Blood Groups

Question 1

Basic Red Cell-Antibody Interactions

Answer 1

1. Agglutination
   a. Clumping of red cells due to antibody coating
   b. Main reaction we look for in Blood Banking
   c. Two stages:
   1) Coating of cells (“sensitization”)
   a) Affected by specificity of antibody, electrostatic charge of RBCs, temperature, relative amounts antigen and antibody
   b) Substances like Low Ionic Strength Saline (LISS) and Polyethylene glycol (PEG) aid in sensitization by helping to overcome physical barriers to let antigens and antibodies get closer to each other.
   2) Formation of bridges
   a) Lattice-like structures formed by antibodies and red cells
   b) IgG isn’t good at this; it is usually too small to bridge the gap between red cells by itself.
   c) IgM is much better at forming bridges.
2. Hemolysis
   a. Direct lysis of a red cell as a result of antibody coating is uncommon, but is just as much a “positive” as agglutination.
   1) Requires complement fixation
   2) IgM antibodies do this more than IgG.

Question 2

Tube testing

Answer 2

1. Immediate spin “phase”
   a. Serum and 2-5% RBC solution together in tube, centrifuge for 15-30 sec and examine.
   1) Most common: 2 drops serum, 1-2 drops RBCs.
2. 37 C “phase”
   a. Take above mixture and incubate at 37 C for specified time, centrifuge and examine.
   1) 10-15 minutes if LISS used to potentiate
   2) 15-30 minutes if albumin or PEG used
   3) 30-60 minutes if no potentiation used
3. Indirect antiglobulin (a.k.a., “antihuman globulin”) “phase”
   a. Wash above mixture to remove unbound globulins.
   b. Add antihuman globulin, centrifuge and examine.

Question 3

Alternatives to tube testing

Answer 3

1. Column agglutination technology (Gel testing-Ortho)
   a. Multiple microtubes filled with gel particles and anti-IgG reagent
   1) Gel particles separate red cell clusters by size (ie, larger clumps of cells are stopped from migrating through gel while individual cells cruise right on through to the bottom).
   2) Anti-IgG grabs onto red cells coated by IgG.
   b. Add red cells and plasma to top of tube, incubate, then centrifuge.
   c. More coating of red cells by antibody = larger agglutinates and more attraction to antiglobulin in gel = less transport through gel
   1) Negative gel tests show cells in a button at the bottom of the microtube.
   2) Positive tests have cells spread in varying degrees through the microtube.
   d. Can be automated (ProVue machine)
2. Solid-phase Red Cell Adherence Testing (Immucor Gamma)
   a. Uses binding of antibody to RBCs that are themselves bound to the sides of microwells
   b. Manufacturer binds RBCs carrying antigens we are interested in to small wells.
   c. Lab adds patient serum, incubates, washes: antibody binds to test RBCs

d. Indicator RBCs (coated with monoclonal anti-IgG) attach to test RBCs via bound antibody.
e. Centrifuge and interpret

1) Negative solid phase tests have cells in a button at the bottom of the microplate, because the indicator cells don’t bind to the test RBCs on the microplate
wall.
2) Positive solid phase tests have cells spread in a “carpet” all along the microplate wall, because the indicator cells have bound to test RBCs all along the wall.

f. Can be automated (Galileo and Galileo Echo machines)

Question 4

Kell Reactions

Answer 4

Question 5

The Antiglobulin Test (“Coomb’s Test”)

Answer 5

1. Indirect: described above; checks for in-vitro coating of RBCs with antibody or complement.
2. Direct: red cells taken directly from patient, washed, then mixed with antihuman globulin; checks for in-vivo coating of RBCs with antibody and/or complement.
3. IAT variations

a. Can be used to check for an unknown antibody by using red cells with a known antigen profile, as in an antibody screen
b. Can be used to check for an unknown red cell antigen by using serum with known antibody specificity, as in RBC antigen testing
c. Can be used to check for a reacting unknown antigen and unknown antibody, as in the crossmatch procedure

