Structure-based design of a bispecific receptor mimic that inhibits T cell responses to a superantigen

Key surface proteins of pathogens and their toxins bind to the host cell receptors in a manner that is quite different from the way the natural ligands bind to the same receptors and direct normal cellular responses. Here we describe a novel strategy for "non-antibody-based" pathogen countermeasure by targeting the very same "alternative mode of host receptor binding" that the pathogen proteins exploit to cause infection and disease. We have chosen the Staphylococcus enterotoxin B (SEB) superantigen as a model pathogen protein to illustrate the principle and application of our strategy. SEB bypasses the normal route of antigen processing by binding as an intact protein to the complex formed by the MHC class II receptor on the antigen-presenting cell and the T cell receptor. This alternative mode of binding causes massive IL-2 release and T cell proliferation. A normally processed antigen requires all the domains of the receptor complex for its binding, whereas SEB requires only the alpha1 subunit (DRalpha) of the MHC class II receptor and the variable beta subunit (TCRVbeta) of the T cell receptor. This prompted us to design a bispecific chimera, DRalpha-linker-TCRVbeta, that acts as a receptor mimic and prevents the interaction of SEB with its host cell receptors. We have adopted (GSTAPPA)(2) as the linker sequence because it supports synergistic binding of DRalpha and TCRVbeta to SEB and thereby makes DRalpha-(GSTAPPA)(2)-TCRVbeta as effective an SEB binder as the native MHC class II-T cell receptor complex. Finally, we show that DRalpha-(GSTAPPA)(2)-TCRVbeta inhibits SEB-induced IL-2 release and T cell proliferation at nanomolar concentrations.

Graphic analysis of femoral growth in young children with Perthes' disease

A cohort of 20 children, younger than 5.5 years at the time of onset of unilateral Perthes' disease, were studied by computer graphic analysis. Graphic outlines derived from each child's series of anterior posterior radiographs of the pelvis and hips were aligned on layers in a computer application such that changes over time could be directly visualized and measured. In these young children, injury to the cartilaginous growth mechanisms accounted for almost all of the abnormal change in the shape of the proximal femur; growth abnormalities had been established by the time of initial radiographs and persisted both as constant growth-rate change and growth-direction change until skeletal maturity. Despite the similar degree of radiographic bone necrosis, outcomes differed, and the specific growth aberrations were highly unique to the individual. At the time of the most recent radiographs, among the diseased hips 7 had spherical femoral heads larger than the normal side, eight had elliptical femoral heads congruent with the acetabulum, and five had elliptical femoral heads with a flat area congruent with the acetabulum. The study did not provide evidence to support a logic for brace or surgical treatment of young children with Perthes' disease.

Surgical management of ankle valgus in children: use of a transphyseal medial malleolar screw

Valgus deformity of the ankle in children is associated with a wide variety of clinical conditions. A retrospective review was performed of 17 children (29 involved extremities) with ankle valgus deformity who had been managed by use of a percutaneously placed, transphyseal medial malleolar screw. Median age at the time of surgery was 11 years, 2 months. Median postoperative follow-up was 2 years, 2 months. Tibiotalar axis and ankle mechanical axis were the best radiographic indicators of ankle valgus deformity. Fibular station and epiphyseal wedging were poor predictors of ankle alignment. Significant improvement in the tibiotalar axis (median, 12 degrees) was noted at follow-up, and the median rate of correction was 0.59 degree/month. Resumption of physeal growth and recurrence of deformity (rate of 0.60 degree/month) was seen when the screws were removed before skeletal maturity. The transphyseal medial malleolar screw is a minimally invasive, minimally morbid, technically simple method of reversible partial epiphysiodesis at the ankle and is an effective technique for the correction of ankle valgus deformity associated with a wide variety of clinical conditions in children.

Same-day versus staged anterior-posterior spinal surgery in a neuromuscular scoliosis population: the evaluation of medical complications

The medical complications occurring in 29 patients with neuromuscular spinal deformity undergoing two-stage anterior-posterior spinal fusion ("staged") were compared with 16 neuromuscular patients undergoing single-stage anterior-posterior spinal fusion ("same day"). Thirty-six (124%) major and minor medical complications occurred postoperatively in the staged patients, whereas 14 (88%) major or minor complication were present in same-day surgery patients. Thirty-five percent of staged patients had no complications, whereas 63% of same-day patients were without complications. Associated findings comparing the two-stage procedure to the single-stage surgery included operative and anesthesia time increase, increased blood-volume loss, increased blood transfusion, decreased nutritional parameters, and longer hospital stays. With either approach, there is the risk of significant complications in this vulnerable population.

