Senior Member of the Staff
Chair, Department of Immunology and Infectious Diseases
Hiroshima University, D.D.S., 1989, Dental Science
Osaka University, Ph.D., 1993, Immunology/Periodontology
Immune responses are an essential means by which the body defends itself from infectious agents. A critical part of this defense system depends upon the body’s ability to discriminate between self and non-self. This raises an interesting fundamental question as to how the body is able to recognize the difference between commensal bacteria, which are beneficial, or at least not harmful, and pathogenic microorganisms which must be eliminated. Clues to the elucidation of this phenomenon might lie in our understanding of mucosal tolerance. Mucosal tolerance is defined as the suppression, or down-regulation, of adaptive immune responses mediated by T- and B-cells via prior challenge with the antigen through the mucosal surface.
In contrast to the well-characterized mucosal tolerance in gastrointestinal systems, the tolerance systems in the oral mucosa remain unclear. However, many lines of evidence imply that the commensal host-bacteria relationship in the oral cavity is maintained by means of oral mucosal tolerance. For this reason, the Kawai Laboratory is investigating the mechanisms underlying the oral mucosal tolerance system that allow commensal organisms to flourish, as well as studying the consequences when such immune tolerance is disrupted. Our ultimate goal is to establish therapeutic approaches to the amelioration of periodontal disease and other systemic disorders where pathogenesis is associated with the loss or reduction of immune tolerance.
Gingival epithelial cells play a key role in educating regulatory dendritic cells (DCr) that can induce regulatory T cells (Tr). In the initial focus of our investigation, we are interested in understanding how cells lining the mucosal surface transfer information to immune regulatory cells in order to induce tolerance. Oral tolerance is characterized by lymphocyte hypo-responsiveness to both food antigens and commensal bacteria. The lymphocyte hypo-responsiveness appears to be controlled by regulatory T (Tr) cells that express a gene encoding Forkhead box protein P3 (FOXP3). A recent report has demonstrated that FOXP3 positive T cells are abundant in the gingival tissues. FOXP3 positive Tr cells produce the immune suppressive cytokine IL-10, which counter-regulates the production of tissue-destructive proinflammatory factors, such as IL-1, TNFå- and RANKL. The results from our experiments have indicated that the dendritic cells (DC) localized in gingival epithelial cells can control the differentiation of FOXP3+ Tr cells.
These dendritic cells (regulatory DC; DCr) present bacterial antigen to naïve T cells, and consequently induce differentiation of FOXP3+ Tr cells. Very interestingly, gingival epithelial cells (GEC) appear to possess a potential to educate peripheral blood monocytes so that the monocytes differentiate into DCr. After in vitro co-culture with GEC, but not with other types of epithelial cells, peripheral blood monocytes differentiated into DCr that produce prominent IL-10 and less IL-12. The DCr, developed via an in vitro "GEC education," induced the differentiation of FOXP3+/IL-10+ Tr cells from peripheral blood naïve T cells. Additionally, the surface marker, Langerin (CD207), was expressed by the DCr as well as very distinct signal transduction molecules that are found in the gingival epithelial DCr.
A second focus of our investigation is the receptor activator of nuclear factor-kB (RANKL) which is a TNF-super family molecule that plays a pivotal role in homeostatic bone remodeling as well as in the development of pathogenic bone resorptive lesions. Our study on clinical gingival samples revealed that concentrations of soluble RANKL (sRANKL), but not its decoy receptor osteoprotegerin (OPG), were significantly elevated in gingival tissues with periodontal disease compared to healthy gingival tissues. Based on double-color confocal microscopic analyses, a majority of B- and T-cells in the diseased gingival tissue expressed RANKL, whereas few lymphocytes expressed RANKL in healthy gingival tissue. Expression of RANKL by monocytes/macrophages, or by other cell types, was not as prominent as B- or T-cells in the diseased gingival tissues. The lymphocytes isolated from patient’s gingival tissue induced in vitro osteoclast differentiation in a RANKL-dependent manner, indicating that RANKL expressed by the periodontal lymphocytes appeared to be functionally active. According to examination using gingival tissue homogenates, the concentration of RANKL and IgG antibodies to some of the oral commensal bacteria showed a positive correlation, thus indicating that immune recognition (i.e., breakdown of tolerance) to oral commensal bacteria is increased in the bone resorpive lesion of periodontal disease.
