Quantitative determination of antibody to capsular polysaccharide in infection with type III strains of group B Streptococcus

Development and validation of a 6-plex Luminex-based assay for measuring human serum antibodies to group B streptococcus capsular polysaccharides

Six serotypes (Ia, Ib, II, III, IV, and V) cause nearly all group B streptococcal (GBS) disease globally. Capsular polysaccharide (CPS) conjugate vaccines aim to prevent GBS disease, however, licensure of a vaccine would depend on a standardized serological assay for measuring anti-CPS IgG responses. A multiplex direct Luminex-based immunoassay (dLIA) has been developed to simultaneously measure the concentration of serum IgG specific for the six prevalent GBS CPS serotypes. Assay validation was performed using serum samples obtained from human subjects vaccinated with an investigational 6-valent GBS CPS conjugate vaccine. Results for the assay are expressed as IgG concentrations (µg/mL) using a human serum reference standard composed of pooled sera from vaccinated subjects. The lower limits of quantitation (LLOQ) for all serotypes covered in the 6-plex GBS IgG dLIA fell within the range of 0.002-0.022 µg/mL IgG. Taken together, the 6-plex GBS IgG dLIA platform is specific for the six GBS serotypes included in Pfizer's investigational vaccine, has a wide dilution adjusted assay range, and is precise (<18.5% relative standard deviation) for all serotypes, and, therefore, is suitable for quantitatively measuring vaccine-induced or naturally acquired serotype-specific anti-CPS IgG responses against GBS.

Life-threatening infections in human newborns: Reconciling age-specific vulnerability and interindividual variability

In humans, the interindividual variability of clinical outcome following exposure to a microorganism is immense, ranging from silent infection to life-threatening disease. Age-specific immune responses partially account for the high incidence of infection during the first 28 days of life and the related high mortality at population level. However, the occurrence of life-threatening disease in individual newborns remains unexplained. By contrast, inborn errors of immunity and their immune phenocopies are increasingly being discovered in children and adults with life-threatening viral, bacterial, mycobacterial and fungal infections. There is a need for convergence between the fields of neonatal immunology, with its in-depth population-wide characterization of newborn-specific immune responses, and clinical immunology, with its investigations of infections in patients at the cellular and molecular levels, to facilitate identification of the mechanisms of susceptibility to infection in individual newborns and the design of novel preventive and therapeutic strategies.

Surface Structures of Group B Streptococcus Important in Human Immunity

The surface of the Gram-positive opportunistic pathogen Streptococcus agalactiae, or group B Streptococcus (GBS), harbors several carbohydrate and protein antigens with the potential to be effective vaccines. Capsular polysaccharides of all clinically-relevant GBS serotypes coupled to immunogenic proteins of both GBS and non-GBS origin have undergone extensive testing in animals that led to advanced clinical trials in healthy adult women. In addition, GBS proteins either alone or in combination have been tested in animals; a fusion protein construct has recently advanced to human clinical studies. Given our current understanding of the antigenicity and immunogenicity of the wide array of GBS surface antigens, formulations now exist for the generation of viable vaccines against diseases caused by GBS.

Serocorrelates of protection against infant group B streptococcus disease

Group B streptococcus (GBS) is a leading cause of young infant mortality and morbidity globally, with vaccines being developed for over four decades but none licensed to date. A serocorrelate of protection against invasive disease in young infants is being considered to facilitate vaccine early licensure, followed by demonstration of efficacy assessed postlicensure. In this Review, we synthesise the available scientific evidence to define an immune correlate associated with GBS disease risk reduction on the basis of studies of natural infection. We summarise studies that have investigated GBS serum anticapsular or anti-protein antibodies, and studies measuring the association between antibody function and disease risk reduction. We highlight how knowledge on the development of correlates of protection from existing vaccines could be harnessed to facilitate GBS vaccine development. These lessons include aggregation of serocorrelates of protection for individual serotypes, understanding the relationship between immunity derived from natural exposure of adults and vaccine-induced immunity, or using extrapolation of protection from in-vitro immunoassay results. We also highlight key considerations for the assessment of the role of antibodies to derive a serocorrelate of risk reduction in future seroepidemiological studies of GBS disease.

Progress toward a group B streptococcal vaccine

Streptococcus agalactiae (group B Streptococcus, GBS) is a leading cause of severe invasive disease in neonate, elderly, and immunocompromised patients worldwide. Despite recent advances in the diagnosis and intrapartum antibiotic prophylaxis (IAP) of GBS infections, it remains one of the most common causes of neonatal morbidity and mortality, causing serious infections. Furthermore, recent studies reported an increasing number of GBS infections in pregnant women and elderly. Although IAP is effective, it has several limitations, including increasing antimicrobial resistance and late GBS infection after negative antenatal screening. Maternal immunization is the most promising and effective countermeasure against GBS infection in neonates. However, no vaccine is available to date, but two types of vaccines, protein subunit and capsular polysaccharide conjugate vaccines, were investigated in clinical trials. Here, we provide an overview of the GBS vaccine development status and recent advances in the development of immunoassays to evaluate the GBS vaccine clinical efficacy.

A Time to Save

Group B Streptococcus (GBS), characterized by Lancefield in 1933, was not recognized as a human pathogen until the early 1970s when it emerged and replaced Escherichia coli as the most common cause of sepsis and meningitis among neonates and young infants. This article briefly gives a personnel account of the discovery of clinical syndromes of GBS distinguished by age at onset, vertical mode of transmission for early-onset disease, meningeal tropism for GBS capsular (CPS) type III strains, and protective CPS epitopes. It also reviews the difficult evolution of the now routine program for antenatal GBS culture screening and intrapartum antibiotic prophylaxis, development of the first GBS candidate vaccines, clinical trials documenting the immunogenicity and safety of CPS tetanus toxoid conjugate vaccines, ongoing need to prevent morbidity and mortality in neonates and young infants, and critical need for commercial vaccines for routine use in pregnant women.

