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