CHAPTER 137 HUMAN LEUKOCYTE AND PLATELET ANTIGENS Flashcards
Two major classes of HLA and their examples
class I (A, B, and C loci)
class II (DR, DQ, and DP loci)
primarily expressed on B cells and other antigen-presenting cells such as dendritic cells, endothelial cells, and monocytes
class II (DR, DQ, and DP loci)
human leukocyte antigens play key roles in: (3)
1) HSC transplantation acceptance/ rejection
2) allosensitization to non-leukoreduced blood transfusions leading to platelet transfusion refractoriness,
3) lesser, in solid- organ transplantation
HLA are highly polymorphic glycoproteins encoded by a region of genes known as the major histocompatibility complex (MHC) located on
chromosome 6p21
T/F: After ABO antigens, HLA antigens are the major barrier to transplantation.
True
Are ubiquitous and present on most nucleated somatic cells
Class I antigens
Exhibit more restricted distribution, with varying levels of expression on B cells, dendritic cells, monocytes, macrophages, and endothelial cells.
Class II antigens
T/F: class II antigens can be induced on many cell types through activation.
True
nonclassical class Ib antigens
- much less polymorphic
- function less understood
HLA-E, HLA-F, and HLA-G
Antibodies recognizing platelet-specific alloantigens have been discovered in three clinical situations:
- mothers who give birth to infants with FNAIT;
- patients who develop dramatic thrombocytopenia after blood transfusion (PTP);
- and patients who have received multiple transfusions.
principal cause of immunologic platelet transfusion refractoriness
class I HLA antigens
T/F: occasionally patients receiving multiple platelet transfusions will develop antibodies to platelet specific alloantigens.
True
If platelet transfusion refractoriness does develop because of platelet- specific antibodies, compatible platelet products may be identified by: (2)
1) using either platelet crossmatching or
2) by accessing family member or other HPA-typed donors who are compatible with the patient’s antibodies
T/F: Antibodies against some HPA-allelic determinants can inhibit platelet function.
True
_____can inhibit clot retraction and platelet aggregation, presumably because they block the binding of GPIIb/IIIa (α β ) (CD41/CD61) to fibrinogen. –> identify the type of platelet function disease
- Anti–HPA-1 alloantibodies,
- GLANZMANN
______, lack platelet GPIb-V-IX (CD 42a-c)
Bernard-Soulier syndrome
_______ can completely inhibit aggregation of HPA-4 platelets that are homozygous for the allele recognized by the alloantibodies because the epitope is in close proximity to the RGD (arginine-glycine-aspartic acid peptide sequence)
Anti–HPA-4 alloantibodies
T/F: other anti–HPA-alloantibodies, such as those specific for HPA-3, may not significantly interfere with platelet function but nonetheless can cause Fc-mediated platelet destruction and immune thrombocytopenia
TRUE
result from transfusion of antibodies to recipient HPA
passive alloimmune thrombocytopenia
Transfusion of blood components containing antibodies to ____ and _____ have been reported to result in significant thrombocytopenia for 1 to 2 weeks.
HPA-1a and -5b
T/F: Many of the best-documented platelet-specific antibodies detected in such patients are directed against platelet antigens whose phenotypic frequencies are less than 30% in the blood-donor population.
Matching Type:
1. Anti–HPA-1 alloantibodies
2. Anti–HPA-3 alloantibodies
3. Anti–HPA-4 alloantibodies
4. Anti–HPA-1a and 5b alloantibodies
a. inhibit aggregation of HPA-4 platelets that are homozygous for the allele recognized by the alloantibodies because the epitope is in close proximity to the RGD
b. result in significant thrombocytopenia for 1 to 2 weeks
c. can inhibit clot retraction and platelet aggregation, presumably because they block the binding of GPIIb/IIIa (α β ) (CD41/CD61)
d. can cause Fc-mediated platelet destruction and immune thrombocytopenia
1, c
2, d
3, a
4, b
TESTING FOR PLATELET-SPECIFIC ANTIGENS AND ANTIBODIES
The earliest.
Involved mixing of patient serum with normal platelets and used platelet function-dependent end points such as α-granule release, aggregation, or agglutination.
Phase I
TESTING FOR PLATELET-SPECIFIC ANTIGENS AND ANTIBODIES
the only major phase I assay remaining in wide use today
serotonin release assay
TESTING FOR PLATELET-SPECIFIC ANTIGENS AND ANTIBODIES
detect either surface or total platelet-associated immunoglobulin on patient platelets or on normal platelets after sensitization with patient serum
phase II tests
TESTING FOR PLATELET-SPECIFIC ANTIGENS AND ANTIBODIES
An example of a phase II assay in wide use today:
solid-phase red cell adherence test, used for platelet crossmatching
TESTING FOR PLATELET-SPECIFIC ANTIGENS AND ANTIBODIES
developed in which the binding of antibodies to isolated platelet surface GPs is detected.
