Influence of preimmunization antibody levels on the specificity of the immune response to related polysaccharide antigens

Control of Streptococcal Infections: Is a Common Vaccine Target Achievable Against Streptococcus agalactiae and Streptococcus pneumoniae

Both Streptococcus agalactiae [group B streptococcus (GBS)] and Streptococcus pneumoniae (pneumococcus) remain significant pathogens as they cause life threatening infections mostly in children and the elderly. The control of diseases caused by these pathogens is dependent on antibiotics use and appropriate vaccination. The introduction of the pneumococcal conjugate vaccines (PCVs) against some serotypes has led to reduction in pneumococcal infections, however, the subsequent serotype switching, and replacement has been a serious challenge. On the other hand, no vaccine is yet licensed for use in the control of GBS diseases. In this review, we provide an overview of the history and global disease burden, disease pathophysiology and management, vaccines update, and the biology of both pathogens. Furthermore, we address recent findings regarding structural similarities that could be explored for vaccine targets across both mucosal pathogens. Finally, we conclude by proposing future genomic sequence comparison using the wealth of available sequences from both species and the possibility of identifying more related structural components that could be exploited for pan-pathogen vaccine development.

Systematic review of the clinical development of group B streptococcus serotype-specific capsular polysaccharide-based vaccines

INTRODUCTION

Vaccination against group B Streptococcus (GBS) during pregnancy could provide protection against disease in the mother, fetus, and newborn. Immunity through transplacental acquired antibodies in the newborns could persist through early infancy, reducing the risk of early-onset (<7 days age) and late-onset (7-89 days age) disease. We conducted a systematic review of clinical trials on GBS capsular polysaccharide (CPS) vaccine to assess its safety and immunogenicity in pregnant and nonpregnant adults.

AREAS COVERED

We searched literature databases PubMed (Medline), Scopus, and the Cochrane library and identified 25 unique records on GBS CPS vaccines with or without conjugant protein.

EXPERT COMMENTARY

GBS vaccines were well tolerated, with mild local reactogenicity being the main solicited adverse event and no difference in reporting of other serious adverse events compared to placebo recipients. CPS vaccines conjugated to immunogenic proteins induced ≥fourfold increase of serotype-specific antibodies with high longevity (1-2 years); and capable of promoting homotypic GBS opsonophagocytic killing. Feto-maternal transplacental antibody ratio of serotype-specific IgG ranged between 0.49 and 0.81. The clinical relevance of these immunogenicity studies, however, need to be weighed against a correlate of protection against invasive GBS disease in infants, which is yet to be established using a universally accepted standardized assay.

Type I Streptococcus pneumoniae carbohydrate utilizes a nitric oxide and MHC II-dependent pathway for antigen presentation

Some pathogenic bacteria form thick capsules that both block immune responses through inhibition of complement deposition and phagocytosis and stimulate a weak response resulting from a lack of T-cell involvement. Contrary to this model, capsular polysaccharides from 23 serotypes of Streptococcus pneumoniae have been successfully used in a multivalent vaccine in the absence of a carrier protein. Furthermore, type I pneumococcal polysaccharide (Sp1) has been shown to activate T cells in vivo and in vitro via an uncharacterized mechanism. In the present report, we demonstrate that Sp1 utilizes the major histocompatibility complex (MHC) class II pathway in antigen-presenting cells (APCs) for processing and presentation. APCs internalize and process Sp1 through a nitric oxide-dependent mechanism and, once inside the cell, it associates with MHC II proteins in an H-2M-dependent manner that leads to in vivo T-cell activation. These results establish that Sp1 activates T cells which can lead to abscess formation in mice through an H-2M-dependent polysaccharide antigen presentation pathway in APCs, potentially contributing to pneumococcal polysaccharide vaccine efficacy through the recruitment of T-cell help.

