Atypical presentations and pitfalls of achalasia.

Achalasia is a rare disease with significant diagnostic delay and association with false diagnoses and unnecessary interventions. It remains unclear, whether atypical presentations, misinterpreted symptoms or inconclusive diagnostics are the cause. The aim of this study was the characterization of typical and atypical features of achalasia and their impact on delays, misinterpretations or false diagnoses. A retrospective analysis of prospective database over a period of 30 years was performed. Data about symptoms, delays and false diagnoses were obtained and correlated with manometric, endoscopic and radiologic findings. Totally, 300 patients with achalasia were included. Typical symptoms (dysphagia, regurgitation, weight loss and retrosternal pain) were present in 98.7%, 88%, 58.4% and 52.4%. The mean diagnostic delay was 4.7 years. Atypical symptoms were found in 61.7% and led to a delay of 6 months. Atypical gastrointestinal symptoms were common (43%), mostly 'heartburn' (16.3%), 'vomiting' (15.3%) or belching (7.7%). A single false diagnosis occurred in 26%, multiple in 16%. Major gastrointestinal misdiagnoses were GERD in 16.7% and eosinophilic esophagitis in 4%. Other false diagnosis affected ENT-, psychiatric, neurologic, cardiologic or thyroid diseases. Pitfalls were the description of 'heartburn' or 'nausea'. Tertiary contractions at barium swallows, hiatal hernias and 'reflux-like' changes at endoscopy or eosinophils in the biopsies were misleading. Atypical symptoms are common in achalasia, but they are not the sole source for diagnostic delays. Misleading descriptions of typical symptoms or misinterpretation of diagnostic studies contribute to false diagnoses and delays.

German Survey on EUS-Guided Diagnosis and Management of Gastrointestinal Stromal Tumors (GISTs) - Evidence or "Gut-Feeling"?

PURPOSE: To examine practice patterns of endosonographers in diagnosing and managing gastrointestinal stromal tumors (GISTs) in Germany. MATERIALS AND METHODS: A modified published survey (Ha et al., Gastrointest Endosc 2009) was sent to endosonographic ultrasound (EUS) customers in Germany. The survey was also publicized on the homepage of an EUS interest group. To avoid duplicate opinions, participants were asked to return one survey per institution. RESULTS: 142 centers of roughly 850 German EUS centers responded. 25 % were from University hospitals and 74 % from community hospitals. 61 % performed > 2 EUS scans for suspected subepithelial lesions/week. Although 97 % of respondents believed that tissue acquisition with CD117 immunohistochemistry best predicts a GIST, 11 % do not perform EUS-FNA when suspecting a GIST, 68 % perform it occasionally and 18 % perform it regularly. The main EUS criteria used for a suspected GIST are the typical layer (85 %), hypoechoic appearance (80 %) and gastric location (51 %). 69 % would diagnose a GIST with negative CD117 if the EUS criteria and spindle cells are present. FNA was rated helpful in < 50 % by 55 % of participants. Size was the primary criterion for suspecting malignancy. 95 % of respondents would perform surveillance ≥ 1x/year of GISTs that are not resected. CONCLUSION: There is significant variability in the diagnosis and management of GISTs in Germany. Diagnostic certainty of EUS-FNA is suboptimal in many centers and EUS is frequently used for guidance. The diagnosis of a GIST is often guided by a "gut feeling" rather than evidence. Efforts should be made to unify existing guidelines.

[Diagnosis and therapy of benign tumors of the esophagogastric junction]. / Diagnose und Therapie benigner Tumoren des ösophagogastralen Übergangs.

Benign tumors of the esophagogastric junction are rare and mostly found incidentally during endoscopic or radiological procedures which are often performed for unrelated reasons. Epithelial lesions must be distinguished from subepithelial findings, where the latter are far more common and mostly represent benign leiomyomas, especially in the esophagus. Some benign tumors, such as small gastrointestinal stromal tumors, have malignant potential and must therefore be distinguished from completely benign lesions. Epithelial tumors can be diagnosed by standard endoscopic biopsies, whereas tissue acquisition of subepithelial lesions is more challenging. For this purpose endosonography is a valuable tool even before tissue acquisition or resection is performed. Endosonography can identify the gastrointestinal wall layer from which the lesion arises and gives additional information by identification of characteristic echographic features. Endoscopic resection techniques are used to remove those tumors that originate from the mucosa or submucosa. Some authors have even described resection of tumors originating from the deep muscle layer, but these techniques have a significant risk of perforation. Several surgical techniques are available for complete resection ranging from laparoscopic enucleation to combined endoscopic laparoscopic (rendezvous) techniques and abdominothoracic approaches. The current diagnostic and therapeutic challenges regarding benign tumors of the esophagogastric junction are outlined in this review article.

