Pioneer oral streptococci produce immunoglobulin A1 protease

The complement system as a key modulator of the oral microbiome in health and disease

In this review, we address the interplay between the complement system and host microbiomes in health and disease, focussing on oral bacteria known to contribute to homeostasis or to promote dysbiosis associated with dental caries and periodontal diseases. Host proteins modulating complement activities in the oral environment and expression profiles of complement proteins in oral tissues were described. In addition, we highlight a sub-set of bacterial proteins involved in complement evasion and/or dysregulation previously characterized in pathogenic species (or strains), but further conserved among prototypical commensal species of the oral microbiome. Potential roles of these proteins in host-microbiome homeostasis and in the emergence of commensal strain lineages with increased virulence were also addressed. Finally, we provide examples of how commensal bacteria might exploit the complement system in competitive or cooperative interactions within the complex microbial communities of oral biofilms. These issues highlight the need for studies investigating the effects of the complement system on bacterial behaviour and competitiveness during their complex interactions within oral and extra-oral host sites.

Diurnal and eating-associated microbial patterns revealed via high-frequency saliva sampling

The oral microbiome is linked to oral and systemic health, but its fluctuation under frequent daily activities remains elusive. Here, we sampled saliva at 10- to 60-min intervals to track the high-resolution microbiome dynamics during the course of human activities. This dense time series data showed that eating activity markedly perturbed the salivary microbiota, with tongue-specific Campylobacter concisus and Oribacterium sinus and dental plaque-specific Lautropia mirabilis, Rothia aeria, and Neisseria oralis increased after every meal in a temporal order. The observation was reproducible in multiple subjects and across an 11-mo period. The microbiome composition showed significant diurnal oscillation patterns at different taxonomy levels with Prevotella/Alloprevotella increased at night and Bergeyella HMT 206/Haemophilus slowly increased during the daytime. We also identified microbial co-occurring patterns in saliva that are associated with the intricate biogeography of the oral microbiome. Microbial source tracking analysis showed that the contributions of distinct oral niches to the salivary microbiome were dynamically affected by daily activities, reflecting the role of saliva in exchanging microbes with other oral sites. Collectively, our study provides insights into the temporal microbiome variation in saliva and highlights the need to consider daily activities and diurnal factors in design of oral microbiome studies.

A Parallel Tracking of Salivary and Gut Microbiota Profiles Can Reveal Maturation and Interplay of Early Life Microbial Communities in Healthy Infants

In this study, the onset and shaping of the salivary and gut microbiota in healthy newborns during the first period of life has been followed, evaluating the impact of salivary microbiota on the development of early fecal microbial communities. The microbiota of 80 salivary and 82 fecal samples that were collected from healthy newborns in the first six months of life, was investigated by 16S rRNA amplicon profiling. The microbial relationship within and between the saliva and gut ecosystems was determined by correlation heatmaps and co-occurrence networks. Streptococcus and Staphylococcus appeared as early commensals in the salivary microbiota, dominating this ecosystem through the time, while Fusobacterium, Prevotella, Porphyromonas, Granulicatella, and Veillonella were late colonizers. Enterobacteriaceae, Staphylococcus and Streptococcus were gut pioneers, followed by the anaerobic Bifidobacterium, Veillonella, Eggerthella, and Bacteroides. Streptococcus, Staphylococcus, and Veillonella were shared by the gut and saliva ecosystems. The saliva and gut microbiota seem to evolve independently, driven by local adaptation strategies, except for the oral Streptococcus and Veillonella that are involved in gut microbiota development as seeding species. This study offers a piece of knowledge on how the oral microbiota may affect the gut microbiota in healthy newborns, shedding light onto new microbial targets for the development of therapies for early life intestinal dysbiosis.

Temporal development of the infant oral microbiome

The human oral microbiome is becoming recognized as playing roles in health and disease well beyond the oral cavity over the lifetime of the individual. The oral microbiome is hypothesized to result from specific colonization events followed by a reproducible and ordered development of complex bacterial communities. Colonization events, proliferation, succession and subsequent community development are dependent on a range of host and environmental factors, most notably the neonate diet. It is now becoming apparent that early childhood and prenatal influences can have long term effects on the development of human oral microbiomes. In this review, the temporal development of the infant human oral microbiome is examined, with the effects of prenatal and postnatal influences and the roles of specific bacteria. Dietary and environmental factors, especially breastfeeding, have a significant influence on the development of the infant oral microbiome. The evidence available regarding the roles and functions of early colonizing bacteria is still limited, and gaps in knowledge where further research is needed to elucidate these specific roles in relation to health and disease still exist.

