A Murine Antiglycoprotein lb Complex Monoclonal Antibody , SZ 2 , Inhibits Platelet

form in Thrombosis and Haemostasis. Supported by the Science Fund of the Chinese Academy of Sciences (project No. 82-172) and by grants 6K14277 and 6K14443 from the National Health and Medical Research Council of Australia. Michael C. Berndt is the recipient ofa Wellcome Australian Senior Research Fellowship. Address reprint requests to Dr Changgeng Ruan. Suzhou Medical College. Suzhou 215007, China or Dr. Michael C. Berndt, Department of Medicine. Westmead Hospital. Westmead, NS W 2145. Australia. Address editorial correspondence to Dr Michael C. Berndt, Department of Medicine. Westmead Hospital, Westmead, NSW 2145. Australia. The publication costs ofthis article were defrayed in part by page charge payment. This article must therefore be hereby marked “advertisement” in accordance with 18 U.S.C. §1734 solely to indicate this fact. © 1987 by Grune & Stratton, Inc. 0006-4971/87/6902-0030$3.OO/O and also platelet thromboxane A2 formation in response to ristocetin and collagen. SZ 2 was without effect on platelet aggregation or release in response to other platelet stimuli such as ADP. thrombin. or arachidonic acid. The inhibition by SZ 2 of collagenand PAF-induced platelet aggregation is surprising in that Bernard-Soulier syndrome platelets. which lack the glycoprotein lb complex. respond normally to both these stimuli. SZ 2 was unreactive toward BernardSoulier syndrome platelets. as evaluated by fluorescenceassociated cell sorting. and had no effect on the collagenand PAF-induced aggregation of Bernard-Soulier syndrome platelets. The combined results suggest that the inhibition by SZ 2 of collagenand PAF-induced aggregation of normal platelets is steric and are consistent with the glycoprotein lb complex and the platelet collagen and PAF receptor(s) being adjacent in the human platelet plasma membrane. is 1987 by Grune & Stratton, Inc. Soulier syndrome platelets, which lack the components of the glycoprotein lb complex,7 fail to bind von Willebrand factor,8 to agglutinate in the presence of ristocetin,9”#{176} and to adhere normally to subendothelium.5 The glycoprotein lb complex is a heterodimer complex and contains both glycoprotein lb and glycoprotein IX.” On SDS-polyacrylamide gels, glycoprotein lb has an apparent molecular weight of I 70,000 and consists of two disulfide-linked subunits, lb8 and Ib , with apparent molecular weights of I 35,000 and 25,000, respectively. Glycoprotein IX has an apparent molecular weight of 22,000 under both nonreducing and reducing conditions.” The binding domain for von Willebrand factor appears to be present on the a-subunit of glycoprotein lb.6”2 The available evidence suggests that the glycoprotein lb complex does not play an important role in platelet-collagen interaction. Bernard-Soulier syndrome platelets aggregate normally in response to collagen.’3 Further, the murine monoclonal antibody (MoAb), AN 51, directed against the a-subunit of glycoprotein lb,’4 blocks ristocetin-induced, von Willebrand factor-dependent platelet agglutination but has no effect on platelet aggregation induced by types I or III collagen fibrils.’5 In this study we describe a new murine MoAb, SZ 2, directed against the a-subunit of glycoprotein lb. which not only inhibits ristocetin-induced, von Willebrand factordependent platelet agglutination but also collagen-induced and platelet-activating factor (PAF)-induced platelet aggregation. The combined data are consistent with the platelet glycoprotein lb complex, the platelet collagen receptor, and the platelet PAF receptor being sterically adjacent in the human platelet plasma membrane. MATERIALS AND METHODS Materials. Bovine serum albumin (Fraction V), adenosine diphosphate, hypoxanthine, aminopterin, thymidine, A 23187, platelet-activating factor, and arachidonic acid were purchased from Sigma, St. Louis; sodium periodate (Univar) from Ajax Chemicals, Sydney, Australia; pristane from Aldrich, Milwaukee, WI; polyethylene glycol 4000 from Merck, Darmstadt, West Germany; ristocetin sulfate from Lundbeck, Copenhagen, Denmark; epinephrine For personal use only. on September 23, 2017. by guest www.bloodjournal.org From