In order to elucidate the commensal host-bacterial relationship in the oral cavity, we have recently established a mouse model of periodontal disease utilizing commensal bacteria in laboratory mice. It is the mouse oral commensal bacterium, Pasteurella pneumotropica (Pp) that allows us to study the oral mucosal tolerance in the context of periodontal disease. Very importantly, Pp is phylogenically related to a pathogen of localized aggressive periodontitis (LAP), Actinobacillus actimomycetemcomitans (Aa).
In our model, oral colonization of Pp establishes a host-commensal relationship in the oral cavity of BALB/c mice. Mucosal T cell tolerance is then elicited to orally colonized Pp, which, while characterized by salivary IgA responses to 27 kD protein antigen (OmpA) of Pp, produces little, or no, Th1-, Th2- or IgG-responses to this organism. Systemic immunization with Aa (not by oral inoculation) broke the T cell tolerance to Pp in conjunction with the induction of serum IgG antibody to Pp OmpA. It appeared that the strong antigenicity of Aa Omp29 elicited a cross reactive immune response to Pp OmpA, consequently breaking down the tolerance to Pp. The breakdown of tolerance also resulted in periodontal bone resorption in a RANKL-dependent manner, as well as reduction of FOXP+ T cells in the tissue. Adoptive transfer of FOXP+/RANKL-/ CD4+ Treg cells reduced the expression of RANKL in the gingival tissue of animals receiving systemic immunization with Aa, and, as a result, abrogated the periodontal bone resorption. These results suggest that systemic challenge with cross-reactive antigen can disturb T cell tolerance to oral commensal bacteria and can, therefore, result in RANKLmediated periodontal bone resorption. FOXP+ Treg cells appear to play a key role in the maintenance of such T cell tolerance to oral commensal bacteria.
Using this mouse model of periodontal disease as well as previously established rat models, our investigations are directed toward the development of therapeutic approaches to ameliorate periodontal disease. To this end, several different approaches are currently being tested: (1) RNAi-based gene therapy to silence the key signaling molecule that causes pathogenic bio-reactions; (2) Auto-regulatory lymphocyte transplantation therapy; and (3) CAM (complementary and alternative medicine) therapy using natural products that promote the oral commensal host-bacterial relationship.
Kajiya M, Giro G, Taubman MA, Mayer MPA, Kawai T. (2010) Role of periodontal pathogenic bacteria in RANKL-mediated bone destruction in periodontal disease. Journal of Oral Microbiology. Accepted for publication.
Han X, Lin X, Seliger AR, Eastcott J, Kawai T, Taubman MA. (2009) Expression of receptor activator of nuclear factor-kB ligand by B cells in response to oral bacteria. Oral Microbiol. Immunol. 24(3):190-196.
Kajiya M, Silva MJ, Sato K, Ouhara K, Kawai T. (2009) Hydrogen mediates suppression of colon inflammation induced by dextran sodium sulfate. Biochem. Biophys. Res. Commun. 386(1):11-15.
Kajiya M, Sato K, Silva MJ, Ouhara K, Do PM, Shanmugam KT, Kawai T. (2009) Hydrogen from intestinal bacteria is protective for Concanavalin A-induced hepatitis. Biochem. Biophys. Res. Commun. 386(2):316-321.
Rezende TM, Vieira LQ, Sobrinho AP, Oliveira RR, Taubman MA, Kawai T. (2008) The influence of mineral trioxide aggregate on adaptive immune responses to endodontic pathogens in mice. J. Endod. 34(9):1066-1071.
Cortelli JR, Aquino DR, Cortelli SC, Fernandes CB, de Carvalho-Filho J, Franco GC, Costa FO, Kawai T. (2008) An etiological study analyzing initial colonization of periodontal pathogens in oral cavity. J. Clin. Micriobiol. 46: 1322-1329. PMCID: PMC2292974
Kim DM, Koszeghy KL, Badovinac RL, Kawai T, Hosokawa I, Howell TH, Karimbux NY. (2007) The effect of aspirin on gingival crevicular fluid levels of inflammatory and anti-inflammatory mediators in patients with gingivitis. J. Periodontol. 78(8):1620-1626.
