Chapter 7 Other Blood Group Systems, HLA, and Platelet Antigens Flashcards
What can make a clinically significant antibody significant?
- Ones that can cause hemolytic transfusion reactions or HDFN (IgG)
- Cause interference in lab testing (IgM)
- Form due to naturally occurring substances in the environment (IgM) (without exposure to foreign RBCs)
There may be other reasons.
What are the two major antigens in the Kell Blood Group System? What is the gene behavior?
2 major antigens
K (KEL1): ~9% of the population
k (KEL2/Cellano): more than 99.8% of the population
The K and k antigens are antithetical (co-dominant)
Note: The names of the antigens in brackets are old terms. You may encounter them but K and k are the proper names now.
Does someone have the Kell antigens at birth?
Yes, they are well developed at birth.
What is 2nd to D antigen for being immunogenic and stimulating antibody production?
K (KEL1) antigen is very immunogenic (second to the D antigen).
How many K antigens per positive red cell are there?
3500 to 18000 K antigens / positive red cell
Where is the Kell antigens on the RBC?
Kell antigens are integral part of the RBC membrane.
How do enzymes affect Kell antigens?
No effect when treated with enzymes.
What are Kell antigens sensitive to and why?
Sensitive to sulfhydryl reagents because Kell antigens have disulfide-bonded regions on the glycoproteins.
Examples of these reagents are:
2-mercaptoethanol (2-ME)
Dithiothreitol (DTT)
2-aminoethylisothiouronium bromide (AET)
What are other antithetical Kell antigens in the Kell system and frequency in the population?
Kp antigens
Kpa is a low-frequency antigen (only 2%)
Kpb is a high-frequency antigen (99.9%)
Js antigens
Jsa (20% in blacks, 0.1% in Caucasians)
Jsb is a high-frequency antigen (80% to 100%)
Note: a and b are superscripts for Kp and Js.
What is the K_0 or Kell_null phenotype? What is the result of that type?
- Lacks all Kell system antigens (K0K0)
- Expresses related Kx antigen
- As a result of RBC immune stimulation, K_0 individuals can develop anti-Ku
- Ku is on RBCs that have Kell antigens
What are the high and low incidence alleles on the Kell gene?
High-incidence alleles:
k, Kpb, Jsb, and KEL11
Low-incidence alleles:
K, Kpa, Jsa, KEL17
What chromosome is the Kell genes located on?
Chromosome 7
What type of immunoglobulin is stimulated by Kell antigen exposure?
IgG, RBC stimulated from transfusion or pregnancy.
Do Kell antigens bind complement?
No
Which procedure do Kell antigens agglutinate best in the lab?
Indirect antiglobulin Test (IAT)
What are the most common/rare antibodies developed to the Kell antigens?
Anti-K is the most common; anti-k is extremely rare
How is the Kx antigen phenotypically related to the Kell system?
Kell glycoprotein is covalently linked to Kx. Absence of Kx antigen weakens the expression of Kell antigen.
Where is the Kx antigen gene located?
X chromosome
What levels of Kx antigens do people who are Kell_null have?
Kell_null individuals have elevated levels of Kx antigen.
What problems do people have who lack the Kx antigen?
Individuals who lack Kx antigen may demonstrate RBC abnormalities (McLeod phenotype).
What is McLeod Syndrome and symptoms?
- McLeod phenotype is attributed to McLeod Syndrome. Seen in males as it is inherited on the X chromosome
- McLeod Syndrome symptoms:
a) RBC abnormalities,
b) Muscular and neurologic defects
c) Increased creatine kinase
What disease is associated with McLeod Syndrome?
Chronic Granulomatous Disease with impaired phagocytosis such that WGCs engulf but cannot kill.
What chromosome are the Duffy blood group system genes on?
Chromosome 1
Are Duffy Blood group system antigens well developed at birth?
Yes
How many antigens are in the Duffy blood group system?
5 antigens (glycoproteins)
What are the 2 main antigens in the Duffy blood group system?
Main 2 are Fy_a and Fy_b
Most important for transfusion purposes
Codominant alleles
Demonstrate dosage
Are Duffy Blood Group System antigens destroyed by proteolytic enzymes? Give examples?