Differences in Sweet Taste Perception and Its Association with the Streptococcus mutans Cariogenic Profile in Preschool Children with Caries

The aim of the study was to verify the hypothesis about differences in sweet taste perception in the group of preschool children with and without caries, and to determine its relationship with cariogenic microbiota and the frequency of sweets consumption in children. The study group included of 63 children aged 2–6 years: 32 with caries and 31 without caries. The study consisted of collecting questionnaire data and assessment of dental status using the decayed, missing, filled in primary teeth index (dmft) and the International Caries Detection and Assessment System (ICDAS II). The evaluation of sweet taste perception was carried out using a specific method that simultaneously assessed the level of taste preferences and the sensitivity threshold for a given taste. The microbiological analysis consisted of the assessment of the quantitative and qualitative compositions of the oral microbiota of the examined children. The sweet taste perception of children with caries was characterized by a lower susceptibility to sucrose (the preferred sucrose solution concentration was >4 g/L) compared to children without caries (in the range ≤ 4 g/L, p = 0.0015, chi-square test). A similar relationship was also observed for frequent snacking between meals (p = 0.0038, chi-square test). The analysis of studied variables showed the existence of a strong positive correlation between the perception of sweet taste and the occurrence and intensity of the cariogenic process (p = 0.007 for dmft; and p = 0.012 for ICDAS II), as well as the frequency of consuming sweets (p ≤ 0.001 for frequent and repeated consumption of sweets during the day, Spearman test) in children with caries. Additionally, children with an elevated sucrose taste threshold were more than 10-times more likely to develop S. mutans presence (OR = 10.21; 95% CI 3.11–33.44). The results of this study suggest the future use of taste preferences in children as a diagnostic tool for the early detection of increased susceptibility to caries through microbial dysbiosis towards specific species of microorganisms.

Mixed aerobic-anaerobic incubation conditions induce proteolytic activity from in vitro salivary biofilms

Oral biofilms have not been studied using both metabolome and protein profiling concurrently. Bacteria produce proteases that lead to degradation of functional salivary proteins. The novel protocol described here allows for complete characterisation of in vitro oral biofilms, including proteolytic, metabolic, and microbiome analysis.

Biofilms were grown on hydroxyapatite discs from whole mouth saliva, using sterilised saliva as a growth-medium, in different growth environments. Salivary protein degradation was assessed from spent saliva growth-medium using SDS-polyacrylamide gel electrophoresis (SDS-PAGE), and metabolic activity by nuclear magnetic resonance (NMR). Discs were assessed for depth and coverage of biofilms by confocal laser scanning microscopy (CLSM), and biofilms were collected at the end of the experiment for 16S rRNA gene sequence analysis.

There was a significant difference in biofilm viability, salivary protein degradation, and metabolites identified between biofilms grown aerobically and biofilms exposed to an anaerobic environment. Bacterial 16S rRNA gene sequencing showed the predominant genus in the 7-day aerobic biofilms was Streptococcus, in aerobic-anaerobic and anaerobic 7-day biofilms Porphyromonas, and in aerobic-anaerobic and anaerobic 13-day biofilms Fusobacterium.

This data suggests new growth requirements and capabilities for analysing salivary biofilms in vitro, which can be used to benefit future research into oral bacterial biofilms.

The oral commensal Streptococcus mitis activates the aryl hydrocarbon receptor in human oral epithelial cells

