Ambulatory atrioventricular synchronous pacing over time using a leadless ventricular pacemaker: Primary results from the AccelAV study.

BACKGROUND: Previous studies demonstrated that accelerometer-based, mechanically timed atrioventricular synchrony (AVS) is feasible using a leadless ventricular pacemaker. OBJECTIVE: The purpose of this study was to determine the performance of a leadless ventricular pacemaker with accelerometer-based algorithms that provide AVS pacing. METHODS: AccelAV was a prospective, single-arm study to characterize AVS in patients implanted with a Micra AV, which uses the device accelerometer to mechanically detect atrial contractions and promote VDD pacing. The primary objective was to characterize resting AVS at 1 month in patients with complete atrioventricular block (AVB) and normal sinus function. RESULTS: A total of 152 patients (age 77 ± 11 years; 48% female) from 20 centers were enrolled and implanted with a leadless pacemaker. Among patients with normal sinus function and complete AVB (n = 54), mean resting AVS was 85.4% at 1 month, and ambulatory AVS was 74.8%. In the subset of patients (n = 20) with programming optimization, mean ambulatory AVS was 82.6%, representing a 10.5% improvement (P <.001). Quality of life as measured by the EQ-5D-3L (EuroQol Five-Dimensions Three-Level questionnaire) improved significantly from preimplant to 3 months (P = .031). In 37 patients with AVB at both 1 and 3 months, mean AVS during rest did not differ (86.1% vs 84.1%; P = .43). There were no upgrades to dual-chamber devices or cardiac resynchronization therapy through 3 months. CONCLUSION: Accelerometer-based mechanical atrial sensing provided by a leadless pacemaker implanted in the right ventricle significantly improves quality of life in a select cohort of patients with AV block and normal sinus function. AVS remained stable through 3 months, and there were no system upgrades to dual-chamber pacemakers.

Anthropometric indices of First Nations children and youth on first entry to Manitoba/Saskatchewan residential schools-1919 to 1953.

BACKGROUND: First Nations people are experiencing increasing rates of obesity and type 2 diabetes but no anthropometric information exists from before the 1950s to provide context to these epidemics. OBJECTIVE: To compare anthropometric indices of First Nations children and youth on first entering residential schools with historical and contemporary reference groups. METHODS: This observational cross-sectional study used archival records from the Department of Indian Affairs to calculate body mass index (BMI), height for age (HA) and weight for age (WA) of all known children and youth undergoing physical examinations on first entering residential schools in Saskatchewan and Manitoba from 1919 to 1953. Proportions of children and youth in each BMI category were determined by age, sex, time period and residential school. Z-scores for HA and WA were determined by age group and sex. Finally, median heights and weights were compared with a non-Indigenous cohort from the 1953 Canadian survey. RESULTS: On admission to residential schools, 1,767 First Nations children and youth (847 boys, 920 girls) were more likely to have normal BMIs (79.8%) than Canadian children and youth today (66.5%), but lower rates of overweight/obesity (10.9% vs. 32.0%) and higher rates of underweight (9.3% vs. <2.0%). There was an overall trend of diminishing levels of underweight and increasing levels of overweight/obesity over time. Although 6.6% of boys and 7.9% of girls had HA Z-scores >-2, age-specific median heights tended to be higher than Canadian children and youth in 1953. Under 3% of children and youth had WA Z-scores of >-2. CONCLUSIONS: A large majority of First Nations children and youth exhibited normal anthropometric indices on first entering residential schools in Manitoba and Saskatchewan from 1919 to 1953. These historical findings provide an important context to the current epidemics of obesity and type 2 diabetes and suggest that the nutritional conditions in these First Nations children's communities were satisfactory during the residential school era.

Implantation success and infection in cardiovascular implantable electronic device procedures utilizing an antibacterial envelope.

