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

Quantitation of in vitro opsonic activity of human antibody induced by a vaccine consisting of the type III-specific polysaccharide of group B streptococcus

Human antibody, induced by a vaccine consisting of undegraded and highly purified extracellular type III-specific polysaccharide of group B streptococcus, was shown to increase the rate of phagocyte-mediated killing of bacteria of the homologous type. The bactericidal effect was mediated by type III-specific antibody and was complement dependent. An assay which permitted quantitation of "opsonic activity" was developed. In this assay, loss of CFUs occurred at a constant rate, and the rate constant was used as a measure of opsonic activity of antisera. A linear relationship between type III-specific antibody concentration (40 to 500 ng/ml) and the rate constant of killing was observed. When sets of immune sera were tested, some sera reacted anomalously, mediating significantly higher or lower rates than expected on the basis of their antibody content. Since type III-specific antibody in immune sera was found almost exclusively in the immunoglobulin G class, we hypothesize that differences in immunoglobulin G subclass distribution of specific antibody may have been the source of this variation.

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.

Antibody-independent classical pathway-mediated opsonophagocytosis of type Ia, group B streptococcus

The opsonophagocytic requirements of human sera containing endogenous complement for a variety of type Ia, and group B streptococcal strains were defined. Significant reduction (>==90%) in colony-forming units was noted after a 40-min incubation for the highly encapsulated, mouse-passed prototype strain 090 by sera containing moderate to high concentrations of antibody to type Ia polysaccharide (mean, 16.5 mug/ml), whereas bacterial growth occurred in 25 sera with low levels of specific antibody (mean, 2.1 mug/ml). This absolute requirement for a critical amount of specific antibody in promoting opsonophagocytic killing of strain 090 was not found when 18 fresh clinical type Ia isolates were tested. In antibody-deficient and agammaglobulinemic sera, respectively, mean reductions in colony-forming units of 94 and 95% were seen for fresh clinical isolates, whereas strain 090 was not killed by polymorphonuclear leukocytes in the presence of these sera. All strains required a considerable amount of specific antibody for alternative pathway-mediated opsonophagocytosis. That opsonophagocytic killing of clinical type Ia isolates was mediated by the classical pathway in a nonantibody-dependent fashion was shown when MgEGTA chelation of agammaglobulinemic serum or use of serum deficient in C2 resulted in bacterial growth. The addition of C2 to C2-deficient serum restored bactericidal activity of this serum. These experiments indicate that substances other than the exposed surface of the type Ia capsular polysaccharide initiate classical pathway-mediated opsonophagocytosis of clinical isolates of type Ia, group B streptococci by human sera in the absence of immunoglobulin. Perhaps, a deficiency in classical complement pathway function is critical to the susceptibility of neonates to type Ia, group B streptococcal disease.

Group B, type III streptococcal cell wall: composition and structural aspects revealed through endo-N-acetylmuramidase-catalyzed hydrolysis

Cell walls from a group B, type III streptococcus strain were prepared, purified by extraction with sodium dodecyl sulfate, and solubilized by the M-1 fraction of mutanolysin, an endo-N-acetylmuramidase obtained from Streptomyces globisporus. The lysate was resolved into three fractions by ion-exchange chromatography: a fraction containing peptidoglycan (PG) fragments, free of neutral and acidic sugars and of phosphate; a complex of PG fragments and group B-specific polysaccharide; and a complex of PG fragments and group B-specific polysaccharide and type III-specific polysaccharide. The PG-polysaccharide complexes were large and heterogeneous in molecular size. When subjected to base-catalyzed beta-elimination, both complexes were disintegrated, and polysaccharides and low-molecular-weight PG fragments could then be separated by gel filtration. The low-molecular-weight PG fragment-containing fraction contained muramic acid, glucosamine, alanine, lysine, glutamic acid, and serine in molar ratios (to lysine) of 0.92:0.98:3.01:1.00:1.00:0.05. Wall-derived, purified group polysaccharide contained rhamnose, galactose, glucosamine, and phosphorus in molar ratios (to galactose) of 5.03:1.00:1.00:1.05. It also contained an unidentified sugar. Wall-derived, purified type III polysaccharide contained galactose, glucosamine, glucose, and N-acetylneuraminic acid in molar ratios (to glucose) of 1.94:0.85:1.00:1.39. On a dry-weight basis, the whole wall lysate contained 19.8 and 20.6% of group and type polysaccharide, respectively. Neither glycerol nor ribitol was found, and all of the cell wall phosphorus was accounted for as polysaccharide, indicating the absence of a wall teichoic acid.

