The long-term effect on surgery-free survival of biological compared to conventional therapy in Crohn's disease in real world-data: a retrospective study.

BACKGROUND: The introduction of biological drugs has led to great expectations and growing optimism in the possibility that this new therapeutic strategy could favourably change the natural history of Inflammatory Bowel Disease (IBD) and, in particular, that it could lead to a significant reduction in surgery in the short and long term. This study aims to assess the impact of biological versus conventional therapy on surgery-free survival time (from the diagnosis to the first bowel resection) and on the overall risk of surgery in patients with Crohn's disease (CD) who were never with the surgical option. METHODS: This is a retrospective, double-arm study including CD patients treated with either biological or conventional therapy (mesalamine, immunomodulators, antibiotics, or steroids). All CD patients admitted at the GI Unit of the S. Salvatore Hospital (L'Aquila. Italy) and treated with biological therapy since 1998 were included in the biological arm. Data concerning the CD patients receiving a conventional therapy were retrospectively collected from our database. These patients were divided into a pre-1998 and post-1998 group. Our primary outcome was the evaluation of the surgery-free survival since CD diagnosis to the first bowel resection. Surgery-free time and event incidence rates were calculated and compared among all groups, both in the original population and in the propensity-matched population. RESULTS: Two hundred three CD patients (49 biological, 93 conventional post-1998, 61 conventional pre-1998) were included in the study. Kaplan-Meier survivorship estimate shows that patients in the biological arm had a longer surgery-free survival compared to those in the conventional arm (p = 0.03). However, after propensity matching analysis, conducted on 143 patients, no significant difference was found in surgery-free survival (p = 0.3). A sub-group analysis showed shorter surgery-free survival in patients on conventional therapy in the pre-biologic era only (p = 0.02; Hazard Ratio 2.9; CI 1.01-8.54) while no significant difference was found between the biologic and conventional post-biologic groups (p = 0.15; Hazard Ratio 2.1; CI 0.69-6.44). CONCLUSION: This study shows that the introduction of biological therapy has only a slight impact on the eventual occurrence of surgery in CD patients over a long observation period. Nevertheless, biological therapy appears to delay the first intestinal resection.

A novel gene therapy strategy using secreted multifunctional anti-HIV proteins to confer protection to gene-modified and unmodified target cells.

Current human immunodeficiency virus type I (HIV) gene therapy strategies focus on rendering HIV target cells non-permissive to viral replication. However, gene-modified cells fail to accumulate in patients and the virus continues to replicate in the unmodified target cell population. We have designed lentiviral vectors encoding secreted anti-HIV proteins to protect both gene-modified and unmodified cells from infection. Soluble CD4 (sCD4), a secreted single chain variable fragment (sscFv(17b)) and a secreted fusion inhibitor (sFI(T45)) were used to target receptor binding, co-receptor binding and membrane fusion, respectively. Additionally, we designed bi- and tri-functional fusion proteins to exploit the multistep nature of HIV entry. Of the seven antiviral proteins tested, sCD4, sCD4-scFv(17b), sCD4-FI(T45) and sCD4-scFv(17b)-FI(T45) efficiently inhibited HIV entry. The neutralization potency of the bi-functional fusion proteins sCD4-scFv(17b) and sCD4-FI(T45) was superior to that of sCD4 and the Food and Drug Administration-approved fusion inhibitor T-20. In co-culture experiments, sCD4, sCD4-scFv(17b) and sCD4-FI(T45) secreted from gene-modified producer cells conferred substantial protection to unmodified peripheral blood mononuclear cells. In conclusion, continuous delivery of secreted anti-HIV proteins via gene therapy may be a promising strategy to overcome the limitations of the current treatment.

Arbitrary visuomotor mapping in the grip-lift task: dissociation of performance deficits in right and left middle cerebral artery stroke.