Group B streptococcal infections in the newborn infant and the potential value of maternal vaccination

Group B Streptococcus (GBS) is a leading cause of neonatal bacterial infections in developed countries. Early-onset disease (EOD) occurs at day 0-6 and late-onset disease occurs at day 7-89. Currently, the prevention of EOD relies upon intrapartum antibiotic prophylaxis (IAP) given to women who are GBS positive at prenatal screening or women with risk factors for EOD. Although successfully implemented, IAP has not fully eradicated EOD, and incidence rates of late-onset disease remain unchanged. Furthermore, antibiotic resistance may result from widespread antibiotic use. New prophylactic strategies are therefore of critical importance. A vaccine active against GBS, administered during pregnancy and combined with targeted IAP, could overcome these problems and reduce the mortality and morbidity associated with invasive diseases.

The spectrum of perinatal group B streptococcal disease

The progressive unfolding, over four decades, of an understanding of group B Streptococcus (GBS) and its global disease burden support the rationale for maternal immunization as a key strategy to prevent GBS perinatal infections. This review highlights, in historical context, the recognition of GBS as a human pathogen, definition of epidemiologic features of disease, pathogenesis, outcomes, impact of intrapartum antibiotic prophylaxis, development of glycoconjugate vaccines and appreciation of the global scope of GBS perinatal disease. These cumulative advances in the GBS field coupled with an increasing acceptance of immunization during pregnancy suggest the timing is optimal for introduction of a glycoconjugate GBS vaccine for use in pregnant women.

An overview of global GBS epidemiology

Streptococcus agalactiae (group B streptococcus (GBS)), remains the leading cause of neonatal sepsis and meningitis in many countries and an important cause of disease in pregnant women, immunocompromised adults and the elderly. Intrapartum antibiotic strategies have reduced the incidence of early-onset neonatal GBS where applied, but have had no impact on late onset GBS infection and only a limited impact on disease in pregnant women. In low/middle income settings, the disease burden remains uncertain although in several countries of Southern Africa appears comparable to that of high-income countries. Disease may be rapidly fulminating and cases therefore missed before appropriate samples are obtained. This may lead to significant underestimation of the true burden and be a particular issue in many African and Asian countries; comprehensive epidemiological data from such countries are urgently required. The available data suggest that the serotype distribution of GBS isolates is similar in Africa, Western Pacific, Europe, the Americas and the Eastern Mediterranean regions and has not changed over the past 30 years. Five serotypes (Ia, Ib, II, III, V) account for the majority of disease; conjugate vaccines including some or all of these serotypes therefore hold great promise for preventing this important disease.

Considerations for a phase-III trial to evaluate a group B Streptococcus polysaccharide-protein conjugate vaccine in pregnant women for the prevention of early- and late-onset invasive disease in young-infants

In 2010, an estimated 393,000 infection-related neonatal deaths occurred worldwide with Group B streptococcus (GBS) being a leading cause. Prevention of early-onset disease (0-6 days; EOD) is currently focused on intra-partum antibiotic prophylaxis to mothers identified as being at risk; such strategies reduce EOD by 75-80% but are resource-intensive and logistically-difficult to implement in developing countries. Vaccination of pregnant women is an alternate strategy for preventing both EOD and late-onset disease (7-89 days; LOD). A trivalent GBS polysaccharide-protein conjugate vaccine (GBS-CV) composed of capsular epitopes from serotypes Ia, Ib and III is undergoing phase-II evaluation among pregnant women in Europe, North America and Africa. These serotypes cause 70-80% of all invasive GBS disease in early-infancy. Maternal anti-GBS antibodies are associated with protection from EOD, however, since a correlate of efficacy has not been defined, a phase III efficacy trial may be required for licensure. Criteria for selecting appropriate sites include sufficiently high GBS incidence in large birth cohorts, as well as adequate clinical and microbiological diagnostic skills and capacities. Alternate pathways to licensure should be explored, e.g. identification of serological correlates of protection with subsequent phase IV studies establishing vaccine-effectiveness against invasive GBS disease. Conducting a randomized, placebo-controlled efficacy trial, however, has the additional advantage of also being able to evaluate the role of GBS contributing to neonatal culture-negative sepsis, stillbirths, prematurity and low-birth weight.

Maternal antibody at delivery protects neonates from early onset group B streptococcal disease

BACKGROUND

Further reduction in the group B streptococcal (GBS) disease burden in neonates in the United States awaits an additional prevention strategy, such as maternal immunization.

METHODS

We performed a prospective, multicenter, case-control study of 33 mothers delivering neonates with early onset GBS infection (cases), and 99 age- and ethnicity-matched mothers colonized with the same capsular polysaccharide (CPS) types delivering healthy neonates (controls). Relative risk and absolute risk were calculated for early onset disease associated with concentrations of type Ia, III, or V CPS-specific antibody in maternal serum.

RESULTS

For GBS types Ia and III, maternal CPS-specific antibody concentrations of ≥ 0.5 µg/mL were associated with a relative risk of approximately 0.1 (95% confidence intervals [CIs], .01-.74 and 0-.72, respectively; P = .02 for each), corresponding to a 90% risk reduction (by logistic regression). For type V, the relative risk was 0.3 (95% CI, .01-3.1), corresponding to a 70% risk reduction. By Bayesian modeling, the risk of early onset disease would decrease by 70% if maternal CPS-specific antibody concentrations for these 3 GBS types were ≥ 1 µg/mL.

CONCLUSIONS

Maternal CPS-specific antibody serum concentrations of ≥ 1 μg/mL at the time of delivery appear to protect most neonates from early onset GBS type Ia and III disease.

Preventing the broad spectrum of perinatal morbidity and mortality through group B streptococcal vaccination

The development of a group B streptococcal (GBS) glycoconjugate vaccine and its upcoming evaluation in a phase 3 trial in pregnant women highlight the importance of defining the anticipated impact of GBS vaccination upon the broad spectrum of GBS-related perinatal morbidity and mortality. We present the specific pregnancy-associated and neonatal conditions attributable, at least in part, to GBS in high and lower income countries. We offer a rationale to support our contention that implementation of GBS glycoconjugate immunization during pregnancy will reduce the global burden of GBS-related morbidity and mortality in pregnant women and their infants.

