No apparent influence of immunoglobulins on indigenous oral and intestinal microbiota of mice

A lack of role for antibodies in regulating Helicobacter pylori colonization and associated gastritis

BACKGROUND

Helicobacter pylori occupy a unique niche, located within the mucus layer lining the stomach, and attached to the apical surface of the gastric epithelium. As such, antibodies would be expected to play a major role in regulating infection and/or pathogenesis. However, experiments using antibody-deficient mice to study gastric helicobacter infection have yielded inconsistent results, although some pointed toward antibodies increasing colonization levels and decreasing gastritis severity. The variability in these studies is possibly due to their use of nonmatched wild-type controls. This current study presents the first evaluation of the role of antibodies in H pylori infection by comparing antibody-deficient mice with matched wild-type siblings.

METHODS

Matched wild-type and antibody-deficient μMT mice were generated by heterozygous crossings. In two separate experiments, appropriately genotyped sibling littermates were infected with H pylori for 4 months and then sera and stomachs were collected.

RESULTS

There was no difference in H pylori colonization levels between infected μMT mice and sibling wild-type controls. Similarly, there was no significant difference in the severity of gastritis between these groups of mice, although there was a trend toward less severe gastritis in μMT mice which was supported by a significantly lower IFNγ (Th1) gastric cytokine response.

CONCLUSIONS

Comparing matched antibody-deficient and antibody-competent mice indicates that an antibody response does not influence H pylori colonization levels. Contrary to previous studies, these results suggest antibodies might have a minor pro-inflammatory effect by promoting gastric Th1 cytokines, although this did not translate to a significant effect on gastritis severity.

Handling stress may confound murine gut microbiota studies

BACKGROUND

Accumulating evidence indicates interactions between human milk composition, particularly sugars (human milk oligosaccharides or HMO), the gut microbiota of human infants, and behavioral effects. Some HMO secreted in human milk are unable to be endogenously digested by the human infant but are able to be metabolized by certain species of gut microbiota, including Bifidobacterium longum subsp. infantis (B. infantis), a species sensitive to host stress (Bailey & Coe, 2004). Exposure to gut bacteria like B. infantisduring critical neurodevelopment windows in early life appears to have behavioral consequences; however, environmental, physical, and social stress during this period can also have behavioral and microbial consequences. While rodent models are a useful method for determining causal relationships between HMO, gut microbiota, and behavior, murine studies of gut microbiota usually employ oral gavage, a technique stressful to the mouse. Our aim was to develop a less-invasive technique for HMO administration to remove the potential confound of gavage stress. Under the hypothesis that stress affects gut microbiota, particularly B. infantis, we predicted the pups receiving a prebiotic solution in a less-invasive manner would have the highest amount of Bifidobacteria in their gut.

METHODS

This study was designed to test two methods, active and passive, of solution administration to mice and the effects on their gut microbiome. Neonatal C57BL/6J mice housed in a specific-pathogen free facility received increasing doses of fructooligosaccharide (FOS) solution or deionized, distilled water. Gastrointestinal (GI) tracts were collected from five dams, six sires, and 41 pups over four time points. Seven fecal pellets from unhandled pups and two pellets from unhandled dams were also collected. Qualitative real-time polymerase chain reaction (qRT-PCR) was used to quantify and compare the amount of Bifidobacterium, Bacteroides, Bacteroidetes, and Firmicutes.

RESULTS

Our results demonstrate a significant difference between the amount of Firmicutes in pups receiving water passively and those receiving FOS actively (p-value = 0.009). Additionally, we found significant differences between the fecal microbiota from handled and non-handled mouse pups.

DISCUSSION

From our results, we conclude even handling pups for experimental purposes, without gavage, may induce enough stress to alter the murine gut microbiota profile. We suggest further studies to examine potential stress effects on gut microbiota caused by experimental techniques. Stress from experimental techniques may need to be accounted for in future gut microbiota studies.

Regulation of the gut microbiota by the mucosal immune system in mice

The benefits of commensal bacteria to the health of the host have been well documented, such as providing stimulation to potentiate host immune responses, generation of useful metabolites, and direct competition with pathogens. However, the ability of the host immune system to control the microbiota remains less well understood. Recent microbiota analyses in mouse models have revealed detailed structures and diversities of microbiota at different sites of the digestive tract in mouse populations. The contradictory findings of previous studies on the role of host immune responses in overall microbiota composition are likely attributable to the high β-diversity in mouse populations as well as technical limitations of the methods to analyze microbiota. The host employs multiple systems to strictly regulate their interactions with the microbiota. A spatial segregation between the host and microbiota is achieved with the mucosal epithelium, which is further fortified with a mucus layer on the luminal side and Paneth cells that produce antimicrobial peptides. When commensal bacteria or pathogens breach the epithelial barrier and translocate to peripheral tissues, the host immune system is activated to eliminate them. Defective segregation and tissue elimination of commensals result in exaggerated inflammatory responses and possibly death of the host. In this review, we discuss the current understanding of mouse microbiota, its common features with human microbiota, the technologies utilized to analyze microbiota, and finally the challenges faced to delineate the role of host immune responses in the composition of the luminal microbiota.

