This document discusses platelet immunohematology, including definitions of platelet antigens and antibodies. It describes various platelet antigens that are either non-specific (such as ABH antigens expressed on platelets) or specific (such as Human Platelet Antigens). It discusses platelet alloantibodies that can cause conditions like platelet refractoriness, neonatal alloimmune thrombocytopenia, and post-transfusion purpura. Autoimmune conditions involving platelet autoantibodies like immune thrombocytopenia are also covered. Methods for testing platelet antigens and antibodies are described at the end.

1. RAFIQ AHMAD
Platelet Immunohematology

2. Definition
Antigens expressed on platelets , together
with antibodies that arise when individuals
are sensitized to those markers. Those
antigens and the immune responses to
them are of importance in alloimmune,
autoimmune, and drug-induced immune
syndromes

3. Platelet Antigens
Platelet Non-Specific Antigens
- Red cell Antigens
- HLAAntigens
Platelet specific Antigens
- Human Platelet Antigens (HPA)

4. Platelet Non-Specific Antigens
Red Cell Antigens on Platelets
ABH : GPIIb (CD41) & PECAM (CD31)
- Higher expression : 5%-10% in non-O group
individuals
- Immune complex formation
› Immune destruction › Platelet
Refractoriness
Non-ABH antigens
Lewis
Ii
P, Pk
Cromer

5. Platelet Non-Specific Antigens
HLA Antigens on platelets
HLA Class I Antigens
Anti-HLA antibody formation
21-28 days for primary immunization
4 days after secondary exposure
Sensitization : 18% to 50%
- Underlying disease of the patient
- Immunosuppression due to treatment
regimens
- Number of leukocytes present in the
product

6. Platelet Specific Antigens
Platelet Glycoproteins
GP-Ia
GP-Ib-alpha
GP-Ib-beta
GP-IIb
GP-IIIa
CD109 GP-VI (CD36)
Ia/IIa (CD49b/CD29)
IIb/IIIa (CD 41/61)
Ib/IX/V (CD 42c/42a/42d)

7. Platelet Specific Antigens
Allele
frequency
Caucasian
AA
Change
Nucleotide
Change
GlycoproteinOriginal NamesAntigenHPA
System
98%33L176TGPIIIaZwa
, PLA1HPA-1aHPA-1
28%33P176CZwb
, PLA2HPA-1b
99%145T482CGPIbaKob
HPA-2aHPA-2
16%145M482TKoa
, Siba
HPA-2b
84%843I2621TGPIIbBaka
, Leka
HPA-3aHPA-3
63%843S2621GBakb
HPA-3b
100%843S506GGPIIIaYukb
, Pena
HPA-4aHPA-4
<1%143Q506AYuka
, Penb
HPA-4b
99%505E1600GGPIaBrb
, Zavb
HPA-5aHPA-5
15%505K1600ABra
, Zava
, Hca
HPA-5b
<1%R489Q1544G>AGPIIIaCaa
, Tua
HPA-6w
<1%P407A1297C>GGPIIIaMoa
HPA-7w
<1%R636C1984C>TGPIIIaSra
HPA-8w
<1%V837M2602G>AGPIIbMaxa
HPA-9w
<1%R62Q263G>AGPIIIaLaa
HPA-10w
<1%R633H1976G>AGPIIIaGroa
HPA-11w
<1%G15E119G>AGPIbbIya
HPA-12w
<1%T799M2483C>TGPIaSita
HPA-13w
<1%K611del1909_1911delA
AG
GPIIIaOea
HPA-14w
74%703S2108CCD109Govb
HPA-15aHPA-15
76%703Y2108AGova
HPA-15b
<1%T140I497C>TGPIIIaDuva
HPA-16w
<1%T195M662C>TGPIIIaVaa
HPA-17w
<1%Q716H2235G>TGPIaCaba
HPA-18w
<1%K137Q487A>CGPIIIaSta
HPA-19w
<1%T619M1949C>TGPIIbKnoHPA-20w
<1%E628K1960C>AGPIIIaNosHPA-21w
<1%K164T584A>CGPIIbSeyHPA-22w
<1%R622W1942C>TGPIIIaHugHPA-23w
<1%S472N1508G>AGPIIbCab2(a+)HPA-24w
<1%T1087M3347C>TGPIaSwia
HPA-25w
<1%K580N1818G>TGPIIIaSeca
HPA-26w
<1%L841M2614C>AGPIIbCab3(a+)HPA-27w

