Occurrence of antigen-specific B cells following oral or parenteral immunization with Porphyromonas gingivalis fimbriae

Mucosal Vaccination Against Periodontal Disease: Current Status and Opportunities

Approximately 9 out of 10 adults have some form of periodontal disease, an infection-induced inflammatory disease of the tooth-supporting tissues. The initial form, gingivitis, often remains asymptomatic, but this can evolve into periodontitis, which is typically associated with halitosis, oral pain or discomfort, and tooth loss. Furthermore, periodontitis may contribute to systemic disorders like cardiovascular disease and type 2 diabetes mellitus. Control options remain nonspecific, time-consuming, and costly; largely relying on the removal of dental plaque and calculus by mechanical debridement. However, while dental plaque bacteria trigger periodontal disease, it is the host-specific inflammatory response that acts as main driver of tissue destruction and disease progression. Therefore, periodontal disease control should aim to alter the host's inflammatory response as well as to reduce the bacterial triggers. Vaccines may provide a potent adjunct to mechanical debridement for periodontal disease prevention and treatment. However, the immunopathogenic complexity and polymicrobial aspect of PD appear to complicate the development of periodontal vaccines. Moreover, a successful periodontal vaccine should induce protective immunity in the oral cavity, which proves difficult with traditional vaccination methods. Recent advances in mucosal vaccination may bridge the gap in periodontal vaccine development. In this review, we offer a comprehensive overview of mucosal vaccination strategies to induce protective immunity in the oral cavity for periodontal disease control. Furthermore, we highlight the need for additional research with appropriate and clinically relevant animal models. Finally, we discuss several opportunities in periodontal vaccine development such as multivalency, vaccine formulations, and delivery systems.

Enhancing specific-antibody production to the ragB vaccine with GITRL that expand Tfh, IFN-γ(+) T cells and attenuates Porphyromonas gingivalis infection in mice

The outer membrane protein RagB is one of the major virulence factors of the periodontal pathogen Porphyromonas gingivalis (P. gingivalis). In order to induce protective immune response against P. gingivalis infection, an mGITRL gene-linked ragB DNA vaccine (pIRES-ragB-mGITRL ) was constructed. Six-week-old female BALB/c mice were immunized with pIRES-ragB-mGITRL through intramuscular injection and then challenged by subcutaneous injection in the abdomen with P. gingivalis. RagB-specific antibody-forming cells were evaluated by an Enzyme-linked immunosorbent spot, and specific antibody was determined by enzyme-linked immunosorbent assay. In addition, the frequencies of Tfh and IFN-γ(+) T cells in spleen were measured using flow cytometer, and the levels of IL-21 and IFN-γ mRNA or proteins were detected by real time RT-PCR or ELISA. The data showed that the mGITRL-linked ragB DNA vaccine induced higher levels of RagB-specific IgG in serum and RagB-specific antibody-forming cells in spleen. The frequencies of Tfh and IFN-γ(+) T cells were obviously expanded in mice immunized by pIRES-ragB-mGITRL compared with other groups (pIRES or pIRES-ragB ). The levels of Tfh and IFN-γ(+) T cells associated cytokines were also significantly increased in pIRES-ragB-mGITRL group. Therefore, the mice immunized with ragB plus mGITRL showed the stronger resistant to P. gingivalis infection and a significant reduction of the lesion size caused by P. gingivalis infection comparing with other groups. Taken together, our findings demonstrated that intramuscular injection of DNA vaccine ragB together with mGITRL induced protective immune response dramatically by increasing Tfh and IFN-γ(+) T cells and antibody production to P. gingivalis.

Oral immunoadjuvant activity of Lactobacillus casei subsp. casei in dextran-fed layer chickens

