School environmental conditions and links to academic performance and absenteeism in urban, mid-Atlantic public schools.

School facility conditions, environment, and perceptions of safety and learning have been investigated for their impact on child development. However, it is important to consider how the environment separately influences academic performance and attendance after controlling for school and community factors. Using results from the Maryland School Assessment, we considered outcomes of school-level proficiency in reading and math plus attendance and chronic absences, defined as missing 20 or more days, for grades 3-5 and 6-8 at 158 urban schools. Characteristics of the environment included school facility conditions, density of nearby roads, and an index industrial air pollution. Perceptions of school safety, learning, and institutional environment were acquired from a School Climate Survey. Also considered were neighborhood factors at the community statistical area, including demographics, crime, and poverty based on school location. Poisson regression adjusted for over-dispersion was used to model academic achievement and multiple linear models were used for attendance. Each 10-unit change in facility condition index, denoting worse quality buildings, was associated with a decrease in reading (1.0% (95% CI: 0.1-1.9%) and math scores (0.21% (95% CI: 0.20-0.40), while chronic absences increased by 0.75% (95% CI: 0.30-1.39). Each log increase the EPA's Risk Screening Environmental Indicator (RSEI) value for industrial hazards, resulted in a marginally significant trend of increasing absenteeism (p < 0.06), but no association was observed with academic achievement. All results were robust to school-level measures of racial composition, free and reduced meals eligibility, and community poverty and crime. These findings provide empirical evidence for the importance of the community and school environment, including building conditions and neighborhood toxic substance risk, on academic achievement and attendance.

The concurrent emergence and causes of double volcanic hotspot tracks on the Pacific plate.

Mantle plumes are buoyant upwellings of hot rock that transport heat from Earth's core to its surface, generating anomalous regions of volcanism that are not directly associated with plate tectonic processes. The best-studied example is the Hawaiian-Emperor chain, but the emergence of two sub-parallel volcanic tracks along this chain, Loa and Kea, and the systematic geochemical differences between them have remained unexplained. Here we argue that the emergence of these tracks coincides with the appearance of other double volcanic tracks on the Pacific plate and a recent azimuthal change in the motion of the plate. We propose a three-part model that explains the evolution of Hawaiian double-track volcanism: first, mantle flow beneath the rapidly moving Pacific plate strongly tilts the Hawaiian plume and leads to lateral separation between high- and low-pressure melt source regions; second, the recent azimuthal change in Pacific plate motion exposes high- and low-pressure melt products as geographically distinct volcanoes, explaining the simultaneous emergence of double-track volcanism across the Pacific; and finally, secondary pyroxenite, which is formed as eclogite melt reacts with peridotite, dominates the low-pressure melt region beneath Loa-track volcanism, yielding the systematic geochemical differences observed between Loa- and Kea-type lavas. Our results imply that the formation of double-track volcanism is transitory and can be used to identify and place temporal bounds on plate-motion changes.

An Optimized Injectable Hydrogel Scaffold Supports Human Dental Pulp Stem Cell Viability and Spreading.

Introduction. HyStem-C™ is a commercially available injectable hydrogel composed of polyethylene glycol diacrylate (PEGDA), hyaluronan (HA), and gelatin (Gn). These components can be mechanically tuned to enhance cell viability and spreading. Methods. The concentration of PEGDA with an added disulfide bond (PEGSSDA) was varied from 0.5 to 8.0% (w/v) to determine the optimal concentration for injectable clinical application. We evaluated the cell viability of human dental pulp stem cells (hDPSCs) embedded in 2% (w/v) PEGSSDA-HA-Gn hydrogels. Volume ratios of HA : Gn from 100 : 0 to 25 : 75 were varied to encourage hDPSC spreading. Fibronectin (Fn) was added to our model to determine the effect of extracellular matrix protein concentration on hDPSC behavior. Results. Our preliminary data suggests that the hydrogel gelation time decreased as the PEGSSDA cross-linker concentration increased. The PEGSSDA-HA-Gn was biocompatible with hDPSCs, and increased ratios of HA : Gn enhanced cell viability for 14 days. Additionally, cell proliferation with added fibronectin increased significantly over time at concentrations of 1.0 and 10.0 µg/mL in PEGDA-HA-Gn hydrogels, while cell spreading significantly increased at Fn concentrations of 0.1 µg/mL. Conclusions. This study demonstrates that PEG-based injectable hydrogels maintain hDPSC viability and facilitate cell spreading, mainly in the presence of extracellular matrix (ECM) proteins.

