Antibody and T Cell Responses to Fusobacterium nucleatum and Treponema denticola in Health and Chronic Periodontitis

The characteristics of the T cell response to the members of oral flora are poorly understood. We characterized the antibody and T cell responses to FadA and Td92, adhesins from Fusobacterium nucleatum, an oral commensal, and Treponema denticola, a periodontal pathogen, respectively. Peripheral blood and saliva were obtained from healthy individuals and patients with untreated chronic periodontitis (CP, n = 11 paris) and after successful treatment of the disease (n = 9). The levels of antigen-specific antibody were measured by ELISA. In plasma, IgG1 was the most abundant isotype of Ab for both Ags, followed by IgA and then IgG4. The levels of FadA-specific salivary IgA (sIgA) were higher than Td92-specific sIgA and the FadA-specific IgA levels observed in plasma. However, the periodontal health status of the individuals did not affect the levels of FadA- or Td92-specific antibody. Even healthy individuals contained FadA- and Td92-specific CD4+ T cells, as determined by the detection of intracytoplasmic CD154 after short-term in vitro stimulation of peripheral blood mononuclear cells (PBMCs) with the antigens. Patients with CP tended to possess increased numbers of FadA- and Td92-specific CD4+ T cells but reduced numbers of Td92-specific Foxp3+CD4+ Tregs than the healthy subjects. Both FadA and Td92 induced the production of IFNγ and IL-10 but inhibited the secretion of IL-4 by PBMCs. In conclusion, F. nucleatum induced Th3 (sIgA)- and Th1 (IFNγ and IgG1)-dominant immune responses, whereas T. denticola induced a Th1 (IFNγ and IgG1)-dominant response. This IFNγ-dominant cytokine response was impaired in CP patients, and the Td92-induced IFNγ levels were negatively associated with periodontal destruction in patients. These findings may provide new insights into the homeostatic interaction between the immune system and oral bacteria and the pathogenesis of periodontitis.

目前学界对于口腔菌群成员所引发的T细胞应答特征尚不明晰。本研究针对具核梭杆菌（Fusobacterium nucleatum，一种口腔共生菌）来源的黏附素FadA，以及牙周病原体齿垢密螺旋体（Treponema denticola）来源的黏附素Td92，分别表征了宿主针对二者的抗体与T细胞应答。本研究招募了健康个体、未接受治疗的慢性牙周炎（chronic periodontitis, CP）患者（n=11对），以及经成功治疗后的慢性牙周炎患者（n=9），采集其外周血与唾液样本。采用酶联免疫吸附实验（ELISA）检测抗原特异性抗体水平。在血浆中，两种抗原对应的抗体免疫球蛋白亚型均以IgG1丰度最高，其次为IgA，再次为IgG4。FadA特异性唾液免疫球蛋白A（sIgA）水平高于Td92特异性sIgA，同时也高于血浆中检测到的FadA特异性IgA水平。然而，个体的牙周健康状态并未影响FadA或Td92特异性抗体的水平。通过用抗原对体外短期培养的外周血单个核细胞（PBMCs）进行刺激后检测胞内CD154的表达，结果显示即便健康个体体内也存在FadA与Td92特异性CD4+ T细胞。与健康受试者相比，慢性牙周炎患者体内FadA与Td92特异性CD4+ T细胞的数量呈升高趋势，但Td92特异性叉头框P3（Foxp3）阳性CD4+调节性T细胞（Tregs）的数量有所减少。FadA与Td92均可诱导PBMCs产生干扰素γ（IFNγ）与白细胞介素10（IL-10），但会抑制PBMCs分泌白细胞介素4（IL-4）。综上，具核梭杆菌可诱导以3型辅助T细胞（Th3，对应sIgA）与1型辅助T细胞（Th1，对应IFNγ与IgG1）为主的免疫应答，而齿垢密螺旋体则仅诱导以Th1为主的免疫应答。这种以IFNγ为主的细胞因子应答在慢性牙周炎患者体内出现损伤，且Td92诱导的IFNγ水平与患者的牙周组织破坏程度呈负相关。本研究结果可为免疫系统与口腔细菌间的稳态互作，以及牙周炎的发病机制研究提供新的视角。