Bactericidal capacity of newborn phagocytes against group B beta-hemolytic streptococci

The bactericidal capacity of mononuclear and polymorphonuclear phagocytes obtained from normal newborn infants and from healthy adults was evaluated in vitro, using two group B beta-hemolytic streptococci (GBBHS) serotypes (GBBHS-Ia-SS-615/28 and GBBHS-III-SS-620/50) and uniform opsonic conditions. No intertype differences in bacteriolysis of these two serotypes were observed among leukocytes from newborns or adults. As group, only polymorphonuclear phagocytes from newborns disclosed a significantly lower mean bactericidal capacity than their adult cellular counterpart, and only with respect to GBBHS-III-SS-620/50. On the other hand, 4 or 16 polymorphonuclear samples from newborns tested revealed significantly low bactericidal capacities against both GBBHS serotypes, and an additional sample revealed a bactericidal capacity against GBBHS-III-SS-620/50 alone. Interstrain variations in the intrinsic bactericidal capacity of polymorphonuclear phagocytes from newborns against GBBHS-III may exist, as suggested by a single observation made by using four clinical isolates of GBBHS-III. Such deviant phagocytic capacities of polymorphonuclear phagocytes from newborns may constitute an additional selective risk factor in the genesis of GBBHS sepsis of the newborn.

Antibody to group B Streptococcus type III in human sera measured by a mouse protection test

Antibody to group B Streptococcus type III (GBS-III) was measured in human plasma and sera by using a test which measures the ability to protect outbred albino mice from an intraperitoneal challenge of GBS-III calculated to be lethal to 90% of the mice (LD90 dose). Of three samples from three different lots of commercial human immune serum globulin, none were protective despite the presence of antibody to the native type III polysaccharide. Nine specimens were tested from recipients of multivalent pneumococcal vaccine, and none were protective. Five specimens were tested from recipients of GBS-III polysaccharide vaccines who had responded with greater than 50 micrograms of specific antibody per ml in the blood. All of these were protective and could be diluted to titers of 1:10 to 1:40. Of two prevaccination sera with low levels of specific antibody, neither was protective. An unexpected finding which may limit the sensitivity of the mouse protection assay was that the human immune serum globulin and human serum with a very low level of antibody appeared to increase the lethality of the GBS-III test strain, resulting in LD50 values reduced to 0.01 of the usual LD50.

Effects of route and time of administration of antiserum on protection of mice from lethal infection due to group B Streptococcus type III

The present study examines a mouse model of infection due to group B Streptococcus serotype III (GBS-III) as to the route and timing of antiserum administration for protection and quantitation of bacteremia with and without antiserum. Data for these parameters are contrasted with those after challenge with serotype Ia of group B Streptococcus (GBS-Ia). An intraperitoneal injection of GBS organisms and protective antiserum from a single syringe can be used to create an animal model of disease. Intraperitoneal injection of GBS-III resulted in bacteremia at 0.5 h both in animals who did not receive antiserum (17.4 X 10(2) +/- 7.6 X 10(2) colony-forming units per ml of blood samples) and in animals who received antiserum (19.3 X 10(1) +/- 6.8 X 10(1) colony-forming units per ml). Although intraperitoneal injection of GBS-Ia also resulted in bacteremia evident by 0.5 h in unprotected animals (30.1 X 10(2) +/- 3.8 X 10(2) colony-forming units per ml), no bacteremia occurred in protected recipients of this organism. Bacteremia due to GBS-Ia and GBS-III logarithmically increased until at least 7 h. Bacteremia due to GBS-III in protected animals was cleared by 24 h. Protection against GBS disease did not require simultaneous or proximate administration of the organism and the antiserum. Mice could be protected from death after intraperitoneal challenge with GBS-III or GBS-Ia by antiserum administered intravenously or intraperitoneally from 6 h before to 2.5 h after challenge.

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

We studied the influence of preimmunization antibody level on the immune response of adults to one of two structurally related yet immunologically distinct type-specific polysaccharides from Type III Group B streptococcus and Type 14 pneumonococcus. Four weeks after immunization with multivalent pneumococcal vaccine, 20 subjects with low levels of antibody to Type III Group B streptococcus antigen had no significant increase in antibody to this antigen (P greater than 0.05), but all volunteers with moderate to high preimmunization antibody levels who were immunized with Pneumovax had significant increases (P less than 0.01). However, the streptococcal antibody response to pneumococcal Type 14 antigen was weaker and briefer than that in 10 adults given Type III Group B streptococcus vaccine(P less than 0.05). Preimmunization antibody levels influenced the immune response to a structurally similar polysaccharide antigen, but specific Type III polysaccharide antigen appeared necessary to induce a primary antibody response in "nonimmune" adults. We conclude that immunization of mothers with pneumococcal vaccine is not likely to prevent neonatal Type III Group B streptococcal infection, despite immunologic similarities between the two organisms.