A peptide mimotope of type 8 pneumococcal capsular polysaccharide induces a protective immune response in mice

Increasing antibiotic resistance and a rising patient population at risk for infection due to impaired immunity underscore the importance of vaccination against pneumococci. However, available capsular polysaccharide vaccines are often poorly immunogenic in patients at risk for pneumococcal disease. The goal of this study was to explore the potential of peptide mimotopes to function as alternative vaccine antigens to elicit a type-specific antibody response to pneumococci. We used a human monoclonal immunoglobulin A (IgA) antibody (NAD) to type 8 Streptococcus pneumoniae capsular polysaccharide (type 8 PS) to screen a phage display library, and the phage PUB1 displaying the peptide FHLPYNHNWFAL was selected after three rounds of biopanning. Inhibition studies with phage-displayed peptide or the peptide PUB1 and type 8 PS showed that PUB1 is a mimetic of type 8 PS. PUB1 conjugated to tetanus toxoid (PUB1-TT) induced a type 8 PS-specific antibody response in BALB/c mice, further defining it as a mimotope of type 8 PS. The administration of immune sera obtained from PUB1-TT-immunized mice earlier (days 14 and 21) and later (days 87 and 100) after primary and reimmunization resulted in a highly significant prolongation of the survival of naive mice after pneumococcal challenge compared to controls. The survival of PUB1-TT-immunized mice was also prolonged after pneumococcal challenge nearly 4 months after primary immunization. The efficacy of PUB1-TT-induced immune sera provides proof of principle that a mimotope-induced antibody response can protect against pneumococci and suggests that peptide mimotopes selected by type-specific human antibodies could hold promise as immunogens for pneumococci.

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.

Preimmunization anti-pneumococcal antibody levels are protective in a majority of patients with cystic fibrosis

OBJECTIVE

Although invasive pneumococcal disease is infrequent in cystic fibrosis (CF), it is recommended that all patients with CF receive pneumococcal immunization. As part of a comprehensive program to immunize our clinic population, we obtained preimmunization anti-pneumococcal antibody levels. We hypothesized that the percentage of CF patients without protective levels of anti-pneumococcal antibody levels would be high, as they are exposed to frequent antibiotic therapy that may eradicate organisms before generation of an antibody response.

METHODS

An observational study of 100 patients with CF, aged 1 to 39 years, was conducted in a regional CF center. Preimmunization anti-pneumococcal antibody levels against 6 serotypes were measured by enzyme-linked immunosorbent assay. Protective antibody levels were defined as >200 ng/mL.

RESULTS

A majority of CF patients-61% to 100%, depending on age and serotype-had protective levels of pneumococcal antibody. There was a significant positive correlation between antibody level and age for 5 of the 6 serotypes tested.

CONCLUSIONS

In contradistinction to our hypothesis, the majority of CF patients have protective preimmunization anti-pneumococcal antibody levels. However, a significant proportion-between 17% and 39%, depending on the serotype-did not exhibit adequate levels. Therefore, we concur with current recommendations for pneumococcal immunization in CF.

Immunoglobulin GM and KM allotypes and vaccine immunity

Immunoglobulin (Ig) GM and KM allotypes are genetic markers of gamma and kappa-type light chains, respectively. The striking qualitative and quantitative differences in the distribution of these determinants among different races raise questions concerning the nature of the evolutionary selective mechanism that maintains this variation. Associations between Ig allotypes and specific antibody responses could be a selective force for the maintenance of various haplotypes and their frequencies. Data from several studies reporting significant associations between certain GM and KM allotypes and immune responsiveness to polysaccharide vaccines and to particular infectious pathogens support this hypothesis. Possible ways in which constant (C)-region allotypes could contribute to the antibody specificity include the following: (i) certain alleles coding for allotypes may be in linkage disequilibrium with particular variable (V)-region determinants associated with immune responsiveness; (ii) they could directly contribute to the formation of specific idiotypes, as shown for the T15 system in mice; and (iii) allotype-associated structural variability in the C-region could modulate the kinetic competence of the antigen binding sites.

Evaluating children with respiratory tract infections: the role of immunization with bacterial polysaccharide vaccine

Antibody deficiency syndromes are an important cause of recurrent infections in children. Today it is possible to perform a complete evaluation of antibody-mediated immunity leading to a definitive diagnosis of either normal or abnormal immunity in most patients. However, the interpretation of the results of IgG subclass determinations and specific antibody responses is still being defined. At this time our recommendation is that patients who meet the criteria for an evaluation of antibody-mediated immunity be referred to subspecialists trained in this evaluation until better criteria for normal have been developed. The possibility that protective amounts of antibodies against pneumococcal serotypes may develop only transiently must be considered in patients with recurrent infections after initial improvement after immunization, especially if IgG2 subclass deficiency is also present. In the future it may be possible to use a faster and more economical approach to evaluate patients with recurrent infections by immunization with pneumococcal vaccine and then measuring IgM, IgG and IgA along with postimmunization specific antipneumococcal antibody titers 4 to 6 weeks later. For this approach to become feasible, further studies comparing the information obtained from the evaluation of pre- and postimmunization antibody concentrations with that obtained from the evaluation of postimmunization concentrations alone are needed.