Phase III assays
TESTING FOR PLATELET-SPECIFIC ANTIGENS AND ANTIBODIES
detect alloantibodies in the evaluation of suspected FNAIT and PTP, as well as autoantibodies in some cases of ITP
Phase III assays
Examples of phase III assays (2)
- monoclonal antibody immobilization of platelet antigens assay (MAIPA)
- modified antigen capture ELISA (MACE)
because of limited access to rare typing sera and the need to establish platelet typing in patients with very few platelets, they have been largely supplanted by _______
molecular typing using methods based on PCR
Alleles present at gene frequencies greater than 2 percent within the population are designated as ____
public alleles
These alleles are more likely to encode alloantigens involved in PTP.
public alleles
HPA NOMENCLATURE
_____ allele represents the more prevalent form of the protein, while the _____ allele represents the less-common form.
a, b
HPA-lb is expressed on the platelets of approximately _____ percent of persons of European ancestry but of less than____ percent of persons of Asian ancestry
15, 1
Type _____ CD36-deficient individuals can become immunized via transfusion or pregnancy and make isoantibodies against CD36 that have been implicated in cases of FNAIT, PTP, and platelet transfusion refractoriness.
I
T/F CD36 deficiency is common in Asians and Africans, but is rare in white populations.
TRUE
Platelet GPIV (CD36) is expressed on various human cells including (5)
platelets, macrophages, capillary endothelium, erythroblasts, and adipocytes
Matching Type
- ANN
- AIN
- TRALI
a. anti–HNA-2 and anti–HNA-3a
b. anti–HNA-1a, anti–HNA-1b and FcγRIIIb epitopes
c. anti–HNA-1a, anti–HNA-1b, anti–HNA-2, anti-FcγRIIIb
- c
- b
- a
- neutropenia is detected in the first week of life when the neonate becomes febrile or develops an infection
-neutrophil count are 0.1 to 0.2 × 109/L. - Total WBC , platelet count, and hemoglobin are usually normal, but eosinophilia or monocytosis may be present.
- occasionally, infant is asymptomatic, but almost all affected children have an infection.
- The duration of the neutropenia may be as short as a few days or as long as 28 weeks.
-The mean duration of neutropenia is approximately 11 weeks.
Alloimmune Neonatal Neutropenia
Pathophysiology of Alloimmune Neonatal Neutropenia
During pregnancy, mothers can become alloimmunized to fetal neutrophil antigens. Maternal IgG directed to neutrophils can cross the placenta and destroy the neonate’s neutrophils.
T/F: (IVIG) and granulocyte colony-stimulating factor (G-CSF) have a limited role in the treatment of neonatal alloimmune neutropenia
TRUE
In most cases, children presented with severe neutropenia, having neutrophil counts less than 0.5 × 109/L
Monocytosis has been reported to occur in up to 38 percent of patients.
Marrow biopsies in affected patients usually show normal to hypercellular marrow with a decreased number of mature neutrophils.
Autoimmune Neutropenia of Childhood
In AIN, the onset of autoimmune neutropenia of children begins at ___months of age
Most studies have found that neutrophil counts recover spontaneously by the age of ____ years, with a median duration of neutropenia of 13 to 20 months.
8, 5
occurs within 6 hours of a transfusion when hypoxia and noncardiogenic pulmonary edema occur, as measured by a fall in hemoglobin oxygen saturation to less than 90 percent or a partial pressure of arterial oxygen (PaO2)-to-fraction of inspired oxygen (FIO2) ratio (PaO2:FIO2) of less than 300 torr
TRALI
T/F Febrile nonhemolytic transfusion reactions occur within a few hours of a transfusion and can be associated with chills and rigors.
T
Matching Type
- are expressed only on neutrophils
- expressed on neutrophils and subpopulations of neutrophils
- neutrophils, lymphocytes, platelets, endothelial cells, kidney, spleen, and placental cells.
a. HNA 2
b. HNA 1
c. HNA 3
1, b
2, a
3, c
- previously known as Mart(a)
- located on the αM chain (CD11b) of the C3bi receptor (CR3)
- caused by a single nucleotide substitution of G-to-A at position 30283 (Arg->His 61)
- significance unknown
HNA 4
- first described as Ond(a)
- ound to be expressed on the αL integrin unit, leukocyte function antigen-1 (CD11a),
- result of a G-to-C single nucleotide substitution at position 2446 (Arg-> Thr at 766)
HNA 5
result of a single nucleotide change in choline transporter-like protein-2 gene (SLC44A2) at nucleotide 455, which results in an amino acid change at position 152
HNA 3
Role of NB1 Glycoprotein in Neutrophil Function
(3)
binds to platelet endothelial cell adhesion molecule-1 (PECAM-1, CD31) and functions as a cell adhesion molecule.
important in the migration of neutrophils through endothelial cells.
involved with neutrophil–endothelial cell interaction
T/F: CD177 mRNA is overexpressed by neutrophils from patients with polycythemia rubra vera and essential thrombocytosis, but the expression of HNA-2 is not.