The ability to rapidly establish a memory link between arbitrary sensory cues and goal-directed movements is part of our daily motor repertoire. It is unknown if this ability is affected by middle cerebral artery stroke. Eighteen right-handed subjects with a first unilateral middle cerebral artery stroke were studied while performing a precision grip to lift objects of different weights. In a "no cue" condition, a noninformative neutral visual stimulus was presented before each lift, thereby not allowing any judgment about the object weight. In a "cue" condition arbitrary color cues provided advance information about the weight to be lifted in the subsequent trial. Subjects performed both conditions with either hand. During "no cue" trials subjects scaled their grip force according to the weight of the preceding lift, irrespective of the hand performing the lift or the hemisphere affected. The presentation of color cues allowed patients with right hemispheric stroke, but not those with left hemispheric stroke, to scale their grip force according to the weight in the upcoming lift when lifting the weight with the unaffected hand. Color cues did not allow for a predictive scaling of grip force according to the weight of the object to be lifted when lifting with the affected hand, irrespective of the affected hemisphere. These data imply that the ability of visuomotor mapping in the grip-lift task is selectively impaired in the affected hand after right middle cerebral artery stroke, but in both hands after left middle cerebral artery stroke.

[Transcranial magnetic stimulation for psychogenic tremor - a pilot study]. / Der Einsatz der transkraniellen Magnetstimulation beim psychogenen Tremor - eine Pilotstudie.

Psychogenic tremor is the most common psychogenic movement disorder. Its prognosis is widely held to be poor and strongly depends on the patient's insight into the psychogenicity of the syndrome. The clinical value of transcranial magnetic stimulation (TMS) for (i) establishing the diagnosis with a high level of certainty, (ii) modulating symptom severity and (iii) facilitating patients' insight into psychogenicity was tested in 11 patients with psychogenic tremor of the upper limb. After explaining the psychogenic origin of the syndrome and providing a neurobiological model, 30 TMS pulses were applied over the hand area of the primary motor cortex contralateral to the affected hand(s) at a rate of 0.2 Hz. 15 pulses were administered at intensities of 120 % and 140 % of the resting motor threshold, respectively. Kinematic motion analysis was used to document the effectiveness of the TMS procedure. All patients met the diagnostic criteria of conversion disorder. Time elapsed since symptom onset was on average 48 to 57 months. Tremor affected both hands in 8 patients, one patient had additional head tremor. The TMS procedure caused a significant reduction of tremor frequency and thus established the diagnosis of documented psychogenic tremor according to the criteria proposed by Fahn and Williams (1988) in each patient. The duration of symptom relief was transient in 7 patients, 4 patients had lasting symptom relief. The present pilot study demonstrates that TMS is a helpful tool to (i) establish the diagnosis of psychogenic hand tremor with a high level of certainty, (ii) reduce tremor intensity and (iii) facilitate the patient's insight into the psychogenic origin of the syndrome as a prerequisite to obtain adherence to psychotherapy.

Electrical somatosensory stimulation improves movement kinematics of the affected hand following stroke.

AIM: The effect of electrical somatosensory stimulation on motor performance of the affected hand was investigated in 12 chronic subcortical stroke subjects. METHODS: Subjects performed index finger and hand tapping movements as well as reach-to-grasp movements with both the affected and unaffected hand prior to (baseline conditions) and following (1) 2 h of electrical somatosensory stimulation (trains of five pulses at 10 Hz with 1 ms duration delivered at 1 Hz with an intensity on average 60% above the individual somatosensory threshold) of the median nerve of the affected hand or (2) 2 h of idle time on separate occasions at least 1 week apart. The order of sessions was counterbalanced across subjects. RESULTS: Somatosensory stimulation of the median nerve of the affected hand, but not a period of idle time, enhanced the frequency of index finger and hand tapping movements and improved the kinematics of reach-to-grasp movements performed with the affected hand, compared with baseline. Somatosensory stimulation did not impact on motor performance of the unaffected hand. DISCUSSION: The data suggest that electrical somatosensory stimulation may improve motor function of the affected hand after stroke; however, further studies are needed to test if the implementation of somatosensory stimulation in rehabilitation of hand function also impacts on manual activities of daily life after stroke.

Infección por VIH-1 en pacientes no progresores a largo tiempo

El periodo entre la infección por el VIH y el desarrollo de SIDA es de diez años en promedio, pero un 5-10% de personas infectadas, llamadas no progresores a largo tiempo (NPLT), no desarrollan SIDA aún después de diez años de infección. Algunos factores pueden influir en el curso natural de la infección por VIH, tales como: 1) Factores de tipo ambiental, como infecciones por otros patógenos, que podrían estimular la replicación del VIH, acelerando el desarrollo de la inmunodeficiencia; 2) Características genéticas del huésped (repertorio HLA, perfil de citoquinas y quimioquinas, así como sus receptores), podrían justificar una diferente susceptibilidad frente al VIH-1; 3) Intensidad y diversidad de la respuesta inmune del huésped frente al virus; 4)Finalmente, la virulencia de las cepas predominantes del VIH en un individuo, explicaría la diferente progresión de la enfermedad en los pacientes infectados.