4. Specificity possibilities for the antiglobulin
   a. Anti-IgG, -C3d (“polyspecific”)
   1) Will detect red cells coated with either of the above and may also detect other immunoglobulins (because the anti-IgG is not specific)
   b. Anti-IgG and anti-IgG (heavy chains)
   1) Both detect IgG-coated red cells; anti-IgG may also detect light chains associated with other antibody classes (IgA, IgM).
   c. Anti-C3b, -C3d

1) Detects either of the above complement components
2) Useful in evaluating IgM-related hemolysis, cold agglutinin disease and certain warm autoimmune hemolysis without IgG

5. IgG-coated red cells (“Coomb’s control”)

a. Used after negative DAT or IAT to ensure proper functioning of antiglobulin reagent
b. IgG-coated RBCs added to AHG-cell mixture
c. Negative = bad AHG or no AHG added
d. Other errors in the process (leaving out the test serum, bad processing technique, etc) would not be detected by Coomb’s Control test.

Question 6

Dosage

Answer 6

1. Certain antibodies do not react as strongly with RBCs that have antigens coded for by a single gene.
2. For example, imagine a hypothetical anti-Z

a. Patient 1 genotype: ZZ (Homozygous for Z)
b. Patient 2 genotype: ZY (Heterozygous for Z)
c. If anti-Z shows dosage, it will react stronger with patient 1’s RBCs (see below).

3. Most common in Kidd, Duffy, Rh and MNSs blood
   groups

Question 7

Neutralization

Answer 7

1. A particular substance, when mixed with an antibody, eliminates the activity of that antibody against test red cells.
2. Some of these are pretty weird! (See table below)

Neutralization of Antibodies
ABO Saliva (secretor)
Lewis Saliva (secretor for Leb)
P1 - Hydatid cyst fluid / Pigeon egg fluid
Sda Urine
Chido, Rodgers Serum

Question 8

Enzymes

Answer 8

ficin, papain

Enhanced: (A Rotten Kid)

• ABO / H
  
  • ABO
  • Lewis
  • I
  • P
• Rh
• Kidd

Decreased (My Dog Lassie)

• MNS
• Duffy
• Lutheran

Unaffected

• Kell
• Diego
• Colton
  *

Question 9

Blood Groups - General characteristics

Answer 9

1. Guidelines
   a. “Clinically significant” = blood group antibody which causes HTRs or HDN

b. Most significant antibodies are “warm reactive”; meaning they react best at 37 C or IAT.
c. Most insignificant antibodies are “cold reactive”; meaning they react best below 37 C.
d. Warm antibodies are most often IgG, while colds are usually IgM.
e. IgM antibodies are usually “naturally occurring”, meaning no transfusion or pregnancy is required for their formation.

f. *Note that the ABO blood group is the exception in the table above.

“WARM-REACTIVE” ANTIBODIES

IgG

Require exposure

Cause HDN

Cause HTRs

“Significant”

“COLD-REACTIVE” ANTIBODIES

IgM
Naturally occurring
No HDN*
No HTRs*
“Insignificant”*

B antigens are more common than A antigens except in Duffy. (Lewis b > lewis a)

Question 10

The “Enzyme Classification”

Answer 10

Enzyme-enhanced

ABO Family
ABO Blood Group
Lewis Blood Group
I/i Blood Group
P Blood Group
Rh Blood Group
Kidd Blood Group

Enzyme-decreased

MNSs Blood Group
Duffy Blood Group

Enzyme-unaffected

Kell Blood Group

Question 11

ABO Blood Group

Answer 11

1. Basic biochemistry
   a. Type I and II chains

1) Type I: Think of them as primarily glycoproteins in secretions and plasma carrying free-floating antigens
2) Type II: Think of them as primarily glycosphingolipids carrying bound antigens on RBCs.

b. Se gene (FUT2)
1) “Secretor” gene on chromosome 19
a) A secretor is a person able to make A or B antigens in their secretions (saliva, etc).

