Secretory IgM antibodies to Streptococcus mutans in subjects with selective IgA deficiency

Specific antibody activity, glycan heterogeneity and polyreactivity contribute to the protective activity of S-IgA at mucosal surfaces

An explanation of the principles and mechanisms involved in peaceful co-existence between animals and the huge, diverse, and ever-changing microbiota that resides on their mucosal surfaces represents a challenging puzzle that is fundamental in everyday survival. In addition to mechanical barriers and a variety of innate defense factors, mucosal immunoglobulins (Igs) provide protection by two complementary mechanisms: specific antibody activity and innate, Ig glycan-mediated binding, both of which serve to contain the mucosal microbiota in its physiological niche. Thus, the interaction of bacterial ligands with IgA glycans constitutes a discrete mechanism that is independent of antibody specificity and operates primarily in the intestinal tract. This mucosal site is by far the most heavily colonized with an enormously diverse bacterial population, as well as the most abundant production site for antibodies, predominantly of the IgA isotype, in the entire immune system. In embodying both adaptive and innate immune mechanisms within a single molecule, S-IgA maintains comprehensive protection of mucosal surfaces with economy of structure and function.

Neuroendocrine regulation of salivary IgA synthesis and secretion: implications for oral health

Secretory immunoglobulin A (S-IgA) represents the main adaptive immune mechanism in the oral cavity. The regulation of secretion and synthesis of S-IgA is not only dependent on prior antigenic stimulation, but is also under strong neuroendocrine control. Thus, alterations in neuroendocrine functioning (such as induced by stress, exercise, pregnancy, menstrual cycle, and pharmacological interventions) may affect salivary IgA levels. This review deals with the neuroendocrine regulation of synthesis and secretion of salivary IgA and its potential role in the maintenance of oral health.

Oral manifestations in selective IgA deficiency

Selective immunoglobulin A (IgA) deficiency is the most common of the primary immunodeficiencies with a frequency of 1/300-1/3000, depending on the screened population. As secretory IgA (SIgA) has a protective role in mucosal surfaces from invasion of microorganisms, it is thought that IgA-deficient subjects are susceptible to periodontal diseases and oral manifestations. Previous studies show contradictory results, concerning the involvement of the individuals' periodontium with IgA deficiency. The aim of this study was to investigate and compare the oral manifestations in IgA-deficient subjects with controls. Eleven selective IgA-deficient subjects aged 3-18 years with serum IgA levels <10 mg dl(-1) and 11 age-sex-matched healthy children as the controls entered the study. Oral mucosal investigation, dental caries, plaque accumulation and periodontal status were assessed. Serum immunoglobulin levels were measured by single radial immunodiffusion (SRID) method. Saliva immunoglobulins and secretory component levels were measured by enzyme linked immunosorbent assay (ELISA) methods. IgA-deficient patients had serum and saliva IgA levels less than 10 mg dl(-1) and 10 microg ml(-1), respectively, but other serum immunoglobulin levels were normal and saliva immunoglobulin M (IgM) levels were increased, compared with controls. There were no significant differences in oral manifestations between IgA-deficient subjects and controls, which may be a result of compensatory increase of saliva IgM or other non-immunological defence factors in saliva. Thus, it is not necessary to evaluate IgA and SIgA in all the patients with oral and dental lesions and it is thought that it is better to investigate other factors.

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.

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

The role of secretory immunoglobulin A (sIgA) in the control of the indigenous microbiota is not well understood. In this study, we compared the oral and intestinal microbiota of transgenic B-cell-deficient (microMT) mice with their heterozygous (microMT/+) normal littermates. The levels of salivary IgA and serum IgA and IgG were normal in microMT/+ mice, while no immunoglobulins were detected in microMT/microMT mice. The acquisition and proportions of the different species of the oral and intestinal indigenous bacterial populations were not significantly different between the two groups of mice. Our results thus suggest that secretory IgA does not play a major role in the regulation of the indigenous microbiota of mice.

