Role of Tumor Necrosis Factor Alpha, Interleukin-1β, and Interleukin-6 in a Mouse Model of Group B Streptococcal Arthritis

Intravenous inoculation of CD1 mice with 10(7) CFU of type IV group B Streptococcus (GBS IV) results in a high incidence of diffuse septic arthritis. In this study the roles of tumor necrosis factor alpha (TNF-alpha), interleukin-1beta (IL-1beta), and IL-6 in articular pathology were evaluated. Cytokine levels were quantified in the serum and joints by enzyme-linked immunosorbent assay in mice injected with GBS IV and tested or not tested with pentoxifylline (PTF), a methylxanthine that affects cytokine production. PTF was administered intraperitoneally at a dose of 1 mg/mouse (50 mg/kg of body weight) 1 h after GBS infection and then at 24-h intervals for 4 days. High levels of IL-1beta and IL-6, but not TNF-alpha, were detected in the joints of mice injected with GBS IV from 5 to 15 days after infection, when articular lesions were most frequent and severe. IL-1beta and IL-6 concentrations in the joints significantly (P < 0.001) exceeded those detected in the serum, confirming a strong local production. PTF treatment resulted in a strong reduction of cytokine production and in a marked decrease in both the incidence and severity of arthritis. Inoculation of exogenous murine recombinant IL-1beta or IL-6 in mice treated with GBS IV plus PTF resulted in an incidence and severity of articular lesions similar to those obtained with inoculation of GBS IV alone. No significant effect was obtained with TNF-alpha administration. These data show a strong involvement of IL-1beta and IL-6, but not TNF-alpha, in the pathogenesis of GBS arthritis.     

Regulatory role of interleukin-10 in experimental group B streptococcal arthritis

Intravenous inoculation of CD-1 mice with 10(7) CFU of type IV group B Streptococcus (GBS) results in a high incidence of diffuse septic arthritis, associated with high levels of systemic and local production of interleukin-1beta (IL-1beta) and IL-6. In this study, the role of the anti-inflammatory cytokine IL-10 in the evolution of GBS systemic infection and arthritis was evaluated. IL-10 production was evident in sera and joints of GBS-infected mice. Neutralization of endogenous IL-10 by administration of anti-IL-10 antibodies (1 mg/mouse) at the time of infection resulted in worsening of articular lesions and 60% mortality associated with early sustained production of IL-6, IL-1beta, and tumor necrosis factor alpha (TNF-alpha). The effect of IL-10 supplementation was assessed by administering IL-10 (100, 200, or 400 ng/mouse) once a day for 5 days, starting 1 h after infection. Treatment with IL-10 had a beneficial effect on GBS arthritis, and there was a clear-cut dose dependence. The decrease in pathology was associated with a significant reduction in IL-6, IL-1beta, and TNF-alpha production. Histological findings showed limited periarticular inflammation and a few-cell influx in the articular cavity of IL-10-treated mice, confirming clinical observations. In conclusion, this study provides further information concerning the role of IL-10 in regulating the immune response and inflammation and calls attention to the potential therapeutic use of IL-10 in GBS arthritis.     

Severity of group B streptococcal arthritis in selected strains of laboratory mice

The susceptibilities of C3H/HeN, BALB/c, and C57BL/6N mouse strains to group B streptococci (GBS) infection were evaluated. C3H/HeN mice developed severe polyarthitis; mild lesions and no lesions were observed in BALB/c and C57BL/6N mice, respectively. A correlation between the severity of arthritis, the number of GBS in the joints, and local interleukin-6 and interleukin-1beta production was evident.     

Adherence to, invasion by, and cytokine production in response to serotype VIII group B Streptococci

The adherence to and invasion of the human epithelial cell line A549 by group B streptococcus (GBS) serotype VIII strains were compared with those of serotype III strains by a conventional method and the dynamic in vitro attachment and invasion system. Twenty GBS strains, including nine vaginal isolates and one invasive isolate each of serotypes III and VIII, were used in the conventional attachment and invasion assay. Adherence to and invasion of A549 cells by serotype VIII GBS strains were significantly greater (P < 0.0001) than those by serotype III strains for both the invasive strain and vaginal isolates. Cytokine production by A549 cells following stimulation with GBS serotypes III and VIII or their purified capsular polysaccharides (CPS) was measured. Serotype III strains stimulated significantly greater tumor necrosis factor alpha (TNF-alpha) (P < 0.0001) and interleukin-10 (IL-10) (P < 0.05) production than did serotype VIII strains. IL-8 production in response to serotype VIII was significantly higher (P < 0.001) than that in response to serotype III. TNF-alpha, IL-8, and IL-10 production was greater in A549 cells infected with GBS than in the untreated control cells. TNF-alpha production was significantly greater (P < 0.005) after stimulation with purified GBS serotype III CPS than after stimulation with serotype VIII CPS, a result similar to that after stimulation with whole GBS. IL-12 production by A549 cells was observed only in response to infection with GBS serotype III, resulting in the possibility of a greater TH1 response in serotype III GBS. These results suggest differences in immune responses to infection with GBS serotypes III and VIII.     

