Preparation of an antifibrin thrombus-specific murine/human chimeric monoclonal antibody Fab fragment in Escherichia coli

We have successfully developed a murine antifibrin monoclonal antibody designated SZ-63 with property of binding specifically with thrombus both in vitro and in vivo. In order to reduce its immunogenicity and molecular weight, a murine/human chimeric Fab fragment of the antibody was prepared. mRNA was selected on oligo (dT) cellulose from total RNA isolated from SZ-63 hybridoma cells. cDNAs coding for heavy and light variable regions were amplified by reverse transcriptase polymerase chain reaction. The amplified fragments were cloned and sequenced. The nucleotides of SZ-63 VH and VL are 354 and 321 respectively. The variable genes were then linked with human IgG gamma1 CH and kappa CL genes. Expression vector pHEN1-63 Fab/Hu was thereby constructed and chimeric Fab fragment was expressed in E. coli HB2151 cells in soluble form. Western blot and ELISA results showed that it remained the same capability of binding with cross-linked fibrin as the murine SZ-63 antibody, the content in culture is about 125 ug/L.

Milk composition in women from five different regions of China: the great diversity of milk fatty acids

Human milk samples were obtained from 146 lactating women living in five distinct geographic regions of the People's Republic of China. The regions were characterized as follows: pastoral, rural, urban 1, urban 2, and marine. Dietary information obtained on a subsample of women providing milk suggested distinct differences in the food availability in the five regions and the habitual diets of the lactating women studied. The milk concentration of docosahexaenoic acid (DHA) varied greatly (g/100 g total fatty acids): 0.44 +/- 0.29 (pastoral), 0.68 +/- 0.29 (rural), 0.88 +/- 0.34 (urban 1), 0.82 +/- 0.35 (urban 2), and 2.78 +/- 1.20 (marine region). Docosahexaenoic acid is critical for brain and retina development in the infant. Milk arachidonic acid (AA) ranged from 0.80 +/- 0.14 (rural) to 1.17 +/- 0.33 and 1.22 +/- 0.32 g/100 g fatty acids from the marine and pastoral regions. Arachidonic acid is associated with infant growth. The AA to DHA ratio (g/g) was highly variable also: 2.77 (pastoral), 1.18 (rural), 1.01 (urban 1), 1.23 (urban 2), and 0.42 (marine). The DHA concentration found in the milk of women from the marine region was twice as high as any reported previously, but was in a range similar to the amounts found in the milk of women fed fish oil. Seafood consumption by the women residing in the marine region is a likely contributor to the DHA concentration in their milk. These data illustrate the heterogeneity of the fatty acid composition of human milk and suggest a great influence of geography and the maternal diet on concentrations of DHA and AA in human milk.

Design and synthesis of fluorescence energy transfer dye-labeled primers and their application for DNA sequencing and analysis

We have designed and synthesized fluorescent oligonucleotide primers having improved fluorescence and electrophoretic properties by exploiting the concept of resonance fluorescence energy transfer (ET). These primers carry a fluorescein derivative at the 5' end as a common fluorescence donor and other fluorescein and rhodamine derivatives attached to a modified thymidine within the primer sequence as acceptors. These primers all have strong absorption at a common excitation wavelength (448 nm) and fluorescence emission maxima of 525, 555, and 605 nm. The fluorescence emission intensity of the ET primers increases as the spacing between the donor and acceptors is increased, and of the spacings studied the strongest fluorescence was observed when the number of nucleotides between the donor and acceptors is 10. The electrophoretic mobilities of the primers were also found to be a function of the spacing between the donor and the acceptors, and mobilities of the single base extension DNA fragments generated with primers (F10F, F10J, F10T, and F10R) is 2- to 14-fold greater than that of the corresponding primers labeled with only one dye. The increased fluorescence intensity of the ET primers and the substantially similar mobilities of the DNA fragments generated with the four ET primers allow four-color DNA sequencing on a capillary electrophoresis DNA sequencer using a single laser line at 488 nm for excitation and without applying mobility shift adjustments. With single-stranded M13mp18 DNA as the template, a typical run with the ET primers on a commercial sequencer provided DNA sequences with 99-100% accuracy in the first 500 bases using 8-fold less DNA template than that typically required using T7 DNA polymerase.