Prevalence of type-specific group B streptococcal antibody in pregnant women

Immunoglobulin G antibody against the four major serotypes of group B streptococcus was measured by indirect immunofluorescence in the sera of 200 consecutive pregnant women seen in the obstetric screening clinic of an urban teaching hospital. Antibody was detectable in 26% of undiluted sera against serotype Ia, 52% against serotype Ib, 82% against serotype II, and 45% against serotype III. Only 9% had antibody against all four GBS types. When serotype-specific antibody prevalences in 108 women with GBS vaginal colonization were compared with prevalences in noncolonized women, only women colonized with GBS type Ia were more likely to have antibody against Ia than noncolonized women. Antibody prevalences in sera from 54 mothers whose infants developed invasive GBS disease were significantly lower than those in colonized or noncolonized women. Since low titers of IF antibody to GBS III were present in some sera from mothers of infected infants, the data were analyzed based on IF antibody titers associated with passive protection in a chick embryo model of GBS septicemia. None of the sera from mothers of infected infants had antibody levels associated with chick embryo protection. Less than 10% of women had titers associated with chick embryo protection. These data suggest that the majority of pregnant women lack immunity to GBS, regardless of colonization status.

The role of specific antibody in alternative complement pathway-mediated opsonophagocytosis of type III, group B Streptococcus

The native capsular polysaccharide antigen of type III, group B Streptococcus contains a terminal sialic acid residue on each repeating unit that masks all end-group galactopyranose residues and prevents alternative pathway complement activation by adult human sera in the absence of type-specific antibody. The critical role of the sialic acid residues in allowing the organism to evade activating the alternative complement pathway was shown when neuraminidase treatment of the organism converted the bacteria to activators of the alternative pathway as assessed in agammaglobulinemic serum. The requirement for specific antibody in permitting alternative pathway activation by the fully sialated bacteria was shown when sera that contained low levels of specific antibody failed to activate this pathway, and when prior absorption of serum that contained higher type-specific antibody levels with the capsular antigen failed to activate this pathway. The use of C2-deficient sera showed that the calssical pathway was not required for antibody-dependent alternative pathway activation. The use of isotonic, pH 7.5, veronal-NaCl buffer that contained 1% gelatin and that was supplemented to 4 mM Mg++ and 16 mM EGTA and adjusted to pH 7.5 (MgEGTA) ruled out the participation of the C1-bypass pathway. The presence of sialic acid on the bacterial surface is one means of evading an important mechanism of natural immunity, namely activation of complement by the alternative pathway. Only specific antibody, i.e., acquired immunity, can overcome this virulence factor.

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

An investigation of the prevalence and persistence of the concentration of antibody to capsular polysaccharide from type III, group B Streptococcus in sera from 93 pregnant women and their newborn infants is reported. In the majority of women, the concentrations of antibody detected in the sera were low (less than 1 microgram/ml). However, sera from women who were colonized with type III strains of group B streptococci contained significantly higher concentrations of antibody than those from noncolonized women (p = 0.027). No appreciable change in antibody concentration was found in sera collected early in gestation when compared to delivery sera. When maternal-cord serum pairs were analyzed, a significant correlation between concentrations of antibody was found, which indicates that this antibody is transplacentally transferred.

Antibody levels in mothers colonised with group B streptococci during pregnancy and in their newborn infants, as measured by an enzyme linked immunosorbent assay

An enzyme-linked immunosorbent assay (ELISA) was developed to measure serum antibodies to group B streptococci in 20 healthy pregnant women before delivery and in their newborn infants. The sera from 10 of these women who were colonised with group B streptococci and umbilical cord sera from their infants, had higher levels of type-specific IgG antibody than the 10 non-colonised controls and their neonates. All the babies remained well. The results demonstrate that infants from colonised mothers receive type-specific antibody. The possibility that this antibody may provide some degree of protection at birth against this potentially lethal organism warrants investigation.