Streptococcus mitis (S. mitis) is a pioneer commensal bacterial species colonizing many of the surfaces of the oral cavity in healthy individuals. Yet, not much information is available regarding its interaction with the host. We used examination of its transcriptional regulation in oral keratinocytes to elucidate some of its potential roles in the oral cavity. Transcription factor analysis of oral keratinocytes predicted S. mitis-mediated activation of aryl hydrocarbon receptor (AhR). Activation and functionality of AhR was confirmed through nuclear translocation determined by immunofluorescence microscopy and real-time polymerase chain reaction with reverse transcription analysis of CYP1A1, the hallmark gene for AhR activation. Addition of Streptococcus mutans or Streptococcus gordonii did not induce CYP1A1 transcription in the keratinocyte cultures. Introduction of an AhR-specific inhibitor revealed that S. mitis-mediated transcription of CXCL2 and CXCL8 was regulated by AhR. Elevated levels of prostaglandin E2 (enzyme-linked immunosorbent assay) in supernatants from S. mitis-treated oral epithelial cells were also attenuated by inhibition of AhR activity. The observed AhR-regulated activities point to a contribution of S. mitis in the regulation of inflammatory responses and thereby to wound healing in the oral cavity. The concept that the oral commensal microbiota can induce AhR activation is important, also in view of the role that AhR has in modulation of T-cell differentiation and as an anti-inflammatory factor in macrophages.

The Oral Microbiome of Children: Development, Disease, and Implications Beyond Oral Health

In the era of applied meta-omics and personalized medicine, the oral microbiome is a valuable asset. From biomarker discovery to being a powerful source of therapeutic targets and to presenting an opportunity for developing non-invasive approaches to health care, it has become clear that oral microbes may hold the answer for understanding disease, even beyond the oral cavity. Although our understanding of oral microbiome diversity has come a long way in the past 50 years, there are still many areas that need to be fine-tuned for better risk assessment and diagnosis, especially in early developmental stages of human life. Here, we discuss the factors that impact development of the oral microbiome and explore oral markers of disease, with a focus on the early oral cavity. Our ultimate goal is to put different experimental and methodological views into perspective for better assessment of early oral and systemic disease at an early age and discuss how oral microbiomes-at the community level-could provide improved assessment in individuals and populations at risk.

Salivary microbiomes of indigenous Tsimane mothers and infants are distinct despite frequent premastication

Background

Premastication, the transfer of pre-chewed food, is a common infant and young child feeding practice among the Tsimane, forager-horticulturalists living in the Bolivian Amazon. Research conducted primarily with Western populations has shown that infants harbor distinct oral microbiota from their mothers. Premastication, which is less common in these populations, may influence the colonization and maturation of infant oral microbiota, including via transmission of oral pathogens. We collected premasticated food and saliva samples from Tsimane mothers and infants (9–24 months of age) to test for evidence of bacterial transmission in premasticated foods and overlap in maternal and infant salivary microbiota. We extracted bacterial DNA from two premasticated food samples and 12 matched salivary samples from maternal-infant pairs. DNA sequencing was performed with MiSeq (Illumina). We evaluated maternal and infant microbial composition in terms of relative abundance of specific taxa, alpha and beta diversity, and dissimilarity distances.

Results

The bacteria in saliva and premasticated food were mapped to 19 phyla and 400 genera and were dominated by Firmicutes, Proteobacteria, Actinobacteria, and Bacteroidetes. The oral microbial communities of Tsimane mothers and infants who frequently share premasticated food were well-separated in a non-metric multi-dimensional scaling ordination (NMDS) plot. Infant microbiotas clustered together, with weighted Unifrac distances significantly differing between mothers and infants. Infant saliva contained more Firmicutes (p < 0.01) and fewer Proteobacteria (p < 0.05) than did maternal saliva. Many genera previously associated with dental and periodontal infections, e.g. Neisseria, Gemella, Rothia, Actinomyces, Fusobacterium, and Leptotrichia, were more abundant in mothers than in infants.

Conclusions

Salivary microbiota of Tsimane infants and young children up to two years of age do not appear closely related to those of their mothers, despite frequent premastication and preliminary evidence that maternal bacteria is transmitted to premasticated foods. Infant physiology and diet may constrain colonization by maternal bacteria, including several oral pathogens.

Acquisition and maturation of oral microbiome throughout childhood: An update

Traditional microbiology concepts are being renewed since the development of new microbiological technologies, such as, sequencing and large-scale genome analysis. Since the entry into the new millennium, a lot of new information has emerged regarding the oral microbiome. This revision presents an overview of this renewed knowledge on oral microbial community acquisition in the newborn and on the evolution of this microbiome to adulthood. Throughout childhood, the oral microbial load increases, but the microbial diversity decreases. The initial colonizers are related to the type of delivery, personal relationships, and living environment. These first colonizers seem to condition the subsequent colonization, which will lead to more complex and stable ecosystems in adulthood. These early oral microbial communities, therefore, play a major role in the development of the adult oral microbiota and may represent a source of both pathogenic and protective microorganisms in a very early stage of human life. The implications of this knowledge on the daily clinical practice of odontopediatrics are highlighted.