Influence of age on the response to Streptococcus pneumoniae vaccine in patients with recurrent infections and normal immunoglobulin concentrations

BACKGROUND

A deficient antibody response to polysaccharide antigens is determined by measuring the response to the 23-valent pneumococcal polysaccharide vaccine. However, the diagnosis of this specific antibody deficiency is hampered by the lack of sufficient data and standardized testing of the response to pneumococcal polysaccharides.

METHODS

All patients evaluated in our allergy/immunology clinic for recurrent respiratory infections between 1995 and 1997 without immunoglobulin, IgG subclass, or other known primary or secondary immunodeficiency were included in this analysis. IgG antipneumococcal serotypes 1, 3, 4, 6B, 9V, 14, 18C, 19F, and 23F were determined by a modified ELISA protocol. An adequate IgG antibody response to an individual serotype was arbitrarily defined as a postimmunization antibody titer of 1.3 microg/ml or greater or at least four times the baseline value.

RESULTS

A total of 113 patients fulfilling the criteria for inclusion in this analysis were divided into five age groups. The geometric means for preimmunization and postimmunization pneumococcal antibody titers for all serotypes increased with age. For post-immunization antibody concentrations, there was a sharp increase in the specific antibody concentrations in adults in comparison with all pediatric age groups ranging in age from 7 months to 16 years. Similarly, the number of serotypes to which there was an adequate response also increased with age.

CONCLUSION

We conclude that the definition of what constitutes an adequate response to pneumococcal immunization needs further definition. It is clear, however, that age has an important influence on the intensity of the response to most pneumococcal polysaccharides. Correlation studies between antibody concentrations in different IgG subclasses, functional studies, and protection studies against mucosal and invasive pneumococcal infections are in progress, and these should contribute to a refined definition of a normal response. The availability of a standardized method for the measurement of IgG antibodies against relevant pneumococcal serotypes is an important step toward this goal.

Post-immunization pneumococcal antibody titers and IgG subclasses

IgG antibodies against pneumococcal polysaccharides are found predominantly within IgG subclass 2. We wished to evaluate retrospectively IgG subclasses and post-immunization pneumococcal antibody titers in children with recurrent respiratory infections. We examined total immunoglobulin levels and IgG subclasses, as well as pneumococcal antibody titers against serotypes 3, 7F, 9N, and 14 present 4-6 weeks after pneumococcal immunization in 56 children 2-18 years old. Titers > 200 ng Ab N/ml to any of the 4 serotypes tested were arbitrarily considered protective. Four patients did not have protective antibody levels against any of the 4 serotypes tested following vaccination. Of those, 3 had normal IgG subclass levels and 1 had an IgG2 subclass deficiency. Of 3 additional patients with IgG2 deficiency, 2 had protective antibody levels to only 1 serotype and 1 had protective antibody levels to 2 serotypes. Furthermore, in 2 patients with undetectable IgG2 at the time of immunization, the response was only transient. We conclude that patients with IgG2 deficiency may not develop protective antibody levels to all pneumococcal serotypes and that some may have deficient memory for IgG anti-pneumococcal polysaccharide antibodies.

Preimmunization and postimmunization pneumococcal antibody titers in children with recurrent infections

BACKGROUND

Patients with recurrent infections and normal IgG levels may have an abnormal response to pneumococcal polysaccharides. The ability to develop antibodies against different pneumococcal polysaccharides develops gradually in the first years of life, but the sequence of development and the influence of preexisting antibody titers has not been defined.

METHODS

Preimmunization and postimmunization IgG antibody titers against pneumococcal serotypes 3, 7F, 9N, and 14 were evaluated in a population of 100 1- to 18-year-old children referred to a pediatric allergy-immunology clinic because of recurrent respiratory infections. None of the patients had a known immunodeficiency syndrome; all had normal total IgG levels. Postimmunization antibody levels were obtained 4 to 6 weeks after immunization. Patients less than/=5 years of age who failed to develop antibody levels above 200 ng Ab N/mL against any serotype and older patients who failed to develop these levels against a second serotype in addition to serotype 3 were considered for IgG replacement therapy.