Persistence of functional antibodies to group B streptococcal capsular polysaccharides following immunization with glycoconjugate vaccines

The duration of functional activity of group B streptococcal (GBS) glycoconjugate vaccine-induced capsular polysaccharide-specific (CPS) IgG was evaluated among healthy adult responders. Opsonophagocytic activity declined significantly from a 4-week post-immunization peak, but substantial functional activity, exceeding 1 log(10) reduction in GBS cfu/mL, was retained at 18 months to 2 years post-immunization for each GBS type assessed. The persistence of functional antibody activity when GBS CPS-specific IgG concentrations decline, although remaining significantly higher than pre-immunization levels, suggests that long-term protection may be expected from candidate GBS glycoconjugates administered to this population.

Group B Streptococcus and pregnancy: a review

In the 1960s, early onset neonatal sepsis caused by group B Streptococcus (GBS) had an attack rate of 2 per 1000 live births and a 50% fatality rate. Early treatment and then antibiotic prophylaxis were shown to reduce morbidity and mortality rates; however, GBS remains a leading cause of perinatal infection. This article will review our investigations and related studies, including our studies in monkeys, that have contributed to current diagnosis, treatment, and prevention of disease caused by GBS. Although it has not been possible to eradicate GBS colonization, intravenous antibiotic prophylaxis given during parturition has been effective in the prevention of vertical transmission in animals and humans. Recently, diagnostic tests with polymerase chain reaction have offered promise for rapid accurate detection. This could lead to a major shift in the timing of diagnosis from the office setting to delivery suite. The potential for immunization remains a challenge.

Naturally occurring antibodies for the group B streptococcal surface immunogenic protein (Sip) in pregnant women and newborn babies

Sip is a surface-exposed protein of GBS, which causes severe neonatal disease. Because Sip elicits a protective immune response in mice, we assessed whether pregnant women and newborns have Sip antibodies. Sera were collected from 644 pregnant women and 176 of their healthy newborns, and 10 newborns with GBS disease and their mothers. Using ELISA, most (99%) women and newborns (97%) had serum Sip antibodies, as did most newborns followed through 6 months. This suggests that naturally occurring Sip antibodies cross the placenta and persist into infancy, which underscores the need to study Sip further as a potential vaccine candidate.

Serotypes and clinical manifestations of invasive group B streptococcal infections in western Sweden 1998-2001

This study monitored the serotypes of Streptococcus agalactiae (group B streptococcus; GBS) isolated from invasive infections in western Sweden and investigated possible relationships between serotype, age and clinical manifestations. Invasive GBS isolates were collected prospectively during 1998-2001 at six laboratories, covering two counties with a population of 1.8 million, and were serotyped by coagglutination. Clinical data were obtained from hospital notes. In total, 161 invasive strains (50 from neonates and infants aged < 3 months, and 111 from adults) were serotyped. The commonest serotypes from neonates and infants were serotypes III (60%), V (22%) and Ia (10%), and from adults were serotypes V (42%) and III (25%). Serotype V had doubled in frequency among both children and adults compared to a previous study from the same area in 1988-1997. Most (80%) of the adults had an underlying medical condition. No relationship was found between serotype and clinical manifestations. However, the study demonstrated the importance of active surveillance of GBS serotypes and the difficulties of formulating a multivalent polysaccharide conjugate vaccine against GBS.

Protection from group B streptococcal infection in neonatal mice by maternal immunization with recombinant Sip protein

The protective potential of antibodies directed against group B streptococcus (GBS) Sip surface protein was determined by using the mouse neonatal infection model. Rabbit Sip-specific antibodies administered passively to pregnant mice protected their pups against a GBS lethal challenge. In addition, active immunization with purified recombinant Sip protein of female CD-1 mice induced the production of specific antibodies that also confer protection to the newborn pups against GBS strains of serotypes Ia/c, Ib, II, III, and V. These data confirm that Sip-specific antibodies can cross the placenta and conferred protective immunity against GBS infections.

Type III group B streptococcal polysaccharide induces antibodies that cross-react with Streptococcus pneumoniae type 14

Covalent linkage of a bacterial polysaccharide to a protein greatly enhances the carbohydrate's immunogenicity and its binding to solid surfaces in immunoassays. These findings have spurred the development of glycoconjugate vaccines to prevent serious bacterial infections as well as the use of glycoconjugates as coating antigens in bioassays. We evaluated sera from women immunized with unconjugated group B streptococcal (GBS) type III (GBS III) polysaccharide (IIIPS) or with IIIPS covalently linked to tetanus toxoid to assess specificity, sensitivity, and parallelism in dilution curves in two GBS III enzyme-linked immunosorbent assays (ELISAs). One assay used IIIPS mixed with methylated human serum albumin (IIIPS + mHSA) as the coating antigen, and the other used IIIPS covalently linked to HSA (III-HSA). Each coating antigen was associated with a highly specific GBS III bioassay. The sensitivity was higher in the III-HSA ELISA, in which conjugated IIIPS is bound to the plates. Parallelism in titration curves was observed in the III-HSA but not in the IIIPS + mHSA ELISA. The excellent correlation between the concentrations of GBS IIIPS-specific immunoglobulin G (IgG) and the opsonophagocytic activity of these antibodies indicated that the III-HSA assay can predict functionality of vaccine-induced IgG against GBS III disease. The structure of the repeating unit of the capsular polysaccharide of GBS III differs from that of Streptococcus pneumoniae type 14 (Pn14 PS) only by the presence on GBS III of a sialic acid residue at the end of the side chain. The majority of healthy adults responding to GBS III vaccines with a fourfold or greater increase in GBS III-specific IgG antibodies developed antibodies cross-reacting with Pn14 PS (i.e., desialylated GBS IIIPS). The proportion of GBS vaccine responders who developed IgG to the desialylated IIIPS did not depend on whether IIIPS was given in the unconjugated or conjugated form. When present, these vaccine-induced cross-reacting antibodies conferred in vitro antibody-mediated opsonophagocytosis and killing of both GBS III and Pn14, two pathogens that cause invasive disease in young infants.

