The natural history of group B streptococcal colonization in the pregnant woman and her offspring. II. Determination of serum antibody to capsular polysaccharide from type III, group B Streptococcus

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.

Risk of Early-Onset Neonatal Group B Streptococcal Disease With Maternal Colonization Worldwide: Systematic Review and Meta-analyses

Background

Early-onset group B streptococcal disease (EOGBS) occurs in neonates (days 0-6) born to pregnant women who are rectovaginally colonized with group B Streptococcus (GBS), but the risk of EOGBS from vertical transmission has not been systematically reviewed. This article, the seventh in a series on the burden of GBS disease, aims to estimate this risk and how it varies with coverage of intrapartum antibiotic prophylaxis (IAP), used to reduce the incidence of EOGBS.

Methods

We conducted systematic reviews (Pubmed/Medline, Embase, Latin American and Caribbean Health Sciences Literature (LILACS), World Health Organization Library Information System [WHOLIS], and Scopus) and sought unpublished data from investigator groups on maternal GBS colonization and neonatal outcomes. We included articles with ≥200 GBS colonized pregnant women that reported IAP coverage. We did meta-analyses to determine pooled estimates of risk of EOGBS, and examined the association in risk of EOGBS with IAP coverage.

Results

We identified 30 articles including 20328 GBS-colonized pregnant women for inclusion. The risk of EOGBS in settings without an IAP policy was 1.1% (95% confidence interval [CI], .6%-1.5%). As IAP increased, the risk of EOGBS decreased, with a linear association. Based on linear regression, the risk of EOGBS in settings with 80% IAP coverage was predicted to be 0.3% (95% CI, 0-.9).

Conclusions

The risk of EOGBS among GBS-colonized pregnant women, from this first systematic review, is consistent with previous estimates from single studies (1%-2%). Increasing IAP coverage was linearly associated with decreased risk of EOGBS disease.

Seroprevalence of Opsonophagocytic Antibodies against Serotype Ia, Ib, II, III, and V Group B Streptococcus among Korean Population

BACKGROUND

Invasive Streptococcus agalactiae (group B streptococcus, GBS) infection most commonly occurs in infants; however, cases of GBS infection in adults, particularly in the elderly with significant underlying diseases, are being increasingly reported. We analyzed the serotype specific opsonophagocytic antibodies (the major mechanism of protection against GBS) in infants, adults, and the elderly.

METHODS

The opsonization indices (OIs) of antibodies against serotype Ia, Ib, II, III, and V GBS were studied in 89 infants, 35 adults (age, 30-50 years), and 62 elderly individuals (age, 65-85 years) according to the University of Alabama at Birmingham GBS opsonophagocytic killing assay protocol (www.vaccine.uab.edu).

RESULTS

In infants, adults, and elderly groups respectively, geometric mean of OI against GBS serotype Ia were 3, 7, and 32; against GBS serotype Ib were 7, 242, and 252; against serotype II were 93, 363, and 676; against serotype III were 8, 212, and 609; and against serotype V were 4, 639, and 610. The seropositive rate (% of subjects with OI ≥ 4) increased significantly in older age group for all five serotypes.

CONCLUSION

During infancy, only a limited proportion of infants have functional immunity against serotype Ia, Ib, II, III, and V GBS. Furthermore, a lack of opsonic activities against GBS observed in some adults and the elderly might predispose such individuals to the risk of invasive GBS infection. Epidemiological monitoring and development of suitable vaccine for these populations are needed.

Association between functional antibody against Group B Streptococcus and maternal and infant colonization in a Gambian cohort

BACKGROUND

Vertical transmission of Group B Streptococcus (GBS) is a prerequisite for early-onset disease and a consequence of maternal GBS colonization. Disease protection is associated with maternally-derived anti-GBS antibody. Using a novel antibody-mediated C3b/iC3b deposition flow cytometry assay which correlates with opsonic killing we developed a model to assess the impact of maternally-derived functional anti-GBS antibody on infant GBS colonization from birth to day 60-89 of life.

