A novel antigen-specific capture assay for the detection of platelet antibodies and HPA-1a phenotyping.
OBJECTIVE
The antigen-specific assays currently used for the laboratory investigation of platelet antibodies and antigens are technically complex and cannot be used in most routine laboratories. Here, we describe a simple antigen-specific capture assay (ASCA) for the detection of serum platelet antibodies and for human platelet antigen-1a (HPA-1a) phenotyping.


METHODS
For the detection of platelet antibodies, platelets from healthy blood donors were incubated with biotinylated monoclonal antibodies to platelet glycoprotein complexes (GP), then solubilized and mixed with superparamagnetic streptavidin particles. Serum samples from patients with autoimmune thrombocytopenia (n = 39), from patients with platelet alloantibodies (6 HPA-1a, 1 HPA-2b, 1 HPA-3a, 6 HPA-5b), and from healthy blood donors (n = 70), were tested. All serum samples from the patients were investigated in parallel by the indirect monoclonal antibody-specific immobilization of platelet antigen assay (MAIPA). For HPA-1a phenotyping, superparamagnetic particles were coated with a monoclonal antibody to HPA-1a and mixed with diluted whole blood samples from healthy blood donors (n = 139), who had previously been genotyped for platelet alloantigens. Results The indirect MAIPA detected autoantibodies in 18%, and the direct MAIPA in 50% of patients tested. In contrast, the new ASCA demonstrated positive results in 77% of patients. All tested alloantibodies reacted positive by the ASCA, and all serum samples from healthy blood donors were negative. The results of HPA-1a phenotyping were in concordance with those of genotyping in all cases.


CONCLUSIONS
In our opinion, the ASCA is easy to perform and much more sensitive than the currently available antigen-specific assays for the detection of platelet antibodies.
Meyer
O
O
Charité, Universitätsmedizin Berlin, Institut für Transfusionsmedizin, Berlin, Germany.
Agaylan
A
A
Bombard
S
S
Kiesewetter
H
H
Salama
A
A
D016824:Antigens, Human Platelet / Q000276:immunology*; D019921:Biotinylation; D001792:Blood Platelets / Q000276:immunology*; D005838:Genotype; D006801:Humans; D007118:Immunoassay / Q000379:methods*; D016130:Immunophenotyping; D039661:Integrin beta3; D007518:Isoantibodies / Q000032:analysis*; D010980:Platelet Membrane Glycoproteins; D011237:Predictive Value of Tests; D016553:Purpura, Thrombocytopenic, Idiopathic / Q000175:diagnosis / Q000276:immunology
D016824:Antigens, Human Platelet; C061248:ITGB3 protein, human; D039661:Integrin beta3; D007518:Isoantibodies; D010980:Platelet Membrane Glycoproteins