Molecular genetic evidence supporting the neoplastic nature of stromal cells in 'fibrosis' after chemotherapy for testicular germ cell tumours.

A residual retroperitoneal mass containing only fibrosis and necrosis is present in 40-52% of patients with advanced testicular germ cell tumours after chemotherapy. The biological nature and genetic characteristics of the stromal cells in these residual masses have not been adequately investigated. Laser-microdissected stromal cells from 27 patients who underwent retroperitoneal lymph node dissection after chemotherapy for metastatic testicular germ cell tumour were analysed. Allelic loss in the stromal cells of fibrosis was present at one or more of the ten microsatellite DNA loci examined in 23 (85%) of the cases. Chromosome arm 12p anomalies, the hallmark of germ cell neoplasia, were present in nine (33%) cases. The high frequency of allelic losses and chromosome arm 12p anomalies in the stromal cells from residual retroperitoneal fibrous masses after chemotherapy for testicular germ cell tumours suggests that the stromal cells are derived from the same tumour progenitor cells as the pre-existing metastatic germ cell tumour.

OCT4: biological functions and clinical applications as a marker of germ cell neoplasia.

Germ cell tumours (GCTs) are a heterogeneous group of neoplasms, which develop in the gonads as well as in extragonadal sites, that share morphological patterns and an overall good prognosis, owing to their responsiveness to current surgical, chemotherapeutic, and radiotherapeutic measures. GCTs demonstrate extremely interesting biological features because of their close relationships with normal embryonal development as demonstrated by the pluripotentiality of some undifferentiated GCT variants. The similarities between GCTs and normal germ cell development have made it possible to identify possible pathogenetic pathways in neoplastic transformation and progression of GCTs. Genotypic and immunophenotypic profiles of these tumours are also useful in establishing and narrowing the differential diagnosis in cases of suspected GCTs. Recently, OCT4 (also known as OCT3 or POU5F1), a transcription factor that has been recognized as fundamental in the maintenance of pluripotency in embryonic stem cells and primordial germ cells, has been proposed as a useful marker for GCTs that exhibit features of pluripotentiality, specifically seminoma/dysgerminoma/germinoma and embryonal carcinoma. The development of commercially available OCT4-specific antibodies suitable for immunohistochemistry on paraffin-embedded specimens has generated increasing numbers of reports of OCT4 expression in a wide variety of gonadal and extragonadal GCTs. OCT4 immunostaining has been shown to be a sensitive and specific marker for seminomatous/(dys)germinomatous tumours and in embryonal carcinoma variants of non-seminomatous GCTs, whether in primary gonadal or extragonadal sites or in metastatic lesions. Therefore, OCT4 immunohistochemistry is an additional helpful marker both in the differential diagnosis of specific histological subtypes of GCTs and in establishing a germ cell origin for some metastatic tumours of uncertain primary. OCT4 expression has also been reported in pre-invasive conditions such as intratubular germ cell neoplasia, unclassified (IGCNU) and the germ cell component of gonadoblastoma. Additionally, OCT4 immunostaining shows promise as a useful tool in managing patients known to be at high risk for the development of invasive GCTs.

Measurement of the asymmetry in the decay Omega+-->LamdaKappa+-->rhopi+Kappa+.

The asymmetry in the rho angular distribution in the sequential decay Omega+-->LamdaKappa+-->rhopi+Kappa+. has been measured to be alphaOmegaalphaLamda=[+1.16+/-0.18(stat)+/-0.17(syst)]x10(-2) using 1.89x10(6) unpolarized Omega+ decays recorded by the HyperCP (E871) experiment at Fermilab. Using the known value of alphaLamda, and assuming that alphaLamda=-alphaLamda, alphaOmega=[-1.81+/-0.28(stat)+/-0.26(syst)]x10(-2). A comparison between this measurement of alphaOmegaalphaLamda and recent measurements of alphaOmegaalphaLamda made by HyperCP shows no evidence of a violation of CP symmetry.

Overexpression of Pim-1 during progression of prostatic adenocarcinoma.