RESULTS

Prior to immunization, 50% of 51 patients did not have protective antibody levels against any of the serotypes tested. Immunization induced a high response to serotype 3 in all age groups, but responses to serotypes 7F and 14 increased with age. Five of 78 patients (6.4%) failed to develop protective antibody levels against any serotype tested. Three of these patients had clinical criteria that justified the use of IgG replacement therapy; all improved. Three patients were re-immunized 1 to 2 years after the first immunization and all developed protective levels of antibodies against serotype 3 after the second immunization.

CONCLUSION

We conclude that, although measurement of antibody levels against pneumococcal serotype 3 allows a good differentiation of patients who are able to develop anti-polysaccharide antibodies from those who are not, further studies of the development of specific antibodies against other vaccine serotypes in normal populations of different ages are needed to define a normal response to pneumococcal polysaccharides.

Immunology in the pediatrician's office

The development of antibody-mediated immunity is reflected in the maturation of B lymphocytes, in the changing levels of total immunoglobulins, and in the development of specific antibodies first to proteins and then sequentially to different types of polysaccharides. The measurement of anti-pneumococcal antibodies allows us to recognize specific antibody deficiencies, which need to be differentiated from normal developmental phases in the maturation of antibody-mediated immunity. The recognition of the late phase of IgE mediated allergic reactions is important to understanding the chronic manifestations of allergy. Chronic manifestations of allergy are frequently missed because they do not appear to be clearly related to acute triggers of allergic reactions. These conditions can be appropriately diagnosed, prevented, and treated, however, when the mechanisms of the late manifestations of allergy are understood. The integration of knowledge about the development of immunity and of allergic diseases enhances the pediatrician's ability to care for patients with immunologic abnormalities.

Maternal immunization of mice with group B streptococcal type III polysaccharide-beta C protein conjugate elicits protective antibody to multiple serotypes

Group B streptococcal infection is a major cause of neonatal mortality. Antibody to the capsular polysaccharide protects against invasive neonatal disease, but immunization with capsular polysaccharides fails to elicit protective antibody in many recipients. Conjugation of the polysaccharide to tetanus toxoid has been shown to increase immune response to the polysaccharide. In animal models, C proteins of group B streptococci are also protective determinants. We examined the ability of the beta C protein to serve in the dual role of carrier for the polysaccharide and protective immunogen. Type III polysaccharide was covalently coupled to beta C protein by reductive amination. Immunization of rabbits with the polysaccharide-protein conjugate elicited high titers of antibody to both components, and the serum induced opsonophagocytic killing of type III, Ia/C, and Ib/C strains of group B streptococci. Female mice were immunized with the conjugate vaccine and then bred; 93% of neonatal pups born to these dams vaccinated with conjugate survived type III group B streptococcal challenge and 76% survived type Ia/C challenge, compared with 3% and 8% survival, respectively, in controls (P < 0.001). The beta C protein acted as an effective carrier for the type III polysaccharide while simultaneously induced protective immunity against beta C protein--containing strains of group B streptococci.

Capsular polysaccharide regulates neutrophil complement receptor interactions with type III group B streptococci

The capsular polysaccharide of type III group B streptococci contributes substantially to the virulence of this organism. We explored the extent to which capsular polysaccharide influences neutrophil complement receptor interactions by using a poorly encapsulated strain (COH 31r/s), two well-encapsulated strains (M732 and M912), and strains produced from COH 31r/s by transposon mutagenesis that lacked capsule (COH 31-15) or had capsular polysaccharide lacking terminal sialic acid residues (COH 31-21). When tested with normal human serum, each strain had initially high bactericidal indices (85 to 96%). Monoclonal antibody blockade of neutrophil complement receptor 3 (CD11b/CD18) inhibited opsonophagocytosis to a significantly greater extent for the well-encapsulated strain than for the poorly encapsulated, asialo, or unencapsulated mutant strain. The addition of antibody with specificity for capsular polysaccharide reduced the inhibitory effect significantly for the encapsulated but not for the mutant strains. Blockade of neutrophil complement receptor 1 (CD35) effected only low-level inhibition. However, simultaneous blockade of complement receptors 1 and 3 augmented the inhibitory effect. When hypogammaglobulinemic serum was used as an antibody-free complement source, the initial bactericidal index was low (30% +/- 15%) for an encapsulated strain and was not affected for the mutant strains. Blockade of either neutrophil complement receptor 1 or 3 or the combination fully inhibited killing of the encapsulated strain. These results demonstrate that the type III group B streptococcal capsular polysaccharide regulates interactions with neutrophil complement receptors. We conclude that efficient phagocytic killing of encapsulated group streptococci in nonimmune serum requires ligation of complement receptors 1 and 3.

