Immunogenicity and protective efficacy of the alpha C protein of group B streptococci are inversely related to the number of repeats

Infection by group B streptococci (GBS) is an important cause of bacterial disease in neonates. Alpha C protein is a protective cell surface-associated protein of GBS. This protein contains a repeat region flanked by N and C termini. Variable expression of tandem repeating units of alpha C proteins had been found among clinical isolates of GBS. We examined the effect of the number of repeats on the immunogenicity of the alpha C protein and its ability to elicit protection from GBS infection in a neonatal mouse model. Mice were immunized with purified alpha C proteins of constructs containing various numbers of repeats (n = 1, 2, 9, and 16) and the N- and C-terminal regions. Both the N-terminal and the repeat regions contain protective and opsonic epitopes. Antibody responses to the alpha C protein constructs with various numbers of repeats were tested with enzyme-linked immunosorbent assay plates coated with either native, nine-repeat alpha C protein or "repeatless" N-terminal antigen. An inverse relationship was found between the number of repeats and the immunogenicity of the alpha C protein; this effect was most pronounced on titers of antibody to the N-terminal region. An inverse relationship was also observed between the number of repeats and protective efficacy, i.e., mouse dams immunized with 5 microg of one- or nine-repeat alpha C protein transferred protective immunity to 65 or 11% of their pups, respectively (P < 0.0001). Thus, the presence of multiple repeats appears to lessen the antibody response to the complete alpha C protein, and especially the antibody response to its N-terminal region, and suggests a mechanism whereby repeat elements contribute to the evasion of host immunity.

Inactivation of the alpha C protein antigen gene, bca, by a novel shuttle/suicide vector results in attenuation of virulence and immunity in group B Streptococcus

The alpha C protein of group B Streptococcus (GBS) is a major surface-associated antigen. Although its role in the biology and virulence of GBS has not been defined, it is opsonic and capable of eliciting protective immunity. The alpha C protein is widely distributed among clinical isolates and is a potential protein carrier and antigen in conjugate vaccines to prevent GBS infections. The structural gene for the alpha C protein, bca, has been cloned and sequenced. The protein encoded by bca is related to a class of surface-associated proteins of gram-positive cocci involved in virulence and immunity. To investigate the potential roles of the alpha C protein, bca null mutants were generated in which the bca gene was replaced with a kanamycin resistance cassette via homologous recombination using a novel shuttle/suicide vector. Studies of lethality in neonatal mice showed that the virulence of the bca null mutants was attenuated 5- to 7-fold when compared with the isogenic wild-type strain A909. Significant differences in mortality occurred in the first 24 h, suggesting that the role of the alpha antigen is important in the initial stages of the infection. In contrast to A909, bca mutants were no longer killed by polymorphonuclear leukocytes in the presence of alpha-specific antibodies in an in vitro opsonophagocytic assay. In contrast to previous studies, alpha antigen expression does not appear to play a role in resistance to opsonophagocytosis in the absence of alpha-specific antibodies. In addition, antibodies to the alpha C protein did not passively protect neonatal mice from lethal challenge with bca mutants, suggesting that these epitopes are uniquely present within the alpha antigen as expressed from the bca gene. Therefore, the alpha C protein is important in the pathogenesis of GBS infection and is a target for protective immunity in the development of GBS vaccines.

Continuous venovenous haemodiafiltration in the acute phase of neonatal maple syrup urine disease

Maple syrup urine disease results in accumulation of leucine and its metabolites, which may lead in the long term to neurological dysfunction. In acute neonatal crises, large amounts of leucine may be removed by continuous venovenous haemofiltration. This extracorporeal technique has its risks and hazards, which increase with duration of treatment. We report three neonates in life-threatening conditions due to maple syrup urine disease, treated for not more than 12 h with various continuous venovenous techniques: continuous haemofiltration, haemodiafiltration and haemodialysis. The efficiency of and tolerance to these techniques was evaluated. For all three patients, plasma leucine levels decreased dramatically from 2186, 3818 and 2536 mumol/L to 1131, 1275 and 488 mumol/L, respectively. Leucine clearance obtained was 4.28 ml/min in haemodiafiltration. Their patients' neurological status improved rapidly and they have a normal developmental quotient at 22 months, 13 months, and 11 months of age, respectively. Tolerance was good except for hypothermia and drop in haematocrit in all cases. Haemodiafiltration management was more cumbersome and time consuming because it required continual adjustment of the substitution fluid flow rate to precisely balance inflow and outflow rates. We recommend continuous venovenous haemodialysis as the therapy of choice. It might be anticipated that improvement of this technique, by increasing dialysate flow rate and blood flow rate, will allow leucine concentration to be decreased below 1000 mumol/L within 6-8 h, whatever the initial level.