We recently reported that synbiotic Lactobacillus casei subsp. casei together with specific substrate dextran elicited an enhancement in humoral immune response against bovine serum albumin (BSA) as a model antigen in BALB/c mice. The present study was designed to evaluate the oral immunoadjuvant effects of the synbiotic in layer chickens. Using a PCR assay, L. casei subsp. casei was detected specifically in the intestinal chyme of chickens (10 d of age, Julia strain) fed ad libitum on a diet supplemented with 75 mg dextran/kg (dextran-supplemented diet, DSD) and administered orally with 10(7) colony-forming units (CFU) L. casei subsp. casei in 0.1 ml PBS with the aid of an intubation needle at 1, 2 and 3 d of age. Furthermore, oral administration of 10(7) CFU L. casei subsp. casei at 1-3 d of age significantly enhanced the production of anti-BSA antibody in DSD-fed chickens (60 d of age) administered orally with 1 mg BSA at 32 and 33 d of age and subcutaneously with 5 microg BSA at 33 d of age. In addition, among bacterial numbers tested, 10(6) CFU L. casei subsp. casei together with dextran induced an effective increase in humoral immune response to mixed inactivated vaccines against Newcastle disease and avian infectious bronchitis, and the treatment may be advantageous in protecting against these infectious diseases in chickens in actual application. These results suggest that dietary supplementation of L. casei subsp. casei with dextran leads to immunomodulation of humoral immune responses.

Nasopharyngeal-Associated Lymphoreticular Tissue (NALT) Immunity: Fimbriae-Specific Th1 and Th2 Cell-Regulated IgA Responses for the Inhibition of Bacterial Attachment to Epithelial Cells and Subsequent Inflammatory Cytokine Production

To investigate the antibacterial activity of mucosal Th1 and Th2 immune responses induced nasally and orally, mice were immunized with mucosal vaccine containing fimbrial protein of Porphyromonas gingivalis, a causative agent for a destructive chronic inflammation in the periodontium, and cholera toxin (CT) as mucosal adjuvant. Nasal vaccine containing low doses of fimbriae (10 μg) and CT (1 μg) induced Ag-specific Th1/Th2-type response in CD4+ T cells in mucosal effector tissues, including nasal passage and submandibular glands, which accounted for the generation of Ag-specific IgA-producing cells. In contrast, oral immunization required higher amounts of fimbriae and CT for the induction of Ag-specific IgA responses. Fimbriae-specific IgA mAbs generated from submandibular glands of nasally immunized mice inhibited P. gingivalis attachment to and reduced subsequent inflammatory cytokine production from epithelial cells. These findings suggest that nasal vaccination is an effective immunization regimen for the induction of Ag-specific Th1 and Th2 cell-driven IgA immune responses that possess the ability to inhibit bacterial attachment to epithelial cells and subsequent inflammatory cytokine production.

Induction of systemic murine B-cell responses by Fusobacterium nucleatum and Porphyromonas gingivalis

The purpose of this study was to examine the antigenic abilities of Fusobacterium nucleatum strain ATCC 25586 and Porphyromonas gingivalis strain W50 black inbred BALB/cABom mice immunized subcutaneously. Furthermore, we aimed to analyze whether the outer membranes (OM) and whole cells (WC) of F. nucleatum or P. gingivalis had an effect on the levels of antibody response and whether a combination of both could either enhance or suppress the B-cell response. A single-cell assay, solid-phase enzyme-linked immunospot (ELISPOT), was used to analyze the splenic B-cell response (immunoglobulin A (IgA), IgG and IgM). Enzyme-linked immunosorbent assay (ELISA) and immunoblotting were used to verify the specific antibody response in the sera. A statistically significant lower level of spontaneous antibody production was observed in the group immunized with P. gingivalis OM compared with groups immunized with F. nucleatum and saline. The specific antibody titers measured by ELISA indicated that the bacterial preparations were able to induce IgG and IgM response. The preparations containing P. gingivalis OM induced higher humoral response than the preparations containing P. gingivalis WC, but for F. nucleatum such a difference was not observed. The prominent proteins revealed had apparent molecular masses of 40 kDa for F. nucleatum and 115, 55-56 and 43 kDa for P. gingivalis; whereas the immunoreactive proteins were 70, 65 and 40 kDa for mice immunized with F. nucleatum and 115, 55-56, 43 and 33-34 kDa for mice immunized with P. gingivalis. Quantitative analysis of B-cell response at the single cell level with ELISPOT revealed that some component(s) of P. gingivalis OM may have a suppressive ability on splenocytes incubated for a short time.