The P1A alloantigen system is a sensitive indicator of the structural integrity of the amino-terminal domain of the human integrin beta 3 subunit

Within the native integrin alpha pi b beta 3, the conformation of the amino-terminal domain of the beta 3 subunit has a significant influence on the availability of the Leu33/Pro33 polymorphism that defines the A1 and A2 alleles, respectively, of the P1A alloantigen system. The majority of anti-P1A1 IgG antibodies, affinity-purified by adsorption to either (A1/A1)-platelets or purified alpha pi b(A1) beta 3, fail to bind to the Leu33 polymorphic loop within Cys26-Cys38 in native beta 3 unless this sequence is maintained in a proper orientation by two noncontiguous human beta 3 sequences. By comparing IgG binding to recombinant beta 3 molecules composed of segments of human, Xenopus and avian sequences expressed by Spodoptera frugiperda cell lines, we have found that neither region alone is sufficient for full expression of the epitope. One sequence, that most proximal to Leu33/Pro33, lies within beta 3[54-133], and a second distal sequence is located within beta 3[435-490]. Proximity of the distal sequence to the Cys26-Cys38 loop in native beta 3 is confirmed by the fact that both anti-P1A1 IgG and the murine monoclonal antibody SZ21, specific for beta 3[28-35], completely inhibit the binding of rabbit polyclonal IgG specific for the sequence beta 3[479-485]. Anti-P1A1 IgG antibodies from all of the 7 donors selectively bind to the epitope within the native conformation of beta 3. However, in one of the seven donors, roughly 60% of the anti-P1A1IgG binds exclusively to denatured (A1) beta 3, and not to either denatured (A2) beta 3 or nondenatured (native) (A1) beta 3. This IgG subpopulation cannot be purified by adsorption to intact (A1/A1)-platelets or to native alpha pi b(A1) beta 3 integrin. The physiologic relevance of this exceptional type of anti-P1A1 antibody is debatable, but the presence of IgG with this specificity only in an immunized subject suggests that the epitope may well be presented on a "denatured" form of beta 3 in vivo. Regardless, our results indicate that the amino-terminal domain of the native beta 3 molecule associates with noncontiguous beta 3 sequences, and the epitope recognized by a majority of anti-P1A1 antibodies is a sensitive indicator of correct tertiary structure within this region of beta 3.

The impact of three-dimensional structure on the expression of PlA alloantigens on human integrin beta 3

We have compared the binding of affinity-purified anti-PlA1 IgG from seven nonrelated donors with chimeric integrin subunit beta 3 molecules expressed in the baculovirus-Spodoptera frugiperda insect cell system. Beta 3 chimeras were engineered to include segments of antigenic human beta 3 sequences spliced to intervening segments of nonantigenic Xenopus beta 3 sequence. Our results clearly show that antibodies from all seven donors will bind to nondenatured molecules containing the antigenic human beta 3 Cys26-Cys38 loop only when it is presented in a correct orientation that must be maintained by noncontiguous human sequences. Key downstream sequences are located within the region beta 3(288-490), flanking either side of the putative long-range disulfide at Cys435. Although our results confirm unambiguously that the Leu/Pro polymorphism at position 33 in human beta 3 is necessary for the expression of PlA epitopes, they also indicate that this polymorphic sequence alone is not sufficient. The requirement for additional human beta 3 sequence transcends the need to maintain a correct orientation within the Cys26-Cys38 loop itself, because the murine monoclonal antibody SZ21, which recognizes the sequence beta 3(28-35) contained within the Cys26-Cys38 loop, binds to all chimeras containing this loop, even if the same chimeras are not recognized by anti-PlA1. Our results indicate that additional noncontiguous residues encompassed by the sequence 288-490 either directly contribute to the composition of the PlA1 epitope or, more likely, maintain the Cys26-Cys38 loop in a proper orientation with respect to the remainder of the beta 3 molecule and thereby maintain proper antigenic presentation of the sequences in that loop.