Radiographic evaluation of bowed legs in children

Radiographic screening is widely used to distinguish between Blount disease (infantile tibia vara) and physiologic bowing. Thirteen children with Blount disease, evaluated before 3 years of age, with initial radiographs showing no sign of Langenskiold changes, were compared with 50 children with physiologic bowing, also evaluated before 3 years of age with similar radiographic studies. Screening test accuracy was determined retrospectively for measurement of the mechanical axis, the tibial metaphyseal-diaphyseal angle (TDMA), and the epiphyseal-metaphyseal angle (EMA). A radiographic screening method combining the TMDA and the EMA, using cutoff values of 10 degrees and 20 degrees respectively, exhibited the best combination of sensitivity, specificity, and positive predictive value, correctly identifying all cases of Blount disease and 40 of 50 cases of physiologic bowing. Our data suggest that children between 1 and 3 years of age with TMDA <10 degrees, or TMDA > or =10 degrees and EMA < or =20 degrees, are at less risk for development of Blount disease. Children with TMDA > or =10 degrees and EMA >20 degrees are at greater risk for development of Blount disease and should be followed closely.

Epiphyseal changes after proximal femoral osteotomy

This study was conducted to evaluate the risk factors for epiphyseal changes suggestive of osteonecrosis after proximal femoral osteotomy for hip subluxation associated with cerebral palsy. Forty-eight children with 94 hips were reviewed. Two observers rated the radiographs using a written protocol on two occasions each so that reproducibility of these observations could be assured. Concomitant pelvic osteotomy proved to have the greatest association with risk of epiphyseal changes. These findings, suggestive of osteonecrosis, were present in 7 of 68 (10%) hips that had isolated femoral osteotomy, and in 12 of 26 (46%) hips that had concomitant pelvic osteotomy.

Clinical evaluation of bowed legs in children

Early radiographic screening and/or referral to a clinical specialist are often used to distinguish between physiologic bow leg deformity and infantile tibia vara disease in young children. These practices are a consequence of the clinician's inability (based upon the clinical examination) to distinguish between the deformities associated with physiologic and pathologic bow legs. Because the great majority of these children have physiologic bowing, routine radiographic screening and referral are not cost effective and expose children to unnecessary radiation. This study describes and evaluates the efficacy of a simple clinical examination technique, the 'cover up' test, to identify young children with bow legs who are at high risk for having infantile tibia vara. The 'cover up' test qualitatively assesses the alignment of the proximal portion of the shank or lower leg relative to the thigh or upper leg. Obvious valgus alignment is considered a negative test and is indicative of physiologic bowing. Neutral or varus alignment is considered a positive test and suggests that the child is at greater risk for having infantile tibia vara. Eighteen children with infantile tibia vara, evaluated initially prior to 3 years of age, and followed to the time of surgical correction, were compared with 50 children with physiologic bowing, also evaluated initially prior to 3 years of age and followed to resolution (mean follow-up 3 years and 10 months). All of the children with infantile tibia vara had a positive 'cover up' test (sensitivity = 1.00). Eighteen of 25 children with a positive 'cover up' test actually had or developed infantile tibia vara (positive predictive value = 0.72). Forty-three of 50 children with physiologic bowing had a negative 'cover up' test (specificity = 0.86). All of the children with a negative 'cover up' test actually had physiologic bowing (negative predictive value = 1.00). We conclude that the 'cover up' test is an effective screening tool for the assessment of bow legs in children between 1 and 3 years of age. Children with a negative 'cover up' test do not require radiographic evaluation and should be followed clinically for resolution of the bowing. Children with a positive 'cover up' test should have radiographic evaluation of the lower extremities or be referred to a specialist for further evaluation and treatment.