Cognate stimulatory B-cell-T-cell interactions are critical for T-cell help recruited by glycoconjugate vaccines

Covalent linkage of a bacterial polysaccharide to an immunogenic protein greatly enhances the carbohydrate's immunogenicity and induces polysaccharide-specific B-cell memory in vivo. These findings have spurred the development of glycoconjugate vaccines for serious bacterial infections. The specific B-cell-T-cell interactions responsible for recruitment of T-cell help by glycoconjugate vaccines are not well defined. We used mice deficient in molecules critical for stimulatory, cognate B-cell-T-cell interactions to study how T cells improve the immunogenicity of a glycoconjugate vaccine against group B streptococcal disease. Isotype switching to immunoglobulin G (IgG) was abrogated in mice deficient in major histocompatibility complex (MHC) class II antigen (Ag)-T-cell receptor (TCR), B7-CD28, or CD40-CD40L interactions. However, expression of either the B7-1 or the B7-2 molecule on antigen-presenting cells was sufficient for optimal T-cell costimulation. T cells activated by the vaccine also played a pivotal role in determining the magnitude of the IgM response to the polysaccharide. Comparable results were obtained with pathway antagonists. These data suggest that MHC class II Ag-TCR, B7-CD28, and CD40-CD40L interactions are critical for immune responses to glycoconjugate vaccines in vivo.

Minimization of the number of pregnant women to be treated with preventive procedure against GBS infection by means of antibody measurement. GBS Infection Group

To study preventive strategies, it is essential to screen pregnant women having group B Streptococcus (GBS) infection in the birth canal. For the purpose of studying preventive measures against this infection, nationwide multicenter research was performed in GBS-carrying pregnant women. Of a total of 10,267 pregnant women, 1860 cases (18.1%) had GBS. The most common serotypes of detected GBS were type NT6 and JM9, followed by type III, type Ia and then type Ib. Type-specific antibody titer was below the cut-off point of 10 units/mL in 30.9% of Ia carriers, 58.5% of Ib carriers, 45.9% of II carriers and 32.9% of III carriers. Fortunately, no neonatal GBS infection occurred during this research. We concluded that 18.1% of studied pregnant women were GBS carriers and one-third of these GBS carriers required preventive procedures with antibody measurement.

Immune response to type III group B streptococcal polysaccharide-tetanus toxoid conjugate vaccine

Group B Streptococcus (GBS) is an important perinatal pathogen. Because transplacentally acquired maternal antibodies to the GBS capsular polysaccharides (CPS) confer protection, prevention of infant disease may be possible after immunization of women. Unfortunately, the purified CPS of GBS are only variably immunogenic in adults; therefore to enhance immunogenicity we have designed and developed a CPS-protein conjugate vaccine. The lability of a conformationally dependent epitope on the III CPS containing a critical sialic acid residue was important to consider in vaccine design. 100 women were randomized to receive GBS type III CPS-tetanus toxoid conjugate (III-TT) vaccine at one of three doses; unconjugated GBS type III CPS; or saline. Serum samples were obtained before immunization and 2, 4, 8, and 26 wk thereafter, and specific antibody to type III CPS was measured. Vaccines were well tolerated. In sera from recipients of the highest dose of III-TT, CPS-specific IgG levels rose from a geometric mean of 0.09 microg/ml before immunization to 4.53 microg/ml 8 wk later, whereas levels in recipients of unconjugated type III CPS rose from 0.21 microg/ml to 1.41 microg/ml. Lower doses resulted in lower antibody levels. A > or = 4-fold rise in antibody concentration was achieved in 90% of recipients of III-TT compared with 50% of those that received III CPS (P = 0.0015). Antibodies evoked by the conjugate vaccine recognized a conformationally dependent epitope of the III-CPS, promoted opsonophagocytosis and killing of GBS, and, after maternal immunization, protected neonatal mice from lethal challenge with type III GBS. We conclude that directed coupling of type III GBS polysaccharide to a carrier protein yielded a conjugate vaccine with preserved expression of a highly labile conformational epitope involving sialic acid and enhanced immunogenicity compared with uncoupled CPS.

Safety and immunogenicity of a tetravalent group B streptococcal polysaccharide vaccine in healthy adults

Proposed strategies for prevention of neonatal group B streptococcal (GBS) infection have included active immunization of pregnant women and passive immunization of high-risk infants with hyperimmune GBS globulin derived from vaccinated plasma donors. To explore the feasibility of a program for generating hyperimmune GBS globulin, we evaluated the safety and immunogenicity of a candidate multivalent GBS vaccine containing purified polysaccharide from types Ia, Ib, II, and III among subjects most likely to develop an immune response following vaccination, i.e. those with pre-existing antibody to GBS. Thirty volunteers prescreened for serum antibody to type III GBS were immunized with a single subcutaneous injection of vaccine containing either 10, 25, or 50 micrograms of each polysaccharide type (Group 1). An additional ten volunteers prescreened for antibody to type Ia were vaccinated with the 50 micrograms dose (Group 2). Vaccination was generally well tolerated with minor reactions occurring in 27% of subjects. Using a quantitative enzyme-linked immunosorbent assay (ELISA), the seroconversion rates (> or = fourfold rise) and geometric mean antibody concentration (GMC in microgram IgG ml-1) 6 weeks after vaccination in Group 1 to type Ia, II, and III were 33% (GMC 5.2), 17% (GMC 3.6), and 70% (GMC 43.4), respectively. Quantitative titers were not available for type Ib, but a fourfold rise in ELISA units was seen in 13% of subjects. In Group 2, seroconversion rates to type Ia and III were 90% (GMC 73.4) and 40% (GMC 22.2), respectively. No significant dose-response effect was detected. Combined analysis of Groups 1 and 2 demonstrated that subjects with prevaccination antibody concentrations > 2 micrograms IgG ml-1 had significantly higher type-specific antibody concentrations following vaccination compared with subjects possessing lower levels of antibody before immunization. We conclude that our tetravalent GBS polysaccharide vaccine is safe but only modestly immunogenic in healthy seropositive adults. More potent vaccines will be required for public health use.