Successful bronchotracheal reconstruction in esophageal bronchus: two case reports

Esophageal bronchus is the most common congenital bronchopulmonary foregut malformation. Current surgical treatment is resection of anomalous pulmonary tissue, which is often hypoplastic and destroyed by infection. The authors report two cases of bronchotracheal reconstruction. The diagnosis was early, before 15 days of age. The anomalous pulmonary tissue had a pulmonary arterial supply and venous drainage as assessed by angiography and a good functional capacity on selective ventilation. Bronchotracheal anastomosis was successful in both cases: a right main bronchus at 25 days of age and a left main bronchus at 13 days of age. One child underwent reoperation 1 year later for bronchomalacia of the reimplanted bronchus. Both children are well with normal growth 3 and 7 years after surgery. Chest roentgenograms showed normal and symmetrical lung aeration. Tracheal reimplantation may be preferred to pulmonary resection when the anomalous pulmonary tissue is not destroyed. The pulmonary functional capacity is increased and the complications of pneumonectomy avoided.

Characterization of two distinct opsonic and protective epitopes within the alpha C protein of the group B Streptococcus

Group B Streptococcus (GBS) is a major cause of neonatal sepsis, meningitis in early infancy, postpartum endometritis, and serious invasive infections in adults in the United States. We previously cloned, sequenced, and characterized the alpha antigen gene, bca, and showed that the alpha C protein of GBS is a trypsin-resistant, surface-associated polypeptide that contains a signal sequence, a unique N terminus, nine identical tandem repeats, and a C-terminal membrane anchor structure. Polyclonal antiserum raised to the recombinant alpha C protein and an opsonic monoclonal antibody, 4G8, raised to the native protein from GBS have been shown to be protective in a mouse model. The binding site of 4G8 has now been localized to the tandem repeat region of the alpha C protein. To determine whether the N terminus of the alpha C protein contains additional opsonic and/or protective epitopes, the sequence corresponding to the alpha C protein N terminus was subcloned into a pET vector, the expressed peptide from Escherichia coli was purified by Ni2+ affinity chromatography, and rabbit polyclonal antibodies were raised to the purified recombinant peptide. Antibodies to the alpha C protein N terminus were shown to be opsonic by an in vitro opsonophagocytosis assay. In addition, 69% of newborn mouse pups from mothers passively immunized with the antiserum to the recombinant N-terminal polypeptide of the alpha C protein were protected against lethal challenge with GBS A909. These data indicate that at least two distinct regions of the alpha C protein, the N terminus and the tandem repeat region, contain opsonic and protective epitopes.

[Radiological evaluation of integration of bone grafts and bone substitutes after implantation to replace acetabular substance losses in reoperation of total hip prosthesis]

Plain radiograms are insufficient to evaluate the integrity of a graft used to replace acetabular tissue loss in reoperations for total hip replacement. The aim of this work was to compare radiographic, computed tomographic and magnetic resonance imaging findings. Two groups of patients including 12 hip joints in each were evaluated 5 years after undergoing reoperation for annular support. Allografts (5 cases) or xenografts (7 cases) were used in one group. Plain radiograms. CT-scan and MRI were performed in each patient. The graft-receiver bone borders were visible on the CT-scans but were not distinguishable on the radiograms. Bone and graft density and structure in contact with the implant could be determined on the CT-scan. MRI was difficult to interpret in most cases due to implant-induced artefacts and is not recommended in this type of reconstruction.

Accessory soleus muscle. Two case-reports, with a review of the literature

The accessory soleus muscle is a supernumerary leg muscle that is rare and usually clinically silent. The best diagnostic strategy is not agreed on. We report two cases in which magnetic resonance imaging contributed significantly to the diagnosis and to the pretreatment evaluation.