METHODS

Rectovaginal swabs and cord blood (birth) and infant nasopharyngeal/rectal swabs (birth, day 6 and day 60-89) were obtained from 750 mother/infant pairs. Antibody-mediated C3b/iC3b deposition with cord and infant sera was measured by flow cytometry.

RESULTS

We established that as maternally-derived anti-GBS functional antibody increases, infant colonization decreases at birth and up to three months of life, the critical time window for the development of GBS disease. Further, we observed a serotype (ST)-dependent threshold above which no infant was colonized at birth. Functional antibody above the upper 95th confidence interval for the geometric mean concentration was associated with absence of infant GBS colonization at birth for STII (p<0.001), STIII (p=0.01) and STV (p<0.001). Increased functional antibody was also associated with clearance of GBS between birth and day 60-89.

CONCLUSIONS

Higher concentrations of maternally-derived antibody-mediated complement deposition are associated with a decreased risk of GBS colonization in infants up to day 60-89 of life. Our findings are of relevance to establish thresholds for protection following vaccination of pregnant women with future GBS vaccines.

Placental transfer of anti-group B Streptococcus immunoglobulin G antibody subclasses from HIV-infected and uninfected women to their uninfected infants

OBJECTIVES

Placental antibody transfer is impaired in the context of HIV infection, which may render HIV-exposed, uninfected infants vulnerable to group B Streptococcus (GBS) disease. The GBS antibody response predominately consists of immunoglobulin G2 (IgG2) antibody. Thus we determined whether concentration and placental transfer of anti-GBS antibody subclasses was altered in HIV-infected compared with HIV-uninfected mothers.

DESIGN

A retrospective analysis of anti-GBS antibody subclasses in 38 HIV-infected and 33 HIV-uninfected mothers and their uninfected infants.

METHODS

Sera were analysed using a novel flow cytometric assay that quantified binding of IgG1, IgG2, IgG3 and IgG4 to serotype (ST)Ia, STIII and STV GBS bacteria.

RESULTS

IgG2 binding to GBS STIa and V was lower in HIV-infected women compared with HIV-uninfected women. Moreover, IgG2 binding to GBS STIa was also lower in HIV-exposed, uninfected infants compared with unexposed infants. However, there were no statistically significant differences in the transplacental transfer ratio of IgG2 for any GBS serotype. The transplacental transfer of total IgG was reduced for GBS STIII and V and IgG1 subclass for STIII; placental transfer of all other subclasses was comparable in HIV-affected and HIV-unaffected pregnancies.

CONCLUSION

Anti-GBS IgG2 placental transfer is not affected by HIV infection. This is important for functional antibody against the capsular polysaccharide of GBS and provides confidence that maternal GBS vaccination may result in functional activity in HIV-infected and uninfected women.

Natural acquired humoral immunity against serotype-specific group B Streptococcus rectovaginal colonization acquisition in pregnant women

Group B Streptococcus (GBS) rectovaginal colonization in pregnant women is associated with invasive GBS disease in newborns, preterm delivery and stillbirths. We studied the association of GBS serotype-specific capsular polysaccharide (CPS) antibody on new acquisition and clearance of rectovaginal GBS colonization in pregnant women from 20 weeks until 37 to 40 weeks' gestation. Serum serotype-specific CPS IgG antibody concentration was measured by multiplex enzyme-linked immunosorbent assay and opsonophagocytic activity (OPA) titres. Rectovaginal swabs were evaluated for GBS colonization, using standard culture methods and serotyping by latex agglutination, at five to six weekly intervals. Higher serotype III CPS antibody concentration was associated with lower risk of rectovaginal acquisition of serotype III during pregnancy (p 0.009). Furthermore, serotype-specific OPA titres to Ia and III were higher in women who remained free of GBS colonization throughout the study compared to those who acquired the homotypic serotype (p <0.001 for both serotypes). Serum CPS IgG values of ≥1μg/mL for serotype V and ≥3μg/mL for serotypes Ia and III were significantly associated with protection against rectovaginal acquisition of the homotypic serotype. A GBS vaccine that induces sufficient capsular antibody in pregnant women, including high OPA titres, could protect against rectovaginal colonization during the latter half of pregnancy.

