Vaccine prevention of meningococcal disease, coming soon?

The past century has seen the use of a number of vaccines for prevention and control of meningococcal disease with varied success. The use of polysaccharide vaccines for the control of outbreaks of serogroup C infections in teenagers and young adults and epidemic serogroup A disease has been established for 30 years and an effective protein-polysaccharide conjugate vaccine against serogroup C was introduced into the UK infant immunisation schedule in 2000. The next generation of these glycoconjugate vaccines will be on the shelf soon, eventually offering the prospect of eradication of serogroups A, C, Y and W135 through routine infant immunisation. Despite these exciting prospects, serogroup B meningococci still account for a majority of infections in industrialised nations but development of safe, immunogenic and effective serogroup B meningococcal vaccines has been an elusive goal. Outer membrane vesicle vaccines for B disease are already used in some countries, and will likely be used more widely in the next few years, but efficacy for endemic disease in children has so far been disappointing. However, the innovations arising from the availability of the meningococcal genome sequence, public and scientific interest in the disease and recent pharmaceutical company investment in development of serogroup B vaccines may have started the countdown to the end of meningococcal infection in children.

Gene array technology to determine host responses to Salmonella

Gene expression array technology is a powerful new tool that has already been used to expand our understanding of host-pathogen interactions. There has been a rapid increase in published reports describing use of this approach to profile host responses to pathogenic bacteria and viruses. The large number of array studies currently in progress coupled with increasing accessibility of this new technology promises a plethora of gene expression data on host response to infection in the near future. Recent insights into macrophage and epithelial cell responses to Salmonella infection garnered from array studies are outlined and used as a basis to discuss various future research directions using gene arrays that will advance the field of cellular microbiology. There is an exciting potential for the gene expression data generated in such studies to provide insights into host physiology, the pathophysiology of disease and novel therapeutics.

Meningococcal disease and vaccination in North America

In North America, meningococcal disease occurs at a rate of I case per 100000 population per year, producing 2725 cases notified in the US in 1998 and 155 laboratory confirmed cases in Canada in the same year. A majority of these cases occur in the winter season and in early childhood, with a case fatality rate of approximately 10%. There has been an increase in the proportion of cases due to serogroup Y meningococci over the past decade: in 1995-98 in the US, 33% of cases were due to serogroup B, 28% were due to serogroup C and 34% were due to serogroup Y; in Canada in 1995-96, 47% of cases were due to serogroup B, 40% were due to serogroup C and 10% were due to serogroup Y. Outbreaks due to serogroup C were more common in the 1990s in the US and a number of outbreaks have occurred in Canada due to organisms from the hypervirulent ET-37 complex. College freshmen in the US in dormitories were found to be at an increased risk of disease. In addition, over the past 10 years, an outbreak of serogroup B disease occurred in the Pacific North-west of the US, with a fourfold increased rate of disease in that region. The explanations for these changes in epidemiology are unknown, but probably reflect the appearance of hypervirulent clones of meningococci and/or changing levels of population immunity. Meningococcal serogroup C polysaccharide-protein conjugate vaccines have been introduced recently in the UK, seem efficacious and offer the potential to reduce the burden of disease in the US and Canada too. Because serogroups other than serogroup C are prevalent in North America, a combination polysaccharide-protein vaccine, including C, Y and possibly W135 serogroups, would be attractive for this population. Although not currently an issue in industrialized nations, inclusion of serogroup A conjugates in any future vaccine policy would be an important decision in driving global prevention of meningococcal disease. A meningococcal conjugate vaccine against serogroup C was licensed in Canada in April 2001.

The choice of timing for diuresis renography: the F + 0 method

OBJECTIVE

To investigate a method of diuresis renography where the radiopharmaceutical and frusemide (diuretic) are given simultaneously, in contrast to conventional renography which involves an intravenous injection with frusemide 20 min after administering the radiopharmaceutical (F + 20) or 15 min before (F - 15), with particular interest in the effect of this change on assessing split renal function and interpreting upper tract drainage dynamics.

PATIENTS AND METHODS

In a prospective study, 29 patients (18 women and 11 men, mean age 47 years, range 21--86) were assessed. Each patient had two renograms taken over a 48-h period, either by the F + 20 or F - 15, and the F + 0 method: Data for split renal function and drainage curves were obtained in the usual way. Two independent assessments of the drainage curves were obtained and the results compared.