Use of cleaved amplified polymorphic sequences to distinguish strains of Staphylococcus epidermidis

We examined the utility of a PCR-based method termed cleaved amplified polymorphic sequences (CAPS) to type 35 well-characterized isolates of Staphylococcus epidermidis. The results were compared with detailed epidemiologic information and typing obtained by using pulsed-field gel electrophoresis (PFGE). To identify CAPS markers for this study, eight pairs of oligonucleotide primers corresponding to five previously sequenced S. epidermidis genes were synthesized and then used to amplify DNA sequences from the S. epidermidis strains by using PCR. Amplified products were reproducibly obtained for seven of eight primer pairs from chromosomal DNA of 33 of the 35 isolates. Seven restriction site polymorphisms were found in five of the amplified products when they were subjected to digestion with a panel of restriction endonucleases. Each fragment-enzyme combination that was polymorphic demonstrated only two alleles in the 33 S. epidermidis isolates analyzed, corresponding to the presence or absence of a single restriction site. Overall, five distinct combinations of alleles were detected and were designated CAPS types A through E. There was a close correlation between the CAPS grouping, the epidemiologic information for the strains, and grouping by PFGE following SmaI digestion of chromosomal DNA. Although PFGE analysis was more discriminatory than typing based on the limited number of CAPS markers used in this study (isolates from the same CAPS group were sometimes distributed into more than one PFGE group), no isolates from the same PFGE group were found in more than one CAPS group. The CAPS procedure was highly reproducible, in contrast to published experience with arbitrarily primed PCR. These preliminary data suggest that CAPS represents a PCR-based technique for strain typing that is highly reproducible, rapid, utilizes widely available technologies, and provides results that are relatively easy to interpret and express.

Variation in repeat number within the alpha C protein of group B streptococci alters antigenicity and protective epitopes

Variable expression of repeating units of the protective alpha C proteins among clinical isolates of group B streptococci (GBS) may have implications for vaccine development. In this study, alpha C protein genes containing various numbers of repeats (1,2,9, and 16) were cloned in a T7 overexpression vector in Escherichia coli. Expression was induced by isopropyl-beta-D-thiogalactopyranoside, and proteins were purified by anion-exchange, gel filtration, or affinity chromatography or by isoelectric focusing. Rabbits were immunized with purified 1-,2-,9-, or 16-repeat proteins. All proteins appeared to be highly immunogenic. Enzyme-linked immunosorbent assay inhibition with 9-repeat protein as the coating antigen and 9-repeat-antigen-elicited antiserum showed that a 200-fold-higher concentration of 1-repeat antigen than of 9- or 16-repeat antigen was required for 50% inhibition of antibody-antigen binding. The concentration of 2-repeat antigen required for 50% inhibition was intermediate relative to the concentrations of 1- and 9-repeat antigens. These results suggested that antibodies to 9-repeat antigen recognized predominantly a conformational epitope(s) contained in proteins with higher numbers of repeats (9 or 16) but lost considerable binding affinities for an epitope(s) contained in alpha C proteins with fewer repeats (1 or 2). Similar results were obtained with antiserum to 16-repeat antigen. However, antibodies to 1- and 2-repeat antigens recognized 1-,2-,9-,and 16-repeat antigens with equal binding affinities. This finding suggested that 1- and 2-repeat-elicited antibodies recognized an epitope(s) on individual repeats. Loss of repeating units from the alpha C proteins may result in decreased protection because the loss of epitopes (including conformational epitopes) gives the microorganisms the opportunity to escape host antibodies. If 1- and 2-repeat-elicited antibodies bind all alpha C proteins with equal affinity, regardless of their repeat number, they may prevent GBS strains with fewer repeats from escaping host immunity. Protection data obtained with antisera to the proteins with different repeat numbers support this hypothesis: mouse pups challenged with GBS strain A909 were better protected when immunized with 1- or 2-repeat-elicited antiserum (76 and 75%, respectively) than when immunized with 9- or 16-repeat-elicited antiserum (41 and 48%, respectively).