The period between HIV infection and AIDS development is ten years on average, but 5-10% of people infected, named long term non progressors (LTNP), not development AIDS even ten years after infection. Some factors can to have influence in the HIV infection natural course, such as: 1) environment factors, such as infection for others pathogens that could stimulate the HIV replication, racing the immunodeficiency development; 2) host genetic characteristics (HLA repertoire, citokines and chemokines profile as soon as their receptors) justify a different susceptibility against HIV-1; 3) Intensity and diversity of host immunological response against the virus; 4)Finally, HIV predominant isolates virulence in an individual would explain the disease different progression in infected patients.

Frequency of inter- and intraventricular dyssynchrony in patients with heart failure according to QRS width.

AIMS: Cardiac resynchronization therapy (CRT) is an effective treatment for heart failure patients with prolongation of QRS duration. Despite careful patient selection, some do not respond to CRT based on QRS complex duration. We sought to evaluate the presence of left ventricular dyssynchrony using tissue Doppler imaging (TDI) according to QRS duration in heart failure patients. METHODS AND RESULTS: Ninety-nine patients (mean age 52.6 +/- 15.3 years) with severe heart failure [left ventricular (LV) ejection fraction, <35%] were prospectively evaluated. On the basis of QRS width, the patients were divided into two groups. Forty-eight patients (48.5%) had a normal QRS duration (<120 ms), Group I, and 51 (51.5%) had a prolonged QRS duration, Group II. All patients underwent echocardiography coupled with TDI. Spectral displays of six basal and six middle LV segments with pulsed-wave TDI were obtained to assess the time to peak systolic point from R-wave on electrocardiogram (Ts). The standard deviation of Ts (Ts-SD) and the maximal temporal difference of Ts (Ts-diff) were measured. Interventricular dyssynchrony [defined as the presence of an interventricular mechanical delay (IVMD) >40 ms] and intra-LV mechanical delays (defined as Ts-SD >33.4 ms and Ts-diff >100 ms) were correlated with the QRS width and morphology. We found a greater IVMD in Group II patients, compared with patients in Group I (42.5 +/- 22.3 vs. 26.8 +/- 21, respectively, P < 0.001). Intraventricular dyssynchrony defined as Ts-SD > or =33.4 ms was found in 45.1% of patients in Group II compared with 23% of patients in Group I (P = 0.03). Similarly, the Ts-diff was prolonged in Group II patients compared with Group I (P = 0.02). By linear regression analysis, a weak relation was found between Ts-SD and QRS duration (P = 0.055). A substantial portion of patients with prolonged QRS did not exhibit ventricular dyssynchrony defined either as total asynchrony index > or =33.4 ms or as IVMD >40 ms. CONCLUSION: A substantial proportion of patients with prolonged QRS (32.1%) did not exhibit inter- or intraventricular dyssynchrony, which may represent a limitation in identifying the ideal QRS interval for the selection of patients for CRT.

Mid-term follow-up of patients with Brugada syndrome following a cardioverter defibrillator implantation: a single center experience.

BACKGROUND: Brugada syndrome is an arrhythmogenic disease characterized by an ECG pattern of ST-segment elevation in the right precordial leads and an increase risk of sudden cardiac death. Risk stratification for the life-threatening arrhythmic events in Brugada syndrome is not yet established. In the present study, we report our experience in patients with Brugada syndrome, following an ICD implantation. METHODS AND RESULTS: A total of 12 patients (11 men, 1 woman) with a mean age of 46.5+/-11.8 were studied. At diagnosis, 7 patients had syncope of unknown origin, 2 patients were asymptomatic, 2 patients were survivors of cardiac arrest, and 1 had documented clinical VT requiring direct cardioversion for termination. Age was similar between the symptomatic and asymptomatic patients (46.6+/-13 vs. 46+/-2.8, respectively). Two patients reported a family history of sudden cardiac death. In 3 patients, spontaneous coved-type ECG was found at baseline. In 9 patients, a class I antiarrhythmic drug administration unmasked the characteristic type I ECG. In 4 patients (2 symptomatic with syncope at presentation and 2 asymptomatic), who underwent PES, sustained polymorphic VT or VF was induced. VF was induced by single extrastimuli in 2 symptomatic patients (1 from RV apex and 1 from RVOT). In 2 asymptomatic patients, VF was induced by two and triple ventricular extrastimli (1 from RV apex and 1 from RVOT). None of them experienced an event during follow-up. No significant difference was found between symptomatic and asymptomatic patients (p=NS). The mean follow-up period for the entire study population was 27.83+/-11.25 months. During follow-up, 2 patients (one with prior cardiac arrest and another with syncope) had VF. Both of them had a type I ECG after provocation with a class I antiarrhythmic drug. None of them had undergone programmed ventricular stimulation. Five patients (41.7 %) had inappropriate ICD interventions during follow-up. The cause of inappropriate therapy was sinus tachycardia in 2 patients, AF in 2 patients and T wave oversensing in 1 patient. CONCLUSION: Knowledge about Brugada syndrome is steadily progressing but there are still unanswered issues dealing with the risk stratification and the management of patients.