AIMS: Pim-1 is a serine/threonine kinase that has been shown to play an integral role in the development of a number of human cancers, such as haematolymphoid malignancies. Recently, evidence has shown Pim-1 to be important in prostatic carcinogenesis. In order to further our understanding of its role in prostate cancer, we investigated Pim-1 expression in normal, premalignant, and malignant prostate tissue. METHODS: Using immunohistochemistry, Pim-1 expression was analysed in prostate tissue from 120 radical prostatectomy specimens. In each case, Pim-1 staining was evaluated in benign prostatic epithelium, high grade prostatic intraepithelial neoplasia (PIN), and prostatic adenocarcinoma. The number of positively staining cells was estimated, and the intensity of staining was scored on a scale of 0 to 3+. RESULTS: Pim-1 immunoreactivity was identified in 120 cases (100%) of adenocarcinoma, 120 cases (100%) of high grade PIN, and 62 cases (52%) of benign glands. The number of cells staining in benign epithelium (mean 34%) was much lower than that in high grade PIN (mean 80%; p<0.0001) or adenocarcinoma (mean, 84%; p<0.0001). There was no significant difference between high grade PIN and adenocarcinoma in the percentage of cells staining positively for Pim-1 (p = 0.34). The staining intensity for Pim-1 was significantly lower in benign prostatic epithelium than in PIN and adenocarcinoma (p<0.001). There was no statistically significant correlation between the level of Pim-1 expression and Gleason score, patient age, tumour stage, lymph node metastasis, perineural invasion, vascular invasion, surgical margin status, extraprostatic extension, or seminal vesicle invasion. CONCLUSIONS: Pim-1 expression is elevated in PIN and prostatic adenocarcinoma compared with benign prostatic epithelium. This finding suggests that upregulation of Pim-1 may play a role in prostatic neoplasia.

The influence of extent of surgical margin positivity on prostate specific antigen recurrence.

BACKGROUND: Positive surgical margins are an adverse prognostic factor in patients undergoing prostatectomy for prostate cancer. The extent of margin positivity varies and its influence on clinical outcome is uncertain. AIMS: To evaluate the linear extent of margin positivity and the number and location of positive sites as prognostic indicators in a series of prostatectomy specimens evaluated with the whole mount technique. METHODS: Eighty six consecutive margin positive prostatectomy specimens were evaluated, and all pathology data were collected prospectively. The linear extent of margin positivity was measured with an ocular micrometer and the total extent of all positive sites was summed. The total number of sites with positive margins and anatomical sites of the positive margins were analysed. RESULTS: The linear extent of margin positivity ranged from 0.01 to 68 mm (mean, 6.8; median, 3.0) and was associated with prostate specific antigen (PSA) recurrence in univariate logistic regression (p = 0.031). In addition, the extent of margin positivity weakly correlated with preoperative PSA (p = 0.017) and tumour volume (p = 0.013), but not with age, prostate weight, Gleason score, pathological stage, or perineural invasion. The total number of positive sites was significantly higher in patients with PSA recurrence (p = 0.037). The location of the positive margin site was not associated with PSA recurrence. The extent of margin positivity correlated with PSA recurrence in univariate analysis, although it had only marginal predictive value when adjusted for Gleason score (p = 0.076). CONCLUSIONS: The extent of margin positivity correlates with PSA recurrence in univariate analysis, although it has no predictive value independent of Gleason score.

Identification and removal of a promiscuous CD4+ T cell epitope from the C1 domain of factor VIII.

BACKGROUND: The development of inhibitors in hemophiliacs is a severe complication of factor VIII (FVIII) replacement therapy and is a process driven by FVIII specific T helper cells. OBJECTIVES: To finely map T cell epitopes within the whole FVIII protein in order to investigate the possibility of engineering FVIII variants with reduced propensity for inhibitor development. PATIENTS AND METHODS: T cell lines were generated from five patients with severe hemophilia who had developed inhibitors, and were screened for T cell proliferation against pools of overlapping peptides spanning the entire B domain deleted (BDD) FVIII sequence. Positive peptide pools were decoded by screening individual peptides against the T cell lines. Positive peptides, and mutants thereof, were tested for their ability to bind major histocompatibility complex (MHC) Class II and stimulate T cell proliferation in a panel of healthy donors. The activities of the corresponding mutant proteins were assessed via chromogenic assay. RESULTS: One peptide, spanning FVIII amino acids 2098-2112, elicited a vigorous response from one hemophiliac donor, induced strong T cell responses in the panel of healthy donors and bound to a number of HLA-DR alleles. Mutations were made in this peptide that removed its ability to stimulate T cells of healthy donors and to bind to MHC Class II while retaining full activity when incorporated into a mutant BDD-FVIII protein. CONCLUSIONS: Fine T cell epitope mapping of the entire FVIII protein is feasible, although challenging, and this knowledge may be used to create FVIII variants which potentially have reduced immunogenicity.