Estimation, reference ranges and goodness of fit for the three-parameter log-normal distribution

The three-parameter log-normal distribution (3PL) is an appropriate model for many of the continuous variables encountered in medicine. It is shown how to obtain different types of estimate and approximate (sometimes conservative) confidence intervals for the parameters of the 3PL and for certain functions of them, particularly in the calculation of reference ranges of clinical measurements. A simple non-iterative estimate of the shift parameter is described. The Shapiro-Wilk test of non-normality is modified to allow it to be used for testing for departure from the 3PL. Its power is compared with that of other well-known tests. The methods are illustrated using several data sets.

The mouse antibody response to infection with Cryptococcus neoformans: VH and VL usage in polysaccharide binding antibodies

Cryptococcus neoformans is a ubiquitous fungus that can cause serious infections in humans. The fungus has a polysaccharide (C. neoformans capsular polysaccharide; CNPS) capsule that contributes to its pathogenicity and can elicit an antibody response. Nevertheless, only 4 of 60 BALB/c mice chronically infected with C. neoformans had a detectable increase in serum anti-CNPS. The sera of three responder mice contained both IgM and IgG anti-CNPS antibody, and the titers of lambda and kappa anti-CNPS antibody were approximately equal. Eight IgM and one IgG3 monoclonal antibodies (mAbs) were generated from the spleen of one responder mouse, and one IgA was generated from the spleen of another mouse. Seven of the IgMs, the IgG3, and the IgA mAb had lambda light chains and were specific for serotype D CNPS. Molecular analysis confirmed that this was a highly restricted antibody response. All of the D-specific antibodies used VH441, JH3, and either V lambda 2/J lambda 2 or V lambda 1/J lambda 1, and all had the same heavy chain CDR3 amino acid sequence, even though there were differences in the nucleotide sequence of the N/D segment. One IgM mAb reacted with both serotype A and D CNPS, and this mAb used different VH and JH genetic elements and had kappa light chains. All the anti-CNPS mAbs used J proximal VH gene elements that have previously been shown to bind dextran and other polysaccharides. Sequence and Southern blot analysis indicate that the serotype-D CNPS-specific mAbs arose from only a few precursor B cells.

Effect on neutrophil kinetics and serum opsonic capacity of intravenous administration of immune globulin to neonates with clinical signs of early-onset sepsis

This study was designed to test the hypothesis that administration of immune globulin to human neonates with early-onset bacterial sepsis would (1) facilitate neutrophil egress from the marrow, (2) improve serum opsonic capacity, and (3) facilitate recovery from the infectious illness. Twenty-two newborn infants with clinical signs of early-onset sepsis were given an intravenous infusion of either 750 mg of immune globulin (IVIG) per kilogram of body weight or the same volume of a vehicle control (albumin). All 22 infants survived, but significant hematologic, immunologic, and respiratory differences were observed after the IVIG and not after the control infusion. Eleven of the patients had neutropenia; 24 hours after the infusions, the neutropenia had resolved in all six IVIG recipients but persisted in all five control recipients (p less than 0.001). Ten patients had I/T neutrophil ratios (a measure of immature neutrophils to total neutrophils on the leukocyte differential count) of less than 0.2. One hour after completion of the infusions, all five IVIG recipients had elevated I/T ratios (mean +/- SEM:0.10 +/- 0.05 before vs 0.43 +/- 0.03 after infusion; p less than 0.001), suggesting a prompt release of neutrophils from the marrow neutrophil storage pool into the circulation; no increase in the I/T ratio was observed in the control recipients. Six hours after the IVIG infusions, the ratio of arterial oxygen tension to fraction of inspired oxygen increased; no increase was observed after control infusions. Serum concentrations of IgG, IgG1, IgG2, IgG3, IgG4, and total hemolytic complement and the capacity of serum to support opsonophagocytosis of type II and type III group B streptococci increased markedly in the IVIG recipients but not in the control subjects. We conclude that administration of 750 mg IVIG per kilogram to neonates with clinical signs of early-onset sepsis was associated with immunologic, hematologic, and physiologic improvement.