Glucuronoxylomannan, the major capsular polysaccharide of Cryptococcus neoformans, inhibits the progression of group B streptococcal arthritis

Glucuronoxylomannan (GXM), the principal constituent of the Cryptococcus neoformans capsule, modulates the inflammatory response of human monocytes in vitro. Here we examine the efficacy of GXM as a novel anti-inflammatory compound for use against experimental septic arthritis. Arthritis was induced in mice by the intravenous injection of 8 x 10(6) CFU of type IV group B streptococcus (GBS). GXM was administered intravenously in different doses (50, 100, or 200 microg/mouse) 1 day before and 1 day after bacterial inoculation. GXM treatment markedly decreased the incidence and severity of articular lesions. Histological findings showed limited periarticular inflammation in the joints of GXM-treated mice, confirming the clinical observations. The amelioration of arthritis was associated with a significant reduction in the local production of interleukin-6 (IL-6), IL-1beta, macrophage inflammatory protein 1alpha (MIP-1alpha), and MIP-2 and an increase in systemic IL-10 levels. Moreover, peritoneal macrophages derived from GXM-treated mice and stimulated in vitro with heat-inactivated GBS showed a similar pattern of cytokine production. The present study provides evidence for the modulation of the inflammatory response by GXM in vivo and suggests a potential therapeutic use for this compound in pathologies involving inflammatory processes.     

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.     

Effects of fibronectin and group B streptococci on tumour necrosis factor-alpha production by human culture-derived macrophages.

Group B streptococci (GBS) are an important cause of sepsis and shock in the new-born. We have previously reported that GBS induce the production of tumour necrosis factor-alpha (TNF-alpha) by human monocytes and culture-derived macrophages. We have also shown that fibronectin (FN) promotes interaction between GBS and human phagocytes. In the present study, we investigated the effect of FN and GBS on the production of TNF-alpha by adult and neonatal culture-derived macrophages. We report that soluble FN alone was a strong stimulus for the production of TNF-alpha by culture-derived macrophages (FN 50 micrograms/ml = 623.33 +/- 47 pg/ml TNF, versus media alone 3 +/- 1.5 pg/ml; P < 0.0001). While GBS also induce the production of TNF-alpha by macrophages, the addition of FN to GBS had more than an additive effect on TNF-alpha levels. FN-mediated TNF-alpha production by macrophages was inhibited by both soluble arginine-glycine-aspartic acid (RGD) peptide (71%; P < 0.0001) and anti-beta 3-integrin monoclonal antibody 7G2 (54%; P < 0.0001). Neonatal culture-derived macrophages produced significantly more TNF-alpha in response to GBS (356.4 pg/ml +/- 27.7) than adult cells did (222.0 pg/ml +/- 21.0; P = 0.037), and dramatically more in response to FN alone (neonatal 1931.0 pg/ml +/- 23.0 versus adult 463.5 43.5 pg/ml; P < 0.0001). FN may contribute to the high levels of TNF-alpha production implicated in the pathophysiology of GBS sepsis and shock.     

Antibiotic resistance patterns of group B streptococci in pregnant women.

This study examined the antibiotic resistance patterns of group B streptococci (GBS) isolated from gravid women. A total of 156 vaginal and cervical isolates of GBS were examined for resistance to penicillin, ampicillin, clindamycin, cefoxitin, gentamicin, and erythromicin. No resistance to penicillin or ampicillin was found, nor was penicillinase production demonstrated. A high level of resistance to gentamicin was noted (91%). Of the isolates examined, 9, 9.5, and 15.3% exhibited either resistance or intermediate susceptibility to erythromycin, clindamycin, and cefoxitin, respectively. Thirty strains (19%) exhibited a multiple antibiotic resistance pattern. Given the high penicillin and ampicillin treatment failure rates when attempting to eradicate vaginal GBS colonization and our findings of higher and multiple drug resistance patterns of GBS, the selection of an alternative antibiotic regimen is of considerable clinical importance. We recommend that routine reporting of GBS susceptibilities by clinical laboratories be adopted.     