On the radiosensitivity of man in space.

Astronauts' radiation exposure limits are based on experimental and epidemiological data obtained on Earth. It is assumed that radiation sensitivity remains the same in the extraterrestrial space. However, human radiosensitivity is dependent upon the response of the hematopoietic tissue to the radiation insult. It is well known that the immune system is affected by microgravity. We have developed a mathematical model of radiation-induced myelopoiesis which includes the effect of microgravity on bone marrow kinetics. It is assumed that cellular radiosensitivity is not modified by the space environment, but repopulation rates of stem and stromal cells are reduced as a function of time in weightlessness. A realistic model of the space radiation environment, including the HZE component, is used to simulate the radiation damage. A dedicated computer code was written and applied to solar particle events and to the mission to Mars. The results suggest that altered myelopoiesis and lymphopoiesis in microgravity might increase human radiosensitivity in space.

Inactivated recombinant plant virus protects dogs from a lethal challenge with canine parvovirus.

A vaccine based upon a recombinant plant virus (CPMV-PARVO1), displaying a peptide derived from the VP2 capsid protein of canine parvovirus (CPV), has previously been described. To date, studies with the vaccine have utilized viable plant chimaeric particles (CVPs). In this study, CPMV-PARVO1 was inactivated by UV treatment to remove the possibility of replication of the recombinant plant virus in a plant host after manufacture of the vaccine. We show that the inactivated CVP is able to protect dogs from a lethal challenge with CPV following parenteral immunization with the vaccine. Dogs immunized with the inactivated CPMV-PARVO1 in adjuvant displayed no clinical signs of disease and shedding of CPV in faeces was limited following CPV challenge. All immunized dogs elicited high titres of peptide-specific antibody, which neutralized CPV in vitro. Levels of protection, virus shedding and VP2-specific antibody were comparable to those seen in dogs immunized with the same VP2- peptide coupled to keyhole limpet hemocyanin (KLH). Since plant virus-derived vaccines have the potential for cost-effective manufacture and are not known to replicate in mammalian cells, they represent a viable alternative to current replicating vaccine vectors for development of both human and veterinary vaccines.

Cowpea mosaic virus as a vaccine carrier of heterologous antigens.

The plant virus, cowpea mosaic virus (CPMV), has been developed as an expression and presentation system to display antigenic epitopes derived from a number of vaccine targets including infectious disease agents and tumors. These chimeric virus particles (CVPs) could represent a cost-effective and safe alternative to live replicating virus and bacterial vaccines. A number of CVPs have now been generated and their immunogenicity examined in a number of animal species. This review details the humoral and cellular immune responses generated by these CVPs following both parenteral and mucosal delivery and highlights the potential of CVPs to elicit protective immunity from both viral and bacterial infection.

Different effects of a single amino acid substitution on three adjacent epitopes in the gp41 C-terminal tail of a neutralizing antibody escape mutant of human immunodeficiency virus type 1.

The envelope protein of human immunodeficiency virus type 1 (HIV-1) comprises the outer gp 120 SU domain and the anchoring gp41 TM domain, and the conventional view is that it has a single transmembrane region with the following C-terminal sequence situated entirely within the virion. However, we have recently proposed that the gp41 C-terminal region comprises three transmembrane regions and an external loop structure. Part of this loop is the peptide 731PRGPDRPEGIEEEGGERDRDRS752 that carries three antibody epitopes, 734PDRPEG739, 740IEEE743, and 746ERDRD750. PDRPEG is not detected in virions but reacts with its cognate MAb (C8) in Western blots, IEEE is a linear and non-neutralizing epitope, and ERDRD is a conformational and neutralizing epitope. Here we show that escape mutants selected with neutralizing ERDRD-specific antibody had a single 732R-->G substitution, 14 residues upstream of the cognate epitope, and no longer bound the selecting antibody. The same amino acid substitution altered epitope PDRPEG in the virion so that it now reacted with MAb C8, but left epitope IEEE unaffected. Introduction of 732R-->G by site-specific mutagenesis into the gp41 of cloned HIV-1 NL4-3 virions allowed them to escape neutralization by ERDRD-specific IgG, and confirms that 732R makes a major contribution to the neutralizing conformation of the 731-752 region of the C-terminal tail of gp41.