Immunogenicity of group B Streptococcus type III polysaccharide-tetanus toxoid vaccine in baboons

Maternal vaccination has been proposed as a rational approach for the prevention of neonatal group B streptococcal (GBS) disease. In this study, baboons were used as a nonhuman primate model to evaluate the immunogenicity of a GBS type III glycoconjugate vaccine. Type III-specific immunoglobulin G with opsonic activity was induced after vaccination with type III polysaccharide coupled to tetanus toxoid administered with an aluminum adjuvant. This suggests that baboons could be used in evaluating maternal transfer of GBS-specific antibodies by vaccination during pregnancy.

Role of C5a-ase in group B streptococcal resistance to opsonophagocytic killing

Type III group B streptococci (GBS) can be subdivided into three subtypes, RDP III-1, III-2, and III-3, on the basis of numerical analysis of HindIII restriction endonuclease digestion patterns (HindIII RDP) with their chromosomal DNAs. In the present study, the effect of C5a on opsonophagocytic killing of a representative strain from each RDP type was investigated by using a novel optical method for determining opsonophagocytic killing, and the effect of C5a-ase treatment of C5a on opsonophagocytic killing was also investigated. Pre-stimulation of polymorphonuclear leukocytes (PMNs) with C5a significantly increased opsonophagocytic killing of all three strains. The increase in killing was abolished by pretreating the C5a with GBS that express C5a-ase, a treatment that also destroyed the chemoattractant activity of the C5a. The kinetics of killing of the RDP III-2 strain differed from those of the other two strains. The survival of the RDP III-2 bacteria continued to decline over the entire 60-min incubation of the opsonophagocytic assay when PMNs were prestimulated with C5a or with C5a that had been inactivated with GBS C5a-ase (dC5a). In contrast, killing of the RDP III-1 and III-3 strains almost ceased after 20 or 60 min when PMNs were prestimulated with dC5a or C5a, respectively. A difference in bacterial killing between the III-2 strain and the III-1 and III-3 strains therefore became increasingly apparent with prolonged incubation time. The percentage of bacteria surviving in the extracellular fluid was approximately the same as the percentages of bacteria surviving in both intracellular and extracellular locations when PMNs were prestimulated with either C5a or dC5a. These data imply that the majority of bacterial killing occurred following phagocytosis and suggest that the enhanced killing of GBS following prestimulation of PMNs with C5a resulted from increased ingestion of the bacteria.

Recurrent group B streptococcal infections in infants: clinical and microbiologic aspects

OBJECTIVE

To describe the potential for recurrence of group B streptococcal (GBS) infection in infants, using pulsed-field gel electrophoresis as an epidemiologic tool.

DESIGN

Retrospective review of cases identified by laboratory records and review of the literature.

SETTING

Neonatal nurseries of a county hospital system.

METHODS

Retrospective review of infants with second episodes of GBS bacteremia or meningitis. Digestion of chromosomal DNA with the restriction enzyme Sma I and separation of fragments by use of contour-clamped homogeneous electric field.

RESULTS

Nine cases of recurrent GBS infection were identified during a 14-year period. Eight of the nine infants were born at 25 to 36 weeks of gestation, and one was born at term. The first episode of invasive GBS infection occurred at a mean age of 10.4 days (median, 3 days; range, 1 to 27 days). Parenteral antibiotic therapy was administered for a mean of 13.9 days (median, 14 days; range, 10 to 21 days). Recurrence occurred at a mean age of 42.3 days (median, 48 days; range, 23 to 68 days). One patient died during the second episode; eight infants survived to discharge home. Of seven sets of isolates analyzed from first and second GBS episodes, five were confirmed to be the same genotypically.

CONCLUSION

Recurrence of GBS disease in infants may be associated with the original infecting strain or a second acquired strain.

Demonstration of circulating group B streptococcal immune complexes in neonates with meningitis

Group B streptococci are the major cause of sepsis and fatal shock in neonates in the United States. Although a number of clinical features have been associated with enhanced severity of disease, the role of soluble immune complex formation in group B streptococcal infection has not been evaluated. We determined the frequency with which circulating immune complexes occurred in 16 infants with nonfatal type III, group B streptococcal meningitis, using an immunoglobulin-specific C1q enzyme immunoassay. Ten healthy, age-matched infants served as a control group. Elevated levels of immunoglobulin M (IgM)-containing immune complexes were present in the sera of four (25%) patients with group B streptococcal meningitis. Group B antigen was detected in precipitated IgM immune complexes from each of these four infants by competitive enzyme-linked immunosorbent assay. In addition, IgG-containing immune complexes were present in 56% of sick and 60% of control infants. Group B antigen was demonstrated in the serum of a sick neonate containing only IgG immune complexes but not in controls. Our findings indicate that a subset of infants with type III, group B streptococcal meningitis develop IgM immune complexes containing group B-specific antigen, and these may persist for up to 3 months in some patients.

Stability and activity of intravenous immunoglobulin with neonatal dextrose and total parenteral nutrient solutions

OBJECTIVE

To determine in vitro the compatibility of reconstituted intravenous immunoglobulin (IVIG) (Gammagard, Baxter-Hyland) with five different neonatal and pediatric intravenous solutions in Viaflex polyvinyl chloride bags.

DESIGN

In vitro compatibility study.

INTERVENTIONS

Samples were taken at time = 0, 10, 30, 60, 90, and 120 minutes and at 4, 8, 12, and 24 hours and assayed for total immunoglobulin G content and antibodies to hepatitis B surface antigen. Type III group B Streptococcus (GBS) and opsonic activity for type III GBS were analyzed at time = 0, 60, and 120 minutes and 12 and 24 hours. All results were compared with those from pure IVIG.

