THE PLATELET GLYCOPROTEIN-IIB IIIA COMPLEX IS INVOLVED IN THE ADHESION OF ACTIVATED PLATELETS TO LEUKOCYTES/

The adhesion of activated platelets to leukocytes (rosette formation) seems to be mediated by CD62 on platelets and its counterreceptor (CD1 5 or a sialic acid-containing glycoprotein) on polymorphonuclear leuko cytes (PMNL). However, neither treatment of platelets with an anti-CD6 2 antibody or fucoidan nor treatment of PMNL with anti-CD15 antibody o r neuraminidase are able to inhibit completely the adhesion. Therefore , we have studied the platelet GPIIb/IIIa complex (CD41a) for its invo lvement in the adhesion of activated platelets to PMNL. The following evidences point to a participation of CD41a in the adhesion of activat ed platelets to leukocytes: a) inhibition of adhesion by monoclonal an tibodies (mab) raised toward CD41a, b) inhibition of adhesion by pepti des such as RGDS and echistatin, c) inhibition of adhesion by dissocia tion of the CD41a complex with EGTA, and d) inhibition of rosette form ation using platelets from a thrombasthenic patient which have almost no CD41a in the surface membrane but a normal expression of CD62. It i s likely that fibrinogen is involved in the adhesion of platelets to P MNL via CD41a, since fibrinogen increases the rosette formation of ADP -stimulated platelets. Furthermore, the incubation of unstimulated pla telets with fibrinogen and an antibody raised against glycoprotein III a which stimulates fibrinogen binding to the platelet surface results in an enlarged rosette formation.