Enzyme-linked immunosorbent assay for group B streptococcal antibodies

We report here on the development of enzyme-linked immunosorbent assays (ELISAs) for antibodies to types II and III group B streptococci. Streptococcal antigens were prepared by trichloroacetic acid extraction and fractional alcohol precipitation. Microtiter wells were coated with antigen in 0.1 M carbonate buffer at pH 9.6. Lyophilization was found to be an essential step for efficient binding of the streptococcal antigens. After incubation with antibody-containing rabbit serum, bound antibody was detected with peroxidase-labeled goat anti-rabbit immunoglobulin G. Optimal antigen concentrations were 200 micrograms/ml for type II and 100 micrograms/ml for type III. An ELISA is also described that uses intact bacteria as antigen. Hyperimmune rabbit serum reacted at a titer in excess of 512 against trichloroacetic acid-soluble antigen and 4,096 against whole bacteria. Sera from human subjects were also tested. Most human sera contained antibody which bound to intact bacteria but not to trichloroacetic acid-solubilized streptococcal antigens. Antibody titers in human sera against intact bacteria correlated very well with opsonic antibody activity measured in a chemiluminescence assay.

Group B streptococcal infection: a review and update

The problems posed by the sudden increase in serious group B streptococcal disease among infants since the early 1970s are described and discussed. Virtually all offspring of colonised mothers harbour the organism and infection develops in about 1% of these infants. The mortality rate, even with immediate antibiotic treatment of early onset disease, is 30%; delay in treatment leads to much higher mortality. Late onset disease starting around the seventh to ninth day of life, but sometimes as late as the second month, is less frequently fatal. Preventive measures include active and passive immunisation or intravenous ampicillin during labour. Experimental evidence indicates that each of these methods gives protection.

Immunodeterminant specificity of human immunity to type III group B streptococcus

The type III polysaccharides of group B Streptococcus in its native state chemically consists of glucose, galactose, glucosamine, and sialic acid. The core of this polysaccharide lacks sialic acid and precipitates with type III antiserum to give a partial identity with the precipitate between the native antigen and this serum. The core determinant is immunochemically similar to the capsular polysaccharide of type XIV Streptococcus pneumoniae, while the native type III group B streptococcal polysaccharide does not cross-react with type XIV pneumococcal antiserum. In human sera, it is antibody directed to the native antigen which correlates very highly with opsonic immunity (r = 0.94) while a poorer correlation exists between antibody to the core antigen and opsonins (r = 0.51 P less than 0.001). In natural infections, as association exists between low levels of maternal antibody to the native antigen and risk of disease in the infant. This association is not true for antibody to the core structure, where both infected infants and their mothers have much higher levels of antibody to the core than the native antigens. Infected infants are also more likely to respond to infection by developing antibody to the native antigen. Immunization of 12 adults with multivalent pneumococcal polysaccharide induced significantly better antibody response to the core antigen than to the native, and this vaccine induced opsonic activity in only one recipient. Immunization of adults with type III group B streptococcal antigens induced antibody to the native determinant which correlated with opsonic activity. Therefore, it would appear that native group B streptococcal polysaccharides will provide the best candidate antigens for immunization.

Group B streptococcal colonization and antibody status in lower socioeconomic parturient women

This investigation was undertaken to determine the prevalence of group B streptococcal vaginal and throat colonization among lower socioeconomic pregnant women and the antibody concentration to the capsular polysaccharide antigen of type III group B streptococcus in their sera. Group B streptococci were recovered from 28.6 per cent of the 112 women studied; vaginal colonization was detected in 23.4 per cent, throat colonization in 4.7 per cent, and colonization at both sites in 0.9 per cent of the patients, respectively. Among these isolates of group B streptococci, serotypes III (39.5 per cent) and II (30.3 per cent) predominated. No differences were found between colonized and noncolonized women with respect to age, race, marital status, or parity. The majority of all women studied had low concentration of antibody in serum (less than 1.0 microgram per milliliter). However, women with isolation of type III group B streptococci from cultures at the time sera were collected had significantly higher concentrations than did women without group B streptococci from cultures at the time sera were collected had significantly higher concentrations than did women without group B streptococcal colonization.