RESULTS

The split function assessments were identical (< 5% variation) in all but two patients; 26 of 29 (90%) gave identical conclusions about the drainage curves. The three patients with discrepancies between the studies had either hugely dilated upper tracts or otherwise had multiple complicating factors, e.g. impaired renal function, neuropathic bladder.

CONCLUSIONS

F + 0 renography has been used in paediatric urological practice before, but there are no comparative studies and no data on its use in adults. This prospective study confirmed that in investigating dilated upper tracts, the F + 0 technique gives similar results to the conventional techniques. The F + 0 method has the potential to reduce the time required to undertake standard F + 20 renography but it may not be useful in evaluating the grossly dilated upper tract, where the F-15 technique has the best record in terms of reducing equivocal results.

Serial changes in spirometry during an ascent to 5,300 m in the Nepalese Himalayas

The aims of the present study were to determine the changes in forced vital capacity (FVC), forced expiratory volume in 1 sec (FEV1) and peak expiratory flow (PEF), during an ascent to 5,300 m in the Nepalese Himalayas, and to correlate the changes with arterial oxygen saturation measured by pulse oximetry (SpO2) and symptoms of acute mountain sickness (AMS). Forty-six subjects were studied twice daily during an ascent from 2,800 m (mean barometric pressure 550.6 mmHg) to 5,300 m (mean barometric pressure 404.3 mmHg) during a period of between 10 and 16 days. Measurements of FVC, FEV1, PEF, SpO2, and AMS were recorded. AMS was assessed using a standardized scoring system. FVC fell with altitude, by a mean of 4% from sea level values [95% confidence intervals (CI) 0.9% to 7.4%] at 2,800 m, and 8.6% (95% CI 5.8 to 11.4%) at 5,300 m. FEV1 did not change with increasing altitude. PEF increased with altitude by a mean of 8.9% (95% CI 2.7 to 15.1%) at 2,800 m, and 16% (95% CI 9 to 23%) at 5,300 m. These changes were not significantly related to SpO2 or AMS scores. These results confirm a progressive fall in FVC and increase in PEF with increasing hypobaric hypoxia while FEV1 remains unchanged. The increase in PEF is less than would be predicted from the change in gas density. The fall in FVC may be due to reduced inspiratory force producing a reduction in total lung capacity; subclinical pulmonary edema; an increase in pulmonary blood volume, or changes in airway closure. The absence of a correlation between the spirometric changes and SpO2 or AMS may simply reflect that these measurements of pulmonary function are not sufficiently sensitive indicators of altitude-related disease. Further studies are required to clarify the effects of hypobaric hypoxia on lung volumes and flows in an attempt to obtain a unifying explanation for these changes.

Two distinct receptors mediate nonopsonic phagocytosis of different strains of Pseudomonas aeruginosa

Complement receptor 3 (CR3) mediates both opsonic and nonopsonic phagocytosis of bacteria. Leukocyte adhesion deficiency (LAD) allows for the study of CR3-dependent phagocyte-bacterial ingestion, since LAD phagocytes do not express this receptor. Phagocytes from an infant with LAD were unable to ingest 50% of the Pseudomonas aeruginosa strains studied, which indicates a requirement for CR3. However, the remaining strains were phagocytosed in the absence of CR3, and ingestion was blocked by monoclonal antibodies directed at CD14. This CR3/CD14 receptor bias was further confirmed by using thioglycollate-elicited murine peritoneal macrophages, which have nonfunctional CR3 before activation. Results indicate that either CR3 or CD14 is involved independently in nonopsonic phagocytosis of different P. aeruginosa strains. Clearance of P. aeruginosa from the endobronchial space may be facilitated by nonopsonic phagocytosis, since low levels of opsonins are present. The impact of lung infection with P. aeruginosa may be determined, in part, by the phagocytic receptor that mediates ingestion.

Nonopsonic phagocytosis of Pseudomonas aeruginoas: insights from an infant with leukocyte adhesion deficiency

Children with leukocyte adhesion deficiency type I are at risk for overwhelming infection because their neutrophils lack surface beta 2 integrins (CD18/CD11) that normally interact with endothelial cell adhesion molecules and mediate migration to sites of bacterial invasion. In vitro studies of phagocytic cells from an infant with leukocyte adhesion deficiency type I demonstrated that complement receptor 3 (CD18/CD11b) mediates nonopsonic phagocytosis of some Pseudomonas aeruginosa strains and might play a control role in the control of Pseudomonas infections at sites where there are low levels of opsonins.

