fy)
- C, D, and E are transmembrane proteins with multiple extracellular domains
- multitude of epitopes and antigens
- multitude of extracellular domains create possibility of “partial D” phenotype
- Rh null associated with hereditary stomatocytosis (HS)
21
Q
Most commone Rh- and Rh+ genotypes
A
- Most common Rh- genotype is r/r (cde/cde)
- 10-15% of blood donors are Rh-
- highest incidence of Rh negativity is found in Basques (25%)
- prevalence of r/r explains why recipients with anti c or anti e should not be given Rh- blood
- the D- phenotype denotes absence of the D antigen (there is no d antigen)
- Rh null people have no Rh antigens
- also have diminshed expression of LW, Fy5, S, s, and U
- also have enhanced osmotic fragility, chronic hemolysis, and stomatocytosis
- should only receive Rh null RBCs
- if they receive Rh- RBCs, they will form anti total Rh antibody (anti Rh29)
- Most common Rh+ genotypes are R1/R1 or R1/r in whites and R0/R0 or R0/r in blacks
22
Q
Weak D
- what is it
- antibodies?
- how was it defined historically?
- mechanisms
- recipient status
A
- Possess D antigen in smaller quantities
- people with weak D do not form anti D antibody
- transfusion of weak D cells into a D- person can cause sensitization, so these donors are labeled as D+
- weak D defined historically by weak reactivity with anti D reagent, typified by the following reactions
- negative at IS with anti D reagent
- negative after 37 degrees incubation with anti D reagent
- positive at AHG phase with anti D reagent
- modern monoclonal anti D reagents can detect most weak D RBCs at IS such that weak D cells simply look like typical D+ cells
- Mechanisms
- most commonly results from mutations in the RHD gene
- less commonly result from presence of Ce haplotype for RHCE gene on opposite chromosome, which exerts a dampening effect on D expression (“C in trans to D”)
- recipient not tested for weak D, only the donor is
23
Q
Partial D
- mechanism
- transfusion of partial D cells
- pregnancy
- how is it identified
A
- alteration in 1 of the epitope sequences of the D gene
- results in D antigen with some, but not all, epitopes
- people with partial D may form anti D antibody
- transfusion of partial D cells into D- recipients can cause sensitization
- partial D women are at risk for forming anti D antibodies with D+ pregnancies, for these reasons partial D woman recipient should be treated as D-
- partial D is frequently identified because of an apparent discrepancy: the coexistence of D expression and anti D antibodies
24
Q
Rh antibodies
- sensitization rate
- dosage
- enzymes
- clinical consequences
- anti E
- other antigens
A
- IgG antibodies that are acquired through exposure
- D antigen is most immunogenic of all non-ABO antigens
- when Rh+ blood is transfused to Rh- recipients in an emergency setting, the rate of sensitization is 20-30%
- all Rh antibodies except anti D display dosage
- all Rh antigens are enhanced by enzymes
- Rh antibodies may result in hemolytic transfusion reactions and severe HDFN
- If anti E is detected in serum, then the additional presence of anti c should be suspected
- because most people with anti E have R1R1 phenotype (CDe/CDe), and have been likely transfused with R2 blood (cDE)
- anti c may be undetectable but is a common cause of DHTR
-
G antigen is found on all D+ RBCs and most C+ RBCs
- serologically anti G antibodies mimic anti D and anti C
- multiple absorption/elution studies can distinguish anti G from anti D and anti C
- in pregnant women, you must distinguish between anti D, anti C, and anti G since they will need RhIg to prevent formation of anti D
-
anti f (antibody against compound antigen ce) is most common alloantibody directed against compound Rh antigens
- found primarily in DCe/DcE (R1R2)
25
Q
Kidd antigens
- Jkb ethnicity
- Jk(a-b-) seen in what populations
- function of Kidd protein
- effect of enzymes
A
- Jkb negative phenotype is twice as common in blacks than whites
- Jk(a-b-) is rare, encountered in Finns and Polynesians
- Kidd is a urea transport protein
- Jk(a-b-) cells are resistant to hemolysis in 2M urea
- this phenotype causes a mild urine concentrating defect
- Enhanced by enzymes
26
Q
Kidd antibodies
- level of detection
- dosage effect?
