Induction of platelet Ca2+ influx and mobilization by a monoclonal antibody
to CD9 antigen
T Hato, M Sumida, M Yasukawa, A Watanabe, H Okuda and Y Kobayashi
Department of Internal Medicine, School of Medicine, Ehime University,
Japan.
We found that a monoclonal antibody (MoAb) to CD9 antigen, PMA2, induced a
rise in cytosolic free calcium concentration ([Ca2+]i) in fura-2-loaded
platelets, and we examined whether this response was due to direct action
of PMA2 on CD9 antigen. The rise in [Ca2+]i was dependent on the PMA2
concentration, irrespective of the presence or absence of extracellular
Ca2+. The role of secreted adenosine diphosphate (ADP) and thromboxane in
the [Ca2+]i response to PMA2 was studied using creatine phosphate/creatine
phosphokinase (CP/CPK) and aspirin. Combined treatment with CP/CPK and
aspirin abolished the rise in [Ca2+]i, although either CP/CPK or aspirin
alone produced only partial inhibition. Inhibition of adenosine
triphosphate (ATP) secretion and thromboxane B2 synthesis by an MoAb to the
glycoprotein IIb-IIIa complex, PMA1, resulted in little [Ca2+]i response to
PMA2. In contrast, thrombasthenic platelets, in which ATP secretion and
thromboxane B2 synthesis were normal, showed a normal [Ca2+]i response.
When PMA2 was added to CD9+ mononuclear cells, no rise in [Ca2+]i was
observed. Thus, we conclude that binding of monoclonal immunoglobulin G
molecules to the CD9 antigen raises [Ca2+]i through the effect of secreted
ADP and thromboxane on platelets, and that CD9 antigen is not directly
involved in induction of Ca2+ influx and mobilization.
Volume 75,
Issue 5,
pp. 1087-1091,
03/01/1990
Copyright © 1990 by The American Society of Hematology