Resolution of tachycardia-induced cardiomyopathy following ablation of verapamil-sensitive idiopathic left ventricular tachycardia.

Few reports have described tachycardia-induced cardiomyopathy secondary to ventricular tachycardia. We present a 12-year-old boy with dilated cardiomyopathy and incessant verapamil-sensitive idiopathic left ventricular tachycardia. Twelve-lead electrocardiogram showed right bundle branch block QRS morphology with superior axis during tachycardia. Electrophysiology study confirmed the diagnosis, and radiofrequency ablation was done and successfully terminated and prevented induction of ventricular tachycardia. During the follow-up period of 18 months, the patient remained free of symptoms and arrhythmia. Three months after ablation, left ventricular ejection fraction improved and cardiac silhouette became normal on chest x-ray.

Heart rate variability: does it change after RF ablation of reentrant supraventricular tachycardia?

BACKGROUND: Following RF ablation of reentrant supraventricular tachycardia, inappropriate sinus tachycardia may occur. Local parasympathetic denervation is a possible mechanism for these rhythm disturbances. The purpose of this study was to determine the incidence of sinus tachycardia and to determine the relation between endocardial lesions at different ablation sites and alterations in autonomic tone in several different groups of patients with supraventricular tachycardia, using techniques of heart rate variability analysis. METHODS: The subjects of this study were 75 patients (48 women, 27 men) with a mean age of 39.99 (SD = 13.39). They underwent RF ablation of AV nodal slow pathways (40 cases), posteroseptal APs (23 cases), left lateral and right free wall APs (12 cases) because of symptomatic tachycardias. The mean sinus rate and time domain (standard deviation of RR intervals and root mean square of differences of adjacent RR intervals) and frequency domain (low frequency, high frequency and low frequency/high frequency ratio) analyses of heart rate variability were obtained by use of 24 hour Holter monitoring before and 1 month after ablation compared with pre-ablation values. RESULTS: Analysis of 24 hour ambulatory Holter-monitors, performed 1 month after RF ablation, showed no significant changes in time and frequency domain parameters of heart rate variability in different groups. A significant increase in mean heart rate was noted after RF ablation at AV nodal slow pathway group and left freewall/right free wall accessory pathways group. Patients undergoing RF ablation of right or left posteroseptal accessory pathways had no significant increase in the mean heart rate. CONCLUSION: In summary, an increase in sinus tachycardia may be initiated by RF ablation of atrioventricular reentrant tachycardia (AVNRT) and right free wall or left free wall accessory pathways. This finding shows that the modifications of heart rate are not directly related to the posteroseptal region or to the accessory pathways.

Different splice variants of cartilage alpha1(XI) collagen chain undergo uniform amino-terminal processing.

Collagen XI is found mainly as a component of cartilage fibrils. Among the different transcripts identified by RT-PCR for the alpha1 (XI) chain, the major tissue form has been reported to be the splicing product of exons I, III and V. In this study, two other splice isoforms of the alpha1(XI) chain were identified using N-terminal sequencing. Like the major alpha1(XI) chain, the fully processed isoforms begin at Gln254 within the N-terminal domain encoded by exon I. This sequence is followed by sequences encoded by exon IIA or III. An anti-peptide antibody allowed the identification of the exon IV encoded sequence within both isoforms. Therefore, these isoforms of the alpha1(XI) chain correspond to the splicing of exons I, IIA, III, IV and V or of exons I, III, IV and V, thus presenting larger acidic sequences than the major form. They could mediate strong ionic interactions within the cartilage matrix.