- clinical consequences
A
- Difficult to detect (Tricky kidd)
- tend to fall below threshold of detection over time
- Kidd Ab diminish in stored blood (e.g., when sent to a reference lab)
- historical kidd antibodies, despite absence of currently detectable antibody, is reason enough to give Kidd antigen negative blood
- Kidd antibodies display dosage and may only react with homozygous cells
- Dosage effect may result in a false negative crossmatch
- Kidd antibodies most often react only at the AHG phase
- most common cause of DHTR
- Rarely causes HDN because Kidd is weakly expressed by fetus
27
Q
Duffy antigens
A
- Fya and Fyb
- present on DARC (Duffy associated receptor for chemokines), which is a receptor for plasmodium vivax
- Fy(a+b-) is more common than Fy(a-b+)
- Fy(a-b-) is rare in whites, but common in blacks (68%)
- this phenotype confers resistance to plasmodium vivax
- most Fy(a-b-) blacks do not form anti Fy antibodies, but Fy(a-b-) whites do
28
Q
Duffy antibodies
- IgM or IgG
- dosage
- enzymes
- clinical conseqences
A
- Duffy antibodies are warm reacting IgG antibodies acquired through exposure
- Duffy antibodies show dosage effect
- Duffy antigens are destroyed by enzymes
- Duffy antibodies are capable of causing hemolytic transfusion reactions (HTR) and severe hemolytic disease of the newborn
29
Q
MNS antigens
A
- MN and SsU genes display genetic linkage
- most frequent haplotypes are Ns and Ms
- M and N antigens are found on glycophorin A
- 25% of population is M+N-
- 25% of population is M-N+
- 50% of population is M+N+
- S, s, and U antigens reside on glycophorin B
- s and U are high frequency antigens, present in over 98% of the population
- S is present in 50% of whites and 30% of blacks
- It is very difficult to find compatible blood for rare S-s-U recipients, who are usually black
30
Q
MNS antibodies
A
- anti M antibodies are naturally occurring, cold reacting, IgM antibodies that are clinically insignificant
- anti N antibodies are rare because an epitope on glycophorin B has N like antigenicity
- anti Nf antibodies may be formed in dialysis patients who were exposed to formaldehyde used in cleaning dialysis machines and induced formation of Nf antigen on RBCs
- Anti S, anti s, and anti U antibodies are acquired following exposure and are warm reacting, clincally significant, IgG antibodies
- MNS antibodies display dosage
- M and N antigenicity is destroyed by enzymes
31
Q
Kell antigens
A
- Kell group includes antigens K, k, Kpa, Kpb, Jsa, Jsb
- expressed on mature red cells and erythroid precursors; thus allantibodies are capable of suppressing erythropoiesis
- Kell antigens are expressed in covalent association with the Kx antigen
- K (KEL1), Kpa, and Jsa are present in 9%, 2%, and 0.1% of donors
- k antigen (also called Cellano or KEL2), Kpb, and Jsb are high frequency antigens each present in 99% of donors
- Kell null phenotype results from homozygous inheritance of amorph K0 such that red cells have no Kell antigens, but an abundance of XK protein
- mutations in Kx gene encoding XK protein result in McLeod phenotype (X linked recessive)
- lack of Kx depresses the expression of Kell antigens and results in shortened red blood cell survival
- red cells display acanthocytosis
- often associated with coexisting
- chronic granulomatous disease
- late onset type of muscular dystrophy (“neuroacanthocytosis”); elevated CK
- retinitis pigmentosa
- incompatible with both normal and Kell null blood (which expresses Kx antigen)
32
Q
Diego negative
A
- Diego is an epitope on band 3 protein
-
Band 3 deficiency causes some cases of
- HS
- acanthocytosis
- hereditary elliptocytosis
33
Q
Naturally occurring antibodies
A
I, i, ABO, Le, Lu, M, N, P
34
Q
Antigens that display dosage
A
MNS, Kidd, C/c, E/e, Duffy
35
Q
Antibodies that react at room temperature
A
- M
- N
- P1
- Lea
- Leb
36
Q
Nearly always clinically insignificant antibodies
A
M, N, P1, Lewis, Lutheran, and I
37
Q
4 most common antibodies in immediate HTR
A
A, kell, Jka, Fya
38
Q
4 most common antibodies in DHTR
A
Jka, E, D, C
39
Q
Mixed field reactions are expected with
A
Lutheran, Sid, A2 (and post BMT)
40
Q
Antibodies that produce intravascular hemolysis
A
ABO, Kidd, P (PCH)
41
Q
Kell antibodies
A
- most commonly anti K and are acquired through exposure
- warm reacting IgG
- unaffected by enzymes
- Kell antigen expressionis decreased by agents that dissolve S-H bonds; thus they are sensitive to 2-mercaptoethanol (2-ME), ZZAP, and dithiothrietol (DTT)
- Kell antibodies are associated with HTR with extravascular hemolysis and HDFN
42
Q
Lutheran antigens
A
- Lub is high incidence (99% of population)
- Lua is present in 7% of population
- 93% of population is Lu(a-b+) and 7% are Lu(a+b+)
- lutheran antigen expression is increased on surface of sickle cells
43
Q
Lutheran antibodies
A
- Lutheran antigenicity is destroyed by enzymes and 2-ME and DTT
- Lu antibodies are usually anti Lua and clinically insignificant cold reacting IgM
- mixed field reactions are typical
44
Q
MHC classes
also in the region are what genes
A
Class I, II, and III
Also in the 6 p region:
- HFE gene
- 21-hydroxylase gene
- TNF gene
45
Q
MHC Class III
A
Encode complement proteins
46
Q
MHC Class I genes
A
Encode HLA O antigens that are on surface of all cells
- 3 loci: HLA-A, HLA-B, and HLA-C
- Class I genes encode a single polypeptide chain that is
- embedded as a transmembrane protein
- noncovalently associated with a single molecule of alpha-2 microglobulin
- young red blood cells express Class I antigens but lose them as they age
- exception is the Bg (Bennett Goodspeed) antigens, which are expressed in mature red cells
- Bg antigens rarely cause HTR
- major Bg antigens:
- Bga (HLA-B7)
- Bgb (HLA-B17)
- Bgc (HLA-A28/A2)
- platelets have a lot of class I antigens
47
Q
MHC class II
A
- Encode HLA class II antigens on B cells, macrophages, and activated T cells
- 3 loci: HLA-DR, HLA-DP, and HLA-DQ
- 2 polypetide chains (alpha and beta) encoded, each with two domains similar to Ig light chains, in addition to a transmembrane domain
- class II antigens are expressed on neither red cells nor platelets
48
Q
HLA plays a small role in red blood cell compatibility, but is pivotal in?
A
- platelet refractoriness
- solid organ compatibility
- some transfusion reactions:
- febrile reactions
- transfusion related acute lung injury (TRALI)
- transfusion associated GVHD
49
Q
Inheritance of MHC complex
A
- One haplotype is inherited from each parent
- chance of 2 siblings are HLA identical is 25%
- chance of having an HLA identical sibling goes up wtih the number of siblings: with 1 sibling it’s 25%, with 2 it’s 45%, with 3 it is 60%