Immunochemical characterisation and epitope mapping of a novel fimbrial protein (Pg-II fimbria) of Porphyromonas gingivalis

Mouse monoclonal antibody (mAb) Pgf-II specific for a 72-kDa major cell-surface protein (72K-CSP) derived from Porphyromonas gingivalis OMZ 409 was prepared. Immunoblotting analysis revealed that mAb Pgf-II reacted with 72K-CSP but not with 41-kDa fimbrial subunit protein (41K-fimbrilin) derived from P. gingivalis 381. Electron microscopic observation revealed that P. gingivalis OMZ 409 possessed peritrichous, thin fimbriae on their surface. Immunogold electron microscopy also demonstrated that mAb Pgf-II bound to the 72K-CSP examined with the gold particles arranged along the fibril array originating from the cell surface of the bacteria. These findings suggested that P. gingivalis 72K-CSP was identifiable as another fimbriae (termed Pg-II fimbriae) different from the fimbriae (termed Pg-I fimbriae) composed of a 41K-fimbrilin. Using multipin peptide synthesis technology, 102 sequential overlapping peptides covering the entire 514 amino-acid stretch of Pg-II fimbriae were synthesised. Seven immunodominant regions within Pg-II fimbrial protein molecule, which definitely reacted with the serum of patients with periodontal diseases, were detected.

The effects of transforming growth factor-beta and interleukins 2, 5 and 6 on immunoglobulin production in cultured rat salivary gland tissues

The effects of transforming growth factor-beta, alone, and in combination with selected interleukins on immunoglobulin production were investigated using an in vitro rat tissue fragment culture system with either parotid, submandibular or sublingual gland tissue. In the majority of culture groups, TGF-beta alone, or in combination with either interleukin 2 (IL-2), IL-5, IL-6 or IL-5 and IL-6 together, significantly increased immunoglobulin A (IgA) levels over those obtained in untreated cultures. The levels of IgG and IgM were generally not affected, with the exception of one sublingual and two submandibular groups(s), where cytokine administration up-regulated either IgG or IgM production. These data indicate that transforming growth factor-beta in combination with IL-2, IL-5, IL-6 or IL-5 and IL-6 can exert a stimulatory effect on IgA production in vitro, supporting a potential regulatory role for these cytokines in salivary gland IgA responses.

Characterization of cytokine-producing cells in mucosal effector sites: CD3+ T cells of Th1 and Th2 type in salivary gland-associated tissues

The major purpose of this study was to elucidate Th1 [interferon (IFN)-gamma and interleukin (IL)-2] and Th2 (IL-4, IL-5 and IL-6) cytokine-producing CD3+ T cells in salivary glands, which are the major mucosal effector tissues in the oral region. Thus, CD3+ T cells were isolated from salivary gland-associated tissues (SGAT) which consist of the submandibular gland (SMG: approximately 46%), the periglandular lymph node (PGLN: approximately 72%), and the cervical lymph node (CLN: approximately 90%). When SMG CD3+ T cells were examined by Th1 and Th2 cytokine-specific ELISPOT and reverse transcriptase-polymerase chain reaction assay, high levels of both cytokine-specific spot-forming cells (SFC) and mRNA for IFN-gamma, and for IL-5 and IL-6 were noted as representative Th1 or Th2 cytokines, respectively. Following stimulation with concanavalin A (Con A), SMG CD3+ T cells expressed mRNA and produced lymphokines for an array of Th1 (IFN-gamma and IL-2) and Th2 (IL-4, IL-5 and IL-6) cytokines. In comparison to the SMG CD3+ T cells, PGLN and CLN contain lower numbers of IFN-gamma-, IL-5 and IL-6-producing T cells. When these two tissues were compared, PGLN CD3+ T cells contained higher numbers of cytokine-secreting cells than CLN. Further, IL-2 and IL-4 SFC and mRNA were also noted in addition to IFN-gamma, IL-5 and IL-6 after Con A activation. These findings showed that CD3+ T cells in SGAT, especially the SMG, are programmed to produce IFN-gamma, and IL-5 and IL-6 as Th1 and Th2 cytokines, respectively in vivo, although these cells are capable of producing other Th1 and Th2 cytokines after receiving appropriate T cell activation signals.