Late results of balloon pulmonary valvuloplasty in adults.

This study shows late results of adult patients with pulmonary stenosis after successful balloon pulmonary valvuloplasty. Late results of this procedure are as good as early results.

Microfibrillar composition of umbilical cord matrix: characterization of fibrillin, collagen VI and intact collagen V.

Ultrastructural studies made on human umbilical cord revealed that the striated collagen fibrils of the Wharton's jelly matrix are mixed with many microfibrillar structures. Microfibrils were found with a tubular cross-section of 10-12 nm diameter and were organized as beaded filaments characteristic of fibrillin-rich microfibrils. Beads had an average diameter of 25 nm and were spaced at about 50-80 nm. This ultrastructural observation was confirmed by indirect immunofluorescent staining of the jelly matrix using monoclonal antibody to fibrillin. Another constituent of the microfibrillar network was present as typical 100-nm periodic filaments of type VI collagen. Indirect immunofluorescent staining using antibodies to collagen VI showed for the first time that this collagen appeared to be distributed largely in the jelly matrix. In addition, other microfibrils with no specific banding pattern were observed. These microfibrils may constitute an organization of type V collagen different from the one which is generally assembled in heterotypic fibrils with collagen I. Among the latter heterotypic fibrils, type V collagen was studied using an anti-peptide antibody to the most N-terminal non-collagenous region of its alpha 2(V) chain. This antibody recognized a filamentous mesh decorating the bundles of collagen fibrils by immunofluorescent staining. This indicates that at least this part of alpha 2(V) chain may be accessible to the antibody at the surface of the fibrils.

Processing of type XI collagen. Determination of the matrix forms of the alpha1(XI) chain.

Type XI collagen is mainly found as a minor constituent in type II-containing fibrils and presents a alpha1(XI)alpha2(XI)alpha3(XI) stoichiometry. This molecule was shown to be partially processed in its intact tissue form. Moreover, alternative splicing has been demonstrated in the variable region of the N-terminal domain of alpha1(XI) and alpha2(XI) chains. In this work, the processing of a major intact form of alpha1(XI) from matrix laid down by chick chondrocytes in culture was identified using N-terminal sequencing and antibodies to synthetic peptides corresponding to the N-terminal propeptide cDNA-derived sequence. The results show that the fully processed form of alpha1(XI) begins at Gln254 of the N-terminal propeptide, seven residues before the end of the proline/arginine-rich protein region encoded by exon I (Zhidkova, N. I., Justice, S. K., and Mayne, R. (1995) J. Biol. Chem. 270, 9486-9493). This sequence is immediately followed by a sequence encoded by exon III. The processing takes place at an Ala-Gln sequence that corresponds to a consensus sequence for procollagen N-proteinase. The antibody raised against a sequence located within the region corresponding to exon IV (anti-P8) fails to recognize this fully processed form of the alpha1(XI) chain. It recognizes, however, two minor bands of high molecular mass. These results suggest that a major cartilage form of alpha1(XI) is the product of alternative splicing in which sequences encoded by both exons II and IV are skipped. The presence of a highly acidic subdomain encoded by exon III at the N terminus of the major form of the alpha1(XI) chain, as predicted by these data, provides potential sites for interaction of collagen XI with other molecules.

Diversity in the processing events at the N-terminus of type-V collagen.