BACKGROUND: Cardiovascular implantable electronic device (CIED) infection rates are increasing faster than implantation rates. More effective antimicrobial prophylaxis may help reduce CIED infections and improve clinical outcomes. The AIGIS(Rx)(®) antibacterial envelope is a polymer mesh implanted in the generator pocket with the CIED. After implantation it releases two antibiotics, minocycline and rifampin, that have been shown to reduce infections associated with other medical devices. The purpose of this retrospective cohort study is to determine the rate of CIED implantation success and CIED infection in procedures utilizing the antibacterial envelope. METHODS: This study enrolled consecutive CIED procedures utilizing the antibacterial envelope at 10 US academic, community, and Veterans Affairs medical centers. Procedures following an explantation for a prior CIED infection or off-label use of the antibacterial envelope were excluded. RESULTS: The 624 eligible procedures (age 70 ± 13 years, 68.1% men, 27.2% renal insufficiency, 35.4% oral anticoagulant use, 67.8% replacement/revision procedures) utilized pacemakers (35%), implantable cardioverter-defibrillators (ICD)(29%), and cardiac resynchronization therapy with defibrillator devices (CRT-D)(36%). Nearly half of the patients (49%) had at least three predefined risk factors for CIED infection. CIED implantation was successful in 621 procedures (99.5%[95% confidence interval (CI) 98.8-99.9]). There were three major infections (0.48%[95%CI 0.17-1.40]) after 1.9 ± 2.4 months follow-up. The infections followed one ICD revision and two CRT-D replacements. There were seven deaths; none was a result of the antibacterial envelope or the CIED procedure. CONCLUSIONS: CIED procedures that utilized an antibacterial envelope had a high rate of CIED implantation success (>99%). Although the follow-up to date is short, there was also a low rate of infection (<0.50%) in this population at high risk for CIED infection.

PCR-based gene synthesis as an efficient approach for expression of the A+T-rich malaria genome.

The A+T-rich genome of the human malaria parasite Plasmodium falciparum encodes genes of biological importance that cannot be expressed efficiently in heterologous eukaryotic systems, owing to an extremely biased codon usage and the presence of numerous cryptic polyadenylation sites. In this work we have optimized an assembly polymerase chain reaction (PCR) method for the fast and extremely accurate synthesis of a 2.1 kb Plasmodium falciparum gene (pfsub-1) encoding a subtilisin-like protease. A total of 104 oligonucleotides, designed with the aid of dedicated computer software, were assembled in a single-step PCR. The assembly was then further amplified by PCR to produce a synthetic gene which has been cloned and successfully expressed in both Pichia pastoris and recombinant baculovirus-infected High Five(TM) cells. We believe this strategy to be of special interest as it is simple, accessible and has no limitation with respect to the size of the gene to be synthesized. Used as a systematic approach for the malarial genome or any other A + T-rich organism, the method allows the rapid synthesis of a nucleotide sequence optimized for expression in the system of choice and production of sufficiently large amounts of biological material for complete molecular and structural characterization.

PfSUB-2: a second subtilisin-like protein in Plasmodium falciparum merozoites.

Erythrocyte invasion by the malaria merozoite requires the activity of merozoite proteases. We have previously identified a Plasmodium falciparum protein belonging to the superfamily of subtilisin-like serine proteases, which is expressed in a subset of secretory organelles in free merozoites. Here we describe the identification of a second P. falciparum subtilisin-like merozoite protein. Called PfSUB-2, it is encoded by a single copy gene and is expressed as a large putative type I integral membrane protein which undergoes extensive post-translational processing. The terminal processing product is expressed in an apical location in merozoites. PfSUB-2 may mediate one or more of the serine protease activities known to be associated with erythrocyte invasion.

A subtilisin-like protein in secretory organelles of Plasmodium falciparum merozoites.

In the vertebrate host, the malaria parasite invades and replicates asexually within circulating erythrocytes. Parasite proteolytic enzymes play an essential but poorly understood role in erythrocyte invasion. We have identified a Plasmodium falciparum gene, denoted pfsub-1, encoding a member of the subtilisin-like serine protease family (subtilases). The pfsub-1 gene is expressed in asexual blood stages of P. falciparum, and the primary gene product (PfSUB-1) undergoes post-translational processing during secretory transport in a manner consistent with its being converted to a mature, enzymatically active form, as documented for other subtilases. In the invasive merozoite, the putative mature protease (p47) is concentrated in dense granules, which are secretory organelles located toward the apical end of the merozoite. At some point following merozoite release and completion of erythrocyte invasion, p47 is secreted from the parasite in a truncated, soluble form. The subcellular location and timing of secretion of p47 suggest that it is likely to play a role in erythrocyte invasion. PfSUB-1 is a new potential target for antimalarial drug development.

Neutralizing monoclonal antibodies to glycosylphosphatidylinositol, the dominant TNF-alpha-inducing toxin of Plasmodium falciparum: prospects for the immunotherapy of severe malaria.