RESULTS

Our results demonstrate that mixing IVIG with intravenous solutions commonly used in the care of premature infants (dextrose 5% in water [D5W], D15W, D5W/NaCl 0.225%, and total parenteral nutrition [TPN]) does not significantly alter total immunoglobulin G concentrations or concentration of antibodies to hepatitis B surface antigen or type III GBS. As well, the in vitro functional activity for type III GBS of the IVIG, when mixed with these solutions for up to 24 hours, remained intact. An apparent decrease in bactericidal killing was seen with the IVIG/central TPN mixture. This apparent decrease was found to be an artifact of the high concentration of glucose (20 percent) in the solution.

CONCLUSIONS

We propose that Gammagard may be mixed with these solutions through Y-site connections without loss of antibody content or functional activity of the IVIG.

Maternal immunity and antibody response of neonatal mice to pneumococcal type 19F polysaccharide

The effect of immunization of mothers on the antibody response of their young to pneumococcal type 19F polysaccharide was studied. When 2-week-old BALB/c mice from mothers immunized with 23-valent pneumococcal vaccine during gestation were given an additional dose of the same vaccine, mouse pneumococcal antiserum, or both, they produced higher titers of antibodies to the 19F polysaccharide (1.87 to 4.66 micrograms of 19F immunoglobulin M [IgM] antibody per ml of serum; 0.45 to 0.81 micrograms of IgG antibody per ml of serum) than the control group that did not receive any treatment after birth (0.69 micrograms of 19F IgM antibody per ml; 0.28 micrograms of 19F IgG antibody per ml) (P less than 0.01). Furthermore, all 11- to 12-week-old monkeys that received an additional dose of 23-valent vaccine, pneumococcal immunoglobulin, or both produced statistically higher titers of IgG antibody to the 19F polysaccharide than did controls at various ages. The titers (micrograms of IgG antibody per milliliter of serum) were as follows: vaccine group, 7.12 +/- 0.96; control group at 4 months of age, 3.82 +/- 0.74 (P less than 0.01); immunoglobulin-treated group, 6.85 +/- 0.76; vaccinated and immunoglobulin-treated group, 7.80 +/- 1.40; control group at 3 months of age, 3.01 +/- 0.61 (P less than 0.01). These results suggest that immunization of mothers under certain conditions, such as with an optimum dose of antigen at a critical period of gestation or postnatal development, could provide young infants with an enhanced antibody response to pneumococcal polysaccharide immunogens.

Experimental model of type IV Streptococcus agalactiae (group B streptococcus) infection in mice with early development of septic arthritis

We have established an experimental murine model to gain insight into the pathogenicity and clinical features of type IV group B streptococcus (GBS) infections. Adult CD-1 mice were challenged intravenously with 10(7) type IV GBS cells, inducing systemic invasion. Most of the animals were able to clear the infection from the blood, brain, and lungs within 2 weeks and from the spleen and liver within 1 month. However, the animals were unable to clear the microorganism from the joints and kidneys during the 60-day observation period. About 80% of the mice challenged intravenously with type IV GBS manifested early septic arthritis, which evolved from an acute exudative synovitis to permanent lesions characterized by irreversible joint damage and ankylosis. Induction of persistent septic arthritis was dependent on the number and viability of microorganisms inoculated and was unrelated to the strain of type IV GBS and the growth phase of the inoculum. Type-specific antibodies of both immunoglobulin M and G classes could be detected by agglutination and enzyme-linked immunosorbent assay from days 7 and 14, respectively; immunoglobulin G antibodies persisted for more than 40 days. Complexes of antibodies and group- and type-specific antigens were detected in mouse sera 24 h after infection and persisted up to day 22. These results were obtained an experimental model of type IV GBS chronic infection with early development of septic arthritis, which could be useful in future studies of pathogenicity and immune mechanisms involved in the host resistance to this microorganism.

Risk factors for perinatal group B streptococcal disease after amniotic fluid colonization

A group of 1031 parturient women at high risk for intraamniotic infection were studied. Women in whom group B streptococci grew from cultures of the amniotic fluid did not differ in clinical risk factors when compared with similar parturient women without group B streptococcal colonization of amniotic fluid. Patients who had perinatal group B streptococcal disease (maternal or neonatal bacteremia) did not differ from those without disease, by maternal or neonatal acute antibody levels or antibody response, inoculum size, or serotype of the colonizing strain.

Immunization of pregnant women with a polysaccharide vaccine of group B streptococcus

Immunization of pregnant women with a polysaccharide vaccine of group B streptococcus is a promising strategy for the prevention of perinatal infections caused by group B streptococci. To explore the feasibility of this strategy, we vaccinated 40 pregnant women at a mean gestation of 31 weeks with a single 50-microgram dose of the Type III capsular polysaccharide of group B streptococcus. The only adverse effect detected was a mild local reaction in nine women (22 percent). Of the 35 women with low or unprotective antibody levels before immunization (less than 2 micrograms per milliliter), 20 (57 percent) responded to the vaccine. The geometric mean antibody level rose from 1.3 to 7.1 micrograms per milliliter four weeks after vaccination (P less than 0.02), and these levels persisted at delivery and three months post partum. Sixty-two percent of the vaccine-induced immunoglobulin in the mothers was IgG, which readily crosses the placenta. Infant antibody levels in cord serum correlated directly with maternal antibody levels at delivery (r = 0.913, P less than 0.001). Of the 25 infants born to women who responded to the vaccine, 80 percent continued to have protective levels of antibody at one month of age and 64 percent had protective levels at three months. Serum samples from infants with greater than or equal to 2 micrograms of antibody to Type III group B streptococcus per milliliter uniformly promoted efficient opsonization, phagocytosis, and bacterial killing in vitro of Type III strains. This effect could be mediated exclusively by the alternative complement pathway. Although this vaccine with an overall response rate of 63 percent is not optimally immunogenic, we conclude that maternal immunization is feasible and can provide passive immunity against systemic infection with Type III group B streptococcus in the majority of newborns. Larger trials with better vaccines will be required to evaluate the safety and clinical effectiveness of this strategy.