Ernst CW, Lee JE, Nakanishi T, Karimbux NY, Rezende TM, Stashenko P, Seki M, Taubman MA, Kawai T. (2007) Diminished forkhead box P3/CD25 double-postive T regulatory cells are associated with the increased nuclear factor-kappaB ligand (RANKL+) T cells in bone resorption lesion of peridontal disease. Clin. Exp. Immunol. 148(2):271-280.
Kawai T, Paster BJ, Komatsuzawa H, Ernst CW, Goncalves RB, Sasaki H, Ouhara K, Stashenko PP, Sugai M, Taubman MA. (2007) Cross-reactive adaptive immune response to oral commensal bacteria results in an induction of receptor activator of nuclear factor-kappaB ligand (RANKL)-dependent periodontal bone resorption in a mouse model. Oral Microbiol. Immunol.22(3):208-215.
Bartlett JD, Ball RL, Kawai T, Tye CE, Tsuchiya M, Simmer JP. (2006) Origin, splicing, and expression of rodent amelogenin exon 8. J. Dent. Res. 85(10):894-899.
Nichols FC, Riep B, Mun J, Morton MD, Kawai T, Dewhirst FE, Smith MB. (2006) Structures and biological activities of novel phosphatidylethanolamine lipids of Porphyromonas gingivalis. J. Lipid Res. 47(4):844-853.
Ouhara K, Komatsuzawa H, Shiba H, Uchida Y, Kawai T, Sayama K, Hashimoto K, Taubman MA, Kurihara H, Sugai M. (2006) Actinobacillus actinomycemcomitans OMP-100 triggers innate immunity, ß-deficient and CAP18 (LL37) production, through the fibronectin-integrin pathway in human gingival epithelial cells. Infect. Immun. 74(9):5211-5220.
Hosokawa I, Hosokawa Y, Komatsuzawa H, Goncalves RB, Karimbux NY, Napimoga MH, Seki M, Ouhara K, Sugai M, Taubman MA, Kawai T. (2006) Innate immune peptide LL-37 displays distinct expression pattern from beta-defensins in inflamed gingival tissue. Clin. Exp. Immun. 146(2):218-225.
Kawai T, Matsuyama T, Hosokawa Y, Makihira S, Seki M, Karimbux NY, Goncalves RB, Valverde P, Dibart S, Li YP, Miranda LA, Ernst CWO, Izumi Y, Taubman MA. (2006) B and T lymphocytes are the primary sources of RANKL in the bone resorptive lesion of periodontal disease. Am. J. Pathol. 169(3):987-998.
Kawai T. Hypermucoviscosity: An Extremely Sticky Phenotype of KKlebsiella pneumoniae associated with emerging destructive tissue abscess syndrome (editorial comment). (2006) Clinical Infect. Dis. 42(10):1359-1361.
Han X, Kawai T, Eastcott JW, Taubman MA. (2006) Bacterial-responsive B lymphocytes induce periodontal bone resorption.
J. Immunol. 176(1):625-631.
Valverde P, Kawai T, Taubman MA. (2005) Potassium channel-blockers as therapeutic agents to interfere with periodontal bone resorption. J. Dent. Res. 84(1):488-499.
Matsuyama T, Kawai T, Izumi Y, Taubman MA. (2005) Expression of major histocompatibility complex class II and CD80 by gingival epithelial cells induces activation of CD4+ T cells in response to bacterial challenge. Infect. Immun. 73(2):1044-1051.
Mikihito Kajiya, D.D.S., Ph.D.
Kouji Ohta, D.D.S., Ph.D.
Tongbo Zhu, Ph.D.
Cristine Min, B.S.
Soulafa Almazrooa, B.D.S.
Mohammed Howait, B.D.S.
Jennifer Hong, D.D.S.
Peter Ok, D.D.S.
Jane Shin, B.S.
Harrison Mackler, B.S.
Kanika Sharma, B.S.