Predictive value of intraoperative clubfoot radiographs on revision rates

The predictive value of intraoperative radiographic assessment and its correlation with short term revision rates is presented for surgical correction of resistant clubfoot. Seventy-three children (115 feet) who underwent a primary procedure at one institution for idiopathic clubfoot between January 1991 and December 1994 were reviewed. A strategy using sequential release guided by intraoperative radiographs was employed in all cases. The intraoperative radiographic findings correlated with the need for early revision surgery, with residual radiographic evidence of cavus deformity associated with the greatest risk for revision. The sequential release strategy resulted in fewer overcorrections compared with historical controls of more complete subtalar release.

Caps on malpractice awards: update

Tort reform for professional liability is in the best interests of not only all physicians, but for industry and the citizenry as a whole. The enormous sums of money donated by the Trial Lawyers Association, whose livelihood is at stake, makes initial passage of tort reform difficult and, once passed, brings it under constant attack. Even if a well-disposed legislature passes a professional liability law, state supreme courts are ever ready to invalidate such laws. Thus, once tort reform has been passed, the next battleground is the state supreme court. ACS chapters should be preparing their membership for educating the public as well as themselves as to the danger of a state supreme court comprised of members opposed to tort reform, and be prepared to help the election of those individuals who are more sympathetic to tort reform.

DNA recognition properties of the N-terminal DNA binding domain within the large subunit of replication factor C

Replication Factor C (RFC) is a five-subunit protein complex required for eukaryotic DNA replication and repair. The large subunit within this complex contains a C-terminal DNA binding domain which provides specificity for PCNA loading at a primer-template and a second, N-terminal DNA binding domain of unknown function. We isolated the N-terminal DNA binding domain from Drosophila melanogaster and defined the region within this polypeptide required for DNA binding. The DNA determinants most efficiently recognized by both the Drosophila minimal DNA binding domain and the N-terminal half of the human large subunit consist of a double-stranded DNA containing a recessed 5' phosphate. DNA containing a recessed 5' phosphate was preferred 5-fold over hairpined DNA containing a recessed 3' hydroxyl. Combined with existing data, these DNA binding properties suggest a role for the N-terminal DNA binding domain in the recognition of phosphorylated DNA ends.

A modified Harrington technique for scoliosis

Post-Harrington techniques for adolescent idiopathic scoliosis have increased the complexity of scoliosis surgery while contributing only biomechanically more secure fixation and sagittal contour preservation. On the the basis of principles defined by Harrington, the authors developed a simplified technique that accomplishes equivalent outcomes.

Distraction instrumentation outcomes in scoliosis

The short-term outcomes of a new distraction technique using a small rod spinal instrumentation system (WRIGHTLOCK) are reported for adolescent idiopathic scoliosis. No caudally directed thoracic hooks were used. Seventy-four children aged 11.7 to 17.5 years who underwent consecutive posterior instrumentations are reviewed. Their curves improved from a mean of 55.6 degrees to 22.7 degrees (average of 59.2% correction). At 2.7 years mean follow-up, coronal curves lost an average of 4.2 degrees correction. Overall, there was a mean increase of 4.4 degrees in kyphosis. Children with the most preoperative hypokyphosis were afforded the greatest gains in kyphosis. Instrumentation resulted in a mean loss of 8.2 degrees lumbar lordosis. These results compare favorably with published results for other multihook systems.

Surgical corrections in scoliosis: a meta-analysis

A meta-analysis of the acute correction outcomes in adolescent idiopathic scoliosis is reported. Posterior instrumentation systems generally gave similar coronal plane corrections with average corrections for differing systems ranging from 48% to 67%. There was significant overlap of corrections reported for each of the systems. Anterior instrumentation gave better results with average corrections ranging from 71% to 93%. No instrumentation demonstrated a consistent ability to restore a normal thoracic kyphosis, but all seemed to maintain preoperative kyphosis measures. All systems, including newer multihook systems, showed a small loss of lumbar lordosis postoperatively. The available data demonstrates that no posterior implant produces vertebral derotation.

Plantar-advancement skin flap for central ray resections in the foot: description of a technique

A surgical technique using an advancement plantar skin flap to maintain the resection gap closure when performing central ray resections is described and illustrated. The concept, applicable to central polydactyly or polysyndactyly of the foot, was developed with goals of providing a skin tether to maintain a normally narrow foot as well as to improve the appearance of the surgical scar.