Group B streptococci escape host immunity by deletion of tandem repeat elements of the alpha C protein

Group B streptococci (GBS) are the most common cause of neonatal sepsis, pneumonia, and meningitis. The alpha C protein is a surface-associated antigen; the gene (bca) for this protein contains a series of tandem repeats (each encoding 82 aa) that are identical at the nucleotide level and express a protective epitope. We previously reported that GBS isolates from two of 14 human maternal and neonatal pairs differed in the number of repeats contained in their alpha C protein; in both pairs, the alpha C protein of the neonatal isolate was smaller in molecular size. We now demonstrate by PCR that the neonatal isolates contain fewer tandem repeats. Maternal isolates were susceptible to opsonophagocytic killing in the presence of alpha C protein-specific antiserum, whereas the discrepant neonatal isolates proliferated. An animal model was developed to further study this phenomenon. Adult mice passively immunized with antiserum to the alpha C protein were challenged with an alpha C protein-expressing strain of GBS. Splenic isolates of GBS from these mice showed a high frequency of mutation in bca--most commonly a decrease in repeat number. Isolates from non-immune mice were not altered. Spontaneous deletions in the repeat region were observed at a much lower frequency (6 x 10(-4)); thus, deletions in that region are selected for under specific antibody pressure and appear to lower the organism's susceptibility to killing by antibody specific to the alpha C protein. This mechanism of antigenic variation may provide a means whereby GBS evade host immunity.

[Metastatic epidermoid carcinoma in idiopathic CD4+ T lymphocytopenia syndrome]

INTRODUCTION

Skin cancers are more frequent and more aggressive in immunosuppressed patients.

CASE REPORT

A 58-year-old man was seen in January 1994 for squamous cell carcinoma of the right shoulder which had grown to 7 x 7 cm in the last 5 months. The patient had a past history of surgical exeresis of 5 squamous cell carcinomas and 3 basal cell carcinomas. Despite complete exeresis, the disease spread to localized then diffuse skin metastases. Acitretine and alpha-interferon were uneffective. Polychemotherapy stabilized the situation but several bronchopulmonary infections with atypical germs led to death (in February 1995). The patient had CD4 lymphocytopenia with a count < 100/mm3 in January 1994 of unknown origin (viral infection was eliminated).

DISCUSSION

Our patient had idiopathic CD4 lymphocytopenia. In 40 p. 100 of the cases CD4 lymphocytopenia is caused by AIDS and in 53 p. 100 by other diseases, especially skin diseases including Kaposi syndrome, mycosis fungoides, squamous cell or basal cell carcinoma. The cutaneous carcinomas which often develop in AIDS patients with low CD4 counts are usually less aggressive than in our patient. Certain neoplasia could be the cause of the lymphopenia. CD4 counts are usually more variable and lymphopenia of shorter duration in other etiologies.

Amelioration of the metabolic defect in erythropoietic protoporphyria by expression of human ferrochelatase in cultured cells

The cDNA for human ferrochelatase, the enzyme that is defective in the rare genetic disease erythropoietic protoporphyria (EPP), was tested for its ability to allow the expression of ferrochelatase in mammalian cells. The cDNA was ligated to the plasmid expression vectors pCD and pED6 and transfected into COS-1 and CHO-DUKX cells, respectively. In each case, ferrochelatase activity increased. The cDNA was also ligated into the retroviral vector pLXSN, and virus-packaging cells were produced. Supernatants from these cells were used to infect fibroblasts in vitro from a patient with EPP. We found that the infected cells containing the ferrochelatase cDNA had enzyme levels in the range of normal fibroblasts and that they did not accumulate protoporphyrin when grown in the presence of delta-aminolevulinic acid. We conclude that introducing the cDNA for normal ferrochelatase into fibroblasts from an EPP patient restores ferrochelatase enzyme activity to the normal range. These experiments suggest potential for genetic therapy in EPP.

Protection of neonatal mice from group B streptococcal infection by maternal immunization with beta C protein

Group B streptococci (GBS) cause the majority of cases of neonatal sepsis and meningitis in the United States. Immunization of women of childbearing age is one strategy under consideration for the prevention of neonatal disease. The beta C protein, a 130-kDa antigen present in many clinical isolates of GBS, was purified from GBS by extraction into sodium dodecyl sulfate (SDS)-containing buffer, preparative SDS-polyacrylamide gel electrophoresis, and electroelution. Purified beta C protein antigen (25 micrograms) with Freund's adjuvant was used to immunize rabbits. Rabbits developed enzyme-linked immunosorbent assay titers of > 1:1.6 x 10(6), and sera from immunized rabbits were administered to pregnant mice. Their neonatal pups were then challenged with a strain of GBS expressing beta C protein; 68% of these pups were protected by immune antiserum, whereas no controls were protected (P < 0.001). The immune serum (diluted 1:100) facilitated opsonophagocytic killing of GBS strains expressing the beta C protein but not those that do not express the antigen (mean log kill +/- standard deviation = 0.71 +/- 0.8 log10 CFU for beta+ strains and 0.09 +/- 0.2 for beta- strains; P = 0.02). In subsequent experiments, adult female mice were actively immunized with two doses of 2, 5, or 10 micrograms of beta C protein 2 months prior to mating. One- to two-day-old offspring of these dams were challenged with GBS and were protected in a dose-dependent manner, with 96% survival in the high-dose (10-micrograms) group and 20% survival in a sham-immunized control group (P < 0.001). Thus, active immunization of mice with the GBS beta C protein confers protection against lethal infection with beta+ GBS to their offspring.

