Summary
The adhesion of activated platelets to leukocytes (rosette formation) seems to be
mediated by CD62 on platelets and its counterreceptor (CD 15 or a sialic acid-containing
glycoprotein) on polymorphonuclear leukocytes (PMNL). However, neither treatment of
platelets with an anti-CD62 antibody or fucoidan nor treatment of PMNL with anti-CD15
antibody or neuraminidase are able to inhibit completely the adhesion. Therefore,
we have studied the platelet GPIIb/IIIa complex (CD41a) for its involvement in the
adhesion of activated platelets to PMNL. The following evidences point to a participation
of CD41a in the adhesion of activated platelets to leukocytes: a) inhibition of adhesion
by monoclonal antibodies (mab) raised toward CD41a, b) inhibition of adhesion by peptides
such as RGDS and echistatin, c) inhibition of adhesion by dissociation of the CD41a
complex with EGTA, and d) inhibition of rosette formation using platelets from a thrombasthenic
patient which have almost no CD41a in the surface membrane but a normal expression
of CD62. It is likely that fibrinogen is involved in the adhesion of platelets to
PMNL via CD41a, since fibrinogen increases the rosette formation of ADP-stimulated
platelets. Furthermore, the incubation of unstimulated platelets with fibrinogen and
an antibody raised against glycoprotein III a which stimulates fibrinogen binding
to the platelet surface results in an enlarged rosette formation.