Yes, destroyed by proteolytic enzymes (papain or ficin)
What effect do enzymes in general terms have on red cell antigens?
Enzyme Effect – enzymes can destroy some red cell antigens making it impossible for an antibody to agglutinate with it. Other antigens may be more exposed causing it to have stronger reactions.
What are some common enzymes used in the transfusion labs?
Enzyme that are often used are ficin (from fig plants), Papain (from papaya), and Bromelin (from pineapples)
How do you record the phenotype in the Duffy BG System?
For example if Anti-Fy_a reaction is positive and Anti-Fy_b reaction is negative the phenotype is Fy(a+b-).
Fy(a+b-) homozygous for Fya
Fy(a-b+) homozygous for Fyb
Fy(a+b+) heterozygous
Fy(a-b-)
How does the phenotype Fy(a-b-) help people in malaria invested regions?
Certain malarial parasites (Plasmodium knowlesi and Plasmodium vivax) will not invade Fy(a–) and Fy(b–) negative cells
Not resistant to Plasmodium falciparum.
Fya or Fyb acts as a receptor for the merozoite to attach to the RBC.
What population most frequently has the Fy(a-b-) phenotype?
Most African Americans are Fy(a–b–)
People from West and Central Africa.
What type of immunoglobulin are the anti-Fy_a and anti-Fy_b? Optimal Temp and Reactive Phase?
IgG, 37°C, IAT
How does someone get Duffy antibodies?
Stimulated by transfusion or pregnancy
Therefore clinically significant.
Do Duffy antibodies react with enzyme treated RBCs?
Do not react with enzyme-treated RBCs.
This can be very helpful when trying to determine the identification of an antibody
Antigens are destroyed by enzymes
What is the more common Duffy antibody?
Anti-Fya is more common than anti-Fyb
What antigens are in the Kidd BGS?
3 antigens: Jka, Jkb, and Jk3
Jk3 is present whenever Jka and/or Jkb are present
Where are the Kidd_null phenotypes seen and what antibody may they produce?
Kidd null phenotypes: Jk(a–b–)
Usually seen in individuals from the Far East or Pacific Islands (rare)
May produce anti-Jk3 antibody
What compound is Kidd_null phenotype resistant to? What RBC function is related to that?
RBCs are resistant to 2 M urea
Serve urea transport function in RBCs
When are the Kidd BGS antigens well developed on the RBCs?
Antigens are well developed at birth
Do Kidd antigens show dosage?
Yes
What is the effect of enzymes on Kidd antigens?
Enhanced by enzymes
Note: Not ranked high in terms of red cell immunogenicity
Which Kidd BGS phenotype is extremely rare?
Jk(a-b-)
What makes Kidd BGS antibodies clinically significant?
Implicated in HTRs and HDFN (not severe)
Common cause of delayed HTRs
What type of immunoglobulin are the Kidd BGS antibodies? Optimal Temp and Reactive Phase?
IgG, 37°C, IAT
Do Kidd BGS antibodies bind complement?
Yes
How are detection of Kidd BGS antibodies aided?
Usually appear with other antibodies when detected
Detection is aided by enzymes (enhanced)
Do Kidd BGS antigens show dosage? Impact on testing?
Shows dosage - May only see agglutination with homozygous cells.
Why may Kidd BGS antibodies get missed during testing? Impact on patient?
- Levels decline in vivo, may not detect if titre is very low
- Levels drop quickly in vitro, as well
- Do not store well
- May get missed - This is why they can cause delayed HTR’s (delayed hemolytic transfusion reactions).
Where are the Lutheran Blood Group system antigens expressed?
Weakly expressed on cord blood cells
What is the general frequency of occurrence of the Lutheran Blood Group system?
Most are high or low-incidence antigens; antibodies are rare
What are the primary antigens and most common/rare phenotype in the Lutheran BGS?
Primary antigens include Lua and Lub
92.4% Lu(a–b+)
7.4% Lu(a+b+)
0.2% Lu(a+b–)
Lu_null phenotype is rare, inherited recessively
Is the Lutheran BGS affected by enzymes?