Fluorescence energy transfer dye-labeled primers for DNA sequencing and analysis

Fluorescent dye-labeled DNA primers have been developed that exploit fluorescence energy transfer (ET) to optimize the absorption and emission properties of the label. These primers carry a fluorescein derivative at the 5' end as a common donor and other fluorescein and rhodamine derivatives attached to a modified thymidine residue within the primer sequence as acceptors. Adjustment of the donor-acceptor spacing through the placement of the modified thymidine in the primer sequence allowed generation of four primers, all having strong absorption at a common excitation wavelength (488 nm) and fluorescence emission maxima of 525, 555, 580, and 605 nm. The ET efficiency of these primers ranges from 65% to 97%, and they exhibit similar electrophoretic mobilities by gel electrophoresis. With argon-ion laser excitation, the fluorescence of the ET primers and of the DNA sequencing fragments generated with ET primers is 2- to 6-fold greater than that of the corresponding primers or fragments labeled with single dyes. The higher fluorescence intensity of the ET primers allows DNA sequencing with one-fourth of the DNA template typically required when using T7 DNA polymerase. With single-stranded M13mp18 DNA as the template, a typical sequencing reaction with ET primers on a commercial sequencer provided DNA sequences with 99.8% accuracy in the first 500 bases. ET primers should be generally useful in the development of other multiplex DNA sequencing and analysis methods.

Defibrotide stimulates expression of thrombomodulin in human endothelial cells

Cultured human umbilical vein endothelial cells were incubated with defibrotide at concentrations of 0, 5, 50 and 500 micrograms/ml for 4 and 24 h respectively. Thrombomodulin activity and molecules on the surface of the cells were determined by chromogenic assay and radioimmunoassay, thrombomodulin antigen in endothelial cells and in conditioned medium of the cells was measured by immunoradioassay. Thrombomodulin mRNA within the cells was analysed by slot blot. After 24 h of incubation, the activity and molecules of thrombomodulin on the surface of endothelial cells, as well as the antigen and mRNA of thrombomodulin in the cells were significantly increased in a dose dependent manner. However, the level of thrombomodulin antigen in conditioned medium was about equal to that of the control. Our data indicate that defibrotide stimulates expression of thrombomodulin in human endothelial cells. These beneficial effects may play a role in antithrombotic activity of defibrotide.

Radioimmunoimaging of experimental arterial and venous thrombi in dogs with 99Tcm-labelled monoclonal anti-activated platelet antibody SZ-51

In canine experimental models of femoral arterial and venous thrombosis, the feasibility of thrombus imaging with 99Tcm-labelled monoclonal antibody SZ-51 to an alpha-granule membrane protein (GMP-140) on the surface of activated platelets was investigated. Both the arterial and venous thrombi were clearly discernible at 2 to 8 h after injection of 99Tcm-SZ-51. The suitable imaging time was 4 to 6 h. These results were confirmed by ex vivo images of thrombosed arteries and veins followed by killing the dogs at 8 h postinjection of 99Tcm-SZ-51. Quantitative imaging analysis showed that the ratios between the thrombus and the opposite vessel were increased strikingly over time. The ratios of thrombus to blood or surrounding muscle were 57.09 +/- 12.24 and 177.46 +/- 9.00 for arterial thrombi and 6.43 +/- 4.70 and 83.22 +/- 68.98 for venous thrombi at the time of death. Radiolabelled antibody was cleared from the blood with T1/2 alpha of 16.25 +/- 13.39 min and T1/2 beta of 7.28 +/- 1.15 h. These results show that it is feasible to detect noninvasively thrombus formation in vivo using 99Tcm-labelled monoclonal antibody SZ-51.