Lactobacillus plantarum for oral peptide delivery

AIMS

To evaluate strains of lactobacilli for their ability to persist and secrete heterologous protein in the oral cavity.

METHODS AND RESULTS

Four different strains of common oral lactobacilli, Lactobacillus brevis, Lactobacillus johnsonii, Lactobacillus murinus and Lactobacillus plantarum, were transformed with the plasmid pKTH2121, which contains a secretion cassette for beta-lactamase. Lactobacilli isolated from the mouth of host mice were also transformed with pKTH2121 for later feeding. Lactococcus lactis, transformed with pKTH2121, was also fed to mice as a negative control. All transformed isolates were fed to C57Black mice in varying schedules. The number of transformed bacteria persisting in the mouth was reported as a percentage of total oral bacteria recovered by swabbing.

CONCLUSIONS

The transformed L. lactis, L. brevis, L. johnsonii, L. murinus, and the endogenous murine lactobacillus strain failed to persist in the mouth. Transformed L. plantarum, however, persisted in the mouth and comprised up to 25% of the total lactobacilli at 18 h and 10% at 24 h after feeding. L. plantarum recovered after feeding retained its ability to secrete beta-lactamase into culture medium efficiently. Beta-lactamase activity could be detected in oral secretions at 8 h after feedings. After repeated feedings, however, the L. plantarum containing pKTH2121 gradually lost its ability to persist after feedings. This experiment demonstrates that L. plantarum can transiently colonize the oral mucosa in large numbers, while continuously secreting foreign proteins, raising the possibility of using lactobacilli as a vector for delivery of oral mucosal peptides.

Subclass distribution of natural salivary IgA antibodies against pneumococcal capsular polysaccharide of type 14 and pneumococcal surface adhesin A (PsaA) in children

A number of studies have shown that the ratio of IgA1 and IgA2 subclasses in secretions can depend upon the nature of the antigen inducing their production. In order to evaluate the effect of the nature of the antigen on the subclass distribution of the naturally occurring salivary IgA antibodies against Streptococcus pneumoniae, we used enzyme immunoassay to measure the levels of natural IgA, IgA1 and IgA2 antibodies to pneumococcal capsular polysaccharide type 14 (PS14) and pneumococcal surface adhesin A (PsaA) in saliva of children during their first 2 years of life. The sum of anti-PS14 and anti-PsaA IgA1 and IgA2 correlated significantly with the antigen-specific total IgA, which showed that IgA1 and IgA2 add up to IgA. IgA1 was the predominant subclass for both antigens. The median of anti-PS14 and anti-PsaA IgA1 was higher than that of IgA2, and the antigen-specific IgA1 was found in a larger proportion of samples than IgA2. The ratio of IgA1 to IgA2 (IgA1/IgA2 ratio) was lower for anti-PS14 than for anti-PsaA, suggesting that the PS antigen induced more IgA2 than the protein antigen. The possible impact of the IgA subclass distribution on protection of mucosal surfaces by natural or vaccine-induced antibodies needs to be determined.

Clonal diversity and turnover of Streptococcus mitis bv. 1 on shedding and nonshedding oral surfaces of human infants during the first year of life

Streptococcus mitis bv. 1 is a pioneer colonizer of the human oral cavity. Studies of its population dynamics within parents and their infants and within neonates have shown extensive diversity within and between subjects. We examined the genetic diversity and clonal turnover of S. mitis bv. 1 isolated from the cheeks, tongue, and primary incisors of four infants from birth to 1 year of age. In addition, we compared the clonotypes of S. mitis bv. 1 isolated from their mothers' saliva collected in parallel to determine whether the mother was the origin of the clones colonizing her infant. Of 859 isolates obtained from the infants, 568 were unique clones. Each of the surfaces examined, whether shedding or nonshedding, displayed the same degree of diversity. Among the four infants it was rare to detect the same clone colonizing more than one surface at a given visit. There was little evidence for persistence of clones, but when clones were isolated on multiple visits they were not always found on the same surface. A similar degree of clonal diversity of S. mitis bv. 1 was observed in the mothers' saliva as in their infants' mouths. Clones common to both infant and mothers' saliva were found infrequently suggesting that this is not the origin of the infants' clones. It is unclear whether mucosal immunity exerts the environmental pressure driving the genetic diversity and clonal turnover of S. mitis bv. 1, which may be mechanisms employed by this bacterium to evade immune elimination.