Impairment of type III group B Streptococcus-stimulated superoxide production and opsonophagocytosis by neutrophils in diabetes.

The effect of hyperglycemia upon susceptibility to bacterial infection in diabetes mellitus is incompletely elucidated. The present experiments assessed the effect of hyperglycemia upon neutrophil-mediated phagocytosis of type III group B Streptococcus (GBS). Type III GBS was chosen for study because the incidence of invasive GBS disease is substantially increased in type 2 diabetic compared with nondiabetic subjects. The hypothesis tested was that severe hyperglycemia would alter neutrophil metabolism by diverting NADPH from superoxide production into the aldose reductase-dependent polyol pathway that converts glucose into sorbitol and thus would impair opsonophagocytosis (OP) of type III GBS. Neutrophils from 10 adults with type 2 diabetes had no intrinsic phagocytic defect under baseline glycemic conditions. After equilibration in 60 or 120 mM glucose or in 60 mM choline chloride, OP activity was reduced significantly (P < or = 0.03). Neutrophil superoxide production correlated with glucose concentration and also was significantly reduced during hyperglycemia (P < 0.05). Addition of III GBS capsular polysaccharide-specific IgG in a sufficient concentration supported efficient OP, even during hyperglycemia. Alrestatin, an aldose reductase inhibitor, increased superoxide production and significantly improved OP of type III GBS (P = 0.03). Thus, diversion of NADPH into the polyol pathway is one mechanism by which OP of GBS III is impaired during hyperglycemia, and this effect is mitigated when levels of capsular polysaccharide-specific IgG are sufficient.     

Characterization of host immunity during persistent vaginal colonization by Group B Streptococcus

Streptococcus agalactiae (Group B Streptococcus, GBS) is a Gram-positive bacterium, which colonizes the vaginal tract in 10–30% of women. Colonization is transient in nature, and little is known about the host and bacterial factors controlling GBS persistence. Gaining insight into these factors is essential for developing therapeutics to limit maternal GBS carriage and prevent transmission to the susceptible newborn. In this work, we have used human cervical and vaginal epithelial cells, and our established mouse model of GBS vaginal colonization, to characterize key host factors that respond during GBS colonization. We identify a GBS strain that persists beyond a month in the murine vagina, whereas other strains are more readily cleared. Correspondingly, we have detected differential cytokine production in human cell lines after challenge with the persistent strain vs. other GBS strains. We also demonstrate that the persistent strain more readily invades cervical cells compared with vaginal cells, suggesting that GBS may potentially use the cervix as a reservoir to establish long-term colonization. Furthermore, we have identified interleukin-17 production in response to long-term colonization, which is associated with eventual clearance of GBS. We conclude that both GBS strain differences and concurrent host immune responses are crucial in modulating vaginal colonization.     

Seroprevalence of campylobacteriosis and relevant post-infectious sequelae

Post-infectious sequelea such as Guillain Barré syndrome (GBS), reactive arthritis (RA), and inflammatory bowel disease (IBD) may arise as a consequence of acute Campylobacter-enteritis (AE). However, reliable seroprevalence data of Campylobacter-associated sequelae has not been established. The objectives of this study were, first, to identify the most specific and sensitive test antigen in an optimized ELISA assay for diagnosing a previous Campylobacter-infection and, second, to compare the prevalence of anti-Campylobacter antibodies in cohorts of healthy blood donors (BD), AE, GBS, RA, and IBD patients with antibodies against known GBS, RA and IBD triggering pathogens. Optimized ELISAs of single and combined Campylobacter-proteins OMP18 and P39 as antigens were prepared and sera from AE, GBS, RA and IBD patients and BD were tested for Campylobcter-specific IgA and IgG antibodies. The results were compared with MIKROGEN?-recomLine Campylobacter IgA/IgG and whole cell lysate-immunoblot. Antibodies specific for Helicobacter pylori, Mycoplasma pneumoniae, Yersinia enterocolitica, and Borrelia afzelii were tested with commercial immunoblots. ROC plot analysis revealed AUC maxima in the combination of OMP18 and P39 for IgA and in the P39-antigen for IgG. As a result, 34–49 % GBS cases, 44–62 % RA cases and 23–40 % IBD cases were associated with Campylobacter-infection. These data show that Campylobcater-seropositivity in these patient groups is significantly higher than other triggering pathogens suggesting that it plays an important role in development of GBS and RA, and supports the hypothesis that recurrent acute campylobacteriosis triggers IBD.     