The analysis of oral microbial communities of wild-type and toll-like receptor 2-deficient mice using a 454 GS FLX Titanium pyrosequencer

Background

Although mice have long served as an animal model for periodontitis, information on the composition of their indigenous oral microbiota is limited. The aim of the current study was to characterize mouse oral bacterial flora by applying extensive parallel pyrosequencing using the latest model pyrosequencer, a Roche/454 Genome Sequencer FLX Titanium. In addition, the effect of Toll-like receptor (TLR) 2 deficiency on oral microbiota was evaluated.

Results

Eight oral bacterial communities of wild-type (n = 4) and TLR2 knock-out (n = 4) C57BL/6 mice were characterized by analyzing 80,046 reads of 16S rRNA genes obtained by pyrosequencing. Excluding the PCR primers, the average length of each sequencing product was 443 bp. The average species richness of the murine oral bacterial communities was estimated to be about 200, but the communities were dominated by only two main phyla and several species. Therefore, the bacterial communities were relatively simple. The bacterial composition of the murine oral microbiota was significantly different from that of humans, and the lack of TLR2 had a negligible effect on the murine oral microbiota.

Conclusion

Pyrosequencing using the Roche/454 FLX Titanium successfully characterized mouse oral bacterial communities. The relatively simple oral bacterial communities of mice were not affected by TLR2 deficiency. These findings will provide a basis for future studies on the role of periodontal pathogens in the murine model of periodontitis.

Maternal adaptive immunity influences the intestinal microflora of suckling mice

The microflorae in the intestine of breast-fed infants are distinct from those that typically populate the intestine of formula-fed infants. Although the acquisition of passive immunity through breast-feeding may play a critical role in influencing the pattern of bacterial colonization of the gut, the precise mechanisms underlying the differences in the commensal microflorae of breast and formula-fed children have not been established. We hypothesized that the assemblage of commensal microflorae in suckling and weaned mice may be influenced by the maternal adaptive immune system. To test this hypothesis, we analyzed the intestinal microflorae of mice reared in the presence (wild-type) or absence of an intact maternal immune system (T- and B-cell deficient). Several types of bacteria (Lactobacillus, Enterococcus, Clostridium perfringens, Bifidobacterium, and Bacteroides) were isolated and enumerated from both the small and large intestine of 10-, 18-, 25- and 40- to 60-d old mice using selective media. The densities of bacteria were significantly lower in the small intestine of weaned mice that were reared by wild-type (WT) compared with immunodeficient (ID) dams. However, the microflorae were generally more abundant in the large intestine of suckling pups reared by WT compared with ID dams. Our results indicate that intestinal microflorae change throughout the suckling phase of development and that the maternal adaptive immune system influences the pattern and abundance of bacteria within the gut in an age- and site-specific manner.

Intestinal adherent bacteria and bacterial translocation in breast-fed and formula-fed rats in relation to susceptibility to infection

The barrier function of the intestinal mucosa is immature in the newborn mammal, and is strengthened by breast milk. We investigated this effect of breast milk by comparing the susceptibility to infection assessed in terms of adherent bacterial colonization of the intestinal tissue (AdC) and bacterial translocation (BT) between breast-fed and formula-fed newborn rats. Three-day-old rat pups were assigned to one of three groups: mother-reared (MR), pseudo-cannulated (sham), and artificially reared (AR). AR rats were infused with formula through an intragastric cannula, under the control of a computer-regulated pumping machine. MR and sham rat pups were reared with their respective dams and received breast milk until weaning in a specially designed cage. In 10-d-old rats, there was no significant difference in the fecal or cecal flora between the AR and MR groups, whereas the AdC and the BT to the liver were greater in the AR than MR group. Enterobacteriaceae, Streptococcus and/or Enterococcus, and Staphylococcus were dominantly detected as microorganisms in AdC flora and BT. The AdC flora did not directly reflect the bacterial colonization flora. These findings suggest that AR rat pups mature normally, although there is a greater colonization of Enterobacteriaceae and BT in AR than MR pups. Consequently, the intestinal barrier function of the pups reared by artificial feeding may become susceptible to BT, and AdC may be more indicative than bacterial colonization of the susceptibility to BT.