Detection of plasma alpha-granule membrane protein GMP-140 using radiolabeled monoclonal antibodies in thrombotic diseases

There is an assumption that platelet activation and endothelium damage play a critical role in the pathogenesis of thrombotic disorders. A radioimmunoassay based on using two monoclonal antibodies (MAbs) to different epitopes of alpha-granule membrane protein (GMP-140) was used to determine whether plasma GMP-140 can be detected in patients suffering from acute myocardial infarction (AMI) or cerebral thrombosis and in patients during cardiopulmonary bypass (CPB). MAb SZ-51 was used as a solid phase, and 125I-labeled MAb S12 was used as a fluid phase. The assay is so sensitive that it can detect as little as 1 ng/ml of purified GMP-140. The intra- and interassay coefficients of variation were 4.2% (n = 5) and 7.1% (n = 8), respectively. The concentration of plasma GMP-140 was found to be 10.0 +/- 4.5 ng/ml (mean +/- SD, n = 20) in normal subjects. Ten patients undergoing CPB demonstrated a transient increase in the concentration of plasma GMP-140, especially at 2 h after CPB, and the plasma GMP-140 level was inversely correlated with the decreased platelet counts during bypass (r = -0.81, p < 0.01). It was found that the concentration of plasma GMP-140 increased significantly after AMI. Plasma GMP-140 reached the peak within 3 days and changed with the process of AMI (n = 16) patients. The concentration of plasma GMP-140 increased significantly in patients with cerebral thrombosis in the acute phase but not after relief.(ABSTRACT TRUNCATED AT 250 WORDS)

Application of GPIIIa gene Taq I polymorphism to determination of carrier status in Glanzmann's thrombasthenia families of Chinese origin

Glanzmann's thrombasthenia is a bleeding disorder caused by qualitative and/or quantitative defects of platelet membrane glycoprotein (GP) IIb/IIIa complex. The disease is inherited in an autosomal recessive manner. In this paper, cDNA probes were used to study restriction fragment length polymorphisms (RFLPs) in GPIIIa gene. A Taq I polymorphism was identified and this RFLP was composed of variant bands of 6.5 Kb/4.0 and 2.5 Kb with a frequency of 0.46/0.54 in Chinese population. The Taq I polymorphism was further localized by polymerase chain reaction (PCR) method to exon VIII of the GPIIIa gene. In two Glanzmann's thrombasthenia families, the Taq I RFLP studied by both Southern blotting and PCR methods identified the defective GPIIIa gene inherited by patients, and determined the genotype of asymptomatic subjects. Analysis of this Taq I polymorphism by PCR method should be potentially useful in future for the carrier detection and prenatal diagnosis in Glanzmann's thrombasthenia families.

Thrombomodulin as a marker of radiation-induced endothelial cell injury

Cultured confluent human umbilical vein endothelial cells were irradiated in vitro with 60Co gamma rays at doses from 0 to 50 Gy. After irradiation thrombomodulin was measured at different times over 6 days in the supernatants of endothelial cell culture medium, on the surface of the cells, and within the cells. At 24 h after irradiation, an increase in the release of thrombomodulin from irradiated endothelial cells and an increase in the number of molecules and the activity of thrombomodulin on the surface of the cells were observed; these reactions were dependent on radiation dose. The capacity of the cells to produce and release thrombomodulin was decreased from 2 to 6 days after exposure to 60Co gamma rays. Our data indicate that radiation can injure endothelial cells, and that thrombomodulin may be used as a marker of radiation-induced injury in endothelial cells. The interrelationship between the dysfunction of irradiated endothelial cells and the pathological mechanisms of acute radiation disease is also discussed.