2) Codes for a fucosyltransferase (FUT) enzyme that adds fucose to type I chains at terminal galactose; product is type I H antigen
3) 80% gene frequency
c. H gene (FUT1)

1) Closely linked to Se on chromosome 19

2) FUT enzyme adds fucose to terminal galactose of type II chains; product is type II H antigen.
3) Virtually 100% gene frequency (lack of H = “Bombay phenotype” (more to follow).

d. H antigen is required before A and/or B antigens can be made either on red cells (type I H) or in secretions (type II H).
1) A single sugar is added to a type I or II H antigen chain to make A or B antigens; when this happens, the chain no longer has H activity.

a) Group A sugar: N-acetylgalactosamine
b) Group B sugar: Galactose

2) Relationship is reciprocal; the more A or B is made,
the less H remains.

a) Relative amounts of H by blood group
• O > A2 > B > A2B > A1 > A1B

2. ABO antigens and antibodies

a. Antigens based on combinations of three genes on chromosome 9: A, B and O.
b. Antibodies are clinically significant and “naturally occurring.”
c. ABO antigens begin to appear on fetal RBCs in utero (6 weeks gestation); reach adult levels by age 4.
d. ABO antibodies do not begin to appear until after 4 months of age; reach adult levels by about 10 years

1) Conflicting reports about falling titers in elderly patients; most believe there is a decline with advanced age.

Question 12

Group O

Answer 12

Group O

1) Generally the most common blood group
2) Genotype: OO
3) Antigen: H

a) O gene is nonfunctional; no sugars transferred
b) Lectin of Ulex europaeus agglutinates cells with abundant H antigen.
c) Note lectin chart for various specificities

4) Antibodies: anti-A, anti-B and anti-A,B

a) Anti-A and anti-B antibodies in group A and B patients are characteristically IgM, and react strongly at body temperatures.
b) Those antibodies in group O people have a strong IgG component, so they may cross the placenta to cause mild HDFN (most common HDFN).
c) Anti-A,B is also IgG, and reacts against both A and B cells (reactivity can’t be separated into individual specificities).

Question 13

Group A

Answer 13

1) Genotypes: AA, AO
2) Antigens: A, H
3) Antibodies: anti-B (primarily IgM).
4) A subgroups

a) A1 (80%) and A2 (~20%) most important
b) A1 red cells have about 4 times more A antigen on RBC surfaces than A2 cells (quantitative difference).
c) Qualitative differences also exist in the forms of the antigenic chains.
d) Small % of A2’s (1-8% of A2 and 25% of A2B) form anti-A1.

• Anti-A1 is usually a clinically insignificant IgM but it can cause discrepancies in ABO
testing.
• If reactive at 37C, patients should not receive A1 red blood cells.

e) Lectin of Dolichos biflorus agglutinates A1 RBCs, to differentiate A1 from A2.

Question 14

Group B

Answer 14

1) Genotypes: BB, BO
2) Antigens: B, H
3) Antibodies: Anti-A (primarily IgM).
4) B subgroups: usually unimportant and less frequent

Question 15

Group AB

Answer 15

1) Least frequent ABO blood type (about 4%)
2) Antigens: A and B (very little H)

a) Can be further subdivided into A1B or A2B depending on the status of the A antigen
3) Antibodies: none

Question 16

ABO testing

Answer 16

a. Cell typing (“forward grouping”)
1) Patient red cells agglutinated by known sera (anti-A, anti-B).
b. Serum typing (“reverse grouping”, “back typing”)
1) Patient serum (or plasma) against A1 and B RBCs
c. Note the opposite reactions!
1) If forward reactions are not opposite of reverse, an ABO discrepancy is present.
d. Both serum and cell typing are required unless testing babies < 4 months of age or reconfirming ABO testing done on donor blood (requires cell typing only).