Intestinal and circulating antibody-forming cells in IgA-deficient individuals after oral cholera vaccination

In search for a possible explanation for the different susceptibility to mucosal infections in IgA-deficient (IgAd) individuals, the frequency of total immunoglobulin-secreting cells (ISC) and vaccine-specific antibody-secreting cells (ASC) in intestinal mucosa and peripheral blood was determined by the enzyme-linked immunospot (ELISPOT) assay before and after peroral vaccination with a B subunit-whole cell cholera vaccine. Two groups of IgAd individuals, frequently infected and non-infected respectively, and normal controls were studied. Before cholera vaccination there were significantly higher frequencies of total IgM and IgG ISC in the gut, but not in the blood, in the IgAd individuals than in the controls. However, there were no significant differences between healthy and infection-prone IgAd individuals in this respect. In response to oral cholera vaccination, intestinal cholera toxin (CT)-specific IgG and IgM ASC were significantly more abundant among the IgAd individuals with a history of frequent infections than among the healthy IgAd individuals and controls. A similar difference in IgG and IgM ASC, although not significant, was also noted in blood. In IgAd individuals with frequent infections the vaccine induced variable anti-CT IgM ASC responses in the gut, ranging from no increase to a few strikingly high responses. In the controls, the CT-specific responses were dominated by IgA ASC. The data show that oral cholera vaccination evoked strong CT-specific IgG ASC responses, and in some cases also strong IgM ASC responses in the intestinal mucosa of IgAd patients with a history of frequent infections. The healthy IgAd individuals unexpectedly responded with lower numbers of CT-specific IgG ASC and did not show any increase of CT-specific IgM ASC in the intestinal mucosa. Thus, inability to mount a mucosal immune response to an oral antigen cannot in itself explain recurrent infections among many IgAd individuals.

Similar proportions of immunoglobulin A1 (IgA1) protease-producing streptococci in initial dental plaque of selectively IgA-deficient and normal individuals

By comparing the initial colonization of cleaned teeth in immunoglobulin A (IgA)-deficient, IgM-compensating individuals with that in normal individuals, no significant difference in the proportion of IgA1 protease-producing streptococci was found. Thus, as one of several bacterial means of immune evasion, the ability to cleave secretory IgA1 does not appear essential to the successful adherence of oral streptococci.

Dental caries in congenitally athymic rats

The importance of the immune response in dental infection was evaluated in heterozygous (rnu/+) normal and homozygous (rnu/rnu) congenitally athymic "nude" Rowett rats. Animals of both types were infected, or immunized and infected, with mutans streptococci (Streptococcus sobrinus strain 6715). The mean numbers of S. sobrinus cells recovered from the nude rats were higher than those from comparable (immune/nonimmune) normal rats in 10 of 12 possible comparisons. Also, S. sobrinus constituted a greater percentage of the total streptococci in the nude rats compared with normal animals (6 of 6 possible comparisons). Antibody to S. sobrinus whole cells or to S. sobrinus glucosyltransferase from nude rats in serum or in saliva was significantly lower (or absent) than that of comparable normal rats. This was seen after infection, but was most pronounced after immunization (and infection). Dental caries was also significantly elevated in the congenitally athymic animals. Immunologic deficiency of congenitally athymic rats can lead to a greater infection level with mutans streptococci and increased dental caries.

Function of anti-Streptococcus mutans antibodies: inhibition of virulence factors and enzyme neutralization

The levels of parotid salivary IgA and serum IgG antibodies from dental caries-resistant (CR) and caries-susceptible (CS) individuals to Streptococcus mutans antigens were determined. In general, the levels of salivary IgA and serum IgG antibodies to S. mutans antigens were significantly higher in CR subjects than in CS individuals. There were significantly higher levels of IgA2, but not IgA1, salivary antibodies to S. mutans whole cells in CR subjects than in CS individuals. These results led us to investigate the functional effects parotid saliva and sera containing these antibodies had on several factors associated with S. mutans virulence. Parotid saliva and sera from CR subjects significantly inhibited S. mutans growth, adherence, acid production, glucosyltransferase and glucose-phosphotransferase activities to a greater extent than saliva and sera from CS individuals. The data suggest that neutralization of S. mutans enzymes and inhibition of S. mutans virulence factors by saliva and serum may be responsible for the lower numbers of carious lesions in CR subjects.