Inhibition effects of KRDS, a peptide derived from lactotransferrin, on platelet function and arterial thrombus formation in dogs

KRDS (Lys-Arg-Asp-Ser), a tetrapeptide from human lactotransferrin, was tested for its effects in vitro on dog platelet function and in vivo on femoral arterial thrombus formation in dogs. KRDS inhibited ADP (8 microM)-induced platelet aggregation (IC50: 350 microM) and arachidonic acid (2 mM)-induced thromboxane B2 generation (IC50: 175 microM). In addition, the thrombin (0.2 U/ml)-induced serotonin release was inhibited by KRDS (IC50: 525 microM) and the expression of alpha-granule membrane protein (GMP-140) was also inhibited (IC50: 350 microM). The results show that KRDS is an inhibitor for platelet aggregation and secretion to which the inhibition is more potent. Meanwhile, in the experiment of arterial thrombosis in dogs, KRDS (5 microM/kg) and 125I-SZ-51 (a monoclonal antibody against GMP-140) were injected before operation and immediately after the thrombus formation, respectively. In the KRDS group, the weight of removed thrombi was reduced to 50% of that in controls and the radioactivity per mg of labeled thrombi to 33.3% while in blood the radioactivity increased 2 times that in controls at the 4th hour after the injection of 125I-SZ-51. The radioactivity ratio between removed thrombi and blood was only 16% of that in controls. These results indicate that KRDS can inhibit thrombus formation in vivo and is a promising antithrombotic agent.

Common intragenic and extragenic polymorphisms of blood coagulation factors VIII and IX are different in Chinese and Caucasian populations

In order to examine the possibilities of carrier detection and prenatal diagnosis in hemophilia A and B in the Chinese region of Suzhou, we analyzed four different RFLPs within the factor IX gene and two intragenic RFLPs and one extragenic RFLP for the factor VIII gene. The results obtained show important differences between the Chinese and Caucasian populations. No polymorphism was found within the factor IX gene in the Chinese population and the informativity obtained for the factor VIII gene was quite different between the two populations for each RFLP studied.

Ticlopidine in China: comparative study on the effect of two dose levels on bleeding time and platelet function in healthy volunteers

The compared inhibitory effects of two dose levels of ticlopidine (250 and 500 mg/day) on bleeding time and platelet function in Chinese volunteers have been studied in a placebo-controlled study. Ticlopidine exerted several significant effects: namely prolongation of bleeding time, inhibition of ADP-induced platelet aggregation, reduction of the thromboxane B2 synthesis induced by collagen as well as by ADP. The daily dose of 250 mg did not show significantly different effects as compared to the western, usually recommended daily dose of 500 mg. At the daily dose of 500 mg, adverse reactions occurred more frequently than at the daily dose of 250 mg, but no serious side effects necessitating discontinuation of treatment, or abnormalities in hematological and liver function parameters were observed at these two dose levels. In Chinese people, ticlopidine therapy should be administered at a daily dose of 250 mg.

Binding of heparin to human microvascular endothelial cells and the effect on proliferation

We have studied the binding of 125I-heparin to human omental microvascular endothelial cells (HOME cells) and investigated its effect on cell proliferation. At 20 degrees C, the binding reached a steady state from 4 hours onwards. Saturation of 125I-heparin binding occurred at 200 nM. Scatchard analysis indicated one class of binding sites (KD = 0.023 microM, 2 X 10(-6) sites/cell). Using fractionated heparin and other sulfated polysaccharides it was demonstrated that the binding was dependent on the charge and the molecular weight of the compounds. The binding was followed by the partial internalization of the bound ligand (23.8%). Heparin and Stipocus Japonicus mucopolysaccharide (SJAMP) inhibited the proliferation of exponentially growing HOME cells and human umbilical vein endothelial cells (HUVE cells). However, serum-deprived HOME cells were not inhibited by heparin.

