FROZEN PLATELET PLATES FOR PLATELET ANTIBODY DETECTION AND CROSS-MATCH

We performed 2 studies aimed at developing a frozen platelet panel sui table for platelet cross-matching. The stability of the most important platelet membrane glycoproteins and the reactivity of antigens of the human platelet antigen (HPA) and of the human leukocyte antigen (HLA) systems were evaluated with the platelet suspension immunofluorescenc e test (PSIFT) in a panel of platelets frozen in microplates with 6% d imethylsulfoxide. In study No. 1 we evaluated platelet reaction with a broad-spectrum weak anti-HLA and a potent anti-HPA-1a antiserum and t he expression of glycoproteins Ib and IIb/IIIa complex on platelet mem brane before freezing and after 0.5, 1, 2, 3, 4, 5, 6 and 12 months of storage at -80 degrees C. In study No. 2 we examined platelet reactiv ity with anti-HPA-1b, -HPA-2a, -HPA-3a, -HLA-A2, -HLA-A3 of platelets stored frozen for 12 months in parallel with fresh platelets from the same donors. Study No. 1 showed that glycoprotein expression was stabl e and that the weak anti-HLA and the potent anti-HPA-1a antibodies wer e clearly detected during 12 months at -80 degrees C. Of the 35 paired PSIFT performed in study No. 2 with fresh and frozen/thawed platelets incubated with anti-HPA-1b, -HPA-2a, -HPA-3a -HLA-A2, -HLA-A3 antiser a and AB serum, concordant reactions were obtained in all cases with t he exception of 1 case of HLA-A3-positive platelets incubated with ant i-HLA-A3 antiserum, that was reactive with frozen/thawed platelets but nonreactive with fresh platelets from the same donor. The discrepant finding obtained with fresh platelets from 1 donor could be due to the well-known variable and weak association of HLA antigens to platelet membrane. We conclude that frozen platelet plates can be stored and us ed for at least 12 months for detecting platelet-reactive antibodies i n patients' sera.