Chemotaxis of human monocytes by synthetic peptides that mimic segments of Porphyromonas gingivalis fimbrial protein

Porphyromonas gingivalis strain 381 fimbriae and their synthetic peptide segments were assessed for migration-stimulating activity on human peripheral blood monocytes by multiwell chemotaxis assay. P. gingivalis 381 fimbrial protein was found to markedly enhance migration of human monocytes. The observed increase in monocyte migration occurred mainly directed toward a positive stimulus (chemotaxis). Furthermore, lipopolysaccharides extracted from P. gingivalis 381 were shown to induce chemotaxis and chemokinesis. It was also revealed that the migration of monocytes was increased by specific synthetic peptide segments, FP381(61-80) and FP381(171-185), that correspond to GKTLAEVKALTTELTAENQE and DANYLTGSLTTFNGA, respectively, based on the amino acid sequence of the fimbrial subunit protein proposed by Dickinson et al., and the migration stimulation was ascribed to chemotaxis. Furthermore, within the amino acid sequences, the LTXXLTXXN sequence may play an important role in binding the organisms to monocytes and macrophages and in the induction of migration-stimulating activity.

Porphyromonas gingivalis fimbriae and their synthetic peptides induce proinflammatory cytokines in human peripheral blood monocyte cultures

Porphyromonas gingivalis fimbriae as well as synthetic peptides that mimic the fimbrial subunit protein, which includes the amino acid sequence XLTXXLTXXNXX, induced high production of proinflammatory cytokines such as interleukin-1 beta, interleukin-6, interleukin-8, tumor necrosis factor-alpha in human peripheral blood monocyte/macrophage cultures. Responses induced by some peptide segments were comparable to those induced by Escherichia coli lipopolysaccharides. A chemically modified peptide analogous to an active peptide segment was found to be antagonistic with regard to interleukin-6 production induced by the native fimbriae. It may be suggested that P. gingivalis fimbriae and their degraded peptides function as proinflammatory agents in vivo, while certain analog peptides inhibited the process.

Immunobiological properties of chemically defined lipid A from lipopolysaccharide of Porphyromonas (Bacteroides) gingivalis

Porphyromonas gingivalis 381 lipid A, characterized by beta-(1-6)-linked glucosamine disaccharide 1-phosphate, with one hydroxyacyl group and one acyloxyacl group, i.e., 3-hydroxy-15-methyl-hexadecanoyl and 3-hexadecanoyloxy-15-methylhexadecanoyl groups at the 2 and 2' positions, respectively, was less endotoxically active than the synthetic Escherichia-coli-type lipid A (compound 506), which possesses beta-(1-6)-linked glucosamine disaccharide 1,4'-bisphosphate, with two acyloxyacyl groups at the 2' and 3' positions and two 3-hydroxytetradecanoyl group at the 2 and 3 positions and the synthetic Salmonella-type lipid A (compound 516), which has three acyloxyacyl groups at the 2,2' and 3' positions and one hydroxyacyl group at the 3 position. P. gingivalis lipid A exhibited no or very low endotoxic activities, i.e., lethal toxicity in galactosamine-loaded mice, preparative ability for local Shwartzman reaction, pyrogenicity and Limulus test as compared with compounds 506 and 516. However, polyclonal B-cell activation of BALB/c mouse splenocytes was as strong as that of compound 506. Furthermore, P. gingivalis lipid A had stronger immunoadjuvant and hemagglutinating activities than compound 506. The absence of ester-linked phosphate at the 4' position and ester-linked fatty acids, and the presence and positions of fatty acids possessing considerable lengths of acyl chains are unique features of P. gingivalis lipid A, and they differentiate this lipid A from enterobacterial and other lipids A. The good balance between endotoxic properties and beneficial immunobiological activities of P. gingivalis lipid A may be attributable to these features.

Generation of specific antibody-secreting cells in salivary glands of BALB/c mice following parenteral or oral immunization with Porphyromonas gingivalis fimbriae