Intracellular and extracellular cytokine production by human mixed mononuclear cells in response to group B streptococci

Group B streptococci (GBS) are a major cause of severe infection in newborns, pregnant females, and other immunocompromised hosts. Infection often includes septicemia, shock, pneumonia, and respiratory failure. In previous studies, we have reported that GBS induce marked production of tumor necrosis factor alpha (TNF-alpha) by human mononuclear cells. The present study was designed to measure the production of TNF-alpha as well as additional cytokines, including interleukin 1beta (IL-1beta), IL-6, IL-8, IL-12, and gamma interferon (IFN-gamma) but also to determine from what cells and at what time point during incubation with GBS that these cytokines are produced. Mixed mononuclear cells were incubated with heat-killed GBS, media alone, or 1 microg of Escherichia coli lipopolysaccharide (LPS). Brefeldin A was added to each sample prior to staining, which prevented the export of cytokines by the Golgi apparatus. The cells were then stained with the appropriate conjugated antibodies and analyzed by using a flow cytometer. Results indicate that intracellular cytokines appear, in almost all cases, simultaneous to or before secreted proteins are detected. In contrast to the response to LPS, where TNF-alpha, IL-1beta, IL-6, and IL-8 appear almost simultaneously, the human monocyte response to GBS results in the production of TNF-alpha but delayed appearance of IL-1beta, IL-6, and IL-8. The lymphocyte response to GBS was also strikingly different from that to LPS in that both secreted IFN-gamma and IL-12 was detected, while LPS failed to induce production of these critical cytokines. This suggests an important role for TNF-alpha, IFN-gamma, and IL-12 in GBS pathogenesis and/or immunity.     

A Role for Interferon- β in Guillain-Barré Syndrome?

Guillain-Barré syndrome (GBS) is an acute inflammatory demyelinating neuropathy that is associated with long-lasting morbidity and a substantial risk of mortality. The 2 reference treatments, plasma exchange and intravenous immunoglobulins (IVIg), do not change the functional prognosis for the most severely ill patients. The pathogenesis of GBS involves humoral and cellular immune dysfunctions that have only recently been characterised. Antibodies to nerve antigens may participate in complement activation, antibody-dependent macrophage cytotoxicity and reversible conduction failure. The cellular immune reaction is associated with increases in pro-inflammatory cytokines [such as tumour necrosis factor-alpha (TNFalpha)] and matrix metalloproteinases (MMPs; e.g. MMP-9), and a decrease in anti-inflammatory cytokines [such as transforming growth factor-beta1 (TGFbeta1)]. All the changes favour adhesion to and transmigration across the endothelium of immune cells, a key phenomenon associated with GBS. Recovery from GBS is characterised by the normalisation of these changes. Experimental allergic neuritis (EAN), the experimental model of GBS, has strikingly similar immunological characteristics. The usual treatment options for patients with GBS (plasma exchange and IVIg) mainly target the humoral component of the immune response. Interferon-beta (IFNbeta) is a cellular immunomodulator that inhibits antigen presentation and TNFalpha production and binding, and modulates macrophage properties. IFNbeta increases anti-inflammatory T cell functions and the production of anti-inflammatory cytokines, such as TGFbeta1. IFNbeta has important effects on leukodiapedesis, caused by modulating the expression of cell adhesion molecules and the MMP-9 proteinases. It has been used with success in EAN, in some patients with acute exacerbation of chronic inflammatory demyelinating polyneuropathy, and in 1 patient with GBS. The pathophysiology of patients with GBS, an understanding of IFNbeta properties and results of experimental studies support the investigation of IFNbeta in trials of patients with GBS.     

Group B streptococcus-induced nitric oxide production in murine macrophages is CR3 (CD11b/CD18) dependent.

