Heparin-associated thrombocytopenia: antibody binding specificity to
platelet antigens
DM Lynch and SE Howe
Sera from four patients with heparin-associated thrombocytopenia (HAT) were
evaluated by a quantitative enzyme-linked immunosorbent assay (ELISA) to
detect heparin-dependent serum platelet-bindable immunoglobulin (S-PBIg)
and by Western blotting and immunoprecipitation to investigate the
specificity of the antibody binding. All HAT sera showed mildly increased
S-PBIg (mean, 7.8 fg per platelet; normal, less than 6.0 fg per platelet)
to intact target platelets in the ELISA, which was markedly increased in
the presence of heparin (mean, 20.9 fg per platelet). This increase was
20-fold greater than normal control sera, which showed a mean differential
increase of only 0.5 fg per platelet. Immunoglobulin binding specificity to
platelet antigens was investigated using sodium dodecyl
sulfate-polyacrylamide gel electrophoresis of platelet lysate with transfer
of the platelet fractions onto nitrocellulose strips (Western blotting) and
subsequent immunoassay using HAT and normal sera. In the presence of
heparin, the four HAT patients demonstrated increased binding of
immunoglobulin to platelet antigens of apparent molecular weights of 180,
124, and 82 kd. Radiolabeled heparin when incubated with HAT sera, normal
sera, or albumin blanks bound to platelet proteins of the same apparent
molecular weights. These observations are consistent with current
hypotheses suggesting that HAT antibody is directed to heparin-platelet
complexes or, alternatively, that heparin induces conformational change of
antigenic sites on the platelet membrane.
Volume 66,
Issue 5,
pp. 1176-1181,
11/01/1985
Copyright © 1985 by The American Society of Hematology