A model of radiation-induced myelopoiesis in space.

Astronauts' radiation exposure limits are based on experimental and epidemiological data obtained on Earth. It is assumed that radiation sensitivity remains the same in the extraterrestrial space. However, human radiosensitivity is dependent upon the response of the hematopoietic tissue to the radiation insult. It is well known that the immune system is affected by microgravity. We have developed a mathematical model of radiation-induced myelopoiesis which includes the effect of microgravity on bone marrow kinetics. It is assumed that cellular radiosensitivity is not modified by the space environment, but repopulation rates of stem and stromal cells are reduced as a function of time in weightlessness. A realistic model of the space radiation environment, including the HZE component, is used to simulate the radiation damage. A dedicated computer code was written and applied to solar particle events and to the mission to Mars. The results suggest that altered myelopoiesis and lymphopoiesis in microgravity might increase human radiosensitivity in space.

Cursoriality in bipedal archosaurs.

Modern birds have markedly foreshortened tails and their body mass is centred anteriorly, near the wings. To provide stability during powered flight, the avian centre of mass is far from the pelvis, which poses potential balance problems for cursorial birds. To compensate, avians adapted to running maintain the femur subhorizontally, with its distal end situated anteriorly, close to the animal's centre of mass; stride generation stems largely from parasagittal rotation of the lower leg about the knee joint. In contrast, bipedal dinosaurs had a centre of mass near the hip joint and rotated the entire hindlimb during stride generation. Here we show that these contrasting styles of cursoriality are tightly linked to longer relative total hindlimb length in cursorial birds than in bipedal dinosaurs. Surprisingly, Caudipteryx, described as a theropod dinosaur, possessed an anterior centre of mass and hindlimb proportions resembling those of cursorial birds. Accordingly, Caudipteryx probably used a running mechanism more similar to that of modern cursorial birds than to that of all other bipedal dinosaurs. These observations provide valuable clues about cursoriality in Caudipteryx, but may also have implications for interpreting the locomotory status of its ancestors.

Nonavian feathers in a late Triassic archosaur.

Longisquama insignis was an unusual archosaur from the Late Triassic of central Asia. Along its dorsal axis Longisquama bore a series of paired integumentary appendages that resembled avian feathers in many details, especially in the anatomy of the basal region. The latter is sufficiently similar to the calamus of modern feathers that each probably represents the culmination of virtually identical morphogenetic processes. The exact relationship of Longisquama to birds is uncertain. Nevertheless, we interpret Longisquama's elongate integumentary appendages as nonavian feathers and suggest that they are probably homologous with avian feathers. If so, they antedate the feathers of Archaeopteryx, the first known bird from the Late Jurassic.

Properties of a neutralizing antibody that recognizes a conformational form of epitope ERDRD in the gp41 C-terminal tail of human immunodeficiency virus type 1.

The possibility that epitopes from the C-terminal tail of the gp41 transmembrane protein of human immunodeficiency virus type 1 (HIV-1) are exposed the surface of the virion has long been contentious. Resolution of this has been hampered by the absence of any neutralizing monoclonal antibodies, but we have recently epitope-purified a neutralizing polyclonal IgG specific for one of the putative gp41 tail epitopes, (746)ERDRD(750). This was obtained from mice immunized parenterally with a plant virus chimera expressing residues 731-752 from the gp41 tail. The ERDRD epitope is highly conformational and is conserved in 81% of B clade viruses. Here, it is shown that this polyclonal ERDRD-specific IgG is highly potent, with an affinity of 2.2x10(8) M(-1), and a neutralization rate constant (-K(neut)) of 7.8x10(4) M(-1) s(-1) that exceeds that of nearly all other known HIV-1-neutralizing antibodies. ERDRD-specific IgG gave 50% neutralization at 0.1-0.2 microg/ml and 90% neutralization at approximately 3 microg/ml. It also neutralized virus that was already attached to target cells, and this and other data suggest that it neutralized by inhibiting a virion event that precedes the fusion-entry process. Consistent with this conclusion was the finding that neutralizing amounts of ERDRD-specific IgG did not inhibit the attachment of free virus to target cells. ERDRD-specific IgG was also cross-reactive and neutralized all but one of six B clade T cell line-adapted strains tested.