Question 17

ABO discrepancies

Answer 17

a. Disagreement between the interpretations of forward and reverse grouping (eg, forward grouping looks like group A, reverse like group O); caused by either antigen or antibody problems or technical errors.
b. Antigen problems
1) Lack of expected antigens

a) A or B subgroups
b) Transfusion or transplantation
c) Leukemia or other malignancies

2) Unexpected antigens

a) Transfusion/transplantation out-of-group
b) Acquired B phenotype (more below)
c) Recent marrow/stem cell transplant.
d) Autoagglutination
c. Antibody problems

1) Lack of expected antibodies

a) Immunodeficiency
b) Neonates, elderly, or immunocompromised
c) Transplantation or transfusion
d) ABO subgroups

2) Unexpected antibodies

a) Cold auto- or alloantibodies
b) Anti-A1
c) Rouleaux (false positive)
d) Transfusion or transplantation
e) Reagent antibodies

d. Technical errors
1) Errors in preparation of samples, sample mix-ups, or interpretation errors

Question 18

Acquired B phenotype

Answer 18

1) Seen in contact with enteric gram negatives: Colon cancer, intestinal obstruction, gram-negative sepsis
2) AB forward (with weak reactions with reagent anti- B), A reverse
3) Bacteria deacetylate group A sugar (GalNAc); remaining galactosamine cross-reacts with reagent anti-B.
4) Acidify serum (no reaction with anti-B), add acetic anhydride (re-acetylates), autoincubation (no
reaction) , BS-1 lectin (no reaction).

Question 19

B(A) phenotype

Answer 19

1) Similar to acquired B, but with group B (ie, they are really group B but forward test like an AB, with a weak reaction with anti-A).
2) Problem is a cross-reaction with a particular form of monoclonal anti-A; testing using a different anti-A it shows the patient truly to be group B.

Question 20

Bombay (Oh) phenotype

Answer 20

1) Total lack of H, A and B antigens due to lack of H and Se genes (genotype: hh, sese)
2) Naturally occurring strong anti-H, anti-A, anti-B
3) Testing: O forward, O reverse, but antibody screen wildly positive and all units incompatible
4) Require other Bombay donors
5) Para-Bombay phenotype

a) Similar, but these patients have Se to partially compensate for their lack of H.
b) Phenotypes: Ah, Bh, ABh
c) Red cells may type like Bombays, but serum/secretion testing shows free H and A or B
antigen (unless group O).
d) These patients have anti-H in serum.

6. Consequences of ABO incompatibility
   a. Severe acute hemolytic transfusion reactions

1) Most frequent blood bank fatalities
2) Clerical errors

b. Most frequent HDFN; usually mild, however

Question 21

Lewis Blood Group

Answer 21

1. Biochemistry

a. Type I chains only
b. One gene: Le (FUT3)
c. FUT enzyme adds fucose to subterminal GlcNAc (left side of figure below).

1) This makes Lea (Lewis A) antigen.
2) In a non-secretor, Lea is the only Lewis antigen possible.
3) Lea antigens cannot be further modified to make Leb (in contrast to previous thought).

d. In secretors, Se product adds fucose, then Le product adds fucose; this makes Leb (Lewis B).

1) In secretors, this interaction shown on the right of the figure below, occurs preferentially over Lea formation.
2) As a result, the vast majority the chains of secretors who carry Le are Leb rather than Lea

e. Unlike ABO, antigens are not tightly bound (remember, they are made from type I chains); rather, they adsorb onto the surface of RBCs.

1) Leb does this better than Lea, so this is another reason that most adults with both Le and Se will be Le(a-b+).
2) Le(a-b+) people still have Lea, just in much smaller quantities that may not show up on RBCs.

f. Same chain can carry Le and ABO antigens (unlike the inverse relationship with ABO and H).
2. Lewis phenotypes, antigens, and antibodies

a. Phenotypes: Le(a+b-), Le(a-b+), Le(a-b-)
b. Lea, Leb
c. Leb is seen more frequently.
d. 22% of blacks are Le(a-b-), vs. only 6% of whites.
e. Antibodies are naturally occurring.

1) Primarily in Le(a-b-)
2) Cold reacting IgM
3) Neutralize with saliva.
3. Consequences of incompatibility
a. Rare HTRs (more commonly anti-Lea)
b. No HDFN (antibody doesn’t cross placenta and Le antigens are not present on fetal RBCs).
4. Weird stuff about Lewis
a. Lewis antigens decrease during pregnancy.