Comparison of neurologic deficits with atlanto-dens intervals in patients with Down syndrome

Eighty-four patients with Down syndrome had flexion-extension lateral roentgenograms of the C1-C2 articulation for the purpose of dividing the group into subluxators (> or = 4 mm atlanto-dens interval and 2 mm translation) and nonsubluxators (those who did not meet these criteria). Neurologic examinations and chart review were carried out on all patients to ascertain those with a positive neurologic finding or history. Seventeen (20%) were defined as subluxators and 67 (80%) as nonsubluxators. Five (29%) of the subluxators were found to have positive neurologic findings and 18 (27%) of the nonsubluxators had similar types of positive neurologic findings. These percentages are not significantly different. This led us to conclude that positive neurologic findings and an abnormal atlanto-dens interval are not alone adequate criteria to judge need for surgical stabilization of the C1-C2 articulation in patients with Down syndrome.

Replication factor C interacts with the C-terminal side of proliferating cell nuclear antigen

Replication factor C (RF-C) is a heteropentameric protein essential for DNA replication and repair. It is a molecular matchmaker required for loading of proliferating cell nuclear antigen (PCNA) onto double-stranded DNA and, thus, for PCNA-dependent DNA elongation by DNA polymerases delta and epsilon. To elucidate the mode of RF-C binding to the PCNA clamp, modified forms of human PCNA were used that could be 32P-labeled in vitro either at the C or the N terminus. Using a kinase protection assay, we show that the heteropentameric calf thymus RF-C was able to protect the C-terminal region but not the N-terminal region of human PCNA from phosphorylation, suggesting that RF-C interacts with the PCNA face at which the C termini are located (C-side). A similar protection profile was obtained with the recently identified PCNA binding region (residues 478-712), but not with the DNA binding region (residues 366-477), of the human RF-C large subunit (Fotedar, R., Mossi, R., Fitzgerald, P., Rousselle, T., Maga, G., Brickner, H., Messner, H., Khastilba, S., Hübscher, U., and Fotedar, A., (1996) EMBO J., 15, 4423-4433). Furthermore, we show that the RF-C 36 kDa subunit of human RF-C could interact independently with the C-side of PCNA. The RF-C large subunit from a third species, namely Drosophila melanogaster, interacted similarly with the modified human PCNA, indicating that the interaction between RF-C and PCNA is conserved through eukaryotic evolution.

Growth profiles and articular cartilage characterization in a goat model of Legg-Calve-Perthes disease

Numerous animal species, including the goat, have been evaluated as potential models for human Legg-Calve-Perthes disease (LCPD). These models disrupt the vasculature of the femoral head, causing it to collapse, and therefore do not mimic all the clinical patterns of the human disease. Baseline data regarding the weight and femoral length in the growing goat are not available. This study characterized the goat's normal growth for comparison with that of humans. The growth aberrations in the proximal femur created by surgically ablating the capital physis were described and compared with the aberrations observed in human LCPD cases. Age, weight, and femoral length (test and control) data were obtained for goats approximately 1 to 14 months of age. At 4 months of age, a craniolateral surgical approach was used to expose the cranial lateral capital physis so that it could be cauterized. Postoperative radiographs were evaluated by graphic analysis to assess the resultant changes in the morphology of the proximal femur. The articular cartilage of the femoral head and acetabulum was evaluated mechanically, using indentation testing, to determine the apparent modulus of elasticity, and histopathologically regarding its thickness and proteoglycan content. The proximal femurs of goats and humans exhibit similar morphology and growth patterns. There was a positive correlation between age, weight, and femoral lengths in the goat. The surgical procedure was effective in ablating the capital femoral physis as indicated by shorter femoral lengths and fragmented, flattened, and mushroomed femoral heads. The histopathological data revealed that the articular cartilage was significantly thicker in the operated hip joints at the ventrocaudal and cranial acetabula and the dorsal and ventral femoral heads. The test cartilage exhibited significantly less positive staining for proteoglycans in the dorsocaudal and the cranial acetabula as well as the ventral femoral head. The apparent modulus of elasticity, of the test cartilage was significantly lower than the control value at the dorsocaudal acetabulum. These data show that the surgical procedure produced morphological changes that mimic those in human LCPD. The increased thickness of the articular cartilage of the LCPD femoral head may account for the articular degeneration observed in older patients with LCPD, as increased cartilage thickness is associated with decreased tissue quality.