Not affected by enzymes
Is the Lutheran BGS antibody Anti-Lu_a clinically significant? Why or why not?
Not clinically significant
Mild cases of HDFN (if IgG antibody, but note low antigenic expression at birth)
Can Anti-Lu_a occur without RBC stimulation?
May occur without RBC stimulation
What immunoglobulin is Anti-Lu_a? Optimal temperature and agglutination pattern?
Mostly IgM (occasional IgG)
Reacts best at room temperature
Shows mixed-field pattern
Why are cold antibodies not usually clinically significant if they are IgM?
Cold antibodies are not usually clinically significant as if they are IgM they cannot cross the placenta and therefore cannot causes HDFN and they rarely cause HTR. They may cause interference with lab testing at room temperature.
Is Anti-Lu_b clinically significant? Why or why not?
Yes, associated with transfusion reactions (clinically significant), but note
Rare due to high incidence of antigen
What immunoglobulin is Anti-Lu_b? Optimal temperature and agglutination pattern?
IgG
Reacts best at antihuman globulin (AHG), 37°C
Shows mixed-field pattern
How do Lewis antigens come about on the red cell?
Lewis antigens are manufactured by tissue cells secreted into body fluids and then adsorbed onto red cell membranes
–>Are passengers on the red cell membrane NOT intrinsic
Where are Lewis antigens found in the body? Are they present at birth?
Lewis antigens are found in secretions (glycoproteins) and plasma (glycolipids)
Will not be found on the red cells at birth
What genes does the Lewis system depend on?
Lewis system depends on Hh, Se, and Le genes (all found on chromosome 19)
Le gene is (FUT-3). It is related to the H (FUT-1) and secretor (FUT-2) genes. It acts on the precursor chain that is in body fluids.
What product does the Le genes produce?
Le genes = L-fucosyltransferase
If the Le gene is inherited, Le_a substance is produced (in secretions)
le, h, and se do not produce products
What genes must be inherited to convert Le_a to Le_b?
Le, H, and Se genes must all be inherited to convert Le_a to Le_b
Le(a+b+) RBCs are rare
What does the Lewis antigen use as the starting building block?
The H antigen.
How do they get on red cells?
If all H, Le, and Se are inherited then Lea is converted into Leb
What happens if no Se is inherited?
If no Se is inherited then person is a non-secretor and therefore can only produce Lea
What molecules are on the precursor type 1 chain to make Le_b?
Two L-fucose molecules on the precursor type 1 chain This is a Le_b. .
What does it mean for the Lewis phenotype when 20% of the populations are non-secretors?
20% of the population are non-secretors (inherit Se) therefore around 20% of the population will be Le_a
What happens to Lewis antigens when a women with them becomes pregnant?
When women become pregnant they temporarily lose their expression of Lewis antigens (It seems to push them off the blood cells temporarily).
Plasma volume increases, so there is a decrease in plasma Le_b
Are Lewis antibodies clinically significant?
Not clinically significant – never forms HDFN or HTR
What immunoglobulin is Lewis antibodies and at what temperature and process do they best react at?
IgM
Agglutination at immediate-spin (IS) (room temp)
Some at 37° C
How do most people develop Anti-Le_a?
Anti-Lea naturally occurring and common
Do Lewis antigens experience dosage effects?
Dosage not seen
What impact does enzymes have on Lewis antibodies and do they bind complement?
Enzymes enhance antibody reactivity
Antibody binds complement; may cause hemolysis in vitro
What effect can saliva have on Lewis antibody and how is this used?
Neutralization with saliva can confirm the presence or eliminate reactions with Lewis antibody
What are the antigens of the I BGS? What is genetic behavoir?
I and i
I and i antigens are not antithetical antigens
Where do the I and i antigens form?
They form on the precursor A, B, and H chains of RBCs
How does the I BGS antigens vary between newborns and adults?
Newborns have i antigen
Adults have I antigen
i antigen (linear) converts to I antigen (branched) as a child matures (about 2 years of age)
What is the result of the ii phenotype in an adult?
It is very rare for an adult to have i antigen. They may form alloanti-I.
In an ii Adult, I antigen is very weak and i is strong.