Development of oral bacterial flora in young children

The intimate relationship with bacteria is a fundamental factor in the health status of an individual. After birth infants are exposed to continuous person-to-person and environmental contacts with microbes, and the development of the indigenous microflora begins on the surfaces of the human body. In a developing ecosystem microbial colonization may easily occur because of the still inadequate host response. Adhesion is the initial event in the colonization of bacteria. In the mouth, only mucosal surfaces are available during the first months of life. After teeth emerge, the number of attachment sites and potential niches increases significantly. Bacteria adhere not only to oral surfaces but also to each other, forming multigeneric communities where specific partner relationships influence their composition and stability. Viridans streptococci and a strictly anaerobic species, Fusobacterium nucleatum, are of interest in this context. The oral colonization pattern differs between individuals already in infancy; variable bacterial load in saliva of attendants and other close contacts and the frequency of this bacterial exposure may partly account for individual differences. In addition, the exposure of an infant to antibiotics affects the quality of colonizing bacteria. This article presents an overview of the age-related acquisition of oral bacteria and the role of the indigenous oral microflora in health and disease.

Humoral immunity to commensal oral bacteria in human infants: salivary secretory immunoglobulin A antibodies reactive with Streptococcus mitis biovar 1, Streptococcus oralis, Streptococcus mutans, and Enterococcus faecalis during the first two years of life

Secretory immunoglobulin A (SIgA) antibodies reactive with the pioneer oral streptococci Streptococcus mitis biovar 1 and Streptococcus oralis, the late oral colonizer Streptococcus mutans, and the pioneer enteric bacterium Enterococcus faecalis in saliva samples from 10 human infants from birth to age 2 years were analyzed. Low levels of salivary SIgA1 and SIgA2 antibodies reactive with whole cells of all four species were detected within the first month after birth, even though S. mutans and E. faecalis were not recovered from the mouths of the infants during the study period. 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 the four species over this time period. When the concentrations of SIgA1 and SIgA2 antibodies reactive with all four species were normalized to the concentrations of SIgA1 and SIgA2 in saliva, SIgA1 and SIgA2 antibodies reactive with these bacteria showed a significant decrease from birth to 2 years of age. Adsorption of each infant's saliva with cells of one species produced a dramatic reduction of antibodies recognizing the other three species. Sequential adsorption of saliva samples removed all SIgA antibody to the bacteria, indicating that the SIgA antibodies were directed to antigens shared by all four species. The induction by the host of a limited immune response to common antigens that are likely not involved in adherence may be among the mechanisms that commensal streptococci employ to persist in the oral cavity.

Structural integrity of infant salivary immunoglobulin A (IgA) in IgA1 protease-rich environments

IgA1 protease-secreting Streptococcus mitis often dominate the oral flora of the neonate and young infant at a time when salivary IgA concentrations are low and usually enriched in the secretory IgA1 subclass. To study the possible influence of these degradative enzymes on emerging host immunity, the presence of IgA1 protease-secreting streptococci was related to the structural integrity of salivary IgA in 24 infants who were between 3 and 18 weeks of age. At least one IgA1 protease-secreting strain could be isolated from the oral mucosa of 79% of the infants and comprised a mean of 38% of the total streptococcal flora of these infants. Chromatographic analyses of resting whole saliva from 16 infants revealed, however, that 95% of the secretory IgA (range 88-100%) remained intact, indicating that minimal immediate IgA proteolysis occurred in the bulk salivary phase. Proteolysis of infant salivary IgA, presumably by indigenous IgA1 protease, could be observed after extended (more than 7 h) in situ incubation of whole saliva at 37 degrees C. Salivary IgA antibody activities to S. mitis components were demonstrated by Western blot in infants colonized with an IgA1 protease-secreting flora. Preliminary evidence suggested that salivary antibody activity in some infants may be directed to IgA1 protease. Thus, the infant's antibody defenses not only appear very early in life but are substantively intact in the bulk salivary phase, even when the oral cavity is colonized with IgA1 protease-secreting streptococcal flora.