The long-term results of Anderson-Hynes pyeloplasty

OBJECTIVES

To examine the durability of open pyeloplasty for pelvi-ureteric junction obstruction.

PATIENTS AND METHODS

The records of 56 Anderson-Hynes pyeloplasties undertaken by two surgeons between 1981 and 1994 were examined. Attempts were made to trace all patients and for them to undergo diuretic renography to examine the current status of the operated renal unit.

RESULTS

In all, 41 evaluable patients were identified; 24 agreed to return for reassessment. The mean (range) time from surgery was 10.6 (6-19) years. The results showed an improvement over the preoperative split renal function in 19 patients (79%) and an improvement in drainage in 23 (96%).

CONCLUSIONS

The Anderson-Hynes pyeloplasty is an excellent procedure for treating pelvi-ureteric junction obstruction, and produces a lasting improvement in function and drainage in most patients. It is the 'gold standard' against which newer techniques should be compared.

Development of natural immunity to Neisseria meningitidis

Although meningococcal disease is rare in industrialized nations, Neisseria meningitidis holds a prominent position amongst pediatric infections because of the dramatic clinical presentation of the disease, high mortality, epidemic potential and the recent disappearance of many other important infectious diseases in developed countries through improvements in public health and vaccination. The precise nature of natural immunity to meningococci remains unknown, although a complex interaction between the organism and nasopharyngeal mucosal barrier, innate immune mechanisms and acquired immunity is involved. Study of the mechanisms of natural immunity may provide the key to development of vaccines that can reduce the burden of disease in early childhood.

T-cell responses against meningococcal antigens

T-cells recognize protein antigens as short peptide fragments (8-20 amino acids) bound to major histocompatibility complex (MHC) molecules on the surface of antigen-presenting cells (APCs). A prerequisite for antigen-specific T-cell activation is antigen uptake, enzymatic degradation, and recycling of MHC-peptide complexes to the surface of APCs. Whereas CD8+ T cells recognize endogenously derived antigen (virus and other intracellular pathogens) bound to MHC class I molecules, CD4+ T cells recognize exogenously derived antigen in complex with MHC class II molecules. Hence, extracellular bacteria, such as meningococci during invasive disease, will be presented to CD4+ T cells in the context of MHC class II molecules, after uptake and processing by professional APCs like B cells, macrophages, or dendritic cells. Antigen-specific CD4+ T cells can be classified as Th1 or Th2 subpopulations on the basis of different cytokine production and effector functions (1). Intracellular microbes often induce Th1-dominated responses, whereas extracellular pathogens and parasites typically trigger Th2 responses. Th1 cells produce mainly interleukin (IL)-2, interferon (IFN)-γ, and tumor necrosis factor (TNF)-β, which represent important inducers of the cell-mediated immune responses. The principal Th1 cytokine IFN-γ activates macrophages by enhancing their ability to phagocytize and destroy microbes by intracellular bactericidal mechanisms. In contrast, Th2 cells produce IL-4, IL-5, IL-6, and IL-13, which are important factors for inducing and regulating B-cell responses (1).

Clinical studies : an overview

Disease caused by Neisseria meningitidis is a worldwide problem (1). Epi- demics of meningococcal disease regularly occur in the "meningitis belt" of sub-Saharan Africa and in Asia (2-5) and high or increasing levels of endemic meningococcal disease have been reported recently in the UK (6), New Zealand (7), Cuba (8), Brazil (9), Norway (10), and the Pacific Northwest of the United States (11). Meningococcal disease predominantly affects children and has a high mortality, which has remained unchanged for 30 years, despite advances in antibiotics and intensive care (12). Efforts have therefore been made to understand the pathophysiology of the disease and use this knowledge to improve treatment and develop novel therapies.

Immune response and host-pathogen interactions

For the most part, the relationship between the pathogen, Neisseria meningitidis, and humans is uneventful. Colonization of the human nasopharynx at various times during life is an almost universal experience but clinically overt disease is unusual except during epidemics. This overview considers the relationship between the meningococcus and humans, reviewing current immunological and molecular understanding of this interaction of relevance to development of immunogenic vaccines.