Is the I antibody clinically significant?
- Not clinically significant (will not cause HDFN or HTR)
- Does not show dosage
- Usually autoantibody (autoanti-I) – interferes with serological testing
- Alloanti-I is rare
What immunoglobulin is the I BGS and its optimal temperature to react?
IgM
Cold-reacting
How are reactions avoided with anti-I?
Reactions are avoided by prewarming techniques
What compound antibody does anti-I form and the impact of this?
Reacts as compound antibody
Often found as an anti-IH
Stronger agglutination with RBCs having many H sites (O and A2)
Do enzymes enhance I BGS antigens? What issues does this cause?
Antigens are enhanced by enzymes. This can cause problems with IS testing such as ABO typing.
What diseases/infections are Autoanti-I associated with?
Mycoplasma pneumoniae
Cold hemagglutinin disease
What diseases/infections are anti-i associated with?
Infectious mononucleosis
Lymphoproliferative disease
Cold hemagglutinin disease (occasionally)
What is Cold Hemagglutinin disease?
- Autoimmune hemolytic anemia produced by an autoantibody that reacts best in colder temperatures (<37˚C)
- Bind at lower temperatures, complement causes cell lysis (intravascular hemolysis)
Note: There is no cure. Person can try to avoid cold temperatures.
What are the 3 antigens in the P1PK blood group system?
P1PK blood group system: P1 and P_k
Globoside blood group system: P antigen
How many phenotypes are in the P1PK blood group system?
The 3 antigens form 5 different phenotypes
P1 - Most common, has P, P1, and Pk , poorly established at birth
P2 - P and Pk antigens (can form anti-P1)
Other 3 rare
What are the P1Pk and globoside BGS antigens related to?
Structurally related to ABH antigens
Describe the characteristics of anti-P1?
- Found in P2 individuals
- Pigeon handlers (pigeon droppings have P1)
- IgM; enhanced by enzymes, activate complement
- Non-RBC stimulated
- Can be neutralized by P1 substance
What disease is autoanti-P associated with?
Associated with cold paroxysmal hemoglobinuria
What type of immunoglobulin is autoanti-P?
IgG (Donath-Landsteiner antibody - way of testing it); a biphasic hemolysin that binds with P1 or P2 cells at low temperatures before the complement is activated
What can cause the antibody autoanti-P to appear in an individual?
May be idiopathic or secondary to syphilis.
May appear in children after viral infection
What is the antibody Anti-PP1Pk? Is it clinically significant?
Occurs in individuals with the null phenotype
Causes hemolysis in vitro
Clinically significant
What occurs in cold paroxysmal hemoglobinuria disease?
In cold paroxysmal hemoglobinuria, the antibodies attach in the extremities at cold temperatures, Once they travel back to the core and warm up, then complement attaches and lyse the cells. The finger tips, toes, and nose won’t be purple like in cold hemagglutinin disease.
What is the done in the Donath-Landsteiner Test?
Three test tubes are used with the results for cold paroxysmal hemoglobinuria disease:
1. Incubated at 4C then 37C - hemolysis
2. Incubated at 4C only - no hemolysis
3. Incubated at 37C only - no hemolysis
Note: The test in the lab actually means putting the sample in the fridge then to the water bath.
Need to improve/check description with textbook.
Do antigens in the MNS blood group system show dosage?
Show dosage, homozygous inheritance enhances agglutination:
(M+N+) heterozygous
(M+N-) homozygous
How do the M and N alleles behave genetically?
M and N are antitheticals and co-dominant
What is the impact of enzymes on antigens M and N?
Destroyed by proteolytic enzymes
What antigens are in the MNS system and what codes for them?
M, N, S, s and U.
M&N –> Coded by glycophorin A
S, s and U –> Coded by glycophorin B
How are S, s and U inherited?
Inherited as haplotype with M or N
S and s are antitheticals and co-dominant
How does S, s and U antigens react with enzymes?
Destroyed (or reduced) by enzymes (some texts say variable)
When is the U antigen present?
U antigen
Present when S or s is inherited (99.9% of people)
What immunoglobulins are the MNS antibodies?
