Effect of Anti-Thrombospondin Antibodies on the Hemagglutination Activities of the Endogenous Platelet Lectin and Thrombospondin

Abstract

SummaryThe proposal that thrombospondin is the endogenous platelet lectin was evaluated using antisera and monoclonal antibodies to thrombospondin. The platelet-bound hemagglutinin activity of human platelets stimulated with A23187 was inhibited by rabbit anti-thrombospondin sera and by a monoclonal anti-thrombospondin IgG. A second monoclonal IgG did not inhibit platelet- bound agglutinin activity. Preparations of purified platelet thrombospondin differed in their hemagglutination activities. The hemagglutination activity of an active preparation of thrombospondin was inhibited by the monoclonal antibody that inhibited platelet-bound lectin activity. The hemagglutination activity of an almost inactive preparation of thrombospondin was enhanced by the anti-thrombospondin monoclonal antibody that did not block platelet-bound lectin activity. The results demonstrate that expression of the platelet-bound form of the endogenous lectin is thrombospondin-dependent and suggest that thrombospondin must become part of a larger complex, either by binding to the platelet surface or by becoming aggregated in solution, before hemagglutination activity can be expressed.

C-terminal peptide of thrombospondin-1 induces platelet aggregation through the Fc receptor γ-chain–associated signaling pathway and by agglutination

“…It was shown previously that TSP1 reinforces platelet aggregation in response to thrombin and collagen. [3][4][5] Furthermore, it was reported that TSP1 induces agglutination of fixed platelets previously activated by thrombin. 36 However, we did not observe aggregation or tyrosine phosphorylation in response to purified TSP1 at concentrations up to 100 g/mL (data not shown).…”

“…Anti-TSP1 antibodies can inhibit platelet aggregation induced by thrombin and collagen, and it has been proposed that TSP1 acts by stabilizing platelet aggregates initiated by interactions between fibrinogen and ␣IIb␤3. [3][4][5] TSP1 binds to a large number and wide variety of receptors on the platelet surface. Proteolytic digestion of TSP1 and expression of domains as recombinant proteins or synthetic peptides has enabled identification of several sequences that support these interactions, including a heparin-binding domain in the N-terminal region, which binds to proteoglycans 6 ; a region within the type 1 repeats, which binds to CD36 7 ; and an Arg-Gly-Asp sequence within the last of the type III repeats, which bind ␣v␤3 and ␣IIb␤3 integrins.…”

Interactions of thrombospondin with endothelial cells: receptor-mediated binding and degradation.

“…TSP is a major component of platelet alpha-granules and thus is secreted when platetets are stimulated with thrombin or other agents (4). This TSP becomes associated with platelet surfaces and the meshwork of the fibrin clot (5,18,20,21,41,49,53,62). High and low affinity interactions of TSP with unstimulated and stimulated platelets have recently been reported (64).…”

Resolution and Reconstitution of Interplatelet Recognition During Aggregation

“…Concerning the molecular state of thrombospondin, it was previously suggested by Gartner et al (18) and Booth et al (19) that for its haemagglutination activity thrombospondin must become part of a large complex, either by binding to the platelet surface or by becoming polimeric (or "aggregated") in solution.…”