Cross-reacting human and rabbit antibodies to antigens of Histoplasma capsulatum, Candida albicans, and Saccharomyces cerevisiae

Using Western blots of electrophoretically separated antigens, we show that human antibodies react most frequently to antigens shared by three fungi (Histoplasma capsulatum, Candida albicans, and Saccharomyces cerevisiae). Reactivity to antigens specific for individual fungi was relatively uncommon. The pattern of reactivity could not distinguish infected patients from uninfected controls. Rabbits immunized with extracts of each fungus also produced antibodies to cross-reactive or shared antigens of the other two fungi. Furthermore, preimmune sera showed similar but lower reactivity with the same fungal antigens. We believe that the preimmunization antibodies, which probably resulted from earlier fungal colonization or inapparent infections, predisposed the immune responses elicited by the vaccinations. A similar mechanism likely explains the results with human sera.

Recent advances in management of bacterial meningitis in neonates

The current incidence of neonatal sepsis in the United States varies from less than 1 to 8.1 per 1000 live births. The incidence of bacterial meningitis is about one-third of the number of infants with sepsis. The mortality is 20 to 30% and many survivors are severely impaired. Group B streptococcus and Escherichia coli are the most frequent causes of meningitis. Because of the difficulty of clinical diagnosis, many infants receive presumptive therapy for suspected sepsis or meningitis although few have documented infection. Between 5 and 10% of newborn infants born in the United States receive antimicrobial agents in the nursery, usually a penicillin and an aminoglycoside. To lower the continued high mortality and morbidity of meningitis due to gram-negative enteric bacilli, collaborative randomized trials evaluated the efficacy of gentamicin administered via the intrathecal route, gentamicin administered into the ventricle and most recently, the efficacy of moxalactam. Neither intrathecal or intraventricular drug, both in combination with parenteral drug, was advantageous when compared with parenterally administered drug alone. The mortality rate and number of days of culture positive cerebrospinal fluid were similar in infants who received moxalactam and ampicillin and infants who received amikacin and ampicillin. Adjunctive therapies including granulocyte transfusion, administration of hyperimmune gamma globulin and exchange transfusion are now under investigation. Initial studies of prevention of systemic bacterial infection by prophylactic ampicillin administered to the mother at delivery and use of group B streptococcal vaccine administered to susceptible women in the child bearing age show promise.

Capsular polysaccharide vaccines today

Polysaccharide (PS) vaccines are a relatively new class of antibacterial vaccines that have special advantages but also special problems related to their character. Several of them have proven very effective in preventing bacteremic infections caused by encapsulated bacteria such as meningococci, pneumococci and Haemophilus influenzae type b. Protective activity shows excellent correlation with serum anti-PS. However, young children often respond poorly to PS antigens and this limits the use of these vaccines in childhood. Some PS are poor immunizing agents even in adults. The practical implications of these aspects for the use and development of PS vaccines are discussed.

Analysing antibody response based on data obtained from serial dilution methods

We identify several problem areas in statistical analyses of data obtained from serial dilution methods in serology. We provide the mathematical backgrounds of the key elements involved in this field of study and discuss the statistical considerations. The problem areas include the use of the geometric mean as an expression of the average of a set of observations, the use of fold increase to measure antibody response, and the statistical analysis of the change in antibody response with respect to other variables, such as age and pre-titer levels.

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.

Age-dependence of the IgA anti-alpha (1 leads to 3) dextran B1355 response in vitro

The magnitude of the Balb/c mouse IgA anti-alpha (1 leads to 3) dextran B1355 (anti-dex) response in vivo was recently found to be markedly T-cell-dependent and age-dependent. This report demonstrates that the in vitro IgA anti-dex response by mesenteric lymph nodes (MLN) is highly age-dependent and that there is an age-dependent increase of the background IgA anti-dex plaque-forming cell (PFC) response occurring in the absence of added antigen which correlates significantly with the magnitude of the antigen-stimulated response. In aging mice both background and antigen-stimulated IgA anti-dex responses appeared to be significantly higher in MLN than in spleen cultures. Moreover, it is shown that there is a striking increase with age of natural antibody in the serum of normal Balb/c to alpha (1 leads to 3) glucan determinants, particularly IgA and lesser amounts of IgM and IgG3.

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.