Perinatal exposures and Kawasaki disease in Washington State: a population-based, case-control study

BACKGROUND

This study tested the hypothesis that selected perinatal exposures are associated with Kawasaki Disease (KD) in later childhood.

METHODS

A retrospective, population-based, case-control study was performed. Children hospitalized for KD in Washington State from 1987 to 2007 (n = 995) were identified through hospital discharge records and were linked to birth certificates and birth hospitalization discharge records. Controls were randomly selected from remaining birth records. Maternal and infant exposure information was obtained from hospital discharge records. Unconditional logistic regression was used to obtain adjusted relative risk estimates and to explore the effect of gender on observed associations.

RESULTS

After adjusting for race, gender and birth year, the following were significantly associated with KD: maternal age ≥35 years (odds ratio [OR] 1.65; [95% confidence interval: 1.20-2.27]); mother of foreign birth (OR 1.36; [1.06-1.75]); maternal Group B streptococcal colonization (OR 0.51; [0.26-0.97]); and early infancy hospitalization (OR 1.42; [1.04-1.93]). Early hospitalization for bacterial illness was associated with a 2.8-fold increased risk of KD (OR 2.84; [1.59-5.06]). There was weak evidence to suggest that the association between early hospitalization and KD varies by gender.

CONCLUSIONS

This study provides preliminary evidence of association between certain perinatal exposures and KD and raises the possibility of late biological effects of immune exposures during infancy. The association between KD and early infectious exposures deserves further study.

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.

Antibodies raised in animals against the Streptococcus agalactiae proteins c alpha and R4 and normal human serum antibodies target distinct epitopes

The targets for normal human serum antibodies that react with proteins c(alpha) and R4 isolated from group B streptococci (GBS; Streptococcus agalactiae) have been studied and compared with the targets for murine monoclonal and rabbit polyclonal antibodies raised against these proteins. The proteins were extracted by trypsin digestion and purified by precipitations and gel filtration and testing was based on enzyme immunoassays. The immune antibodies showed specificity for the corresponding protein, targeted that protein in Western blotting and recognized their targets after heat treatment (100 degrees C) of the proteins. Human antibodies in a commercial gammaglobulin preparation targeted a site(s) common to c(alpha) and R4. This target failed to bind the antibodies in Western blotting and was destroyed by heating. c(alpha)- and R4-reactive antibodies in sera from healthy pregnant women recognized the common, heat-labile determinant(s), but contained little or no antibodies against the heat-stable c(alpha)- or R4-specific determinants. These results are consistent with the notions that (i) the normal human antibodies and the immunization-induced animal antibodies targeted different sites on the c(alpha) and R4 proteins and that (ii) the natural human antibodies targeted conformational epitopes and the immune antibodies targeted linear epitopes. These findings are important for further clarification of GBS immunology and immunoprotection in humans.

Antibodies against Streptococcus agalactiae proteins c(alpha) and R4 in sera from pregnant women from Norway and Zimbabwe

Group B streptococci (GBS) express strain-variable and surface-localized proteins, which are important serotype markers and targets of protective antibodies. These include the c(alpha) and R4 proteins, one or the other of which is expressed by approximately 75% of clinical GBS isolates. These proteins have been considered vaccine candidates. In this study, the c(alpha) and R4 proteins were extracted by trypsin digestion of GBS and purified by sequential precipitation with trichloroacetic acid and ammonium sulfate followed by gel filtration chromatography. The proteins were used as antigens in an indirect enzyme-linked immunosorbent assay (ELISA) to measure the levels of c(alpha)- and R4-reactive antibodies in sera from pregnant women from Norway (n = 100) and from Zimbabwe (n = 124). Antibody levels in the Norwegian group of women were significantly higher than in the Zimbabwean group, and a higher proportion of the Norwegian women contained appreciable levels of antibodies against both proteins. The antibodies traversed the placental barrier. With individual sera, a significant correlation between the anti-c(alpha) and anti-R4 antibody levels was observed and each of the two protein antigens effectively competed for human serum antibodies both against itself and against the other antigen. Inhibition ELISA results demonstrated specificity for each of the proteins of immune antibodies raised in rabbits. These results demonstrate that (i) the majority of women of childbearing age have antibodies against c(alpha) and R4, (ii) the levels of these antibodies differ among pregnant women in different parts of the world, and (iii) the normal human serum antibodies may target a common c(alpha) and R4 protein site, whereas immune antibodies targeted a different site(s) specific for each protein.

