On the surface of granulocytes and platelets, erythrocyte antigens, antigens of the HLA system and antigens of plate lets and granulocytes can be expressed. This short dissertation will focus on this third type of antigens.
Platelet immunohematology From a clinical point of view, platelet antigens are important as they are implicated in neo natal alloimmune thrombocytopenia (FNAIT) and posttransfusion purpura (PTP). Almost always these clinical manifestations are related to the production of an alloantibody directed against the HPA-1a antigen. Forms of autoimmune thrombocytopenia are also described, in which autoantibodies can be directed against platelet-specific antigens.
Although numerous platelet-specific antigens have been defined, for some of them the platelet-specific denomination is not fully correct, being evidenced in many other cells, especially of endothelial derivation. Of the numerous glycoproteins expressed on the platelet membrane, only some (GP Ia, GP Ibα, GP Ibβ, GP IIb, GP IIIa, and CD109) show polymorphisms that make them immunogenic.
Granulocyte immunohematology Granulocyte antigens and related allo-antibodies can be implicated in several clinical syndromes, the two most relevant being neonatal immune neutropenia (FNAIN) and transfusion-related acute lung injury (TRALI). Antibodies directed to leukocyte anti gens may also be the cause of the most common complication of blood component transfusion, namely the nonhemolytic posttransfusion febrile reaction. As reported in Table 1, seven proper granulocyte antigens have been described. The HNA-1a antigen and its antithetic HNA-1b antigen are expressed on CD16 (FcγRIIIb), both have been associated with TRALI and NAIN. The HNA-2a antigen is found on CD177, and is also associated with TRALI and NAIN. Further antigens have also been described (5b or HNA-3a, MARTa or HNA-4a and ONDa or HNA-5a) which, although present on granulocytes, are also identifiable on other cells. They are therefore not granulocyte specific. In neonatal autoimmune neutropenia, auto antibodies are directed towards HNA-1a or HNA-1b antigens in more than half of cases (Tables 2 and 3).
Table1. Principal RH gene and antigens encoded
Table2. Platelet antigens
Table3. Granulocytes antigens
