Inhibition of enzymes by human salivary immunoglobulin A

Biological Functions of IgA

Immunoglobulin A (IgA) is the most enigmatic of immunoglobulins. It is by far the most abundant of human Igs, being present in the blood plasma at concentrations approximating 2–3mg/mL, as well as the dominant isotype in most secretions where its output amounts to some 5–8g/day in adults. Furthermore, its evolutionary origins appear to precede the synapsid– diapsid divergence in tetrapod phylogeny (>300 million years ago) because it is present in both mammals and birds and therefore possibly also in reptiles (reviewed in Peppard et al., 2005); an IgA-like molecule has now been identified in a lizard (Deza et al., 2007).

Effect of IgA1 protease on the ability of secretory IgA1 antibodies to inhibit the adherence of Streptococcus mutans

Secretory IgA (SIgA) is the principal immunoglobulin isotype present in the mucosal secretions of humans. SIgA is thought to play a major role in host defense at these surfaces by inhibiting the colonization of potentially pathogenic microorganisms. A number of bacteria that are mucosal pathogens of humans produce a protease that specifically cleaves the IgA1 subclass of humans and great apes at the hinge region to produce Fab and Fc fragments. In order to study the effect of IgA1 protease on the ability of SIgA1 antibodies to inhibit bacterial adherence, an in vitro assay that quantifies the adsorption of radiolabeled Streptococcus mutans to hydroxyapatite (HA) beads was employed. High titer S. mutans-specific SIgA1 and SIgA2 antibodies were induced in chimpanzee milk for use in the assay. Fab alpha1 fragments had significantly reduced ability to inhibit adherence of S. mutans to saliva-coated HA compared to intact SIgA1 or SIgA2 anti-S. mutans antibodies. These data support the potential importance of IgA1 proteases as an ecological determinant in the oral cavity and their role as a determinant of pathogenesis of pathogenic bacteria whose portal of entry is the mucosal surface.

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.

Hyaluronic acid and hyaluronidase activity in gingival exudate from sites of acute ulcerative gingivitis in man

Gingival exudates from sites of acute ulcerative gingivitis (AUG) and chronic gingivitis (CG) in adults were investigated by cellulose-acetate electrophoresis for the hyaluronic acid (HA) content and assayed for the levels of HA-degrading enzymes. HA was the only glycosaminoglycan (GAG) in gingival exudate from CG sites. HA was not detected at untreated AUG sites but was evident, at increasing levels, after two and seven days of effective antibacterial treatment. In AUG exudates, the total HA-degrading enzyme activity, of bacterial origin, decreased to approx. 30 and 10 per cent of the high initial levels after two and seven days of treatment respectively, to that level found at sites of CG. The specific activity of HA-degrading enzyme of lysosomal origin was low initially and increased with treatment to a level comparable to CG. The notable absence of HA from gingival exudate from sites of untreated AUG thus appears to result from the increased levels of bacterial hyaluronidase. Electrophoresis of gingival exudate may be an indirect method of monitoring the rate of response of AUG to different antibacterial treatments.

Inhibition of glucan and levan synthesis and neuraminidase activity of oral streptococci by monkey antiserums

A demonstration that antiserums from monkeys immunized with fructosyltransferase and glucosyltransferase reduced the activities of the enzymes in producing glucans and levans was done. The nature of the inhibiting factor has not yet been identified. The local immunization of monkeys with glycosidic hydrolases produced a sufficient amount of inhibiting principle, presumably antibody, to inhibit neuraminidase one month after the first immunization and this degree of immunization, which reached degrees of 50%, remained constant throughout 11 months of immunization of these monkeys. The immunizing principle has not yet been found in saliva. A criterion for the feasibility for immunization has been met. A significant reduction in streptoccal glucosyltransferase, fructosyltransferase, and neuraminidase activity was noted after immunization with enzymes.