Tumour necrosis factor-alpha (TNF-alpha) is an endogenous mediator of shock and inflammation. Many of the life-threatening and severe pathologies associated with complicated and cerebral malaria are thought to result from the overproduction of this cytokine in response to agents of parasite origin. The identification and characterization of these agents may therefore provide the molecular basis for a detailed understanding of the disease process. Recently it has been shown that glycosylphosphatidylinositols are a novel class of glycolipid toxin produced by the parasite, which substitute for the endogenous inositolglycan-based signal transduction pathways of the host. Glycosylphosphatidylinositol stimulates high levels of TNF-alpha and interleukin-1 production by macrophages and induces hypoglycaemia through an insulin-mimetic activity, and may therefore contribute to the cerebral syndrome and other malarial pathophysiology. That monoclonal antibodies to parasite-derived glycosylphosphatidylinositol can neutralize the toxic activities of whole parasite extracts is also demonstrated here. These findings suggest a central role for glycosylphosphatidylinositol of parasite origin in the aetiology of severe malaria and suggest novel approaches for the immunotherapy or immunoprophylaxis of disease.

Regional cardiac sympathetic denervation in patients with ventricular tachycardia in the absence of coronary artery disease.

OBJECTIVES: The aim of this study was to determine whether patients with ventricular arrhythmias in the absence of coronary artery disease also have abnormalities in sympathetic innervation. BACKGROUND: We have previously shown by cardiac sympathetic scintigraphy using iodine-123-metaiodobenzylguanidine (I-123-MIBG) that patients with ventricular tachycardia after myocardial infarction have regional cardiac sympathetic denervation. It is not known whether patients with ventricular tachycardia in the absence of coronary artery disease also have regional cardiac sympathetic denervation. METHODS: We performed cardiac I-123-MIBG and thallium-201 single-photon emission computed tomographic (SPECT) scans at rest in 18 patients (mean age 47 +/- 18 years) with cardiomyopathy (n = 6), left ventricular hypertrophy (n = 1), valvular disease (n = 2) or a structurally normal heart (n = 9) who presented with monomorphic (n = 15) or polymorphic (n = 3) ventricular tachycardia. These scans were compared with scans in 12 control patients without ventricular tachycardia (mean age 30 +/- 17 years) who had cardiomyopathy (n = 3) or a structurally normal heart (n = 9). Cardiac sympathetic denervation was defined as myocardial areas having thallium uptake with reduced or absent I-123-MIBG uptake. RESULTS: Twelve (67%) of 18 patients with ventricular tachycardia had regional cardiac sympathetic denervation compared with 1 (8%) of 12 patients who did not have ventricular tachycardia (p = 0.002). In the nine patients with a structurally normal heart and ventricular tachycardia, five (55%) patients had regional cardiac sympathetic denervation compared with zero of nine control patients with a structurally normal heart (p = 0.029). Five patients underwent right ventricular radiofrequency ablation for ventricular tachycardia, and sympathetic denervation was adjacent to the ablation site in one of these patients. CONCLUSIONS: Patients with ventricular tachycardia in the absence of coronary artery disease have abnormal cardiac sympathetic innervation detectable by cardiac sympathetic scintigraphy. The role of regional cardiac sympathetic denervation in arrhythmogenesis remains to be determined.

Radiofrequency catheter ablation of Mahaim fibers at the tricuspid annulus.

BACKGROUND: The purpose of this study was to test the feasibility of radiofrequency catheter ablation of Mahaim fibers at the tricuspid annulus. METHODS AND RESULTS: Four patients who fulfilled criteria for having Mahaim fibers and preexcited reciprocating tachycardia underwent radiofrequency catheter ablation. Three patients had atriofascicular connections, and one patient had an atrioventricular connection. The mean age was 27 years (age range, 11-48 years). All patients had highly symptomatic tachycardias, producing syncope in one patient and presyncope in the remaining three patients. Symptoms were present for a mean of 13 years (range, 4-23 years). All pathways conducted only anterogradely, and preexcitation resulted in a left bundle branch block QRS morphology. Adenosine caused block in the accessory pathway in the three patients in whom it was tested. The stimulus to delta interval increased by 75 msec (range, 35-90 msec) during rapid atrial pacing. The atrial insertion of the Mahaim fiber was in the right lateral atrium in one patient, right posterolateral atrium in two patients, and right posterior atrium in one patient. The ventricular insertion was in the distal right bundle branch in three patients and in the posterolateral right ventricle near the tricuspid annulus in the patient with an atrioventricular connection. Stimulus to delta wave mapping was used to help localize the atrial insertion of the atriofascicular connections. A mean of 15 radiofrequency pulses (range, 10-19 pulses) delivered to the tricuspid annulus in the posterior to lateral regions eliminated accessory pathway conduction in all patients. No complications occurred. Tachycardia did not recur during a mean follow-up of 8 months (range, 2-15 months). CONCLUSIONS: Radiofrequency current applied to the tricuspid annulus can safely eliminate tachycardia in patients with Mahaim fibers.