Magnetic resonance cholangiopancreatography (MRCP) for suspected bilio-pancreatic disease: should the endoscopist take a second look?

INTRODUCTION: MRCP enables a planar ductography of the pancreatobiliary system, which for diagnostic purposes may render ERCP unnecessary. However, the interpretation of MRCP findings is primarily performed by radiologists, and it is unclear whether additional interpretation of the MRCP results by the endoscopist alters clinical management. PATIENTS AND METHODS: One-hundred and fifty-five consecutive patients, who were referred for further endoscopic procedures (EUS/ERCP) based on MRCP findings (performed within 4 weeks prior to admittance; a written radiological report as well as the digital images were available) were enrolled. Before the endoscopic examinations were done, the MRCP images were re-evaluated by an experienced endoscopist who was in charge of the further endoscopic management. The interpretations of the MRCP images by the radiologist and the endoscopist were then compared with the final diagnosis after the further endoscopic evaluation. Additionally, the recommendations made by the endoscopist for further patient management before and after MRCP image analysis were evaluated. RESULTS: The MRCP image quality was judged sufficient by the endoscopist in the majority of the cases (80 %).The diagnostic accuracy of the MRCP findings was 73 % based on the interpretation by the radiologist and 86 % from the interpretation of the endoscopist. In 14 patients the endoscopist scheduled an EUS instead of an ERCP after he had viewed the MRCP images. Overall, the endoscopic work-flow was modified by the additional interpretation of the MRCP by the endoscopist in 25/155 (16 %) of the cases. LIMITATIONS: This is a non-randomized, unblinded single-observer assessment. CONCLUSION: MRCP images should be additionally interpreted by an endoscopist before further endoscopic procedures are scheduled.

Etiopathological aspects of achalasia: lessons learned with Hirschsprung's disease.

The etiology of primary esophageal achalasia is largely unknown. There is increasing evidence that genetic alterations might play an important but underestimated role. Current knowledge of the genetic base of Hirschsprung's disease in contrast is far more detailed. The two enteric neuropathies have several clinical features in common. This association may also exist on a cellular and molecular level. The aim of this review is to enlighten those etiopathogenetic concepts of Hirschsprung's disease that seem to be useful in uncovering the pathological processes causing achalasia. Three aspects are looked at: (i) the genetic base of Hirschsprung's disease, particularly its major susceptibility gene rearranged during transfection and its potential reference to achalasia; (ii) the altered motor functions in both conditions with loss of inhibitory innervation and interstitial cell pathology; and (iii) the involvement of these motility disorders in genetic syndromes.

Management and outcomes of haemorrhage after pancreatogastrostomy versus pancreatojejunostomy.

BACKGROUND: Postpancreatectomy haemorrhage (PPH) is a major cause of morbidity and mortality after pancreaticoduodenectomy (PD). It remains unclear whether performance of a pancreatogastrostomy (PG) instead of a pancreatojejunostomy (PJ) improves outcomes owing to better endoscopic accessibility. METHODS: A large retrospective analysis was undertaken to compare outcomes of PPH, depending on whether a PG or PJ was performed. The primary outcome was the rate of successful endoscopy. A secondary outcome was the therapeutic success after adding surgery. RESULTS: Of 944 patients who had a PD, 8·4 per cent developed PPH. Endoscopy was the primary intervention in 21 (81 per cent) of 26 patients with a PG and 34 (64 per cent) of 53 with a PJ; it identified the bleeding site in 35 and 25 per cent respectively (P = 0·347). Successful endoscopic treatment was more common in the PG group (31 versus 9 per cent; P = 0·026). Surgery was performed for PPH in 15 patients (58 per cent) with a PG and 35 (66 per cent) with a PJ (P = 0·470). The majority of haemorrhages that required surgery were non-anastomotic intra-abdominal haemorrhages (12 of 15 versus 21 of 35; P = 0·171). Endoscopic or conservative treatment for PPH was successful in 42 per cent of patients with a PG and 32 per cent with a PJ (P = 0·520). The success rate increased to 85 and 91 per cent respectively when surgery was included in the algorithm (P = 0·467). CONCLUSION: The type of pancreatic anastomosis and its inherent effect on endoscopic accessibility had very little impact on the outcome of PPH. This was because haemorrhage frequently occurred from intra-abdominal or non-anastomotic intraluminal lesions.