8. Platelet Antibodies
Alloantibodies
-Alloimmune Platelet Refractoriness
-Neonatal Alloimmune Thrombocytopenia (NAIT)
-Post Transfusion Purpua (PTP)
Autoantibodies
- Autoimmune Thrombocytopenia (ITP)
- Chronic ITP
- Drug induced antibody

9. Platelet Alloantibodies
Platelet Refractoriness
Immune Cause:
CCI = BSA (m2) × PCI × 1011/ Number of Platelets
Transfused
PPR(%) = TBV × PCI/Number of Platelets
Transfused
Tested 10 – 60 minutes after transfusion
CCI of 7500 platelets × m2 body surface area/μL or
PPR of 20 % can be considered acceptable

10. Platelet Refractoriness
Non-Immune Cause
- Massive bleeding
- Fever
- Sepsis
- Splenomegaly (splenic sequestration)
- DIC
- Allogeneic HSCT
- Poor storage of platelets before transfusion
- Effects of drugs (may include immune mechanisms)
- Intravenous amphotericin B
- TTP

11. Platelet Alloantibodies
Platelet
Refractoriness
Platelet Specific HLA antibody
detection
Serological
- PRA
Molecular
- DNA based

12. Platelet Refractoriness
Platelet Transfusion
Degree of Matching for HLA-Matched Platelets
Recipient
A1, 3; B8, 27
Donor
DescriptionMatch Grade
A1, 3; B8, 274-antigen matchA
A1, –; B8, 271 antigen unknown or blankB1U
A1, 3; B8, 71 cross-reactive groupB1X
A1, –; B8, 71 antigen blank and 1 cross-
reactive
B2UX
A1, 3; B8, 351 mismatched antigen
present
C
A1, 32; B8, 352 or more mismatched
antigens present
D
A2, 28; B7, 35RandomR

13. Platelet Alloantibodies
Neonatal alloimmune thrombocytopenia (NAIT)
Risk of major bleeding complications, especially
intracranial
hemorrhage (ICH)
- HPA1a antibody common cause
- Maternal serum tested for antibody
- Father serum tested to confirm the diagnosis
- Parental platelet genotyping by molecular method
Treatment
- IVIG
- Antigen compatible platelets
- Antenatal treatment IVIG with steroids (prevents fetal
ICH)

14. Platelet Alloantibodies
Posttransfusion Purpura (PTP)
5-10 days after blood transfusion
Common antiplatelet antibody is HPA-1a
Others specificity with GPIIb/IIIa
Treatment
- IVIG
- Plasmapheresis
- Antigen negative platelets (may have reduced in-
vivo survival)

15. Prevention of Platelet
Immunization
Leukocyte -reduction in the platelet products and
the use of
ultraviolet B (UVB) irradiation
- It reduced the incidence of HLA antibody
generation from 45% to 17% - 21%
- The prevalence of platelet refractoriness also
reduces from 16% to between 7% -10%

16. Platelet Autoantibodies
Autoimmune Thrombocytopenia (ITP)
Acute
children, following viral infection
abrupt onset, with severe thrombocytopenia, bleeding
Resolves spontaneously with 2 to 6 months
Chronic
adults, idiopathic or secondary to HIV, malignancy or
other autoimmune disorders
Moderate thrombocytopenia for months to years
GPIIb/IIIa binding of
autoantibodies
can block fibrinogen binding

17. Drug-induced Platelet Antibodies
Abciximab, Heparin ,Ranitidine, Acetaminophen,
Ibuprofen Rifampin, Carbamazepine,
Levofloxacin, Sceftazidime, Loracarbef,
Sulfisoxazole, Ceftizoxime, Naproxen, Suramin,
Ceftriaxone, Orbofiban, Tirofiban, Ciprofloxacin,
Oxaliplatin, Trimethoprim, Eptifibatide,
Phenytoin, Vancomycin, Esomeprazole,
Propoxyphene, Xemilofiban Fentanyl, Quinidine,
Fexofenadine,
Quinine.Heparin Induced
Thrombocytopenea

18. Testing for Platelet-Specific Antigens
and Antibodies
Mixed Passive Hemagglutination Assay (MPHA)
PIFT ( ELISA or Flow Cytometry)
Flow cytometric beads
antibody detection assay
Fluorescent labelled anti
human immunoglobuline
under the
microscope

19. Testing for Platelet-Specific Antigens
and Antibodies
Monoclonal Antibody-
Specific Immobilization of
Platelet Antigen (MAIPA)
Assay
HPA-1 genotyping
Taqman PCR
results (ntc=negative
control

20. The end!!
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