Genetic aspects of immunoglobulin A deficiency

IgA deficiency is one of the most common of all immune defects. While it is often not associated with clinical illness, presumably due to compensation from other sectors of the immune system, IgA-deficient individuals are distinctly more likely to become ill and have one or more of specific groups of diseases. While the unifying immunologic perturbation in IgA deficiency is a lack of mature IgA-secreting B cells, a host of other, usually minor, immunologic abnormalities have been reported in such patients. IgA deficiency can be inherited in an autosomal dominant or autosomal recessive fashion, but most individuals who are IgA deficient have no other affected family members. From a genetic point of view, IgA deficiency has been associated with three chromosomes, 18, 14, and 6. Many IgA-deficient individuals who have cytogenically detectable abnormalities of chromosome 18 have been reported, but all the individuals with these defects have severe congenital defects of other kinds. Obscuring the relationship between chromosome 18 and IgA deficiency is the fact that both short- and long-arm deletions have been reported in IgA deficiency. The chromosome deletions in the individuals who are IgA deficient thus appear to have no common pattern. While a rare individual can be IgA1 deficient on the basis of heavy-chain deletions of alpha 1 genes in concert with other heavy-chain genes on chromosome 14, such individuals are quite rare, and from a clinical point of view, those reported have usually been healthy. Absence of both IgA1 and IgA2 genes (presumably in concert with other heavy-chain genes) has never been reported. For chromosome 6, a more complex puzzle emerges. IgA-deficient individuals have been reported to have one of a few specific HLA haplotypes. While many individuals with these supratypes are not IgA deficient, these findings encourage the notion that the secretion of IgA could be at least partly controlled by genes residing in the major histocompatibility locus.

IgA antibody-producing cells in peripheral blood after antigen ingestion: evidence for a common mucosal immune system in humans

The finding that ingestion of antigens results in the selection induction of IgA antibodies in external secretions suggests that antigen sensitizes Peyer's patch lymphoid cells, which migrate to mucosal sites and generate local secretory IgA (S-IgA) antibody responses. Evidence for a common mucosal immune system in humans has been scanty because of the difficulty in demonstrating migratory behavior of Peyer's patch cells. In the present study, peripheral blood mononuclear cells (PBMC) from human volunteers who had ingested capsules containing killed Streptococcus mutans were assayed for spontaneous antibody-producing cells. Four of five volunteers exhibited circulating IgA-producing cells within 7 days and reached maximum responses by days 10-12. One IgA-deficient subject exhibited IgM responses with identical kinetics. Pokeweed-mitogen-stimulated PBMC produced anti-S. mutans antibodies predominantly of the IgA isotype. Significant S-IgA anti-S. mutans antibodies were detected in saliva and tears by day 14, and the antibodies reached maximum titers by 3 weeks. No changes in serum anti-S. mutans antibodies were noted. The IgA-deficient subject produced salivary secretory IgM antibodies. These results suggest that, after antigen ingestion, peripheral blood contains antigen-specific precursors of IgA plasma cells and that their presence precedes the appearance of S-IgA antibodies in external secretions. Therefore, these experiments provide further support for the existence of a common mucosal immune system in humans.

Immunochemical quantitation of alpha-amylase and secretory IgA in parotid saliva from people of various ages

The alpha-amylase (128 subjects) and secretory IgA (118 subjects) concentration in stimulated parotid saliva of healthy individuals aged 23-84 years, was determined. They were divided into three age groups: I, 23-39; II, 40-59; and III, 60-84 years old. The concentrations (microgram/ml) of alpha-amylase for group I = 803.6; II = 648.0; and III = 652.4; the concentrations for secretory IgA for group I = 96.2; II = 101.8; and III = 97.7. The Kruskal-Wallis test revealed no significant differences between groups for alpha-amylase or secretory IgA.

The nasal mucosa in immunodeficiency. Surface morphology, mucociliary function and bacteriological findings in adult patients with common variable immunodeficiency or selective IgA deficiency

Twenty-two adult patients suffering from common variable immunodeficiency (CVID) and sixteen patients with selective IgA deficiency were examined with regard to the mucocilliary function of the nose. The surface structures of the nasal mucosa, e.g. cell distribution and degree of destruction and metaplasia, were judged from scanning electron microscopy of nasal biopsies. Bacteria were isolated from nasopharyngeal swabs. The results of the clinical and morphological investigations were analysed with regard to the duration of the disease and possible benefit of adequate prophylaxis with immunoglobulin. It was found that patients with CVID had a slower mucociliary transport rate and more extensive mucosal damages than patients with selective IgA deficiency. Most likely these alterations were due to repeated infections as patients who had had few infections or adequate immunoglobulin prophylaxis (CVID patients) had better mucociliary function and showed less extensive mucosal changes. Potentially pathogenic bacteria in the nasopharynx were found in equal numbers in both patient groups.