Open access colonoscopy in the training setting: which factors affect patient satisfaction and pain?

BACKGROUND AND STUDY AIM: Patient satisfaction with colonoscopy is important for quality assurance; it may be affected by various factors, including patient characteristics, physician training level, and procedural or organizational features. We aimed to analyze how these factors influenced patient satisfaction and pain in an outpatient training setting. METHODS: Consecutive patients for open access colonoscopy (OAC) were enrolled in a prospective, single-blinded, controlled study. Primary and secondary outcomes were satisfaction and pain scores with and without trainee participation. A multivariate analysis was designed to achieve an 80 % power with an alpha value of 0.05. RESULTS: 368 patients were enrolled. Satisfaction with the procedure was high (mean score 1.36; 1 = best to 5 = worst). In the multivariate analysis only waiting time in the endoscopy suite was significantly associated with lower satisfaction scores ( P = 0.024). Satisfaction was unaffected by patient factors (gender, American Society of Anesthesiologists' [ASA] score, anxiety, etc). Higher pain scores were associated with higher anxiety levels ( P = 0.02), female gender ( P = 0.02), longer procedure ( P< 0.001), and lower sedation levels ( P = 0.001); trainee involvement (49 % of procedures) did not adversely affect satisfaction or pain scores. CONCLUSIONS: Patient satisfaction with OAC using sedation appears to depend primarily on organizational factors (waiting time beforehand). In contrast, pain is associated with patient characteristics (female gender, anxiety) and procedural factors (lower sedation, longer procedure). Trainee participation did not affect satisfaction or pain scores, a finding which may help to reassure patients undergoing OAC with trainee participation.

Does scant hematochezia necessitate the performance of total colonoscopy?

BACKGROUND AND STUDY AIMS: Controversy exists as to whether all patients with lower intestinal bleeding need to undergo total colonoscopy. This study compares the prevalence of colonic neoplasms in patients reporting scant hematochezia with the prevalence in controls. PATIENTS AND METHODS: Structured interviews were carried out with 4265 consecutive patients referred for colonoscopy. Of these, 468 patients had scant hematochezia, 299 had occult rectal bleeding and 57 reported dark rectal bleeding. Patients with scant hematochezia were matched for age and sex with those having no risk factors for colorectal neoplasms. For all groups, we determined the prevalence of adenomas and cancers below and above 50 cm. RESULTS: Colonic neoplasms were found in 18 % of patients with scant hematochezia and in 7.5 % of controls. However, most of these tumors were located within the reach of a sigmoidoscope. Compared with controls, patients with scant hematochezia had no increased risk for proximal neoplasms (odds ratio [OR] = 1.2), while this risk was significantly increased in patients with occult rectal bleeding (OR = 3.1) and patients who had observed maroon-colored blood in their stool (OR = 4.8). CONCLUSIONS: Flexible sigmoidoscopy appears to be a sufficient work-up for young patients who have observed trace amounts of bright red blood on the surface of their stool.

Administration of a potent antagonist of protease-activated receptor-1 (PAR-1) attenuates vascular restenosis following balloon angioplasty in rats.

Human platelets possess two distinct thrombin-activated receptors, PAR-1 (protease-activated receptor-1) and PAR-4, whereas human vascular smooth muscle cells possess only PAR-1. Although such thrombin receptors have been studied extensively in vitro, their physiological roles are still rather ill-defined. We have now employed a potent, selective PAR-1 antagonist, RWJ-58259, to probe the in vivo significance of PAR-1 in thrombosis and vascular injury. RWJ-58259 was examined in two thrombosis models in guinea pigs: the arteriovenous (A-V) shunt assay (monitoring thrombus weight) and the Rose Bengal intravascular photoactivation assay (monitoring time to occlusion). Administration of RWJ-58259 (10 mg/kg, total i.v. dose) did not inhibit thrombus formation in either thrombosis model, although local, intrashunt delivery in the A-V shunt model did elicit a modest antithrombotic effect (thrombus weight reduction from 35 +/- 2 to 24 +/- 4 mg). These results are consistent with the presence of more than one thrombin-sensitive receptor on guinea pig platelets, in analogy with human platelets. Indeed, we were able to establish that guinea pig platelets express three thrombin receptors, PAR-1, PAR-3, and PAR-4. We also examined RWJ-58259 in a vascular restenosis model involving balloon angioplasty in rats. Perivascular administration of RWJ-58259 (10 mg) significantly reduced neointimal thickness (77 +/- 5 microm to 45 +/- 5 microm, P < 0.05), clearly demonstrating an important role for PAR-1 in vascular injury. From these results, it is evident that a PAR-1 antagonist is not especially effective for treating platelet-dependent thrombosis; however, it could well be beneficial for treating restenosis attendant to arterial injury.