MSCRAMM-mediated adherence of microorganisms to host tissues

Microbial adhesion to host tissue is the initial critical event in the pathogenesis of most infections and, as such, is an attractive target for the development of new antimicrobial therapeutics. Specific microbial components (adhesins) mediate adherence to host tissues by participating in amazingly sophisticated interactions with host molecules. This review focuses on a class of cell surface adhesins that specifically interact with extracellular matrix components and which we have designated MSCRAMMs (microbial surface components recognizing adhesive matrix molecules). MSCRAMMs recognizing fibronectin-, fibrinogen-, collagen-, and heparin-related polysaccharides are discussed in terms of structural organization, ligand-binding structures, importance in host tissue colonization and invasion, and role as virulence factors.

The immature goat as an animal model for Legg-Calvé-Perthes disease

Legg-Calvé-Perthes disease (LCPD) results from avascular necrosis of the capital femoral epiphysis in growing children. This disease often yields a significant deformity of the proximal femur, which may result in osteoarthritis. Its cause is unknown, although extensive radiographic, clinical, and histologic evaluations have been performed. Attempts at developing an animal model for LCPD have been unsuccessful. Previous models have been based predominantly on determining the vascular etiology of the disease. There is a need for an animal model that mimics the growth pattern of the proximal femur seen in LCPD. Such a model would allow for the development and testing of new treatments. Thus far, no treatment strategy has been completely successful. A study involving graphic analysis of radiographs found that arrested anterolateral physeal growth with continued or accelerated perichondrial ring and posteromedial epiphyseal growth would account for the most severe morphologic changes observed in the femoral heads of patients with LCPD. A surgical procedure was performed to ablate the capital femoral physis in goat kids in an attempt to mimic the changes noted in this study. The procedure was evaluated with radiographs, gross specimens, and histopathologic slides. Graphic analysis of the radiographs revealed changes in the shape of the operated femoral head compared with the unoperated femoral head. While bone, fibrous, and fibrocartilaginous bridges were histologically observed across the physis, the resultant deformities did not mimic the changes identified in the graphic analysis study, perhaps because of inconsistencies in the surgical ablative techniques, which will require further modification. This study provides the basis for further research to develop a successful model.

Fimbriation, capsulation, and iron-scavenging systems of Klebsiella strains associated with human urinary tract infection

Thirty-two strains of Klebsiella pneumoniae and seven strains of Klebsiella oxytoca isolated from urinary tract infections in elderly adults were analyzed for capsular antigens, iron-scavenging systems, and fimbriation. All strains were capsulated. Twenty-seven different K antigens were identified among the strains, with no particular antigen dominating. All strains produced the iron-scavenging system enterochelin as analyzed by bioassay and DNA hybridization. In contrast, the aerobactin iron-sequestering system was not detected in any of the strains. All strains caused hemagglutination of tannin-treated human erythrocytes and reacted with an anti-type 3 fimbriae antiserum as well as in DNA hybridization with a type 3 fimbria-specific probe, indicating that the Klebsiella strains possessed this fimbrial type. Possession of type 1 fimbriae was analyzed by agglutination tests and by hybridization with DNA probes from two distinct Klebsiella type 1 fimbria gene clusters. Phenotypic expression of the type 1 fimbriae was found in 29 of 32 K. pneumoniae strains, whereas 30 strains reacted with either of the two type 1 fimbrial cluster DNA probes. In K. oxytoca, however, only three of seven strains expressed type 1 fimbriae and reacted with the DNA probes. The type 3 fimbriae were found to bind to a fraction of epithelial cells exfoliated in normal human urine, whereas the type 1 fimbriae bound strongly to urinary slime. No inhibitors of type 3 fimbrial binding were detected in human urine.