Secretory antibodies do not affect the composition of the bacterial microbiota in the terminal ileum of 10-week-old mice

Terminal restriction fragment length polymorphism (T-RFLP) analysis was conducted on the 16S rRNA genes of the bacterial communities colonizing the epithelial surfaces of the terminal ilea of open conventionally housed mice in an institutional small-animal facility. Polymeric-immunoglobulin-receptor-deficient (pIgR(-/-)) mice that were unable to secrete antibodies across mucosal surfaces were cohoused with normal and otherwise genetically identical wild-type (C57BL/6) mice for 4 weeks. If secretory antibodies played a role in modeling the gastrointestinal microbiota, C57BL/6 mice would have had a more distinct and uniform microbiota than their pIgR(-/-) cage mates. The T-RFLP profiles of the bacterial communities were compared by using Sorensen's pairwise similarity coefficient, a newly developed weighted pairwise similarity coefficient, and on the basis of Shannon's and Simpson's diversity indices. No systematic differences were observed between the dominant components of the mucosa-associated bacterial communities of the terminal ileal walls of the two types of mice, indicating that secretory antibodies do not control the composition of this microbiota. Similar analyses of experiments conducted at two different times, between which the bacterial community composition of the mouse colony in the small-animal facility appeared to have changed, showed that differences could have been detected, had they existed.

Engineering the microflora to vaccinate the mucosa: serum immunoglobulin G responses and activated draining cervical lymph nodes following mucosal application of tetanus toxin fragment C-expressing lactobacilli

The delivery of antigens to mucosal-associated lymphoid tissues in paediatric and immunocompromised populations by safe, non-invasive vectors, such as commensal lactobacilli, represents a crucial improvement to prevailing vaccination options. In this report, we describe the oral and nasal immunization of mice with vaccines constructed through an original system for heterologous gene expression in Lactobacillus in which the 50 000-molecular weight (MW) fragment C of tetanus toxin (TTFC) is expressed either as an intracellular or a surface-exposed protein. Our data indicate that L. plantarum is more effective in this respect than L. casei and that, under the experimental conditions investigated, delivery of TTFC expressed as an intracellular antigen is more effective than cell-surface expression. Immunization of mice with live recombinant lactobacilli induced significant levels of circulating TTFC-specific immunoglobulin G (IgG) following nasal or oral delivery of vaccine strains. In addition, following nasal delivery, secretory immunoglobulin A (sIgA) was induced in bronchoalveolar lavage fluids, as were antigen-specific antibody-secreting cells and antigen-specific T-cell activation in draining lymph nodes, substantiating their potential for safe mucosal delivery of paediatric vaccines.

Characterization of the mucosal immune response in breast milk after peroral immunization of chimpanzees (Pan troglodytes) with Streptococcus mutans

The characteristics of the mucosal immune response to Streptococcus mutans cells, antigen A, antigen B, glucosyltransferases and glucan-binding proteins were examined in four pregnant chimpanzees that had been immunized perorally with Strep. mutans. Six pregnant chimpanzees served as non-immunized controls. None of the chimpanzees harbored S. mutans. Samples of milk were collected from all animals throughout the experiment. Peroral immunization resulted in an overall 17-fold median increase in SIgA in milk. Although SIgA1 comprised almost two-thirds of milk SIgA, Strep. mutans whole-cell antibody activity was contained predominantly in the SIgA2 subclass. The difference between the specific activities of anti-Strep. mutans SIgA1 and SIgA2 antibodies compared over time reached the borderline of statistical significance (p = 0.08). The avidity of anti-Strep. mutans antibodies was low in three of four chimpanzees and there was no evidence of affinity maturation. SIgA antibodies from the milk of all four immunized chimpanzees recognized antigen A. In three animals these antibodies were restricted to the SIgA1 subclass and, in one animal, anti-A antibodies were confined to SIgA2. Antibodies from all of the immunized chimpanzees recognized degradation products of antigen B in both the SIgA1 and the SIgA2 subclasses. Only two of four immunized chimpanzees responded to glucosyltransferases and these antibodies were restricted to the SIgA1 subclass. None of the chimpanzees responded to the 74-kDa glucan-binding protein. However, three animals produced SIgA1 antibodies against the 59-kDa glucan-binding protein and two of these also produced SIgA2 antibodies against this protein.

