The human platelet membrane glycoprotein complex GP IIb-IIIa expresses
antigenic sites not exposed on the dissociated glycoproteins
JP Rosa, N Kieffer, D Didry, D Pidard, TJ Kunicki and AT Nurden
A number of recent reports have described murine monoclonal antibodies that
react specifically with the complex formed by human platelet membrane
glycoproteins (GP) IIb and IIIa. We show that the IgG L, a previously
described human alloantibody isolated from a polytransfused thrombasthenia
patient, has similar properties. When used in non- precipitating amounts in
crossed immunoelectrophoresis (CIE), 125I-IgG L bound strongly to the
IIb-IIIa complex. However, after dissociation of the complex with EDTA,
only a weak binding to GP IIb and no binding to GP IIIa was detected. In
further studies, increased amounts of IgG L were interacted with
125I-labeled membrane glycoproteins in (a) CIE and (b) classical indirect
immunoprecipitation experiments. Although the antibody was able to
quantitatively precipitate the IIb-IIIa complex from Triton X-100-soluble
extracts of platelet membranes, no precipitation of GP IIb or GP IIIa was
observed after divalent cation chelation. Addition of EDTA to
immunoprecipitates containing GP IIb- IIIa resulted in dissociation and
partial release of both glycoproteins. The interaction of the IgG L with
electrophoretically separated GP IIb and GP IIIa was studied using a
Western blot procedure in the presence of Ca2+, Mg2+, or EDTA. The presence
of divalent cations did not increase the reactivity of the antibody with
the individual glycoproteins. Overall, our results show that acquired
antibodies to IIb-IIIa, such as the IgG L, may predominantly react with
complex-dependent determinants.
Volume 64,
Issue 6,
pp. 1246-1253,
12/01/1984
Copyright © 1984 by The American Society of Hematology
