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J Arnott, P Horsewood and JG Kelton
Platelet-associated IgG (PAIgG) is elevated in idiopathic thrombocytopenic
purpura (ITP), but it also is elevated in other thrombocytopenic disorders
traditionally considered to be nonimmune. Consequently it is possible that
elevated PAIgG is a nonspecific finding secondary to thrombocytopenia. To
study this issue we developed a rabbit model of immune and nonimmune
mediated thrombocytopenia. The mechanism of the thrombocytopenia was
validated by platelet survival studies. Immune thrombocytopenia was
produced by injection of antirabbit platelet serum that was raised in
guinea pigs. Nonimmune aregenerative thrombocytopenia was produced by
irradiation of the animals; nonimmune consumptive thrombocytopenia was
produced by injection of adenosine diphosphate (ADP). PAIgG was measured in
a direct binding assay using 125I-labeled staphylococcal protein A (SpA).
Washed platelets from normal, nonthrombocytopenic rabbits bound an average
of 81 molecules of SpA per platelet (81 +/- 168, mean +/- 2 SD, n = 39).
Infusion of the antiplatelet antiserum produced thrombocytopenia with a
rise in PAIgG that was closely correlated with the level of PAIgG (r =
0.86, n = 12). The thrombocytopenia was consumptive, as shown by a very
short platelet life span using 111In- labeled platelets. In contrast, both
nonimmune thrombocytopenic states resulted in an equal or greater drop in
the platelet count but no change in the level of PAIgG. The animals with
aregenerative thrombocytopenia had normal or only moderately reduced
platelet life spans; however, in every animal the level of PAIgG was not
different from the nonthrombocytopenic controls, irrespective of the
platelet count. Similarly, the level of PAIgG was unchanged in those
rabbits with nonimmune consumptive thrombocytopenia following infusion of
ADP (82 +/- 55 molecules of SpA per platelet, mean +/- SD, n = 6). These
studies indicate that elevated PAIgG is a specific finding of immune
thrombocytopenia and is not secondary to thrombocytopenia itself.
Indirectly these results support our hypothesis that immune mechanisms
contribute to more thrombocytopenic disorders than was once thought likely.
This article has been cited by other articles:
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| Copyright © 1987 by American Society of Hematology Online ISSN: 1528-0020 | |||||||||