Design, synthesis, and biological characterization of a peptide-mimetic antagonist for a tethered-ligand receptor.

Protease-activated receptors (PARs) represent a unique family of seven-transmembrane G protein-coupled receptors, which are enzymatically cleaved to expose a truncated extracellular N terminus that acts as a tethered activating ligand. PAR-1 is cleaved and activated by the serine protease alpha-thrombin, is expressed in various tissues (e.g., platelets and vascular cells), and is involved in cellular responses associated with hemostasis, proliferation, and tissue injury. We have discovered a series of potent peptide-mimetic antagonists of PAR-1, exemplified by RWJ-56110. Spatial relationships between important functional groups of the PAR-1 agonist peptide epitope SFLLRN were employed to design and synthesize candidate ligands with appropriate groups attached to a rigid molecular scaffold. Prototype RWJ-53052 was identified and optimized via solid-phase parallel synthesis of chemical libraries. RWJ-56110 emerged as a potent, selective PAR-1 antagonist, devoid of PAR-1 agonist and thrombin inhibitory activity. It binds to PAR-1, interferes with PAR-1 calcium mobilization and cellular function (platelet aggregation; cell proliferation), and has no effect on PAR-2, PAR-3, or PAR-4. By flow cytometry, RWJ-56110 was confirmed as a direct inhibitor of PAR-1 activation and internalization, without affecting N-terminal cleavage. At high concentrations of alpha-thrombin, RWJ-56110 fully blocked activation responses in human vascular cells, albeit not in human platelets; whereas, at high concentrations of SFLLRN-NH(2), RWJ-56110 blocked activation responses in both cell types. Thus, thrombin activates human platelets independently of PAR-1, i.e., through PAR-4, which we confirmed by PCR analysis. Selective PAR-1 antagonists, such as RWJ-56110, should serve as useful tools to study PARs and may have therapeutic potential for treating thrombosis and restenosis.

Complications and adverse effects of colonoscopy with selective sedation.

BACKGROUND: Cardiopulmonary adverse effects are commonly observed in patients undergoing colonoscopy with sedation. This study determines the incidence of such events when sedation is given only when required. METHODS: In 2500 consecutive patients, colonoscopies were started without premedication but sedation was offered if significant discomfort occurred. Parameters of blood pressure, heart rate, oxygen saturation and patient appearance were continuously recorded by a nurse assistant. Additional adverse effects occurring during or after the procedure were noted in the patients' protocol. Risk factors for the development of complications were evaluated with the use of a logistic regression model and the odds ratio. RESULTS: Ninety-five percent of all patients required neither sedation nor analgesia. Adverse effects occurred in 59 patients (2. 4%). Twenty-six of these patients (1.0%) had short-lasting episodes of oxygen desaturation and 22 patients (0.9%) experienced vasovagal reactions. Mechanical complications occurred in a total of 8 patients (0.3%) and consisted of 2 perforations and 6 episodes of hemorrhage. In the logistic regression model, impaired physical status was the single most important risk factor for the development of cardiopulmonary complications (odds ratio 4.7; 95% confidence interval [2.0, 11.4]). CONCLUSIONS: In experienced hands, patients undergoing colonoscopy rarely require sedation. If selective sedation is used, cardiopulmonary adverse effects occur in approximately 2% of all patients, most of whom require no medical intervention.

Differential regulation of human keratinocyte growth and differentiation by a novel family of protease-activated receptors.