Radiofrequency ablation for atrioventricular node reentrant tachycardia: comparison between fast (anterior) and slow (posterior) pathway ablation.

OBJECTIVES: We compared the electrophysiologic effects on atrioventricular (AV) node physiology of selective "fast" versus selective "slow" pathway radiofrequency ablation in 42 patients with drug-resistant AV node reentrant tachycardia who underwent 51 ablation attempts to prevent tachycardia recurrence while preserving AV conduction. BACKGROUND: The recent introduction of radiofrequency ablation to treat AV node reentrant tachycardia allows the opportunity to study the effects of selective elimination of the different limbs involved in AV node reentrant tachycardia. METHODS: Selective fast pathway ablation was attempted in 13 patients by delivering radiofrequency energy anteriorly across the tricuspid valve anulus. Selective slow pathway ablation was attempted in 29 patients by delivering radiofrequency energy posteriorly across the tricuspid valve anulus at sites where putative slow pathway potentials were recorded. RESULTS: Selective fast pathway ablation eliminated AV node reentrant tachycardia without AV block in 6 (46%) of 13 patients after one ablation session and in an additional 3 patients (69% of total) after repeat ablation sessions. Slow pathway ablation eliminated AV node reentrant tachycardia without AV block in 26 (90%) of 29 patients after one radiofrequency ablation session and in an additional 2 patients (97% of total) after repeat ablation sessions. Selective fast pathway ablation increased the PR interval (140 to 220 ms, p = 0.0001) and AH interval (66 to 153 ms, p = 0.0001), whereas slow pathway ablation did not change these intervals. Fast pathway radiofrequency ablation caused retrograde block in 7 (64%) of 11 patients, whereas no patients undergoing slow pathway ablation developed selective retrograde block. Single AV node echo beats were commonly induced after slow but not fast pathway ablation (17 of 29 patients vs. 1 of 11 patients, respectively, p = 0.01) and did not predict recurrence of AV node reentrant tachycardia. CONCLUSIONS: Successful selective radiofrequency ablation of fast or slow pathways in patients with AV node reentrant tachycardia resulted in different electrophysiologic properties after ablation. Slow pathway ablation produced more successful outcomes, with a decreased prevalence of recurrent AV node reentrant tachycardia or AV block.

Signal transduction in host cells by a glycosylphosphatidylinositol toxin of malaria parasites.

In this study, we have identified a dominant glycolipid toxin of Plasmodium falciparum. It is a glycosylphosphatidylinositol (GPI). The parasite GPI moiety, free or associated with protein, induces tumor necrosis factor and interleukin 1 production by macrophages and regulates glucose metabolism in adipocytes. Deacylation with specific phospholipases abolishes cytokine induction, as do inhibitors of protein kinase C. When administered to mice in vivo the parasite GPI induces cytokine release, a transient pyrexia, and hypoglycemia. When administered with sensitizing agents it can elicit a profound and lethal cachexia. Thus, the GPI of Plasmodium is a potent glycolipid toxin that may be responsible for a novel pathogenic process, exerting pleiotropic effects on a variety of host cells by substituting for the endogenous GPI-based second messenger/signal transduction pathways. Antibody to the GPI inhibits these toxic activities, suggesting a rational basis for the development of an antiglycolipid vaccine against malaria.

Catheter ablation for cardiac arrhythmias.

With the introduction of radiofrequency energy, catheter ablation has become an established technique for managing many cardiac rhythm disturbances. High efficacy and safety have been reported for accessory pathway ablation, selective fast and slow atrioventricular nodal pathway ablation to eliminate atrioventricular nodal reentrant tachycardia (while preserving atrioventricular conduction), atrioventricular junctional ablation to control the ventricular response to atrial tachyarrhythmias, ablation of the right bundle branch to eliminate bundle branch reentrant ventricular tachycardia, and ablation of the site of tachycardia origin in patients with ventricular tachycardia unassociated with structural heart disease. In addition, there has been active investigation into ablation techniques for more complex arrhythmias such as atrial tachycardia, atrial flutter, and ventricular tachycardia associated with structural heart disease.