1) Pregnant patients may appear Le(a-b-) and have transient, insignificant Lewis antibodies.
2) Thought to be due to increased plasma volume diluting the antigen

b. Le(a-b+) people don’t make anti-Lea.
1) As above, these people still have Lea, just not visibly on their red cells.

c. Children’s Lewis type may vary, as antigen chains are converted [they may have more Lea than Leb, and have a transient period of Le(a+b+)].
d. Helicobacter pylori may attach via Leb antigen.
e. Le(a-b-) in children increases risk of urinary tract infections.

Question 22

I/i Blood Group

Answer 22

1. Antigens built on chains related to ABO.
2. Expression is age-dependent.

a. Simple chains found on neonates make i antigen.
b. More branched chains in adults make I antigen.
c. “Big I in big people, little i in little people”

3. Antibodies

a. Cold reacting IgM
b. Naturally occurring
c. Autoantibodies very common
4. Classic associations

a. Auto-anti-I

1) Cold agglutinin disease
2) Mycoplasma pneumoniae infection

b. Auto-anti-i

1) Associated with infectious mononucleosis
2) Less often a problem than auto-anti-I

Question 23

P Blood Group (the cool one)

Answer 23

1. Also built on ABO-related chains
2. P1 only P group antigen

a. P, Pk not officially in P system anymore

1) Still, combination of these three antigens defines the P phenotype.
2) Most common P phenotype is P1 (positive for P1 and P and negative for Pk).

b. Very rare people lack all three and make anti-PP1Pk.
1) Associated with acute HTRs, HDFN and early, spontaneous abortions

c. P antigen is parvovirus B19 receptor.
d. Pk antigen is receptor for various bacteria and toxins

3. Antibodies (anti-P1)
   a. Cold reacting, naturally occurring, insignificant IgM
   b. Titers elevated in those with hydatid cyst disease (Echinococcus) and bird handlers
   1) Bird feces has P1-like substance.
   c. Neutralized by hydatid cyst fluid and pigeon egg fluid (Really! I’m not kidding!)
4. Association with paroxysmal cold hemoglobinuria
   a. Biphasic IgG with anti-P specificity

1) Binds in cold temps, hemolyzes when warmed
2) “Donath-Landsteiner biphasic hemolysin”

b. Classically associated with syphilis, now with viral infections in children

Question 24

Rh Blood Group

Answer 24

1. Second most important blood group (after ABO)
2. Terminology systems

a. Fisher-Race (DCE or CDE)
1) Five major antigens: D, C, E, c, e

a) “Rh positive” really means “D positive.”
b) Absence of D designated “d” (later found not to be a real antigen)

2) Eight potential combinations (“haplotypes”) named based on presence of genes for above antigens (ie, “DCe”, “dce”, etc.)
b. Wiener (Rh-Hr)

1) Used different names for the five main antigens; these are not used very often by non-geeky people.
2) Believed that main Rh genes (for presence or absence of D, for C or c and for E of e) were inherited as one genetically linked group, or “haplotype.”
3) Gave shorthand names to the eight potential combinations alluded to above; this nomenclature is still in use and is essential to know (even though his theory of how these are inherited has been disproven).

a) Rules for converting Wiener’s shorthand into Fisher-Race terminology:
• “R” = D, “r” = d
• “1” or “prime” = C
• “2” or “double prime” = E
• “0” or “blank” = ce
• Any superscript letter = CE

c. “The Big Four”
1) Fortunately, only four of the above combinations occur frequently enough to memorize their relative order: R1, R2, R0 and r. (~97% of blacks and whites use only these four).

a) How to remember?
• R0 is most common in blacks, least common in whites.
• r is always second in frequency.
• R1 always comes before R2.
“The Big Four”
Whites: R1 > r > R2 > R0 (120)
Blacks: R0 > r > R1 > R2 (012)

2) FYI, Asians have much less r; the order in that group is R1 > R2 > r and R0.
d. The real story of Rh inheritance

1) Two main genes: RHD and RHCE, on chromosome 1 code for main Rh antigens
2) D type determined by presence/absence of RHD
3) CE combination by which variants of RHCE are present (four combinations: CE, Ce, cE, ce)