Gastrointestinal flora and its alterations in critical illness

The normal indigenous flora of the human gastrointestinal tract comprises a remarkably complex yet stable colony of more than 400 separate species, living in a symbiotic relationship with the human host. Stability of that flora is accomplished by multiple mechanisms including gastric acidity, gut motility, bile, products of immune cells in the gut epithelium, and competition between microorganisms for nutrients and intestinal binding sites. The indigenous flora influences multiple aspects of physiologic homeostasis and forms a key component of normal host defenses against infection by exogenous pathogens. Critical illness is associated with striking changes in patterns of microbial colonization, best described in the oropharynx and upper gastrointestinal tract. Pathological colonization occurs with the same species that is predominate in nosocomial infections, and descriptive studies suggest that such colonization is a risk factor for infection. Moreover, prophylactic measures that prevent pathological gut colonization in experimental circumstances reduce rates of nosocomial infection in critically ill patients and, in the case of selective decontamination of the digestive tract, reduce mortality risk. Conventional approaches to infectious diseases have conceptualized microorganisms as inimical and focused on eradicating them as rapidly and fully as possible. Insights from the study of critically ill patients suggest that that relationship is better understood as a symbiotic one and that preservation, rather than elimination, of the indigenous flora provides the greatest promise of clinical benefit to this vulnerable population.

Humoral immunity to commensal oral bacteria in human infants: salivary antibodies reactive with Actinomyces naeslundii genospecies 1 and 2 during colonization

The secretory immune response in saliva to colonization by Actinomyces naeslundii genospecies 1 and 2 was studied in 10 human infants from birth to 2 years of age. Actinomyces species were not recovered from the mouths of the infants until approximately 4 months after the eruption of teeth. However, low levels of secretory immunoglobulin A1 (SIgA1) and SIgA2 antibodies reactive with whole cells of A. naeslundii genospecies 1 and 2 were detected within the first month after birth. Although there was a fivefold increase in the concentration of SIgA between birth and age 2 years, there were no differences between the concentrations of SIgA1 and SIgA2 antibodies reactive with A. naeslundii genospecies 1 and 2 over this period. When the concentrations of SIgA1 and SIgA2 antibodies reactive with whole cells of A. naeslundii genospecies 1 and 2 were normalized to the concentrations of SIgA1 and SIgA2 in saliva, the A. naeslundii genospecies 1- and 2-reactive SIgA1 and SIgA2 antibodies showed a significant decrease from birth to 2 years of age. The fine specificities of A. naeslundii genospecies 1- and 2-reactive SIgA1 and SIgA2 antibodies were examined by Western blotting of envelope proteins. Similarities in the molecular masses of proteins recognized by SIgA1 and SIgA2 antibodies, both within and between subjects over time, were examined by cluster analysis and showed considerable variability. Taken overall, our data suggest that among the mechanisms Actinomyces species employ to persist in the oral cavity are the induction of a limited immune response and clonal replacement with strains differing in their antigen profiles.

Oral microbial ecology and the role of salivary immunoglobulin A

In the oral cavity, indigenous bacteria are often associated with two major oral diseases, caries and periodontal diseases. These diseases seem to appear following an imbalance in the oral resident microbiota, leading to the emergence of potentially pathogenic bacteria. To define the process involved in caries and periodontal diseases, it is necessary to understand the ecology of the oral cavity and to identify the factors responsible for the transition of the oral microbiota from a commensal to a pathogenic relationship with the host. The regulatory forces influencing the oral ecosystem can be divided into three major categories: host related, microbe related, and external factors. Among host factors, secretory immunoglobulin A (SIgA) constitutes the main specific immune defense mechanism in saliva and may play an important role in the homeostasis of the oral microbiota. Naturally occurring SIgA antibodies that are reactive against a variety of indigenous bacteria are detectable in saliva. These antibodies may control the oral microbiota by reducing the adherence of bacteria to the oral mucosa and teeth. It is thought that protection against bacterial etiologic agents of caries and periodontal diseases could be conferred by the induction of SIgA antibodies via the stimulation of the mucosal immune system. However, elucidation of the role of the SIgA immune system in controlling the oral indigenous microbiota is a prerequisite for the development of effective vaccines against these diseases. The role of SIgA antibodies in the acquisition and the regulation of the indigenous microbiota is still controversial. Our review discusses the importance of SIgA among the multiple factors that control the oral microbiota. It describes the oral ecosystems, the principal factors that may control the oral microbiota, a basic knowledge of the secretory immune system, the biological functions of SIgA, and, finally, experiments related to the role of SIgA in oral microbial ecology.