An etiologic shift in infantile osteomyelitis: the emergence of the group B streptococcus

Twenty-one infants from six to 52 days of age (mean 23.3 days) with osteomyelitis were studied between 1965 and 1977. The etiologic agents were group B streptococcus (8), staphylococcus aureus (6), gramnegative bacilli (4), Streptococcus pneumoniae (1), and unknown (2). Patients with group B streptococcal osteomyelitis were characterized by an uncomplicated neonatal course, single bone involvement with a predilection for involvement of the proximal humerus, and lack of inflammatory signs. In contrast, patients with osteomyelitis due to other organisms frequently had had manipulative procedures predisposing to infection and were more likely to have multiple bone involvement, fever, and leukocytosis at the time of diagnosis. Functional impairment was detected in only one of 17 patients evaluated a mean of 36 months after diagnosis.

Association of elevated levels of extracellular neuraminidase with clinical isolates of type III group B streptococci

The level of total extracellular neuraminidase produced by 74 clinical isolates of group B streptococci isolated from diseased or asymptomatically colonized infants was assayed. Extracellular neuraminidase was obtained from concentrated filtrates of exponentially growing cultures of group B streptococci grown in a chemically defined medium (FMC) containing supplemental protein. The total activity of extracellular enzyme produced by these clinical isolates ranged from less than 10 to 360 nmol of sialic acid released per min per mg of cell dry weight. Strains were arbitrarily classified as either nonproducers (less than 10 nmol/min per mg of cell dry weight), low producers (greater than 10 to less than or equal 140 nmol/min per mg of cell dry weight), or high producers (greater than 140 to 360 nmol/min per mg of cell dry weight). Type III isolates from diseased infants were significantly more often classified as high producers than strains of group B streptococci of other serotypes from diseased infants (P less than 0.001). Furthermore, the serotype III strains isolated from neonatal infections were more often high producers than those of the same serotype from asymptomatically colonized infants (P less than 0.025). These results suggest that the ability to produce elevated levels of neuraminidase may be related to the frequent association of type III strains with disease among neonates.

Immunogenicity of polysaccharides from type III, group B Streptococcus

The immunogenicity and safety of two polysaccharides isolated from type III, group B Streptococcus, were tested in adults selected for existing low concentrations of natural antibody to the capsular polysaccharide of this organism. Both vaccine preparations (trichloroacetic acid and EDTA) were found to lack pyrogenicity and toxicity for experimental animals. A single 50-microgram subcutaneous injection of either polysaccharide in human subjects elicited significant increase in antibody concentration in immunized compared with control individuals receiving phosphate-buffered saline. Antibody responses were maximal by 2 wk and remained at 21 wk after immunization. Vaccine-induced antibody was primarily of the IgG class. Of the two vaccines, the larger molecular size polysaccharide was significantly more immunogenic. Although no systemic reactions were recorded, mild transient local reactions occurred in 45% of vaccinees.

Detection of group B streptococcal antibodies in human sera by radioimmunoassay: concentrations of type-specific antibodies in sera of adults and infants infected with group B streptococci

Current interest in determining the possible protective role of antibodies against group B streptococcal disease prompted this study of the feasibility of using a radioimmunoassay to measure type-specific immunity in humans. The radioimmunoassay was standardized as a quantitative test for antibodies against the carbohydrate (CHO) antigens of all five group B types. The data showed that the CHO antigens extracted by a cold trichloroacetic acid-sonification method measure more antibodies than do the corresponding CHO antigens extracted by hot hydrochloric acid; that the Ia CHOs extracted from two different types, Ia and Ic, measure the same quantity of Ia antibodies; and that human sera contain antibodies reactive with all five type-specific CHOs. No evidence of "protective" antibody was found in the serum samples studied, although there was evidence of and antibody response in adults to prolonged colonization by group B streptococci. The wide ranges of antibody concentration in a serum bank collection, the broad reactivity of all human sera tested, and the mixed populations of antibodies in human sera that react with different determinants on the same type-specific CHO antigen (type III) indicate that further studies must be done to better define normal and susceptible populations and to determine antigenic components important in protection.

Group B streptococcal long-chain reaction

The streptococcal long-chain reaction was adapted for the measurement of type-specific antibodies to group B beta-hemolytic streptococci (GBBHS). Rabbit antisera incubated with homologous but not heterologous GBBHS produced chains that were 18 to 33 times longer than chains produced by normal rabbit sera. The long chains were easily apparent, in most instances, by scanning the slides. Human sera with mouse protective and opsonic activity against GBBHS serotype Ia produced chains that were always significantly longer than those produced by incubation in nonimmune human sera. Absorption of rabbit or human sera with homologous but not heterologous organisms inhibited the capacity to induce the formation of long chains. The long-chain assay is a simple, rapid, and reproducible test that could constitute a valuable tool for the rapid identification of anti-GBBHS antibodies.