ANALYSIS OF PLATELET ANTIGENS FOR ANTI-PLATELET ANTIBODIES IN ITP USING FLOW CYTOMETRY

Idiopathic thrombocytopenic purpura (ITP) is a syndrome caused by circulating antibodies reactive with the platelet membrane. The antigenic specificity of these antibodies is unknown. We have characterized new monoclonal antibodies that react with a determinant specific to GP Ib and GP Ib- Ia complex, and used flow cytometry to investigate platelets in ITP for antigenic determinants to which autoantibodies are directed. Forty cases of ITP were analyzed in detail by the platelet suspension immunofluorescence test(PSIFT) of von dem Borne et al. The monoclonal antibodies used were 5 against GP Ib-Ia complex (NNKY1-32, NNKY2-5, NNKY2-6, NNKY2-11, NNKY2-18) and 2 against GP lb (NNKY5-4, NNKY5-5). The reactivity of monoclonal antibodies was inhibited by the presence of autoantibody on platelets in some ITP patients. Differences in inhibition were found not only between monoclonal antibodies but also between cases.

These results suggest that some ITP patients have circulating antibodies to GP Ib or GP II b - Ia, and that heterogeneous antibodies are present on platelets. Moreover, the presence of these autoantibodies may aggravate or initiate a bleeding tendency.