Intermittent subcutaneous injections for symptom control in hospice care: a retrospective investigation.

An alternative route to oral medications used by some hospice programs is intermittent injections of medications using an indwelling subcutaneous butterfly needle. The nurse places the infusion sets and instructs caregivers on medication administration. Although this method has become more common in hospice care, it has not received much attention in part because of a lack of data to support its efficacy. This study describes the use of intermittent subcutaneous medications for symptom relief in a home hospice program. A chart review was conducted of the 191 patients who received medications by this route during three calendar years; 77% had cancer. The average duration of hospice care was 25 days; on average, intermittent subcutaneous medications were instituted 4 days prior to the patient's death. The main indications for this route were inability to swallow/somnolence (65%), and pain unresponsive to oral medication (19%). Symptoms to be controlled by this method were pain (88%), anxiety (72%), and dyspnea (4%). Morphine was used most frequently for pain, and Ativan was used most frequently for anxiety. Side effects from the medications and problems with this route of administration were rarely reported, thereby supporting the practicality of this method in hospice care. These results form the foundation for a prospective study that is documenting staff, patient, and caregiver variables that impact on the effectiveness and manageability of this method of symptom management in hospice care.

An active contour model for measuring the area of leg ulcers.

Leg ulcers are chronic skin wounds that affect many people and take a long time to heal. The progress of wound healing and the effect of clinical treatments can be monitored partly by measuring the area of the wound. Measurements taken via manually based methods, such as using a computer pointing device to delineate the wound boundary in a digitized image, suffer from variations due to manual dexterity and differences of opinion between observers. An active contour model is presented that models the contour using piecewise B-spline arcs and uses the minimax principle to adaptively regularize the contour according to the local conditions in the wound image. The model makes use of the existing manual delineation process in order to initialize the solution and is shown to reduce the effect of the inherent variations upon the repeatability and consistency of area measurements in many cases.

Immunogenic and antigenic dominance of a nonneutralizing epitope over a highly conserved neutralizing epitope in the gp41 envelope glycoprotein of human immunodeficiency virus type 1: its deletion leads to a strong neutralizing response.

The Kennedy peptide, (731)PRGPDRPEGIEEEGGERDRDRS(752), from the cytoplasmic domain of the gp41 transmembrane envelope glycoprotein of HIV-1 contains a conformationally dependent neutralizing epitope (ERDRD) and a linear nonneutralizing epitope (IEEE). No recognized murine T cell epitope is present. The peptide usually stimulates virus-specific antibody, but this is not always neutralizing. Here we show that IEEE (or possibly IEEE plus adjacent sequence) is immunogenically and antigenically dominant over the ERDRD neutralizing epitope. Thus rabbits immunized in a variety of routes, doses, and adjuvants with a chimeric cowpea mosaic virus (CPMV) expressing the Kennedy peptide on its surface (CPMV-HIV/1) synthesized IEEE-specific serum antibody but no ERDRD-specific or HIV-1-neutralizing antibody. To test if this resulted from immunodominance or from a hole in the antibody repertoire, we immunized rabbits with chimera CPMV-HIV/29, which expresses the GERDRDR part of the Kennedy sequence. This chimera readily stimulated ERDRD-specific, neutralizing antibody. In mice the situation was less extreme, but individual animals with low neutralizing titers had a high ratio of IEEE-specific:ERDRD-specific antibody. Data are consistent with immunodominance of IEEE over ERDRD in the Kennedy peptide. IEEE-specific antibody was also antigenically dominant and prevented ERDRD-specific antibody from binding to its epitope and from neutralizing HIV-1. It may be that HIV-1 has evolved a nonneutralizing immunodominant epitope that allows it to possess a neutralizing epitope without suffering the consequences, and this idea is supported by the covariance of both epitope sequences. To our knowledge this is the first example of a defined sequence that controls the activity of an adjacent epitope.