Prevention of Streptococcus mutans colonization by salivary IgA antibodies

The levels of salivary and serum IgA, IgG, and IgM antibodies to the seven serotypes (a-g) of Streptococcus mutans were established in 12 laboratory volunteers using a sensitive enzyme-linked immunosorbent assay. Salivary IgA antibody levels to the serotype c organism were significantly lower (P less than 0.005) than antibody levels to the other six serotypes of S. mutans. Similar results were found with a purified S. mutans serotype c carbohydrate. Serum IgG and IgM antibody titers to the serotype c whole cells were significantly higher (P less than 0.05) than to four other S. mutans serotypes (a, e-g). The abilities of S. mutans serotypes c and d to colonize molar tooth surfaces were examined in eight volunteers. S. mutans serotype d was cleared from the tooth surfaces within 24 hr of challenge, whereas S. mutans serotype c was detected in six of the eight volunteers after 2 weeks and in three of eight after 3 weeks. These results provide additional evidence for the role of salivary IgA antibodies in regulating S. mutans infection and suggest that the low levels of salivary IgA antibodies to S. mutans serotype c may contribute to the predominance of this serotype in the U.S. population.

Distribution of immunoglobulin-containing cells in normal and neonatally thymectomized rats

The distribution of immunoglobulin-containing cells (ICC) of the immunoglobulin A (IgA), IgG, and IgM isotypes was examined in various lymphoid and secretory tissues of rats. The effect of neonatal thymectomy of rats on T cells, B cells, and ICC in these tissues was determined by immunofluorescence. The results showed that although T cells were severely depleted in both lymphoid and secretory tissues of the thymectomized (Tx) rats, Tx and normal rats showed comparable numbers of B cells staining for IgA, IgG, and IgM. After neonatal thymectomy, IgA ICC in both lymphoid and secretory tissues were significantly decreased. However, the Tx rats exhibited a compensatory increase in IgM ICC in the identical tissues. Local injection of normal and Tx rats with Streptococcus mutans 6715 resulted in an increase in all isotypes of ICC in the secretory tissues. Although the primary increase in normal rats was due to IgA ICC, Tx rats exhibited the greatest change in the number of IgM ICC.

Longitudinal study of salivary IgA in children from 1 to 4 years old with reference to dental caries

The concentration of salivary IgA was measured and clinical examinations performed annually in 39 children over a period of 36 months. The age of the children ranged from 1 to 4 yr during the observation period. The geometric mean value of salivary IgA increased rapidly between the age of 1 and 2, from 0.021 g/l (log mean - 1.68 +/- 0.33) to 0.052 g/l (log mean - 1.28 +/- 0.24). After this age the mean level of salivary IgA remained fairly constant during the observation period. When the study population was divided into two groups: the caries-free group and the caries-susceptible group, it was found that in the caries-free group the mean salivary IgA value increased rapidly during the second year of life, then more slowly after the age of 2. In the caries-susceptible group the increase in the mean value between the ages of 1 and 2 was marked and at the age of 2 the values were significantly higher compared to those of the caries-free group. The concentrations did not, however, remain high, but fell to lower level and at the age of 4 there was a marked overlap in the values of the groups.

Effect of neonatal thymectomy on dental caries in rats

The effect of T-cell depletion on susceptibility to dental caries after infection with Streptococcus mutans was studied. Rats were neonatally thymectomized (Tx) and infected with S. mutans 6715 or locally immunized with the homologous organism before infection. The Tx rats uniformly exhibited a higher level of infection with S. mutans and subsequently showed a greater extent of carious activity. Correlation studies were performed comparing the level of salivary and serum anti-S. mutans antibodies and the relative amount of dental caries. The results demonstrated that salivary immunoglobulin A antibody after immunization and infection, or infection only, showed a significant negative correlation with dental caries. Also, after local immunization, serum immunoglobulin G antibody showed a negative correlation with dental caries in the rats. These findings further support a major protective role for salivary immunoglobulin A in experimental dental caries in rats.

