A NEW MONOCLONAL ANTIBODY TO PLATELET MEMBRANE GLYCOPROTEINIV: EXPRESSION OF GLYCOPROTEIN IV ON PLATELETS, MEGAKRYOCYTES AND ERYTHROBLASTS

A New monoclonal antibody, designated as TP85, was produced by fusion of the X63.Ag8.653 murine myeloma cell line with splenocytes from BALB/C mice immunized with washed human platelets. TP85 monoclonal antibody precipitated a single petide of 97,000 daltons in both reduced and nonreduced states by immune precipitation of ¹²⁵I-labelled solubilized membrane. An isoelectric point was around pH 5.0. The antibody was IgG2b in isotype, as determined by the Ouchterlony immunodiffusion method.

The reactivity of TP85 was examined by using indirect immuno-fluorescent assays and ABC immunoperoxidase method. TP85 reacted with platelets, megakaryocytes and erythroblasts from normal human and patients with myeloproliferative disorders, but not with lymphocytes, granulocytes and other bone marrow cells. In a panel of cultured cell line, only 5-10% cells of K652 myeloid/ erythroid cell line were positive, but other cell lines, including common ALL(Reh), T lymphoid(Molt-3, CCRF-CEM), B lymphoid(Raji ,Daudi), myeloid(KG-l, HL-60) and monoblastoid(U937, THP-l) cell lines, were all negative.

TP85 did not inhibit platelet aggregations induced by ADP, collagen, epinephrine and ristocetin while TP80 which was an antibody for GPIIb/IIIa inhibited these aggregations except induced by ristocetin.

It is concluded that glycoprotein IV, which is immunoprecipitated by TP85, may exist not only on platelet membrane, but also on megakaryocytes and erythroblasts, and has no role on platelet aggregation.