Summary
Chronic immune thrombocytopenic purpura is due to platelet destruction induced by
autoantibodies against platelet surface antigens. Prior studies show that some serum
autoantibodies are light-chain restricted, suggesting a clonal origin. Since plasma
and platelet-associated antibody from the same patient may bind to different epitopes,
it is important to evaluate the clonality of platelet-associated antibody. Platelet-associated
autoantibodies from 28 ITP patients were studied. Of 23 platelet-associated antibodies
tested directly, 16 showed significant light chain restriction (7 complete and 9 partial)
when compared to plasma IgG light chain distribution. Similarly, 9 of 12 platelet-associated
antibody eluates were light chain restricted, 5 complete and 4 partial. In all cases
where platelet-associated antibody and antibody eluate from the same patient were
studied, the results were concordant. We conclude that a significant proportion of
platelet-associated antibodies from ITP patients show apparent clonality, as evaluated
by light chain restriction. These results are consistent with other studies in ITP
suggesting a limited antigenic repertoire.
Keywords
ITP - autoantibody - platelet - clonality