Thrombin receptor (ThrR) and protease-activated receptor-2 (PAR-2) are members of a unique G protein-coupled receptor family, which are characterized by the unveiling of a tethered peptide ligand upon proteolysis of their NH2 terminus. We have previously shown that cultured human basal keratinocytes express both receptors (R.J. Santulli et al., Proc. Natl. Acad. Sci. USA, 92: 9151-9155, 1995); however, their functional role in epidermal physiology has yet to be described. In the present study, we determined the effects of receptor activation on keratinocyte cell growth and differentiation using thrombin (selective for ThrR), SLIGRL (selective for PAR-2), and SFLLRN (stimulates ThrR and PAR-2), as agonists. ThrR stimulation enhanced cell growth in a dose-dependent manner in the absence of growth factors (epidermal growth factor and bovine pituitary extract). In contrast, under the same conditions, activation of PAR-2 led to the inhibition of cell growth. This inhibitory activity by PAR-2 activation was also observed in the presence of growth factors. Activation of both receptors diminished protein expression of the differentiation marker transglutaminase type 1 induced by either calcium or IFN-gamma. Calcium-induced involucrin expression was also decreased. These results indicate that PAR-2 and ThrR differentially modulate keratinocyte function and may provide an important regulatory function in the epidermis by altering the functional state of keratinocytes.

Circulating ICAM-1 (sCD54) and LFA-3 (sCD58) in chronic hepatitis B--a longitudinal study in patients treated with interferon-alpha.

The intercellular adhesion molecule 1 (ICAM-1, CD54) and the lymphocyte associated antigen 3 (LFA-3, CD58) have been found in soluble form (sCD54 and sCD58) in human sera. Data concerning their role in chronic liver disease and their usefulness in disease monitoring are contradictory. We addressed the question whether elevated sCD54/sCD58 correlated either with disease activity or with decreased elimination secondary to reduced liver function in chronic hepatitis B. We studied 31 patients with chronic hepatitis B undergoing interferon alpha therapy in a longitudinal fashion. Serum concentrations of sCD54 and sCD58 were measured at four weeks interval by specific Sandwich ELISA during a follow-up period of ten months. The maximal difference in concentration of each biochemical parameter, e.g., delta AST, delta gGt, delta bilirubin, was determined for each patient during the whole follow-up period. These differences were correlated with the variation in sCD54 (delta sCD54) and sCD58 (delta sCD58) at the respective time points. Using this method, we were able to eliminate interindividual differences in serum concentrations for sCD54 and sCD58 and to avoid bias due to preselection of patients. We found that delta sCD54 correlated with delta AST (p = 0.001) and delta ALT (p = 0.002), whereas there was no such correlation for delta sCD58. Interferon therapy did not affect sCD54 or sCD58 levels. Neither hepatitis B viremia nor the immune response to hepatitis B during the time of seroconversion to anti-HBe did significantly increase sCD54 or sCD58 levels. However, delta sCD54 was associated with delta gamma GT (p = 0.005) and delta sCD58 correlated with delta bilirubin (p = 0.037); a negative correlation was found for delta sCD54 with delta cholinesterase (p = 0.007). Our findings imply that sCD54 and sCD58 may be associated with a decrease in liver function that accompanies hepatic disease activity. sCD54 and sCD58 did not prove useful to monitor disease activity or response to interferon therapy in chronic hepatitis B. From our data we conclude, that decreased elimination of soluble adhesion molecules sCD54 and sCD58 in advanced liver disease may be responsible for increased serum concentrations detected.

Thrombin receptor-dependent prostaglandin E2 synthesis in hamster fibroblasts: synergistic interactions with interleukin-1beta.

Cellular responses to alpha-thrombin are mediated through a G-protein-coupled receptor that undergoes proteolytic cleavage, unveiling a tethered peptide ligand with the amino-terminal sequence SFLLRN. The synthetic peptide SFLLRN can mimic many of thrombin's actions via directly stimulating the thrombin receptor. Thrombin has been implicated in several cellular events associated with tissue injury, including fibroblast growth, matrix deposition, and inflammatory responses. The role of the thrombin receptor in fibroblast-dependent release of the inflammatory mediator prostaglandin E2 was evaluated and compared to its well-characterized effect on cell proliferation. Both thrombin and SFLLRN stimulated [3H]thymidine incorporation into DNA but failed to induce prostaglandin E2 release from CCL39 cells. The inflammatory cytokine interleukin-1beta synergized with thrombin and SFLLRN to induce the release of prostaglandin E2, whereas it had no effect on thrombin receptor-mediated DNA synthesis. Interleukin-1beta had no direct effects on thrombin receptor-mediated phosphoinositide hydrolysis, suggesting that its effects were downstream from early signal transduction events. Thrombin and interleukin-1beta together significantly increased the expression of prostaglandin H synthase-2 in accordance with the prostaglandin E2 results. These studies indicate that the fibroblast thrombin receptor differentially couples to intracellular signaling pathways leading to distinct functional responses and that thrombin receptor-effector interactions could be modulated by interleukin-1beta.