Survival of oral bacteria

The global distribution of individual species of oral bacteria demonstrates their ability to survive among their human hosts. Such an ubiquitous existence is the result of efficient transmission of strains and their persistence in the oral environment. Genetic analysis has identified specific clones of pathogenic bacteria causing infection. Presumably, these express virulence-associated characteristics enhancing colonization and survival in their hosts. A similar situation may occur with the oral resident flora, where genetic variants may express specific phenotypic characteristics related to survival. Survival in the mouth is enhanced by dental plaque formation, where persistence is associated with the bacteria's capacity not only to adhere and grow, but also to withstand oxygen, wide fluctuations in pH and carbohydrate concentration, and a diverse array of microbial interactions. Streptococcus mutans has been discussed as a 'model' organism possessing the biochemical flexibility that permits it to persist and dominate the indigenous microflora under conditions of stress.

The effect of fluoride on Streptococcus sanguis 7863 IgA1 protease production and activity

Fluoride was found to affect the production of the bacterial IgA1 protease but to have no effect on IgA1 protease activity. The concentrations of fluoride that do affect Streptococcus sanguis growth and IgA1 protease production are higher than those normally seen in vivo under normal circumstances. The concentrations of fluoride in dental plaque following use of a fluoride rinse or dentifrice would be sufficient to reduce Strep. sanguis IgA1 protease production.

Clonal diversity of Streptococcus mitis biovar 1 isolates from the oral cavity of human neonates

The clonal diversity of 101 isolates of the pioneer bacterium Streptococcus mitis biovar 1 obtained from the oral cavities of 40 human neonates 1 to 3 days, 2 weeks, and 1 month postpartum was examined by using rRNA gene restriction patterns. There was a high degree of genetic diversity, with the 101 isolates comprising 93 unique PvuII ribotypes. There were eight identical pairs of ribotype patterns, and seven of the eight pairs were obtained from individual neonates. Only one identical pair comprised isolates obtained from different neonates. In all but two cases, isolates with matching ribotypes were obtained at one visit. Two pairs of isolates with matching ribotype patterns were obtained from neonates on successive visits. The ribotype patterns of the isolates were examined by cluster analysis. The isolates forming each cluster were very similar, yet each cluster was well separated from its neighbors. When several isolates were obtained from individual neonates at a particular visit, in some instances they were contained in a single cluster, whereas in other cases each isolate was contained in a separate cluster. Isolates obtained from individual neonates on successive visits tended to be contained in different clusters. This high degree of diversity, which has been observed in other mucosal commensal bacteria, may serve as a mechanism for avoiding immune elimination of these bacteria.

Extracellular proteinase activity of Cryptococcus neoformans

Extracellular proteinase activity was studied for eight strains of Cryptococcus neoformans var. neoformans and two strains of Cryptococcus neoformans var. gattii. Proteinase activity was measured by protein agar clearance, azoalbumin hydrolysis, gelatin liquefaction, and protein substrate polyacrylamide gel electrophoresis. All strains of C. neoformans produced extracellular proteolytic activity. Maximal extracellular proteinase activity in supernatants of C. neoformans cultures was associated with late logarithmic- and stationary-phase cultures. C. neoformans was able to utilize murine immunoglobulin G1, bovine immunoglobulin G, and human complement factor 5 for growth in media containing these proteins as the sole sources of carbon and nitrogen, suggesting a capacity to degrade immunologically important proteins. Protein substrate polyacrylamide gel electrophoresis revealed several bands with proteolytic activity at apparent molecular masses of 200, 100, and 50 kDa. The results confirm the existence of extracellular proteinase activity for C. neoformans.