Epidemiology of group B streptococcal disease in the United States: shifting paradigms

Since its emergence 25 years ago, group B streptococcus has become recognized as a cause of serious illness in newborns, pregnant women, and adults with chronic medical conditions. Heavy colonization of the genital tract with group B streptococcus also increases the risk that a woman will deliver a preterm low-birthweight infant. Early-onset infections (occurring at < 7 days of age) are associated with much lower fatality than when they were first described, and their incidence is finally decreasing as the use of preventive antibiotics during childbirth increases among women at risk. New serotypes of group B streptococcus have emerged as important pathogens in adults and newborns. Clinical and laboratory practices--in obstetrics, pediatrics, and clinical microbiology--have an impact on disease and/or its prevention, and protocols established at the institutional level appear to be critical tools for the reduction of perinatal disease due to group B streptococcus. Since intrapartum antibiotics will prevent at best only a portion of the full burden of group B streptococcal disease, critical developments in vaccine evaluation, including study of polysaccharide-protein conjugate vaccines, offer the potential for enhanced prevention in the relatively near future.

Prevention of neonatal group B streptococcal sepsis: is routine antenatal screening appropriate

Four strategies for prevention of early onset neonatal group B streptococcal (GBS) sepsis were considered: A: routine antenatal screening for GBS vaginal carriage at 26-28 weeks' gestation and intrapartum antibiotic prophylaxis for all carriers; B: screening as above and prophylaxis only for carriers with risk factors for sepsis; C: prophylaxis for all women with risk factors; D: as for C plus screening at 37 weeks' gestation and prophylaxis for carriers. The outcomes considered for each option were: the proportion of women given prophylaxis; the risk of anaphylaxis; cases of neonatal GBS sepsis and deaths prevented; costs of screening, prophylaxis and of acute care of remaining cases. Published local and overseas studies of neonatal GBS sepsis, effectiveness of antenatal screening and prophylaxis and estimated costs were evaluated. Any of the proposed strategies can prevent a significant proportion of cases of neonatal GBS sepsis and a strategy for prevention of neonatal group B streptococcal sepsis should be part of routine obstetric practice. Strategy C is simple, effective, inexpensive and avoids unnecessary antibiotic use; it is recommended particularly when antenatal care is provided mainly in community or private practice. Strategy A (using vaginal and rectal swabs for screening) could prevent more cases, but at greater cost which could be justified only if protocols can be properly implemented and monitored.

Solid-phase antigen density and avidity of antibodies detected in anti-group B streptococcal type III IgG enzyme immunoassays

Two enzyme immunoassays which measure anti-group B streptococcal type III capsular carbohydrate IgG antibodies were compared. One utilised poly-L-lysine conjugated coating antigen while the other used tyraminated coating antigen. Both carbohydrate antigens appeared to be antigenically identical but the poly-L-lysine based assay gave significantly lower values for some sera. Sera were identified which had low and high avidity anti-group B streptococcal type III IgG antibodies by the thiocyanate elution method. These antibodies gave results on a dilution range of coating concentrations consistent with their relative avidity. Comparison of dilution ranges of the two conjugates used for coating suggests that the poly-L-lysine conjugate coats with a ten-fold lower efficiency than the tyramine conjugate and therefore detects only higher avidity antibodies. Four fractions containing different relative avidities of affinity-purified IgG were produced from a single serum. These fractions behaved in the same manner as sera containing antibodies of different avidities. The results of this study suggest that the method of polysaccharide conjugation in enzyme immunoassays may affect the antigen concentration on the solid phase and thence the detection of antibodies of various avidities.