Colonoscopy without premedication versus barium enema: a comparison of patient discomfort.

BACKGROUND: Colonoscopy is considered a painful procedure requiring routine intravenous sedation. We investigated whether unsedated colonoscopy causes more discomfort than barium enema. METHODS: Procedure-related discomfort was determined in 100 consecutive patients undergoing colonoscopy without premedication and in an equal number of patients referred for sigmoidoscopy and barium enema. All patients underwent such examinations for the first time and had no history of previous bowel surgery. During colonoscopy, sedation was offered if significant pain or discomfort occurred. RESULTS: In patients without stenosis and with satisfactory preparation, the completion rate of colonoscopy was 95%. Five percent of all patients undergoing endoscopy required sedation. On an analog scale ranging from 1 to 9, patients undergoing colonoscopy and barium enema reported similar ratings for procedure related discomfort (3.2 +/- 1.7 and 3.1 +/- 1.9) and for discomfort caused by bowel preparation (3.2 +/- 2.1 and 3.1 +/- 1.8). Eighty-seven percent of all patients undergoing colonoscopy stated that they would prefer no premedication in the event of repeated examinations. CONCLUSIONS: Colonoscopy with sedation on demand does not cause more discomfort than barium enema and will be accepted by the vast majority of patients undergoing this procedure.

Evidence for the presence of a protease-activated receptor distinct from the thrombin receptor in human keratinocytes.

Thrombin receptor activation was explored in human epidermal keratinocytes and human dermal fibroblasts, cells that are actively involved in skin tissue repair. The effects of thrombin, trypsin, and the receptor agonist peptides SFLLRN and TFRIFD were assessed in inositolphospholipid hydrolysis and calcium mobilization studies. Thrombin and SFLLRN stimulated fibroblasts in both assays to a similar extent, whereas TFRIFD was less potent. Trypsin demonstrated weak efficacy in these assays in comparison with thrombin. Results in fibroblasts were consistent with human platelet thrombin receptor activation. Keratinocytes, however, exhibited a distinct profile, with trypsin being a far better activator of inositolphospholipid hydrolysis and calcium mobilization than thrombin. Furthermore, SFLLRN was more efficacious than thrombin, whereas no response was observed with TFRIFD. Since our data indicated that keratinocytes possess a trypsin-sensitive receptor, we addressed the possibility that these cells express the human homologue of the newly described murine protease-activated receptor, PAR-2 [Nystedt, S., Emilsson, K., Wahlestedt, C. & Sundelin, J. (1994) Proc. Natl. Acad. Sci. USA 91, 9208-9212]. PAR-2 is activated by nanomolar concentrations of trypsin and possesses the tethered ligand sequence SLIGRL. SLIGRL was found to be equipotent with SFLLRN in activating keratinocyte inositolphospholipid hydrolysis and calcium mobilization. Desensitization studies indicated that SFLLRN, SLIGRL, and trypsin activate a common receptor, PAR-2. Northern blot analyses detected a transcript of PAR-2 in total RNA from keratinocytes but not fibroblasts. Levels of thrombin receptor message were equivalent in the two cell types. Our results indicate that human keratinocytes possess PAR-2, suggesting a potential role for this receptor in tissue repair and/or skin-related disorders.

Characterization of an antibody raised against reduced glycoprotein IIIa of human platelets.

A polyclonal antibody against reduced and vinylpyridylethylated human glycoprotein IIIa was raised in rabbits. Its reactivity with reduced GPIIIa was about 500 times higher than that of the antibody against native GPIIIa. The lowest amounts of purified reduced and native GPIIIa recognized by the antibody against reduced GPIIIa were 25 and 400 ng, respectively. The antibody did not recognize native GPIIIa (about 1-2 micrograms) in platelet extracts and chymotryptic degradation products of GPIIIa. It inhibited ADP-induced platelet aggregation but it did not inhibit fibrinogen binding to ADP-stimulated platelets. Our experiments suggest that the antigenicity of GPIIIa (beta 3 integrin) depends on the conformation of the molecule determined by numerous S-S bridges between cysteine residues.