Center for Immunochemistry,l Departments ofMedicine2 and Laboratory Medicine,4 Veterans .... standard (Gamimume-N; Cutter Laboratories, Berkeley,. Calif.) ...
Vol. 56, No. 11
INFECTION AND IMMUNITY, Nov. 1988, p. 2907-2911
0019-9567/88/112907-05$02.00/0 Copyright C) 1988, American Society for Microbiology
Role of Immunoglobulin G in Platelet Aggregation by Viridans Group Streptococcit PAUL M. SULLAM,l.23* GARY A. JARVIS,"3'4 AND FRANK H. VALONE23 Center for Immunochemistry,l Departments of Medicine2 and Laboratory Medicine,4 Veterans Administration Medical Center 113-A, and University of California,3 4150 Clement Street, San Francisco, California 94121 Received 31 March 1988/Accepted 27 July 1988
The aggregation of human platelets by the viridans group streptococci requires both direct plateletbacterium binding and plasma components. Some of these extracellular constituents (e.g., fibrinogen) are cofactors for ADP, which mediates the terminal events in platelet activation by these organisms. In addition, other plasma components which are specific for viridans group streptococci are necessary. To better define these latter cofactors, we examined the role of immunoglobulin G (IgG) in platelet aggregation by two strains of viridans group streptococci. The addition of either strain to washed human platelets suspended in normal plasma resulted in a 5- to 12-min lag phase, followed by brisk and irreversible platelet aggregation. In contrast, neither strain aggregated platelets suspended in IgG-depleted plasma (IgG concentration,