Catheter ablation of ventricular tachycardia using radiofrequency techniques in patients without structural heart disease.

It has been previously demonstrated that radiofrequency (RF) energy can be safely applied to successfully eliminate accessory pathways in patients with the Wolff-Parkinson-White syndrome. This technique may also be used to successfully eliminate atrioventricular (AV) nodal reentrant tachycardia by elimination of either the fast or slow AV nodal pathways. However, RF energy has achieved only limited success in eliminating ventricular tachycardia (VT) in patients with structural heart disease, such as coronary artery disease and dilated cardiomyopathy. Direct-current catheter techniques have successfully eliminated VT in patients with and without structural heart disease, but this technique is limited by the risk of barotrauma and proarrhythmia. We used RF catheter ablation techniques to eliminate VT in patients without structural heart disease. Our results from the basis of this report. 16 patients (nine women and seven men; mean age 38; range 18 to 55 years) who did not have any identifiable structural heart disease by echocardiography where included in this study. These patients underwent RF catheter ablation to eliminate VT. Two patients had presented with syncope, nine with presyncope and five with palpitations only. The mean duration of symptoms was 6.7 years (range 0.5 to 20 years). VT was successfully eliminated by RF catheter techniques in 15 of the 16 patients (a 94% success rate). Importantly, successful ablation sites included regions other than the right ventricular outflow tract. Areas of VT origin therefore included the high right ventricular outflow tract (twelve patients), right ventricular septum near the tricuspid valve (three patients), and the left ventricular septum (one patient). The only ablation failure was in a patient whose VT arose from a region near the His bundle. Successful ablation occurred in patients in whom an accurate pace map could be obtained and early local endocardial activation was obtainable. Further, firm catheter contact with endocardium was required for successful elimination of VT. RF ablation did not cause any identifiable arrhythmia and produced a minimal cardiac enzyme rise. It also resulted in no detectable change in cardiac function by Doppler echocardiography. Based on these findings, we conclude that RF catheter ablation of VT in patients without structural heart disease was highly effective and safe. It may therefore be considered as early therapy in these patients.

Radiofrequency catheter ablation of ventricular tachycardia in patients without structural heart disease.

BACKGROUND: Radiofrequency energy has been used safely and successfully to eliminate accessory pathways in patients with the Wolff-Parkinson-White syndrome and the substrate for atrioventricular nodal reentrant tachycardia. However, this form of ablation has had only limited success in eliminating ventricular tachycardia in patients with structural heart disease. In contrast, direct-current catheter ablation has been used successfully to eliminate ventricular tachycardia in patients with and without structural heart disease. The purpose of this study was to test whether radiofrequency energy can safely and effectively ablate ventricular tachycardia in patients without structural heart disease. METHODS AND RESULTS: Sixteen patients (nine women and seven men; mean age, 38 years; range, 18-55 years) without structural heart disease who had ventricular tachycardia underwent radiofrequency catheter ablation to eliminate the ventricular tachycardia. Two patients presented with syncope, nine with presyncope, and five with palpitations only. Mean duration of symptoms was 6.7 years (range, 0.5-20 years). Radiofrequency catheter ablation successfully eliminated ventricular tachycardia in 15 of 16 patients (94%). Sites of ventricular tachycardia origin included the high right ventricular outflow tract (12 patients), the right ventricular septum near the tricuspid valve (three patients), and the left ventricular septum (one patient). The only ablation failure was in a patient whose ventricular tachycardia arose from a region near the His bundle. An accurate pace map, early local endocardial activation, and firm catheter contact with endocardium were associated with successful ablation. Radiofrequency ablation did not cause arrhythmias, produced minimal cardiac enzyme rise, and resulted in no detectable change in cardiac function by Doppler echocardiography. CONCLUSIONS: Radiofrequency catheter ablation of ventricular tachycardia in patients without structural heart disease is effective and safe and may be considered as early therapy in these patients.

Structure of Sm25, an antigenic integral membrane glycoprotein of adult Schistosoma mansoni.