3. Rh antibodies

a. Exposure required
b. Warm-reacting IgG

4. Consequences of Rh incompatibility

a. Very immunogenic blood group, with D inducing the most antibodies, then c and E
b. Up to 80% (reported as wide range of 30-85%) of D negativepatients make anti-D with a one unit D-pos RBC transfusion.
c. Exposed: HTRs with extravascular hemolysis

Question 25

Weak D phenotype (formerly known as Du)

Answer 25

1) D testing is typically done with monoclonal antibodies today and most truly D+ people test that
way.
2) Some D+ individuals, however, require an Indirect Antiglobulin Test (IAT) to detect D antigen.

3) Possible reasons for weak D

a) C on opposite chromosome to D (“C in trans”)
b) Weak form of RHD gene
c) Mosaic forms of D antigen (“partial D”, “D mosaic”) lack portions of D antigen.

• Probably better considered separately from first two.
• Patients with partial D may develop antibodies against portions of the antigen they
lack; this may lead to what looks like an anti- D in a D-positive person.

4) Testing requirements

a) Weak D test for all D negative blood donors
b) Not required for D negative blood recipients

• This was previously a concern, for fear of wasting d-negative units on D+ patients
• Monoclonal antibodies mentioned above make this very unlikely
• In transfusion services, the only patients who definitely need weak D testing are apparently d-negative babies with d-negative moms.

Question 26

Rhnull phenotype

Answer 26

1) No Rh antigens whatsoever
2) Hemolytic anemia with stomatocytes
3) Also associated with altered activity of S, s and U antigens (See MNSs system later)

Question 27

Warm autoimmune hemolytic anemia (Rh)

Answer 27

1) Antibody seems to have relative specificity to basic Rh structural antigens.

Question 28

Compound Rh antigens

Answer 28

1) G = antigen present when either C or D are present.
2) f = antigen present when c and e are on the same chromosome (as in r and R0).

Question 29

Kidd Blood Group

Answer 29

1. Kidd antigens

a. Jka, Jkb
b. Jka slightly more common

2. Kidd antibodies

a. Exposure required
b. Warm reacting IgG

1) Unusually good at fixing complement, in contrast to most IgG antibodies
c. Marked dosage effect
1) A Kidd antibody may not react at all against cells with heterozygous expression of Kidd antigens, but may react very strongly against a homozygous cell.
d. Variable antibody expression
1) Antibody often disappears with time/storage.
3. Weird stuff about Kidd
a. Delayed HTRs

1) Kidd’s most famous association
2) Anamnestic response
3) Intravascular and often severe

b. Mild HDFN at worst
1) Child can only be one antigen different from mom; remember dosage discussion above.

Question 30

MNSs Blood Group

Answer 30

1. Basic biochemistry

a. Glycophorin A carries M and N antigens.
b. Glycophorin B carries S, s and U antigens.

2. MNSs antigens

a. M frequency roughly equals N
b. s > S
c. If S-s- (as seen in 2% of African-Americans), may also be U negative (U is extremely high frequency).

3. MNSs antibodies
   a. M and N antibodies are mostly opposite of S, s and U antibodies (see below)

b. Enzymes destroy M, N and S antigens, but do not greatly affect s antigens.
c. Anti-M is generally insignificant, but has been associated uncommonly with HDFN.

4. Weird stuff about MNSs
   a. N-like antigen (‘N’)
   1) Glycophorin B has a terminal 5 AA sequence that matches glycophorin A’s last 5 when coding for actual N antigen; this is known as ‘N’.
   a) This is not really true N antigen, but it is close enough that it prevents most M+N- people from making anti-N.
   2) Everyone except those who lack glycophorin B (Ss-U-) have ‘N’.

a) For this reason, the majority of people who make clinically significant anti-N are African- Americans (<1% lack S, s and U).
b. Anti-N induced by hemodialysis

1) Formaldehyde sterilization of machine
2) Modification of N antigen

c. Another lectin!
1) Vicea graminea lectin used commonly as an Ntyping reagent

Anti-M & anti-N - Naturally occurring | Cold IgM | Dosage | Insignificant

Anti-S, -s and -U - Require exposure | Warm IgG | Minimal dosage |Significant

Question 31

Duffy Blood Group

Answer 31

1. Duffy antigens

a. Fyb > Fya
b. Fy(a-b-) is the most common Duffy phenotype in blacks (68%).
c. Fya is much more common in Asians than in Caucasians.