Anti-M –> IgM, sometimes IgG (rarely encountered in HDFN)
Anti-N –> Rare IgM
Anti-S, anti-s & anti-U –> IgG
What MNS antibodies are clinically significant? Which one is rare?
Anti-S, anti-s & anti-U
Anti-U is rare but can be found in S–s– persons (black population)
Do the MNS antibodies show dosage?
Yes, they all do.
What does Anti-M reactions depend on?
Variable reactions depend on reagent pH.
What treatment has N-like antibodies associated with it? Why?
N-like antibodies found in dialysis patients from formaldehyde-sterilized instruments
What is the most frequent phenotype in the MNS BGS?
U+ (99.9% in whites and 99% in blacks)
s+ (89% in whiles and 93% in blacks)
What antigens are associated with cold antibodies?
Lewis, MN, P and I.
When you write them out like
LeMN PI – it looks like lemon pie.
What antigens do proteolytic enzymes denature?
Proteolytic enzymes denature
Fy_a, Fy_b, M, N (S,s)
Which antigens show dosage?
C, c, E, e, M, N, S,s, Fy_a, Fy_b Jk_a, Jk_b
Where are human leukocyte antigens found?
HLAs are found on leukocytes and tissue cells
Any nucleated cells; not RBCs
How do HLA antibodies develop in an individual?
- HLA antibodies are produced as a result of transfusion and/or pregnancy
- Antibodies have been associated with refractoriness (unresponsiveness to platelet transfusions) and transfusion reactions.
Why is HLA testing performed?
- HLA testing is used to assess risk factors for disease susceptibility
- Matching for organ and Hematopoietic Progenitor Cell (HPC) transplants
What genes code for HLA?
Genes that code for HLA are part of the Major Histocompatibility Complex (MHC) on Chromosome 6
MHC role in determining self from non-self
What are the 3 classes MHC genes are divided into?
MHC genes are divided into 3 classes
Class I: platelets, leukocytes, nucleated cells
Class II: macrophages, dendritic cells, B cells
Class III: code for complement and cytokines.
How do individuals inherit HLA genes?
Individuals inherit one haplotype (closely linked genes) from each parent
Extremely polymorphic so very difficult to find matches
Are leukocytes transfused?
We never transfuse leukocytes and we filter out as many as possible, in a filtering technique called leukoreduction but a few smaller ones still will be found in the packed red cell units.
How has HLA testing been performed and with what type of testing is it being replaced with?
- Serologic identification requires the lymphocytotoxicity test method –>
Complement and dye are used to determine whether there is antigen–antibody recognition. This technique uses a fluorescent dye and a fluorescent microscope. - Being replaced with molecular methods
Why is matching HLAs in patients with existing antibodies important?
Matching HLAs in patients with existing antibodies is important for graft survival
HLA matching at the allelic level is important to avoid rejection and Graft vs. Host disease
How may patients get antibodies to HLAs?
Patients may become sensitized to HLAs by the following exposures:
1. Pregnancy
2. Blood transfusions
3. Previous transplant
Where can hematopoietic progenitors cells be obtained from?
Hematopoietic Progenitor Cells (HPCs) can be obtained from bone marrow, peripheral blood, and cord blood
What diseases can hematopoietic progenitors cells be used to treat?
HPCs can be used to treat diseases such as aplastic anemia, leukemia, lymphoma, and Hodgkin’s disease
What is graft-versus-host disease?
Occurs when grafted immunocompetent cells from a donor mount an immune response against the host tissue
Rash, diarrhea, jaundice, can lead to death
Can also occur in immunocompromised patient receives a blood components from a family member
How can graft-versus-host disease be prevented?
Can be prevented by irradiation of blood components
What conditions can antibodies to platelets cause?
Antibodies to platelets may cause:
Neonatal alloimmune thrombocytopenia (NAIT): destruction of newborn platelets by maternal antibody
Post-transfusion purpura (PTP): destruction of platelets after transfusion
Why are there antibodies to platelets?
Platelet proteins can elicit immune responses
What is the most common platelet antibody?
- The most common platelet antibody is directed against HPA-1a (or P1A1)
- HPA-1a is present on platelets of about 98% of population