The processing of human collagen type-V chains was studied using anti-peptide polyclonal antibodies raised against peptide sequences at the N-terminal non-triple-helical region of pro-alpha 1(V) and pro-alpha 2(V) chains. The anti-peptide polyclonal antibody raised against positions 48-57 of the N-terminal alpha 2(V) sequence recognized the mature form of the human alpha 2(V) chain extracted without any proteolytic treatment from several tissues in the presence of a mixture of protease inhibitors. It also recognized the pro-alpha 2(V) and pN-alpha 2(V) collagen chains secreted in the cell-culture media of the rhabdomyosarcoma A204 cell line. The pN-alpha 2(V) collagen chain from this cell line migrated during electrophoresis with the alpha 2(V) chain obtained from tissues. This demonstrates that the alpha 2(V) chain in tissues is incompletely processed and is present as the pN-alpha 2(V) collagen chain which lacks the C-propeptide. In comparison, an anti-peptide polyclonal antibody raised against residues at positions 284-299 of the N-terminal alpha 1(V) human sequence failed to recognize the mature form of the alpha 1(V) chain while it reacted with the pN-alpha 1(V) collagen chain form. These results suggest that the alpha 1(V) chain undergoes a processing event in the N-terminal region that involves the removal of at least the first 284 residues. Amino acid sequence analysis was performed on cyanogen-bromide-generated or trypsin-generated peptides of the two electrophoretic bands obtained for the tissue form of collagen V. The slower-migrating band corresponding to the intact alpha 1(V) chain gave, as expected, only sequences corresponding to the alpha 1(V) chain. However, the band previously considered to be the intact alpha 2(V) chain also gave sequences for the alpha 1(V) chain in addition to the alpha 2(V) chain. This result indicates the presence in tissue extracts of a further processed form of alpha 1(V) chain which migrates with the intact alpha 2(V) chain. On further analysis, we observed that the two bands of the tissue form of collagen V occurred in a 1:1 ratio whereas, after the pepsin digestion to remove non-collagenous regions, two bands were observed with an alpha 1(V)/alpha 2(V) chain ratio of 3:1. These results indicate that the alpha 1(V) chain exists in an additional stoichiometry, different from [alpha 1(V)]2 alpha 2(V).(ABSTRACT TRUNCATED AT 400 WORDS)

Common topology within a non-collagenous domain of several different collagen types.

The secondary structure of a conserved non-collagenous module in alpha 1(V), alpha 1(XI), alpha 1(IX), alpha 1(XII), alpha 1(XIV) and alpha 1(XVI) collagen chains and in proline- and arginine-rich protein was analyzed using different algorithms. The results predict that a common anti-parallel beta-sheet structure composed of nine consensus beta-strands is present in these non-collagenous modules. A model for the packing of these beta-sheets is proposed which suggests that the predicted beta-sheet structure may be involved in molecular recognition functions.

Synteny between the loci for a novel FACIT-like collagen locus (D6S228E) and alpha 1 (IX) collagen (COL9A1) on 6q12-q14 in humans.

A 1.8-kb cDNA encoding portion of a novel collagenous chain was isolated from a human rhabdomyosarcoma cell line by cross-hybridization using a chicken type V collagen probe. Sequence analysis suggests that this chain belongs to the recently discovered group of collagens, termed the FACIT class of macromolecules. This cDNA was used to locate the corresponding gene (D6S228E) to chromosome 6, notably at position 6q12-q14. Interestingly, within this region of human chromosome 6 residues the alpha 1 (IX) collagen gene (COL9A1), a member of the FACIT group.

Post traumatic tricuspid insufficiency: when to intervene?

Isolated post traumatic tricuspid insufficiency is a rare entity with an increasing incidence. It is associated with insidious yet unequivocal hemodynamic alterations leading to severe incapacity. Early surgery rather than medical treatment is the therapeutic modality of choice.

Localization on the mitochondrial F1 ATPase alpha subunit of an epitope masked in the membrane-bound enzyme using a monoclonal antibody and synthetic peptides.

The epitope of the monoclonal antibody 20D6 was localized by N-terminal sequencing of the smallest immunoreactive peptides obtained after CNBr and trypsin cleavage of the F1 alpha subunit of the mitochondrial ATPase/ATP synthase. Immunochemical analysis of overlapping synthetic octapeptides, covering the immunoreactive peptide sequence, has defined the seven-amino-acid sequence recognized by 20D6 as 84EGDIVKR90. The binding of 20D6 was lost after substituting either I87 by K or S, or R90 by C or A as it occurs in the alpha subunit sequence of Escherichia coli or chloroplast ATPase, respectively. This explained the lack of immunoreactivity of 20D6 to these species and indicated the importance of charged as well as hydrophobic residues in the epitope. Immunochemical analysis of synthetic peptides by polyclonal anti-F1 antisera showed that this region is highly immunodominant. In a competitive ELISA, the monoclonal antibody bound with similar affinity to F1 in the presence and absence of substrate as well as to cold dissociated F1, indicating that the epitope was located on the surface of the alpha subunit and not buried between F1 subunits. The lack of binding of 20D6 when F1 is bound to the membrane showed that the epitope exposed at the surface of purified soluble F1 became masked after binding to the membrane. This suggests that it is located at the interface between F1 and the membrane.