Modulation of platelet responses to collagen by Clq receptors.
We recently described specific binding sites for Clq on human blood platelets that cross-react with antibodies against Clq receptors (ClqR) on lymphoblastoid cells. Inasmuch as Clq inhibits collagen-induced platelet aggregation, we compared the effects of ClqR occupancy by purified Clq, monoclonal (IIl/B5) and polyclonal anti-ClqR antibodies on collagen-induced platelet adhesion, release, and aggregation. Washed platelets in buffered Tyrode's solution containing 2 mM magnesium were preincubated (30 min, 22 degrees C) with antibodies, Clq, or appropriate control buffers and antiserum. Platelet aggregation and release measurements were made using 14C-serotonin-labeled platelets stimulated with type I collagen. Adhesion assays were performed in the presence of magnesium under static conditions at 22 degrees C with 51Cr-labeled platelets and collagen-coated microtiter wells. Concentrations of IIl/B5, polyclonal anti-Clq R antiserum, or Clq causing 82 to 92% (n = 7) inhibition of collagen-induced release and 67 to 98% inhibition of aggregation, failed to inhibit magnesium-dependent platelet adhesion to collagen. Inasmuch as divalent cation-independent platelet-collagen interactions have also been described, further studies were performed to compare the divalent cation requirement of ClqR occupancy by Clq and inhibition of platelet-collagen interactions. Whereas, Clq binding to platelets was divalent cation independent, neither Clq nor anti-ClqR antibodies prevented platelet adhesion to collagen in the presence of EDTA. These data suggest that under defined in vitro conditions, ClqR modulate collagen-induced platelet aggregation and secretion, but not platelet adhesion.
Department of Pathology, Suny, Stony Brook 11794.
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Peerschke
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Ghebrehiwet
D000911:Antibodies, Monoclonal / Q000276:immunology; D001792:Blood Platelets / Q000502:physiology*; D002122:Calcium Chloride / Q000494:pharmacology; D002352:Carrier Proteins; D003094:Collagen / Q000502:physiology*; D006801:Humans; D018960:Hyaluronan Receptors; D007158:Immunologic Techniques; D066298:In Vitro Techniques; D008562:Membrane Glycoproteins; D024101:Mitochondrial Proteins; D015539:Platelet Activation; D010973:Platelet Adhesiveness; D010974:Platelet Aggregation; D011951:Receptors, Complement / Q000502:physiology*; D012701:Serotonin / Q000378:metabolism
D000911:Antibodies, Monoclonal; C087299:C1QBP protein, human; D002352:Carrier Proteins; D018960:Hyaluronan Receptors; D008562:Membrane Glycoproteins; D024101:Mitochondrial Proteins; D011951:Receptors, Complement; C032402:complement 1q receptor; D012701:Serotonin; D003094:Collagen; D002122:Calcium Chloride