Nitric oxide (NO) is produced by murine macrophages in response to cytokines and/or gram-negative bacterial lipopolysaccharide. NO induction by gram-positive bacteria such as group B streptococci (GBS), the major etiologic agents of neonatal pneumonia and meningitis, has received little study. GBS as well as two other gram-positive bacterial species, Staphylococcus aureus and Staphylococcus epidermidis, were found to stimulate NO production in thioglycolate-elicited murine macrophages and in the mouse macrophage cell line J774A.1 in the presence of gamma interferon. Serotype Ia and III GBS were both stimulatory, as were asialo- and type antigen-deficient mutant strains of type III GBS. NO production was dose dependent, inhibitable by L-arginine analogs, and unaffected by polymyxin B. Since phagocytosis by murine and human phagocytes of GBS is dependent on complement receptor type 3 (CR3), the role of CR3 in the NO response to GBS was tested in the CR3-deficient myelomonocytic cell line WEHI-3. GBS did not induce NO, whereas S. aureus or lipopolysaccharide did induce NO in WEHI-3 cells. S. epidermidis, whose nonopsonic phagocytosis is also CR3 dependent, failed to induce NO in WEHI-3 cells. Monoclonal anti-CR3 (anti-CD11b or anti-CD18) in the presence of interferon also induced NO production in thioglycolate-elicited macrophages and in J774A.1 cells but not in WEHI-3 cells. This evidence suggests that ligated CR3 and gamma interferon act synergistically to induce NO production and that CR3 mediates the GBS-induced signal for NO production in interferon-treated macrophages.     

Validation of an ELISA for the diagnosis of recent Campylobacter infections in Guillain–Barré and reactive arthritis patients

Weeks or months following Campylobacter infection, a small proportion of infected individuals develop Guillain-Barré syndrome (GBS) or reactive arthritis (ReA). Stool culture for Campylobacter is often negative in these patients, and serology is therefore the method of choice for diagnosing a recent infection with Campylobacter. This study developed a capture ELISA system to detect anti-Campylobacter IgA and IgM antibodies indicative of a recent infection. The sensitivity of the assay was 82.0% in uncomplicated Campylobacter enteritis patients, 96.2% in GBS patients who were culture-positive for Campylobacter, and 93.1% in culture-positive ReA patients, with a specificity of 93.0%. The assay allows identification of Campylobacter infection in patients with post-infectious neurological and rheumatological complications.     

Induction of tumor necrosis factor alpha by the group- and type-specific polysaccharides from type III group B streptococci.

Previous studies suggested that circulating tumor necrosis factor alpha (TNF-alpha) may have a pathophysiologic role in experimental neonatal sepsis induced by group B streptococci (GBS). This study was undertaken to investigate the ability of the type III and group-specific polysaccharides of GBS to induce TNF-alpha production and TNF-alpha-dependent lethality in neonatal rats. The cytokine was detected in plasma samples by the L929 cytotoxicity assay. Intracardiac injections of either polysaccharide induced dose-dependent, transient elevations in plasma TNF-alpha levels that returned to baseline values after 5 h. The group-specific antigen induced significantly higher mean peak TNF-alpha levels than the type III antigen (125 +/- 47 versus 44 +/- 15 U/ml with 70 mg/kg of body weight). Glycogen (70 mg/kg), used as a negative control, did not induce TNF-alpha. The lipopolysaccharide-neutralizing agent polymyxin B did not decrease TNF-alpha levels induced by either polysaccharide, ruling out contamination with endotoxin as a possible cause of TNF-alpha induction. Fifty percent lethal doses of the type III and group-specific antigens given as intracardiac injections were 105 and 16 mg/kg, respectively. Salmonella endotoxin, used as a positive control, had a 50% lethal dose of 0.1 mg/kg. The lethal activities of GBS polysaccharides, as well as endotoxin, were completely prevented by pretreatment of neonatal rats with the respective specific antibodies or anti-murine TNF-alpha serum. To assess the relative importance of the type-specific substance in TNF-alpha induction by whole bacteria, two unrelated GBS transposon mutants devoid of only the type-specific capsular polysaccharide (COH1-13 and COH31-15) were employed. Each of the heat-killed unencapsulated mutants was able to produce plasma TNF-alpha level elevations or TNF-alpha-dependent lethality but was significantly less efficient in these activities than the corresponding encapsulated wild-type strain. These data suggest that the presence of type-specific material on GBS is not necessary for the stimulation of TNF-alpha production. Type III capsular polysaccharide, however, can significantly increase the ability of GBS to induce TNF-alpha. Further studies will be needed to assess the importance of TNF-alpha induction by the group- and type-specific antigens in the pathophysiology of GBS disease.     