Biological significance of IgA1 proteases in bacterial colonization and pathogenesis: critical evaluation of experimental evidence

IgA1 protease activity, which allows bacteria to cleave human IgA1 in the hinge region, represents a striking example of convergent evolution of a specific property in bacteria. Although it has been known since 1979 that IgA1 protease is produced by the three leading causes of bacterial meningitis in addition to important urogenital pathogens and some members of the oropharyngeal flora, the exact role of this enzyme in bacterial pathogenesis is still incompletely understood owing to lack of a satisfactory animal model. Cleavage of IgA1 by these post-proline endopeptidases efficiently separates the monomeric antigen-binding fragments from the secondary effector functions of the IgA1 antibody molecule. Several in vivo and in vitro observations indicate that the enzymes are important for the ability of bacteria to colonize mucosal membranes in the presence of S-IgA antibodies. Furthermore, the extensive cleavage of IgA sometimes observed in vivo, suggests that IgA1 protease activity results in a local functional IgA deficiency that may facilitate colonization of other microorganisms and the penetration of potential allergens. It has been hypothesized that IgA1 protease activity of Haemophilus influenzae, Neisseria meningitidis, and Streptococcus pneumoniae, under special immunological circumstances, allows these bacteria to take advantage of specific IgA1 antibodies in a strategy to evade other immune factors of the human body. The decisive factor is the balance between IgA antibodies against surface antigens of the respective bacteria and their IgA1 protease. Recent studies have shown that serine-type IgA1 proteases of H. influenzae, meningococci, and gonococci belong to a family of proteins used by a diverse group of Gram-negative bacteria for colonization and invasion.

Analysis of human immunoglobulin-degrading cysteine proteinases of Trichomonas vaginalis

Trichomonas vaginalis is a protozoan parasite that causes a widely distributed sexually transmitted disease (STD). Since immunoglobulin G (IgG) antibodies to specific trichomonad immunogens are found in serum and vaginal washes (VWs) from patients with trichomoniasis, a potential mechanism of immune evasion by this parasite might be the ability of T. vaginalis proteinases to degrade human immunoglobulins (Igs). Incubation of human IgG with lysates of T. vaginalis organisms resulted in time- and concentration-dependent degradation of the heavy chain. Secretory IgA was degraded similarly. Inhibitors of cysteine proteinases, when added to trichomonal lysates, abolished IgG and IgA degradation, while EDTA, a metalloproteinase inhibitor, did not. Substrate-gel electrophoresis with human IgG, IgM, or IgA copolymerized with acrylamide revealed several distinct cysteine proteinases in both lysates and culture supernatants from logarithmically growing parasites that degraded all classes of human antibodies. Trichomonal lysates and supernatants of numerous isolates tested all had Ig-degrading activity. Finally, proteolytic activity against IgG was detected in most (26 of 33; 78%) VWs from patients with trichomoniasis. In contrast, 18 of 28 (65%) VWs from women without trichomoniasis or from patients infected with other STDs had no detectable proteinases when tested in an identical manner. The other 10 of these 28 VWs (35%) had smaller amounts of detectable Ig-degrading proteinases. These differences in Ig-degrading proteinase activity between patients with and without trichomoniasis, regardless of coinfecting STDs, were statistically significant (P = 0.001). These results illustrate that T. vaginalis is capable of degrading human Igs.

Active release of bound antibody by Streptococcus mutans

Previous studies have shown that Streptococcus mutants is capable of releasing many surface protein antigens, particularly antigen P1. Antigen P1 is immunodominant and has been implicated in adherence of S. mutants to the acquired pellicles. The purpose of this study is to investigate the significance of release of this antigen by the cells. S. mutants NG8 (serotype c) was incubated with an anti-P1 rabbit immunoglobulin G (IgG) or a human colostral IgA which contains natural anti-P1 activity. Results indicated that the bound antibodies were released by the cells in a pH- and time-dependent manner. The optimal pH for release was between 6 and 8, and the release rate reached a plateau in 1 h at 37 degrees C. The release of bound antibodies was considered an active process, since heat-killed cells remained capable of antibody binding but failed to release the antibodies. The release was also dependent on the age of the culture, with early-exponential-phase cells releasing the maximum amount of bound IgG. The released IgG was isolated by polyethylene glycol precipitation and protein A-Sepharose column chromatography and found to be associated with antigen P1, indicating that the antibodies were released together with the antigen in the form of immune complexes. The binding of S. mutans by secretory IgA (SIgA) inhibited the adherence of the cells to salivary agglutinin-coated hydroxylapatite. However, when the SIgA-coated S. mutans was allowed to release the bound antibodies, the inhibitory effect of SIgA on adherence was abrogated. These results suggest that S. mutans is capable of shedding surface-bound antibodies in the form of antibody-antigen immune complexes. Such an action may be a strategy employed by the cells to counter the neutralizing effect of naturally occurring antibodies in the oral cavity.