Uncoupling in the expression of platelet GP IIb/IIIa in human endothelial cells and K562 cells: absence of immunologic crossreactivity between platelet GP IIb and the vitronectin receptor alpha chain

Platelet glycoproteins (GP) IIb and IIIa exist as noncovalently associated Ca++-dependent heterodimer complexes within the platelet membrane and express the major platelet alloantigens Leka (Baka) and PIA1 (Zwa), which are genetic markers of GP IIb and GP IIIa, respectively. Since heterodimers immunologically related to platelet GP IIb/IIIa have been identified in a number of nucleated cell types, we tested anti-Leka and anti-PIA1 antiserum, polyclonal anti-platelet GP IIb/IIIa IgG, as well as a panel of 28 monoclonal anti-GP IIb, GP IIIa, or complex dependent anti-GP IIb/IIIa antibodies on endothelial cells, peripheral blood mononuclear cells, and the erythroleukemic cells HEL and K562 in order to determine whether nucleated cell GP IIb/IIIa related proteins and platelet GP IIb/IIIa are immunologically related. Using immunofluorescence, immunoblotting, and immunoprecipitation experiments, evidence is presented that (1) the alloantigen Leka is not expressed in endothelial cells of an individual whose platelets are of the Leka/PIA1 phenotype, whereas the PIA1 alloantigen is readily detectable in these cells, (2) that in contrast to HEL cells, which express platelet GP IIb/IIIa and are of the Leka/PIA1 phenotype, platelet GP IIb is immunologically undetectable in 12-O-tetradecanoyl-phorbol-13-acetate (TPA)-treated K562 cells despite the presence of platelet GP IIIa, and (3) that peripheral blood mononuclear cells do not express platelet GP IIb or GP IIIa on their cell surface.

Glycoprotein Ib and glycoprotein IX are fully complexed in the intact platelet membrane

Two new murine monoclonal antibodies, AK 1 and SZ 1, reactive with the human platelet glycoprotein (GP) Ib-IX complex have been produced by the hybridoma technique. Both AK 1 and SZ 1 immunoprecipitated the GP Ib-IX complex from Triton X-100-solubilized, periodate-labeled platelets. With trypsinized, labeled platelets, AK 1, SZ 1, and FMC 25 (epitope on GP IX) immunoprecipitated a membrane-bound proteolytic fragment of the GP Ib-IX complex consisting of GP IX and an congruent to 25,000 mol wt remnant of the alpha-chain of GP lb disulfide-linked to the beta-subunit. Unexpectedly, although AK 1 and SZ 1 immunoprecipitated purified GP Ib-IX complex, neither antibody immunoprecipitated the individual components of this complex, GP Ib or GP IX. When GP Ib and GP IX were recombined, however, AK 1 and SZ 1 again immunoprecipitated the reformed complex, strongly suggesting that both antibodies were recognizing an epitope present only on the intact complex. Cross-blocking studies indicated that AK 1 and SZ 1 recognized a very similar or identical epitope that was proximal to the epitope for FMC 25. Both AK 1 and SZ 1 bound to a similar number of binding sites (congruent to 25,000) on intact platelets as monoclonal antibodies directed against either GP lb or GP IX. The combined data suggests that GP lb and GP IX are fully complexed in the intact platelet membrane.