TRUE
gene encoding NB1 glycoprotein, ____, is located on chromosome ____
CD 177
19q13.31
HNA 1
_____ of neutrophilic metamyelocytes, and on approximately ____ of neutrophilic myelocytes
one-half
10%
T/F The four HNA-1 system antigens are encoded by three alleles.
True
The antigen frequencies of three of the alleles vary widely among different racial groups.
Among whites, _____ is the most common antigen, but in Japanese and Chinese populations ____ is most common.
HNA-1b
HNA-1a
Function of HNA-1 Antigens
Neutrophils that are homozygous for HNA-1b have a lower affinity for immunoglobulin (Ig) G3 than those homozygous for HNA-1a.
Neutrophils from those who are homozygous for HNA-1b phagocytize erythrocytes sensitized with IgG1 and IgG3 anti-Rh monoclonal antibodies and bacteria opsonized with IgG1 at a lower level than neutrophils homozygous for HNA-1a.
Patients requiring platelet transfusions may be broadly sensitized to _____ (i.e., have high PRA) through prior transfusions (particularly nonleukoreduced) or pregnancies.
HLA-A, and -B
_____ ankylosing spondylitis
_____ narcolepsy
_____ associated with hypersensitivity to abacavir
HLA- B27
HLA-DQ2
HLA-B*5701
The HLA antigens coded by the MHC play a central role in
(3)
- transplantation - most common application
- regulation of immune responses, and
- susceptibility to a variety of diseases.
HLA typing for matching of kidneys and pancreas is performed at the ________ loci at low resolution (serologic or antigen level by DNA).
HLA-A, HLA-B, and HLA-DR
T/F: HLA matching is not prospectively performed for hepatic or cardiac transplantation.
TRUE
_____ and ______ prime importance for kidney and heart transplants where its existence could cause a hyperacute rejection and graft failure.
Detection of alloantibody by screening techniques and the donor specific crossmatch
T/F In HSC, the graft may recognize the host tissue as foreign and mount an immune response resulting graft-versus-host disease (GVHD)
T
HUMAN LEUKOCYTE ANTIGEN TYPING
Tissue typing for HLA antigens can be performed by various methods using (3) technologies
serologic, cellular, and molecular
common prior to the widespread adoption of DNA methods.
are labor-intensive and require the use of radioisotopes;
mainly used in research laboratories.
Cellular assays
Cellular assays
mixed lymphocyte reaction and the primed lymphocyte test
a suspension of lymphocytes is incubated with human alloantisera or monoclonal antibody in a microtiter tray.
CDC
test has been a fundamental procedure for defining HLA antigens for more than 30 years
CDC
Serology for class II (DR and DQ) antigens requires enrichment for B lymphocytes, which can be accomplished with antibody or _____
immunomagnetic bead reagents.
involve amplification of genomic DNA from selected portions of HLA genes with oligonucleotide primer pairs
PCR
primarily of clinical interest in marrow/blood stem cell transplantation.
Molecular HLA typing
described as massively parallel allowing for many overlapping reads of the same sequence area
NGS
This is very important for solid-organ transplantation where the presence of ______ can cause irreversible rejection upon transplantation.
detection of antibodies to HLA antigens.
have become standard practice as they are more sensitive than the CDC method.
solid phase assays
T/F The α chain of HLA-DR is constant for all HLA-DR molecules, whereas the β chain is polymorphic and determines specificity of the molecule.
T
Class II molecules: extracellular regions of each chain contain only two domains. The two domains of the α chain are designated α1 and α2, and the two domains of the β-chain are called β1 and β2.
In all class II antigens the______represents the most polymorphic region.
β1 domain
Class I Antigens
Antigenicity resides in the_____, the areas of highest polymorphism
α1 and α2 domains
T/F
Platelets express HLA-A antigens, but lack some HLA-B and most HLA-C antigens.
T
Include genes that encode other proteins that participate in immune response such as complement, heat shock proteins, tumor necrosis factor, and other lymphocyte antigens.
class III genes
Class____ genes are the most centromeric
Telomeric are the class____ genes
II
I
