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DM Reid, CE Jones, JG Vostal and NR Shulman
Clinical Hematology Branch, National Institute of Diabetes, Digestive, and
Kidney Diseases, National Institutes of Health, Bethesda, MD 20892.
We have found that Western blots (WBs) of whole platelets exposed to normal
autologous or homologous sera commonly have bands at 90 to 95 (95) Kd, and
less often at 100 to 110, 80 to 85, 60 to 75, and 50 to 60 Kd when
developed with antiglobulins. The percentages of normal sera producing a
95-Kd band with anti-immunoglobulin G (IgG), -IgA, and -IgM are 85, 50, and
30, respectively. Antiglobulin reagents alone also produce background bands
on WBs that we have shown correspond to levels of platelet-associated Igs
(PAIgs) or their derivatives. Titers of 95 Kd-reactive IgG in normal sera
range from 10 to 1,280 (85% less than or equal to 50), and the reaction
appears to be partially F(ab')2- mediated. The 95-Kd protein is internal
and differs in many respects from surface glycoproteins IIIa, IV, and V of
similar apparent molecular weight. In thrombocytopenic patients there was
no correlation between severity of thrombocytopenia or PAIgG of platelet
eluates and corresponding serum titers of 95 Kd-reactive IgG. Some WB
reactions previously reported as evidence of autoimmunity may represent
normal variations in reactions of Igs with internal platelet proteins.
These reactions may be immunospecific or analogous to nonspecific,
partially F(ab')2-dependent binding of Igs by certain bacterial proteins.
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