Passive protection by human sera in mice against challenge with strains of group B streptococci

The passive protective activity of 100 human sera in mice challenged with strains of group B streptococci (GBS), types Ia, Ib, Ic, II and III, was investigated. The number of sera which offered protection against type strains III, II and Ib were 10, 6 and 1, respectively, while 5 sera gave protection against type strains Ia and Ic. The activity was 2-mercaptoethanol sensitive while anti-human IgG, IgA and IgM rabbit sera were capable of negating the protective activity. Furthermore, type antigens removed the protective activity, resulting in the reduction of the amounts of IgG, IgA and IgM in normal human serum. These findings suggest that the protective activity of human sera is related to specific immunoglobulins against type antigens of GBS.

Immunoprophylaxis and immunotherapy of neonatal group B streptococcal infections

With emphasis on work from our laboratory, this paper briefly reviews previous studies which have established the basis for immunity to group B streptococcal infections. Quantitative data are presented on the concentration of antibody to the type-specific polysaccharides of group B streptococci in normal adults and infected infants, the protective level in experimental animals, and the influence of prematurity on transplacental passage of antibody. The role of the polymorphonuclear leukocyte in immunity to group B streptococcal infections is critical as supported by in vitro and in vivo experiments as well as clinical observations. Strategies for prevention include antimicrobial chemoprophylaxis and active immunization. Alternative approaches to adjunctive therapy such as administration of specific immune globulin, polymorphonuclear leukocytes, and exchange transfusions are discussed.

Immunoglobulin G and M composition of naturally occurring antibody to type III group B streptococci

Human sera were examined by an enzyme-linked immunosorbent assay for immunoglobulin G (IgG) and IgM antibodies to purified type III polysaccharide of group B streptococci. The antigen-binding capacity of a reference human serum was determined by a radioimmunoassay, and the total antibody content was determined by quantitative precipitation. The serum was then depleted of IgM and IgA to determine the effect on the antigen-binding capacity. Duplicate samples of 81 sera were tested by the enzyme-linked assay in comparison with reference standard serum. Although levels of IgG antibody were greater in subjects who had carried type III streptococci during pregnancy, concentrations of this antibody were generally low. Only 2 of 28 sera (7%) from parturient subjects and 7 of 25 sera (28%) from adult volunteers contained greater than or equal to 1 microgram of IgG antibody per ml; the mean levels were 0.13 and 0.53 micrograms/ml, respectively. In contrast, 19 of 28 maternal sera (68%) and 22 of 25 (88%) volunteer adult sera contained greater than or equal to 1 microgram/ml of IgM antibody; mean levels were 1.33 and 1.54 micrograms/ml, respectively. The cord serum levels of IgG antibody were almost identical to maternal serum concentrations, whereas IgM antibody was essentially undetected.

The mode of action of antibody in neutrophil bactericidal activity against highly pathogenic group-B streptococci

An investigation was undertaken into the post-phagocytic action of specific antibody in initiating neutrophil bactericidal activity against highly pathogenic group-B streptococci that survive within these cells. Specific antibody appears to gain access to the interior of the neutrophil and binds to the intracellular bacteria. Activation of Fc receptors on the neutrophil surface is not sufficient to initiate bactericidal activity, but the antibody may utilise the surface Fc receptors to gain access to the ingested organisms. Fusion of the lysosomes with the phagosomes containing the streptococci occurs normally in the cells, and proceeds in both the presence and absence of specific antibody. The organisms are resistant, however, to the microbicidal agents of lysosomes. A significant role is demonstrated for specific antibody in "masking" protective determinants on the bacterial surface during the destruction of these organisms by neutrophils. The relevance of antibody entry into neutrophils in relation to the treatment of bacterial infection is discussed.

Class specificity of naturally acquired and vaccine-induced antibody to type III group B streptococcal capsular polysaccharide: determination with a radioimmunoprecipitin assay

A radioimmunoprecipitin test was developed to determine the immunoglobulin class distribution of naturally acquired and vaccine-induced antibody to the native capsular polysaccharide of type III group B streptococci (III-GBS). In sera from adults and pregnant women with naturally acquired antibody, the mean percentage of antigen bound by immunoglobulin G (IgG) was 74.9 and 78.6, respectively, whereas antigen bound by IgM comprised less than 10% of the total. In contrast, early-convalescent-phase sera (mean, 16.3 days) from neonates responding to III-GBS infection with an increase in specific antibody had significantly more IgM (mean, 36%; P less than 0.001, unpaired t test). However, in late convalescence, the immunoglobulin class distribution in sera from these neonates was similar to that of naturally immune adults. Four weeks after immunization with III-GBS polysaccharide vaccine, sera from adults with low (less than 2 micrograms/ml) preimmunization antibody levels in their sera and from those with moderate (mean, 5.5 micrograms/ml) preimmunization levels contained specific antibody predominantly of the IgG class. Although the percentage of IgG-specific antibody was greater in sera from naturally immune adults than in that from vaccinees with a presumed primary immune response, the major portion of antigen bound by sera at 4 weeks postimmunization (62.5%) was associated with IgG. These observations support the opinion that immunization of pregnant women with III-GBS capsular polysaccharide could be efficacious for the prevention of invasive neonatal III-GBS disease.

Type-specific capsular antigen is associated with virulence in late-onset group B Streptococcal type III disease

Strain differences have been postulated to explain the observation that group B Streptococcus type III (GBS III) late-onset disease occurs in only a fraction of colonized infants. To determine the distribution of type-specific polysaccharide antigen (Ag) in GBS III, Ag was measured by rocket immunoelectrophoresis in both supernatant fluids and EDTA extracts and by radial immunodiffusion in multiple HCl extracts of the pellet from cultures of 10 strains of GBS III. Capsular Ag was defined as the sum of Ag in EDTA extracts + Ag in multiple HCl extracts. Both Ag in EDTA extracts and Ag in supernatant fluids correlated with capsular Ag (r = 0.94). GBS III strains were obtained from the blood of 19 infants with late-onset sepsis, from the cerebrospinal fluid or blood of 22 infants with late-onset meningitis, and from mucosal surfaces of both 18 infants and 12 mothers of infants with low levels of type-specific antibody and asymptomatic colonization. Mean values of Ag in supernatant fluids in strains from infants with late-onset sepsis (1.50 +/- 0.08 micrograms/ml) and late-onset meningitis (1.67 +/- 0.09 micrograms/ml) were significantly greater than those in asymptomatic colonization strains (1.14 +/- 0.05 micrograms/ml; P less than 0.001). The number of organisms required for a 50% lethal dose in the chick embryo, determined in 29 strains, was inversely related to Ag in supernatant fluids (r = -0.60). The demonstration that the quantity of capsular Ag produced by GBS III strains is related to their virulence in chick embryos and to their invasiveness in susceptible infants supports the hypothesis that Ag is a virulence factor in humans.