Serum and salivary antibodies to cariogenic bacteria in man

Antibodies in serum and parotid saliva against cell wall preparations from four serotypes of S mutans were examined in 110 subjects aged 18 to 25 years. In subjects with no detectable carious lesions, significant negative correlations were found between the DMF index and serum IgG and IgM antibodies, especially in S mutans of serotype c, whereas positive correlations were found between the DMF index and salivary IgA antibodies. In subjects with active caries, positive correlations were found between serum IgG antibodies and S mutans (serotypes c and a) and the DMF index. Sequential antibody analysis during a period of up to 32 months showed that development of carious lesions was associated with a rise in serum antibody titer to S mutans, but no change was detectable in salivary antibodies. Treatment of caries led to a decrease in serum IgG and IgM antibodies to S mutans cell wall, but in parotid saliva an increase in antibody titer to a culture extract of S mutans was found. The results support the concept of dental caries as an infective disease and suggest that serum antibodies may contribute to caries immunity in man.

Immunoglobulin classes and biological functions of Campylobacter (Vibrio) fetus antibodies in serum and cervicovaginal mucus

Serum and cervicovaginal mucus (CVM) antibodies from heifers after genital infection or systemic immunization with Campylobacter (Vibrio) fetus were classified according to their immunoglobulin class, antigenic specificities, and biological functions. Only immunoglobulin (Ig) A antibodies, specific both for O and superficial, heat-labile, whole-cell (W) antigens, were detected in CVM of convalescent animals. After systemic immunization, antibodies in serum were directed principally to W antigens and were located in IgG(1), IgG(2), and IgM classes; CVM antibodies of the same specificity were detected only in the IgG subclasses. Functional tests revealed that antibodies of W specificity, whether of the IgA or IgG class, were capable of immobilizing the organism. However, IgG antibodies immobilized with clumping, whereas IgA antibodies immobilized single organisms within the 3-min period. None of the antibody preparations was bactericidal in the presence of homologous complement when the infecting strain was used as the target organism, but a bactericidal effect was observed when the target strain was rough and non-encapsulated. Both serum and CVM from systemically immunized animals opsonized C. fetus organisms, but CVM from locally immunized animals containing IgA antibodies was not opsonic. It is hypothesized that functions of immobilization for IgA and IgG and of opsonization for IgG are important features of protective immunity in venereal vibriosis.

Effects of local immunization with Streptococcus mutans on induction of salivary immunoglobulin A antibody and experimental dental caries in rats

The effect of local immunization with Streptococcus mutans on dental caries in conventional and gnotobiotic rats was studied. Injection of these animals with S. mutans strain 6715 incorporated into complete Freund adjuvant consistently resulted in the presence of antibody in saliva directed to this organism. This antibody was primarily of the immunoglobulin A class as demonstrated by specific antiglobulin augmentation and gel filtration of antibody activity. Serum antibody was also present. Five experiments have been completed in conventional rats and two in gnotobiotic animals. The immunized group of animals always had lower mean caries scores than comparably sham-immunized or nonimmunized control groups. The numbers of lesions were also always lower in the immunized animals, suggesting a possible interference with the formation of new lesions in immunized animals. The reductions in dental caries and lesions were greater on smooth surfaces than on occlusal surfaces. which might be explained as interference with adherence phenomena demonstrated by S. mutans. It is proposed that salivary immunoglobulin A antibody may be viewed as an ecological determinant in the oral cavity by affecting oral microorganisms and possibly their by-products.

Acceleration of dextransucrase activity of Streptococcus mutans by secretory immunoglobulin A

The effect of immunoglobulins on the activity of dextransucrase purified from Streptococcus mutans strain HS-6 is described. When human salivary immunoglobulin A (IgA) or colostral IgA, either natured or denatured, was incubated with dextransucrase, the rate of the dextran synthesis was markedly accelerated, whereas human serum IgA or IgG neither accelerated nor inhibited the enzyme activity. The results suggest that a portion unique for secretory IgA, the secretory component, might be related to the enzyme acceleration. On the other hand, specific rabbit antiserum against the dextransucrase inhibited completely dextran synthesis by the enzyme.