IgG subclasses compared in maternal and cord serum and breast milk

Total and specific IgG subclass antibodies against 14 pneumococcal capsular polysaccharide antigens on the cord serum from 11 healthy term infants at birth and on serum from their mothers at delivery were evaluated. The same evaluation was performed five days after delivery on the serum and the milk obtained from the six mothers who were breast feeding their infants. Mean neonatal: maternal serum ratio of total IgG1 was significantly higher than the ratios of total IgG2, IgG3, and IgG4 and higher than the ratios of pneumococcal IgG subclass antibodies. Total IgG3 and IgG4 ratios were higher than the specific antibody ratios of the same IgG subclass. Type 1 and type 14 IgG1 antibodies were the highest antipneumococcal ratios. Although the maternal milk:serum ratios of total IgG subclasses were very low, significant amounts of specific antibodies were found in the milk, at about half the concentration observed in mother's serum.

Altered humoral immunoregulation during human pregnancy

The in vitro production of immunoglobulins in response to stimulation with pokeweed mitogen (PWM) and fixed/killed Staphylococcus aureus Cowan 1 (SAC) was measured in conjunction with in vivo assays of plasma immunoglobulin levels to examine the quality and quantity of humoral immunity during human pregnancy and at parturition. Following stimulation with PWM, there is a significant enhancement of in vitro immunoglobulin-G (IgG) production during pregnancy. Following stimulation with PWM and SAC, there was a significant reduction in in vitro immunoglobulin-M (IgM) production immediately following parturition. There was a significant decrease in the plasma levels of IgG during pregnancy, although no change in the plasma levels of IgM were observed. The decrease in plasma immunoglobulin levels during pregnancy cannot be explained as the result of hemodilution and transplacental transfer. Altered humoral immunoregulation is the most likely means whereby an increase in immunoglobulin production during human pregnancy could occur. The possible effects of this on the outcome of pregnancy are discussed.

Sexually transmitted diseases and pregnancy

The association of adverse pregnancy outcome with Treponema pallidum, Neisseria gonorrhoeae and herpes simplex infections is well known and specific recommendations for management have been formulated. However, other agents that are not so well known can be transmitted sexually and threaten an otherwise healthy pregnancy. These agents are discussed in order to make the nurse more aware of related maternal and fetal diseases.

Immunospecificity and quantitation of an enzyme-linked immunosorbent assay for group B streptococcal antibody

Type-specific antigen was purified from the supernatant of type III group B streptococcal cultures, tyrosylated, and bound to microtiter wells for an enzyme-linked immunosorbent assay. The immunological specificity of the antigen and the assay was shown by (i) reaction only with homologous unabsorbed rabbit sera and (ii) inhibition after incubation of human serum with homologous but not heterologous purified antigen. The assay was quantitated by relating optical density readings to absolute amounts of human immunoglobulin G bound to the microtiter wells.

Mouse protection assay for group B streptococcus type III

The mucin model for group B Streptococcus (GBS) type III was used to assay the protective effect of sera against a type III challenge in mice. Hyperimmune rabbit sera, prepared by the Lancefield method against the laboratory reference strain (SS620) and a clinical isolate (M732), protected against a lethal challenge with either strain of GBS type III. Absorption of the sera with either of these type III strains removed the protective effect. Neither normal rabbit sera nor heterologous antisera (anti-Ia, SS615) provided protection; however, protection was obtained with pooled human gamma globulin. Sera from adult volunteers were tested to assay protective levels in the mouse model. Human sera enhanced the mouse lethality of the clinical isolate, M732, but not the laboratory reference strain, SS620. Sera from adults vaccinated with type III polysaccharide of GBS were also tested. The murine-mucin-GBS model may be developed as a screening test to measure protective antibody levels in the pre- and postvaccine treatment period. The model may also be used to measure protective antibody in pooled human gamma globulin for use in the passive immunization of high-risk individuals.