Abnormality of glycoprotein Ib in two cases of "pseudo"-von Willebrand's disease

Two unrelated patients with "pseudo" ("platelet-type")-von Willebrand's disease (vWD) are described demonstrating thrombocytopenia with a prolonged bleeding time, ristocetin-induced platelet aggregation at low stimulus concentrations, decreased levels of ristocetin-cofactor activity (vWF:RCo), slight cryoprecipitate-induced platelet aggregation in the absence of ristocetin, and a lack of the high molecular weight factor VIII-von Willebrand factor (FVIII/vWF) multimers in plasma. Isolated washed patient platelets bound more FVIII/vWF at high (1 and 0.75 mg/ml) and low (0.5 and 0.25 mg/ml) ristocetin concentrations than control platelets. Fresh or paraformaldehyde-fixed washed platelets from these patients also bound more specific monoclonal antibody to glycoprotein Ib (25,000 binding sites per cell) than normal platelets (15,000 +/- 3,300 binding sites per cell). Results obtained in control patients with thrombocytopenia and increased platelet size (May-Hegglin anomaly and vWD type IIB) excluded a nonspecific increase of glycoprotein Ib in the platelets of the patients with pseudo-vWD. These data indicate that in pseudo-vWD, the primary abnormality lies in the platelet and is related to a quantitative and/or qualitative anomaly of platelet membrane glycoprotein Ib.

Monoclonal antibody to human platelet glycoprotein I. II. Effects on human platelet function

The effect on platelet function of a monoclonal platelet antibody to platelet membrane glycoprotein I was tested. This antibody, AN51, inhibited ristocetin or bovine factor VIII-induced aggregation but did not modify ADP, collagen type I or type III, thrombin or arachidonic acid induced aggregations. Furthermore, the adhesion-aggregation of platelets induced by microfibrils was also inhibited by the antibody. Platelet adhesion to rabbit aorta subendothelium was impaired by the antibody. The persistent adhesion of platelets to collagenase-treated subendothelium was also inhibited. These findings strongly suggested that platelet membrane glycoprotein I could interact with a non-collagenic microfibrillar component of subendothelium. The binding of factor VIII/von Willebrand factor to platelet membrane in the presence of ristocetin was decreased in the binding site for factor VIII/von Willebrand factor to allow platelet adhesion to subendothelium.

Monoclonal antibody to human platelet glycoprotein I. I. Immunological studies

A monoclonal hybridoma antibody specific for platelet glycoprotein I complex is described. The nature od the antigen was determined by demonstration that it was chymotrypsin sensitive and gave a peak at 150 000 daltons on SDS-PAGE after immunoprecipitation. The expression of the antigen is restricted to platelets and megakaryocytes with at least 1.6 x 10(4) molecules of antigen per platelet. The antibody failed to bind to platelets from patients with Bernard Soulier syndrome, where there is known to be a deficiency of glycoprotein Ib/Is expression. Binding to platelets from patients with Glanzmann's thrombasthenia was normal.

The in vitro effect of ticlopidine on fibrinogen and factor VIII binding to human platelets

The mode of action of the antiplatelet agent ticlopidine is not yet fully understood. Its multiple effects on platelet function include prolongation of the bleeding time, reduction in primary and secondary waves of ADP-induced aggregation and inhibition of collagen and thrombin-induced aggregation. We have studied the in vitro effects of ticlopidine on fibrinogen binding induced by ADP and adrenaline as well as factor VIII/vWF binding induced by ristocetin. 125I-fibrinogen binding was measured in suspensions of freshly-washed normal platelets stimulated by 10 microM ADP or 10 microM adrenaline. The binding of 125I-factor VIII/vWF in the presence of 1 mg/ml ristocetin was measured in both washed and paraformaldehyde-fixed platelets. Ticlopidine at final concentrations of 200, 100, 50 and 25 microM inhibited both ADP and adrenaline-induced fibrinogen binding in a dose-dependent manner. The mean % inhibition of ADP-induced fibrinogen binding was 82, 73, 42 and 32 respectively. The mean % inhibition of adrenaline-induced fibrinogen binding was 86, 82, 60 and 35 respectively. In contrast, the factor VIII/vWF binding was unaffected by ticlopidine at all concentrations except at 200 microM using fresh platelets where a slight inhibition (19%) was observed. These results suggest that ticlopidine either inhibits platelet activation and consequently fibrinogen binding, or inhibits the binding directly, presumably by having an effect on the specific configuration of the platelet membrane required for normal fibrinogen binding.