2. Duffy antibodies

a. Anti-Fya much more common and significant than anti-Fyb
b. Require exposure
c. Warm-reacting IgG
d. Marked dosage
e. May have variable expression like Kidd antibodies

3. Consequences of incompatibility

a. Severe HTRs, usually delayed and extravascular
b. Generally mild HDFN (for same reason as Kidd above)

4. Weird stuff about Duffy
   a. Fy(a-b-) and malarial resistance
   1) Fy(a-b-) humans are resistant to Plasmodium vivax and P. knowlesi infection.

Question 32

Kell Blood Group

Answer 32

1. Extremely important group clinically and serologically
2. Kell antigens

a. Low frequency: K, also known as “K1” (9% whites, 2% blacks), Jsa, Kpa
b. High frequency: k, also known as “K2” (99.8%), Jsb, Kpb
c. Kx: important antigen that may help stabilize RBC membrane (more later); is closely associated with K antigens on the red cell membrane.

1) Kx has a strange relationship to Kell antigens.
2) When Kell antigens decrease in number, Kx increases (as in “Kell null” phenotype, aka K0); thought to be due to decrease in masking Kell antigens.

a) This led to Kx originally postulated as a precursor; not true.
3) When Kx decreases (as in “McLeod phenotype”, see later), Kell antigens decrease, too.

a) Kx may be required for proper Kell antigen expression.
d. Kell system antigens destroyed by thiol reagents (2- ME, DTT, ZZAP) but not by enzymes alone.

3. Kell antibodies
   a. Anti-K

1) Very common (most common non-ABO antibody after anti-D)
2) Warm reacting IgG

b. Anti-k

1) Very uncommon due to high antigen frequency
2) Analogous to anti-K

4. Consequences of incompatibility
   a. Severe HTRs
   1) May be acute or delayed; usually extravascular.
   b. Severe HDN
5. Weird stuff about Kell
   a. Kell null phenotype (“K0”)

1) Absence of all Kell antigens
2) Kx increased
3) Significant anti-Ku (“universal”) with exposure

b. McLeod phenotype

1) Absence of Kx
2) Markedly decreased (not absent) Kell system Ags
3) No anti-Ku!

4) Hemolytic anemia with acanthocytes
5) Occasional association with X-linked chronic granulomatous disease

a) NADPH oxidase deficit
b) Organisms phagocytized but not killed
c) Catalase-positive organisms (Staph)

6) Also associated with cardiac and nervous system abnormalities

Question 33

Lutheran

Answer 33

a. Lua and Lub antigens
b. Linked to Se on chromosome 19
c. Antibodies uncommon and not usually significant
d. Enzymes decrease Lu antigen activity

Question 34

Xg

Answer 34

a. Gene carried on X chromosome (“X-linked”)
1) Seen in approximately 2/3 of males and 90% of females
b. Antibody insignificant

Question 35

Diego system

Answer 35

a. Two pairs of antigens, Dia/Dib, Wra/Wrb (“Wright A” and “Wright B”)
b. Anti-Dia may be significant, but is uncommon.
c. Anti-Wra is common but is not usually significant.

Question 36

Sda (“Sid”)

Answer 36

a. High frequency
b. Refractile immune complexes
c. Lectin of Dolichos biflorus agglutinates Sid positive RBCs (like A1)
d. Neutralize with urine of the guinea pig!

Question 37

HTLA (“high titer, low avidity”)

Answer 37

a. High frequency
b. Chido, Rodgers most frequent

1) Complement components (C4)

c. Clinically insignificant (no HTRs or HDN)
d. Neutralize with serum.

Question 38

Frigid Five

Answer 38

Lewis A, Lewis B, M, N, P

Cold reacting, usually not clinically significant