Adherence to respiratory epithelia by recombinant Escherichia coli expressing Klebsiella pneumoniae type 3 fimbrial gene products

We examined the role of Klebsiella fimbrial types 1 and 3 in mediating adherence to human buccal and tracheal cells and to lung tissue sections. We found that clinical isolates of Klebsiella pneumoniae producing type 3 fimbriae and Escherichia coli HB101 containing a recombinant plasmid encoding expression of Klebsiella type 3 fimbriae (pFK10) demonstrated increased adherence to tracheal cells, trypsinized buccal cells, and lung tissue sections, in contrast to nonfimbriate and to type 1 fimbriate bacteria. Adherence by type 3 fimbriate bacteria was inhibited by purified type 3 fimbriae and Fab fragments derived from type 3 fimbrial-specific polyclonal immunoglobulin G. Type 3 fimbriae mediated attachment to the basolateral surface of tracheal cells and to the basal epithelial cells and the basement membrane regions of bronchial epithelia. Using an E. coli transformant (pDC17/pFK52), which expresses nonadherent P fimbrial filaments, along with the type 3 fimbrial adhesin (MrkD), we demonstrated that type 3 fimbrial attachment to respiratory cells was attributable to the MrkD adhesin subunit. Subsequent experiments demonstrated that the epithelial target of the type 3 fimbrial adhesin was most likely a peptide molecule rather than a carbohydrate. The results of this study demonstrate that, in vitro, the Klebsiella type 3 fimbrial adhesin mediates adherence to human respiratory tissue.

Fimbrial types among respiratory isolates belonging to the family Enterobacteriaceae

Bacterial attachment is believed to be an early step in gram-negative nosocomial pneumonia. The frequency of fimbria-associated adhesins among respiratory pathogens has not been studied in detail. In this study isolates belonging to the family Enterobacteriaceae, prospectively obtained from intensive care unit patients who were suspected of having nosocomial pneumonia, were examined for fimbria-associated adhesins. Type 3, P, type 1, and other fimbrial phenotypes were identified by specific hemagglutination and electron microscopy. The Klebsiella type 3 fimbrial phenotype was further characterized by using a monoclonal antibody. Also, both type 3 and Escherichia coli P fimbrial genotypes were detected by using DNA colony blot assays. The frequencies of genera or species isolated were as follows: Enterobacter (38.6%), Klebsiella (26.8%), Serratia (17.7%), E. coli (13%), and Proteus (5.2%). Isolates of Klebsiella oxytoca, K. pneumoniae, and Enterobacter cloacae most commonly possessed the type 3 fimbrial phenotype and genotype. The phenotype and genotype for E. coli P fimbriae (46.2 and 50%, respectively), a known pathogenic determinant in the urinary tract, were detected more frequently than expected. In addition, a previously unspecified hemagglutinin that was specific for porcine erythrocytes was almost uniformly expressed among isolates of Enterobacter aerogenes. Finally, the expression of the type 1 fimbrial phenotype was widely detected among the isolates tested but notably absent among K. oxytoca and Proteus mirabilis isolates. The frequency of the various fimbrial types identified suggests a role for these bacterial organelles in adherence to respiratory epithelia.

Design and evaluation of a posterior laminar clamp spinal fixation system

A new spinal instrumentation system for posterior applications was designed with the intent of minimizing intrusion of hardware into the neural canal during and postinsertion. Basic biomechanical measurements of posterior pullout strength led to the establishment of a clamp as an effective mechanism for gaining purchase on the vertebral lamina. These experiments defined the appropriate instrumentation size, as well as establishing that there was no loss of strength with the spinous process removed and the posterior laminar cortex compromised. There was no statistically significant difference between the maximum pullout strength achievable, using a band around the lamina as a control, and that produced by the implant system, in the thoracic spine. Comparative testing of a prototype system in flexion, extension, lateral bending, and torsion showed that the system, in general, had stiffness greater than segmental wiring and less than or equal to Cotrel-Dubousset fixation.

Nucleotide sequence and functions of mrk determinants necessary for expression of type 3 fimbriae in Klebsiella pneumoniae

The nucleotide sequence of six genes involved in the expression of type 3 fimbriae of Klebsiella pneumoniae was determined. In addition to the genes that encode the fimbrial subunit (mrkA) and adhesion (mrkD), the mrkB, mrkC, and mrkE genes appear to be involved in assembly of the fimbrial filament and regulation of type 3 fimbrial expression. The mrkF gene product is required to maintain the stability of the fimbrial filament on the cell surface.