Alloimmunization to platelet‐specific antigens on glycoproteins IIb‐ IIIa and Ib/IX in multiply transfused thrombocytopenic patients

The rate of alloimmunization to platelet‐specific antigens associated with platelet glycoproteins (GPs) IIb‐IIIa and Ib/IX was studied in 293 multiply transfused thrombocytopenic patients. Antibodies to platelet‐ specific antigens were measured with a solid‐phase assay using platelet GP IIb‐IIIa or Ib/IX as the antigenic targets. Nine patients were found to have antibodies to platelet GP IIb‐IIIa, and no patients had antibodies to platelet GP Ib/IX. In six of these nine patients, the specificity of the antibody was shown by using GP IIb‐IIIa from donors with different platelet‐specific antigen phenotypes. In the remaining three patients with antibodies to platelet GP IIb‐IIIa, no specificity could be identified. These patients had autoimmune thrombocytopenia in association with lymphoma. The alloimmunization rate to platelet‐ specific antigens associated with GP IIb‐IIIa was 2 percent, whereas the rate of alloimmunization to HLA antigens was 23 percent. Of the patients alloimmunized to HLA antigens, 9 percent also had antibodies to platelet‐specific antigens. A poor response to HLA‐identical platelet transfusions was observed only in those patients with positive assays in the solid‐phase test. These results suggest that the incidence of antibodies to platelet‐specific antigens carried on GP IIb‐ IIIa is low. Platelet‐specific antibodies may be found more frequently in patients alloimmunized to HLA antigens than in those not so alloimmunized. 1990 AABB