Concentration of immunoglobulins in human whole saliva: effect of physiological stimulation

The concentrations of total protein, albumin, IgA, IgG and IgM in human whole salivas were measured with a solid phase radioimmunoassay before and after physiological stimulation of salivary secretion. The geometric mean concentrations (mg/l) before stimulation were: total protein 1600, albumin 60, IgA 140, IgG 16 and IgM 4.1. Physiological stimulation of salivary secretion caused an increase of the total protein concentration to 2400 mg/l, had little effect on the concentrations of albumin and IgG, but lowered the concentrations of IgA and IgM to 56 mg/l and 1.7 mg/l, respectively. These findings indicate that a considerable portion of salivary IgA and IgM are produced locally depending on selective transport and that the release from local storage sites is not increased during stimulation as much as the total volume of the saliva.

Mice refractory to lipopolysaccharide manifest high immunoglobulin A responses to orally administered antigen

Lipid A-nonresponding C3H/HeJ mice manifested high immune responses to orally administered (either by feeding or by intragastric immunization) heterologous erythrocytes when compared with syngeneic lipid A-responding C3H/HeN mice. Prolonged consumption of horse erythrocytes resulted in a significant secretory immune response in both C3H mouse strains as evidenced by high salivary agglutinin titers. Although salivary agglutinin titers were only slightly greater in C3H/HeJ mice than those of C3H/HeN mice, serum agglutinin titers and immunoglobulin A (IgA) levels were consistently higher (two- to fourfold) in C3H/HeJ mice. The appearance of anti-horse erythrocyte plaque-forming cell responses in spleens of immunized animals was followed by an increase in salivary anti-horse erythrocyte agglutinin activity. Peak levels of both responses were attained after approximately 3 weeks of immunization. Differences in immune responsiveness between C3H mouse strains were also evident at the cellular level since splenic IgA anti-horse erythrocyte plaque-forming cell responses in fed C3H/HeJ mice were twofold higher than those in similarly treated C3H/HeN mice. This higher response pattern was also observed when C3H/HeJ mice manifested threefold higher splenic IgM and IgA plaque-forming cell responses to intragastrically administered sheep erythrocytes. Thus, higher responsiveness was observed in the C3H/HeJ mice given heterologous erythrocytes by the oral route. Furthermore, levels of serum IgA in 10- to 12-month-old nonimmunized C3H/HeJ mice were higher than those of C3H/HeN mice. These findings suggest that lack of host responsiveness to lipopolysaccharide affects the manifestation of subsequent immune responses to orally administered antigens. The possible mechanisms and implications of this high responsiveness are discussed.

Biology, immunology, and cariogenicity of Streptococcus mutans

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Comparison of the plaque microflora in immunodeficient and immunocompetent dental patients

The nature and extent of the immune dysfunctions in 20 immunodeficient patients, as well as the immunocompetence of 22 control subjects, were verified by cell-mediated responsiveness and immunoglobulin quantitations. Comparisons of the microbial composition of supragingival plaque between the two populations showed that a greater number of immunodeficient than control subjects harbored Candida sp. and Staphylococcus sp. Conversely, a lower number of immunodeficient than control subjects harbored Streptococcus mutans. Also, patients with immune dysfunctions had a lower dental caries experience than their immunocompetent counterparts.

Secretory component of epithelial cells is a surface receptor for polymeric immunoglobulins

Epithelial cells of human fetal intestines and of a colonic carcinoma cell line (HT-29) exhibited intracellular and surface binding of polymeric immunoglobulins of IgA and IgM classes; monomeric IgA and IgG did not bind to these cells. Secretory component was identified as the receptor involved in the immunoglobulin binding. This conclusion was confirmed by the following experiments: trypsin abrogated the surface binding of polymeric immunoglobulin, reappearance of surface secretory component (SC) restored immunoglobulin binding; the appearance of SC in developing fetal tissues coincided with their potential to bind polymeric immunoglobulin; anti-SC reagents inhibited the binding of immunoglobulins to epithelial cells; and SC-containing secretory IgA did not bind to the surface of HT-29 cells.

Secretory immunity and immunodeficiency

1) Certain selective IgA-deficient subjects are capable of synthesizing functional secretory antibodies (s-IgM or s-IgA class) to indigenous oral microorganisms. 2) The presence or absence of these secretory antibodies in saliva can be correlated with the extent of caries involvement. 3) Lysozyme activity is significantly increased in saliva from immune deficient subjects though no correlation can be made with caries experience.