Immunoprophylaxis and immunotherapy of neonatal group B streptococcal infections

With emphasis on work from our laboratory, this paper briefly reviews previous studies which have established the basis for immunity to group B streptococcal infections. Quantitative data are presented on the concentration of antibody to the type-specific polysaccharides of group B streptococci in normal adults and infected infants, the protective level in experimental animals, and the influence of prematurity on transplacental passage of antibody. The role of the polymorphonuclear leukocyte in immunity to group B streptococcal infections is critical as supported by in vitro and in vivo experiments as well as clinical observations. Strategies for prevention include antimicrobial chemoprophylaxis and active immunization. Alternative approaches to adjunctive therapy such as administration of specific immune globulin, polymorphonuclear leukocytes, and exchange transfusions are discussed.

Antibody to type III group B Streptococcus in the rhesus monkey

Susceptibility to infection due to intra-amniotic type III group B streptococcal infection was studied in 27 rhesus monkeys. Sera from mothers and their offspring were tested to determine the concentration of antibody to the native type III group B Streptococcus antigen. Among 17 controls there was a statistically significant association between the concentration of maternal antibody prior to infection and both the neonatal survival rate and survival time (P less than 0.05). Neonatal survival was decreased to less than or equal to 6 hours (P = 0.005) if the maternal antibody concentration was less than 0.5 micrograms/ml. Modified immune serum globulin was given intravenously to the mothers prior to intra-amniotic infection with (five animals) or without (five animals) neonatal modified immune serum globulin. Neither of the modified immune serum globulin groups demonstrated a significant reduction in the neonatal mortality rate; however, the addition of the modified immune serum globulin provided protection against rapid neonatal death among those animals born to mothers which had low or no detectable antibody. All maternal groups developed a significant increase in the concentration of antibody in postpartum sera. These results indicate that both naturally acquired and passive (modified immune serum globulin) antibodies to type III group B Streptococcus antigen are partially protective against intra-amniotic infection.

Isolation, chemical composition, and molecular size of extracellular type II and type Ia polysaccharides of group B streptococci

Polysaccharides carrying the type II- and type Ia-specific determinants of Lancefield group B streptococci were isolated and purified by anion-exchange chromatography and gel filtration from the supernatant culture medium after growth of strain 18RS21/67/1 (type II) and strain DS/1204/78 (type Ia), respectively. The average molecular weights of these polysaccharides were 97,000 (type II) and 94,000 (type Ia), as determined by reducing end group analyses. These molecular weights were in reasonably good agreement with molecular weights determined by gel filtration at high ionic strength on calibrated columns. The polysaccharides did not cross-react with antisera specific for the other type-specific determinants or with group B-specific antisera. Their content of galactose, glucose, glucosamine, and neuraminic acid (the last two calculated as N-acetyl derivatives) accounted for over 96% of their dry weight. The two polysaccharides differed from each other (and from type III polysaccharide) in their relative content of these monosaccharides. The molar ratios of galactose, glucose, and neuraminic acid to glucosamine were 3.3:2.3:1.35:1.0 for the type II polysaccharide and 2.0:0.8:1.4:1.0 for the type Ia polysaccharides. The results obtained indicate that these extracellular type II and Ia polysaccharides contain larger amounts of neuraminic acid than can be accounted for by previously proposed structures of their repeating units.

Immunochemical analysis and immunogenicity of the type II group B streptococcal capsular polysaccharide

The relationship between group B streptococcal (GBS) type-specific antisera and the type II-specific polysaccharide is evaluated from a structural and immunologic viewpoint. Although all GBS type-specific polysaccharides are composed of the same monosaccharides, the type II antigen is more complex structurally and contains these sugars in a molar ratio different from the other antigens. Type II polysaccharide has two side chains. One contains only sialic acid and is less susceptible to acid cleavage than sialic acid residues found on types III, Ia, and Ib polysaccharides. The other side chain is composed of galactose as the only sugar. Immunochemical studies demonstrate that the type II polysaccharide has several immunodeterminants. One of these determinants is likely to be the side-chain galactose, while sialic acid appears to comprise part of another immunodeterminant, more complex than sialic acid alone. A series of cross-reactions is demonstrated between the type II native antigen and antisera to serotypes Ia, III, and Ib by a sensitive radioactive antigen-binding assay, which account for additional, complex immunodeterminants. The strongest of these cross-reactions is with type Ia antiserum and the weakest with Ib antiserum. Since Ia and Ib polysaccharides differ in only one linkage, these findings suggest that the trisaccharide beta D-N-acetyl-glucosamine-p(1 leads to 3) beta D-galactose-p(1 leads to 4) beta D-glucose-p [[beta D-GlcNAcp(1 leads to 3) beta D-Galp(1 leads to 4)beta D-Glcap]] is the likely common site responsible for the interaction of the type II native polysaccharide and type Ia antiserum. Another cross-reaction is observed between type III antiserum and type II native antigen. Inhibition studies indicate that the most likely cross-reactive determinant in this case is [beta D-Galp(1 leads to 4)beta D-GlcNAcp]. Type II polysaccharide has been utilized in a human vaccine trial to test safety and immunogenicity. The polysaccharide is highly immunogenic, inducing an antibody response in 95% of recipients, and nontoxic, with side-effects confined to minimal local reactions. Despite the cross-reactions observed between type-specific antigens and antibody prepared by immunization of rabbits with whole bacteria, which suggest shared immunodeterminants, similar cross-reactions were not detected in human sera after immunization with purified type II polysaccharide.