Production of low-avidity antibody by infants after infection with serogroup B meningococci

Experimental serogroup B meningococcal vaccines have induced only poor immune responses and have had little protective efficacy in children younger than 1 year of age. We used ELISA with potassium thiocyanate to compare the average avidity of antibody produced by infants with that of children older than 10 years after systemic disease. Infants produced specific antibody of lower average avidity than older children--a finding that correlates with absence of serum bactericidal activity in the serum samples of the same infants.

A prospective evaluation of scrotal ultrasonography in clinical practice

OBJECTIVES

To prospectively evaluate scrotal ultrasonography (SUS) in patients presenting with scrotal symptoms and to make recommendations about use of SUS in clinical practice.

PATIENTS AND METHODS

Forty-eight men with scrotal symptoms were examined by a urologist and independently underwent SUS by one radiologist with no knowledge of the clinical diagnosis. The clinical and SUS diagnoses were compared and the effect on subsequent management recorded.

RESULTS

The clinical and SUS diagnoses agreed in 35 men (73%) although SUS provided an additional diagnosis in half of these men. The SUS diagnosis differed in 13 men (27%) although the management was altered in only four patients.

CONCLUSION

The clinical diagnosis is correct in most men with scrotal symptoms; the routine use of SUS is inappropriate and should be reserved for specific indications.

Emerging infectious diseases in the 21st century

The emergence of novel infectious diseases, and the re-emergence of others, is not new. The global ecosystem is constantly changing, influencing the micro- and macroenvironments in which humans and their microbial companions reside and interact. Sometimes the environmental circumstances favour the pathogen and there is an unexpected increase in disease activity or emergence of a new infection. Alternatively, pathogenicity factors are acquired by the microbe, allowing new diseases to emerge or old diseases to increase in importance. The forces that drive the emergence, submergence and re-emergence of infectious diseases are varied, but the influence that humans have on the global ecosystem is often of central importance. This review considers infections that are of particular emerging importance.

Metal hyperaccumulation: a model system for coevolutionary studies

Recent years have seen a flurry of research activity concerning the hyperaccumulation of heavy metals by plants. Much of the interest in hyperaccumulation has been fueled by the commercial potential of phytoremediation, the use of plants to clean up contaminated soils (Baker et al., 1994; Salt et al., 1995; Chaney et al., 1997, 2000). These applications have in turn spurred many studies of the genetics and physiology of metal uptake (e.g. Krämer et al., 1996; Lasat et al., 1996; Salt & Krämer, 1999; Baker et al., 2000; see also Krämer, 2000; Lombi et al., 2000). Although phytoremediation provides an intriguing and potentially profitable backdrop, the ecology and evolution of hyperaccumulation in natural populations are interesting subjects in their own right. Two papers in this issue (Ghaderian et al., pp. 219-224; Davis & Boyd, pp. 211-217) are exciting contributions to the growing consensus that hyperaccumulation may act as a defense against herbivores and pathogens, and suggest that hyperaccumulation may become a model system for research in this area.

Spatio-temporal expression of the trans-acting splicing factors SF2/ASF and heterogeneous ribonuclear proteins A1/A1B in the myometrium of the pregnant human uterus: a molecular mechanism for regulating regional protein isoform expression in vivo

Many of the human myometrial proteins associated with uterine quiescence and the switch to coordinated contractions at the onset of labor exist as alternatively spliced isoforms. There is now extensive evidence to indicate that the nuclear concentrations of the trans-acting splicing regulators SF2/ASF and hnRNP A1/A1B are fundamental in regulating the expression of specific protein isoforms derived from alternative splicing of single precursor messenger ribonucleic acid transcripts. The question thus arose as to whether these factors were also involved in regulating the expression of specific myometrial protein species within different uterine regions during human gestation and parturition. SF2/ASF and hnRNP A1/A1B expression was therefore determined in paired upper (corpus) and lower segment myometrial samples taken from individual women at term/during spontaneous labor and compared with nonpregnant control samples using specific monoclonal antibodies. We report that SF2/ASF levels were substantially increased in the lower uterine region, and this was associated with a parallel decrease in levels of hnRNP A1/A1B during gestation. Conversely, the opposite pattern was observed within the upper uterine region during pregnancy, where hnRNP A1/A1B was significantly up-regulated and SF2/ASF levels were much less than those found in the lower uterine segment. The differential expression of hnRNP A1/A1B and SF2/ASF in the upper and lower uterine segments may have a primary role in defining the formation of specific myometrial protein species associated with the known contractile and relaxatory properties of these regions before and during parturition.