Sm25 is the principal antigen recognised by antibodies from mice protectively vaccinated with isolated tegumental membranes of adult Schistosoma mansoni. The full-length amino acid sequence of this protein has been deduced from the sequence of two cDNAs, one isolated by screening a cDNA library and the other, including the 5' end of the gene, amplified directly from adult worm RNA using the polymerase chain reaction. The predicted sequence represents a nascent polypeptide of Mr 21,500. Following cleavage of a predicted signal sequence, the Mr of the resulting polypeptide is 17,600. The polypeptide contains 2 potential sites for N-linked glycosylation and a hydrophobic domain at the C-terminus that could facilitate membrane association. Analysis of the mature gene product confirmed that Sm25 is an N-glycosylated integral membrane protein and that the Mr of the deglycosylated polypeptide is between 15,000 and 20,000.

Epitopes expressed on very low Mr Schistosoma mansoni adult tegumental antigens conform to a general pattern of life-cycle cross-reactivity.

The relationship between antigens associated with the surface of newly transformed schistosomula of Schistosoma mansoni and the tegumental surface membrane of adult S. mansoni worms has been further explored. Immunoprecipitation of detergent-solubilized 125I-tegumental surface membrane antigens of adult S. mansoni with antibodies from mice vaccinated with highly irradiated S. mansoni cercariae revealed major antigens of Mr 32, 20, 15 and 8K. The Mr 32 and 20K antigens have been previously demonstrated to be antigenically and electrophoretically identical to major antigens on the schistosomulum surface. The Mr 15 and 8K antigens, on the other hand, have not been identified by the immunoprecipitation of 125I-schistosomulum surface antigens, although a distinct schistosomulum surface antigen of Mr 15K is precipitated by antibodies from mice vaccinated with highly irradiated cercariae. Nevertheless, it was shown that antibodies to the Mr 15 and 8K antigens were specifically absorbed from vaccinated mouse serum by intact, live schistosomula, demonstrating that the Mr 15 and 8K antigens are exposed on or released from the schistosomulum surface. In contrast, absorption of the antiserum with eggs failed to remove antibody against any of the four tegumental membrane antigens examined. The Mr 15 and 8K antigens were shown to be recognized via polypeptide epitopes and not periodate-sensitive carbohydrate epitopes, further emphasizing the similarity of these to the well-characterized Mr 32 and 20K tegumental surface membrane antigens. A general relationship between schistosomulum surface, adult tegumental membrane and egg antigens was demonstrated by ELISA, using antibodies raised against the three antigenic fractions.(ABSTRACT TRUNCATED AT 250 WORDS)

Protective immunization of mice against Schistosoma mansoni with purified adult worm surface membranes.

Immunity to Schistosoma mansoni in the mouse was induced by vaccination with adult worm surface membrane (mb-S). Of several adjuvants tested, including Freund's, BCG and alum, 50 micrograms of saponin per mouse given subcutaneously with the antigen was the easiest to administer, and gave consistent protection, approaching levels usually seen in our mouse model after exposure to irradiated cercariae. An antibody response to the schistosomular surface was detected in mice immunized with mb-S plus saponin which was predominantly anti-polypeptide, not anti-carbohydrate, and thus similar to the antibody response of mice exposed to irradiated cercariae. The level of antibodies to Mr 90,000 and 38,000 schistosomular surface antigens as well as to Mr 25,000 adult surface membrane antigen was significantly correlated with the presence of protection.

Variable species and stage specificity of schistosomulum surface epitopes recognized by mice vaccinated with highly irradiated cercariae.

Antibodies from mice vaccinated with highly irradiated Schistosoma mansoni or S. haematobium cercariae were used to characterize schistosomulum surface epitopes which were found to be diverse in their species and stage specificities. The epitopes recognized on the Mr greater than 200,000 and 15,000 schistosomulum surface antigens of S. mansoni and the Mr greater than 200,000 schistosomulum surface antigen of S. haematobium were found to be cross-specific whereas those on the Mr 38,000, 32,000 and 20,000 schistosomulum surface antigens of S. mansoni and the Mr 35,000, 30,000 and 24,000 schistosomulum surface antigens of S. haematobium were only immunoprecipitated by homologous antibody and are thus possible targets of the protective species-specific immunity stimulated by highly irradiated cercariae. The epitopes recognized on the Mr greater than 200,000 and 38,000 antigens of S. mansoni were shown to cross-react with both the egg and the adult worm whereas those on the Mr 32,000 and 20,000 antigens only cross-reacted with the adult worm, and those on the Mr 15,000 antigen cross-reacted with neither the adult worm nor the egg. In addition the epitopes on the Mr 38,000 and 32,000 antigens were demonstrated to be polypeptide in nature. Those on the Mr greater than 200,000, 20,000 and 15,000 antigens, on the other hand, could not be conclusively defined.