Induction of cyclooxygenase-2 by human monocytes exposed to group B streptococci

Group B streptococcal (GBS) infections are associated with high morbidity and mortality. The molecular pathways mediating the pathophysiological events in GBS infection are not fully delineated. Cyclooxygenases (COX) are the enzymes that convert arachidonate to active eicosanoids. To identify the effects of GBS on eicosanoid metabolism and regulatory mechanisms, we exposed human monocytes to GBS and found that they secreted prostaglandin E2, prostacyclin, and thromboxane A2. Exposure to GBS caused monocytes to express COX-2 mRNA and protein in both a time- and concentration-dependent manner that correlated with eicosanoid production. COX-1 protein was unchanged. Addition of the anti-inflammatory cytokines interleukin (IL)-4 or IL-10 markedly attenuated GBS-induced COX-2 protein accumulation after GBS exposure, as did inhibition of p38 MAPK. Our experiments are the first to show that exposure of monocytes to a gram-positive bacterium (GBS) results in induction of functional COX-2, suggesting that eicosanoids may play important roles in the pathogenesis of GBS infections.     

Seroprevalence of antibodies to group B streptococcal polysaccharides in Gambian mothers and their newborns.

In developing countries, little is known about the relationship between group B streptococcal (GBS) colonization in pregnant women and serum antibody levels to capsular polysaccharide antigens of these organisms. This study examined the prevalence of antibodies to two polysaccharides of GBS, Ia and III, in 124 Gambian women with known GBS colonization at delivery and their newborns. Mean antibody levels in maternal-cord serum pairs were 4.06 +/- 0.25 micrograms/mL and 2.64 +/- 0.20 micrograms/mL for type Ia GBS, and 1.1 +/- 0.52 microgram/mL and 0.78 +/- 0.43 microgram/mL for type III GBS. Women colonized with type V GBS had significantly higher antibody levels to type III GBS than did noncolonized women, but no difference was found when these groups were compared for antibody levels to type Ia GBS. Women > or = 20 years had significantly higher antibody levels to type III GBS compared with younger women and those colonized by other GBS serotypes. Maternal antibodies to types la and III GBS were transferred across the placenta to newborns. The rarity of GBS disease in Gambia and other developing countries may be due to the prevalence of maternally derived GBS antibodies, the low prevalence of colonization with serotype III strains, or other undefined factors.     

Deficiency of mannose-binding lectin greatly increases antibody response in a mouse model of vaccination

Mannose-binding lectin (MBL), a pattern recognition innate immune molecule, selectively binds distinct chemical patterns, including carbohydrates expressed on Group B streptococcus (GBS). MBL interacts with IgM, resulting in the activation of MBL-associated serine proteases (MASPs), thus is initiating a lectin complement pathway. Complement proteins and IgM modulate production of antigen specific antibody. In this study, we investigated the relative effect of MBL in antibody response against tetanus toxoid-conjugated GBS polysaccharide vaccines (GBS PS-TT) by comparing wild type and null mice for MBL, complement 3 (C3), IgM, MBL/C3, and MBL/IgM. We found that GBS PS specific IgG response was upregulated in MBL deficient mice following immunization with GBS PS-TT but not GBS PS. B1 cells were expanded in peritonium but not in spleen of MBL null mice. The mechanisms of heightened IgG response in MBL null mice were related to C3, and share the same pathway with IgM.     

The enhancement of biofilm formation in Group B streptococcal isolates at vaginal pH

Group B streptococcus (GBS) is a common asymptomatic colonizer in acidic vagina of pregnant women and can transmit to newborns, causing neonatal pneumonia and meningitis. Biofilm formation is often associated with bacterial colonization and pathogenesis. Little is known about GBS biofilm and the effect of environmental stimuli on their growth along with biofilm formation. The objective of this study was to investigate the survival and biofilm formation of GBS, isolated from pregnant women, in nutrient-limited medium under various pH conditions. Growth and survival experiments were determined by optical density and viable counts. Crystal violet staining, scanning electron microscopy, and atomic force microscopy (AFM) were used to analyze the capacity of biofilm production. Our results showed that GBS isolates proliferated with increasing pH with highest maximum specific growth rate (μ_max) at pH 6.5, but survived at pH 4.5 for longer than 48 h. Biofilm formation of the 80 GBS isolates at pH 4.5 was significantly higher than at pH 7.0. This difference was confirmed by two other methods. The low elastic modulus obtained from samples at pH 4.5 by AFM revealed the softness of biofilm; in contrast, little or no biofilm was measured at pH 7.0. Under acidic pH, the capability of biofilm formation of serotypes III and V showed statistically significant difference from serotypes Ia and Ib. Our finding suggested that survival and enhanced biofilm formation at vaginal pH are potentially advantageous for GBS in colonizing vagina and increase the risk of vaginosis and neonatal infection.