Assessment of immune response to meningococcal disease: comparison of a whole-blood assay and the serum bactericidal assay

A whole-blood assay (WBA), which assesses the complete bactericidal activity of blood, was compared with the serum bactericidal assay (SBA), which measures antibody and complement mediated cell lysis. Twenty children infected with serogroup B strains and 25 infected with serogroup C strains were studied 8-12 weeks after disease, and 29 healthy children were used as controls. The infecting strain (convalescent children only) and two reference strains, MC58 (B:15:P1.7, 16) and NCTC 8554 (C:NT:P1.5) were used. In children previously infected with a serogroup B strain, bactericidal activity was detected in 95% and 85% to their infecting strain by the WBA (>50% killing) and the SBA (s), respectively. Bactericidal activity to the reference serogroup B and C strain was detected by WBA in 70 and 75% of children, respectively, and the SBA in 45% and 20%. In contrast bactericidal activity was detected to both serogroup C strains in >80% of children previously infected with a serogroup C strain using either assay and in 48% (WBA) and 20% (SBA) to the reference serogroup B strain. Levels of bactericidal activity were detectable in fewer control children. Children convalescing from meningococcal disease develop an immune response to their infecting strain, detectable by both the WBA and SBA, which is independent of age. However, the WBA appears to be a more sensitive measure of bactericidal activity to heterologous strains than the SBA.

The effect of high altitude on platelet counts, thrombopoietin and erythropoietin levels in young Bolivian airmen visiting the Andes

Recognition of thrombosis as a complication of exposure to high altitude has stimulated interest in rheological changes resulting from hypobaric hypoxia. Previous studies of platelet counts at high altitude have yielded conflicting results and have not been studied in conjunction with potential mediating cytokines. We studied the effects of high-altitude exposure on platelet numbers, thrombopoietin (tpo) and erythropoietin (epo) levels in man. A group of 28 volunteers from the Bolivian Airforce stationed at Santa Cruz (600 m altitude) were studied 48 h and 1 week after their ascent to La Paz (3600 m). In addition 105 volunteers based at Santa Cruz for at least 1 year were compared with 175 age- and sex-matched residents at El Alto (4200 m). Platelet counts were measured immediately after sampling and serum samples assayed for tpo and epo. In the ascending group, mean platelet counts were 251 x 10(9), 367 x 10(9) and 398 x10 (9)/l at 600 m and following 48 h and 1 week at 3600 m respectively. Mean tpo levels were 132.5, 76 and 92 pg/ml with epo values of 2.98, 11.6 and 7.9 mIU/ml respectively. In the resident populations mean platelet counts were 271 x 10(9)/l in the low- and 471 x 10(9)/l in the high-altitude groups. Mean tpo and epo levels measured 69.3 pg/ml and 4.5 mIU/ml respectively at 600 m and 58.5 pg/ml and 5.1 mIU/ml at 4200 m. In conclusion we have demonstrated a significant and sustained elevation in platelet numbers within 48 h of ascent to high altitude. Our findings do not support a role for tpo as a mediator of the increased platelet count. However, these data do not discount epo as a potential candidate.

Humoral immune responses to Neisseria meningitidis in children

An understanding of the nature of immunity to serogroup B meningococci in childhood is necessary in order to establish the reasons for poor responses to candidate vaccines in infancy. We sought to examine the nature of humoral immune responses following infection in relation to age. Serum bactericidal activity was poor in children under 12 months of age despite recent infection with Neisseria meningitidis. The highest levels of bactericidal activity were seen in children over 10 years of age. However, infants produced levels of total immunoglobulin G (IgG) and IgG subclass antibodies similar to those in older children in a meningococcal enzyme-linked immunosorbent assay. Most antibody was of the IgG1 and IgG3 subclasses. This striking age dependency of bactericidal antibody response following infection is not apparently due to failure of class switching in infants but might be due to qualitative differences in antibody specificity or affinity.