Large, identical, tandem repeating units in the C protein alpha antigen gene, bca, of group B streptococci

Group B Streptococcus (GBS) is the leading cause of neonatal sepsis and meningitis in the United States. The surface-associated C protein alpha antigen of GBS is thought to have a role in both virulence and immunity. We previously cloned the C protein alpha antigen structural gene (named bca for group B, C protein, alpha) into Escherichia coli. Western blots of both the native alpha antigen and the cloned gene product demonstrate a regularly laddered pattern of heterogeneous polypeptides. The nucleotide sequence of the bca locus reveals an open reading frame of 3060 nucleotides encoding a precursor protein of 108,705 Da. Cleavage of a putative signal sequence of 41 amino acids yields a mature protein of 104,106 Da. The 20,417-Da N-terminal region of the alpha antigen shows no homology to previously described protein sequences and is followed by a series of nine tandem repeating units that make up 74% of the mature protein. Each repeating unit is identical and consists of 82 amino acids with a molecular mass of 8665 Da, which is encoded by 246 nucleotides. The size of the repeating units corresponds to the observed size differences in the heterogeneous ladder of alpha C proteins expressed by GBS. The C-terminal region of the alpha antigen contains a membrane anchor domain motif that is shared by a number of Gram-positive surface proteins. The large region of identical repeating units in bca defines protective epitopes and may play a role in generating phenotypic and genotypic diversity of the alpha antigen.

[Mediastinal hemangiopericytoma. Apropos of a case]

The authors report a new case of hemangiopericytoma in an elderly man. An asymptomatic mediastinal mass was found on a routine chest film. C.T. guided fine-needle biopsy was diagnostic. These rare lesions are clinically and radiologically aspecific and require pathologic proof. The value of percutaneous biopsy before therapeutic decision is emphasized.

Phenotypic diversity in the alpha C protein of group B streptococci

Group B streptococci (GBS) is the leading cause of neonatal sepsis and meningitis. C proteins are an immunologically important group of surface-associated antigens in GBS that remain incompletely characterized. Two C proteins have been designated alpha and beta on the basis of protease susceptibility. We recently used a monoclonal antibody to describe a protective epitope of the GBS alpha (or trypsin-resistant) C protein in the prototype Ia/c GBS strain. In the present study, we examined 51 GBS isolates for expression of C-protein alpha and beta antigens. The alpha antigen, as detected with monoclonal antibody in sodium dodecyl sulfate (SDS) extracts, appears as a heterogeneous series of proteins spaced 8 kDa apart on SDS-polyacrylamide gel electrophoresis, but has a maximum molecular mass that varies among strains from 62.5 to 167 kDa. By immunoblotting with human immunoglobulin A, polyclonal antiserum, or monoclonal antibody, the beta antigen, in contrast, appears as a single protein of molecular mass between 124 and 134 kDa. The amount of alpha antigen expressed by each strain was quantified by enzyme immunoassay inhibition and was found to vary markedly from strain to strain. The susceptibility of strains of GBS to opsonization and killing by human polymorphonuclear leukocytes in the presence of either complement alone or complement with alpha-specific monoclonal antibody was examined. Strains expressing the alpha antigen were less readily killed in the absence of specific antibody than were alpha-negative strains. Killing in the presence of alpha-specific monoclonal antibody was found to correlate directly with the maximum molecular mass of the alpha antigen and with the quantity of antigen on the bacterial cell surface. Isolates of GBS that express the alpha C protein vary widely in the quantity and molecular mass of the alpha antigen produced, and this heterogeneity appears to have biologic importance.