The humoral immune response and induction of antigen-specific antibody-secreting cells in mucosal lymphoid tissues were examined in mice immunized subcutaneously or orally with fimbrial protein purified from Porphyromonas gingivalis strain 381. A group of BALB/c mice was immunized subcutaneously with P. gingivalis fimbriae and semisynthetic adjuvant GM-53 in Freund's incomplete adjuvant on days 0 and 28. Another group of mice was immunized perorally with liposome containing fimbriae and GM-53 on days 0, 1, 27 and 28. In the mice immunized subcutaneously, salivary anti-fimbrial IgM antibodies were detected transiently on day 5, followed by the appearance of specific IgG and IgA antibodies on day 14. Higher concentrations of salivary IgG and IgA anti-fimbrial antibodies were found after the second immunization. Fimbria-specific IgM and IgG spot-forming cells (SFC) were detected in cervical lymph nodes of the immunized mice by the ELISPOT method. Fimbria-specific IgA SFC but not IgM and IgG appeared in the parotid and submandibular glands of subcutaneously immunized mice. On the other hand, mice immunized by gastric intubation generated almost exclusively salivary anti-fimbrial IgA antibodies. In agreement with this finding, increased numbers of antigen-specific IgA but not IgM and IgG SFC were seen in parotid and submandibular glands, but not in cervical lymph nodes of orally immunized mice. It can be concluded that systemic or oral immunization with fimbrial antigen induces distinct immune responses in specific lymphoid tissues or in the salivary glands in respect of their temporal sequences and the numbers of plasma cells secreting antigen-specific and non-specific immunoglobulins.

Cytokine production and T cell receptor expression by salivary gland T cells and intraepithelial T lymphocytes for the regulation of the IgA response

The IgA effector sites such as the salivary glands and the intestinal tract contain several distinct T cell subsets which possess unique biologic characteristics. Freshly isolated CD3+ T cells from the salivary glands, the LP region of the small intestine and IELs all harbor T cells which spontaneously produce Th1 (IFN-gamma)- and Th2 (IL-5 and IL-6)-type cytokines. Interestingly, a high frequency of IL-5-producing Th2-type cells is always associated with the occurrence of increased numbers of IgA plasma cells (e.g., the salivary glands and the LP region of the small intestine). Further, the salivary gland CD3+ T cells can be divided into three distinct subsets including those of CD4+, CD8- (12-23%), CD4-, CD8+ (18-25%) and DN (6-16%) T cells. In terms of TCR expression, CD4+, CD8- and DN T cells exclusively expressed alpha/beta TCR and gamma/delta TCR, respectively. One of the unique features of the salivary gland T cells is that like IELs, relatively high numbers of gamma/delta TCR-bearing cells are seen in the CD4-, CD8+ T cell fraction. Since our study has provided important new evidence that these gamma/delta TCR-bearing T cells from IELs of mice orally immunized with TD antigen possess the capability of abrogating oral tolerance to antigen-specific immune responses including the IgA isotype, one can visualize that gamma/delta TCR+ T cells can be essential regulatory T cells which protect (or enhance) alpha/beta TCR+, CD4+ Th cells for maximum IgA responses at IgA effector tissues including the salivary glands, and the gastrointestinal tract in the presence of an active state of systemic unresponsiveness or oral tolerance.

Induction of mucosal and serum immune responses to a specific antigen of periodontal bacteria

The dynamics of the host immune response to periodontal bacteria not only may be informative from the standpoint of specific mucosal protection to these pathogens, but also may reveal the capacity of the mucosal immune response to provide protection of the host. To this end, we have examined the immune response to chromatographically purified fimbriae of P. gingivalis administered orally or systemically with liposomes and adjuvant in BALB/c mice, high responders to this antigen. Oral administration of P. gingivalis fimbriae clearly enhanced the fimbriae-specific salivary IgA response. ELISPOT analysis revealed that significant numbers of fimbriae-specific IgA SFC were seen in lamina propria and mesenteric lymph nodes but not in Peyer's patches of mice immunized orally. In contrast, antigen-specific IgM and IgG SFC were seen mainly in the circulating blood mononuclear cells. On the other hand, subcutaneous injection of fimbriae with GM-53 also raised the fimbriae-specific IgG followed by IgM and IgA responses in serum, and both IgA and IgG responses in saliva. Oral immunization was less effective than subcutaneous injection in terms of the serum antibody response. However, the salivary antibody level of mice injected subcutaneously was similar to that of mice immunized orally. In the subcutaneously immunized mice, fimbriae-specific SFC were detected in the spleen, blood, and brachial lymph nodes by ELISPOT assay. Fimbriae-specific IgM SFC appeared earlier and antigen-specific IgG SFC were seen later. These results show that the combined use of fimbriae together with the adjuvant results in sharply increased IgA responses in saliva and IgG responses in serum. In summary, it is clear that the nature of the host's antibody response in serum and mucosal secretions is distinct, and depends on the route of antigen administration, the use of adjuvant and/or liposomes, and the temporal phase of the humoral immune response following various immunization regimes.