These results demonstrate that periodontal lesions induced with different A. actinomycetemcomitans serotypes elicited distinct alveolar bone resorption and immune response. In particular, serotype b was more pathogenic than the others and induced stronger Th1 and Th17 patterns of immune responses during experimental periodontitis.

Background Encapsulation of Porphyromonas gingivalis has been demonstrated as responsible of several host immunological changes, which have been associated with the pathogenesis of periodontitis. Using a murine model of periodontitis and two isogenic non‐capsulated mutants of P. gingivalis, this study aimed to analyze whether P. gingivalis encapsulation induces more severe alveolar bone resorption, and whether this bone loss is associated with a T‐helper (Th)1 and Th17‐pattern of immune response. Methods Experimental periodontal infections were generated by oral inoculation with the encapsulated W50 wild‐type strain or isogenic non‐encapsulated ΔPG0116‐PG0120 (GPA) and ΔPG0109‐PG0118 (GPC) mutants of P. gingivalis. Periodontal infections induced with the encapsulated HG184 or non‐encapsulated ATCC 33277 strains of P. gingivalis were used as controls. Alveolar bone resorption was analyzed using microcomputed tomography and scanning electron microscopy. The expression levels of Th1, Th2, Th17, or T regulatory‐associated cytokines and RANKL, as well as the periodontal bacterial load, were quantified by quantitative polymerase chain reaction. The detection of Th1 and Th17 lymphocytes was analyzed by flow cytometry. Results In the periodontal lesions, both capsular‐defective knockout mutant strains of P. gingivalis induced less alveolar bone resorption than the encapsulated W50 wild‐type strain. This decreased bone loss was associated with a dismissed RANKL expression, decreased Th1‐ and Th17‐type of cytokine expression, reduced Th1 and Th17 lymphocyte detection, and low osteoclast finding. Conclusion These data demonstrate that encapsulation of P. gingivalis plays a key role in the alveolar bone resorption induced during periodontitis, and this bone loss is associated with a Th1‐ and Th17‐pattern of immune response triggered in the periodontal lesions.

Background and Objective Over the past few years, the importance of interleukin‐22 (IL‐22) and T‐helper (Th)22 lymphocytes in the pathogenesis of periodontitis has become apparent; however, there are still aspects that are not addressed yet. Cells expressing IL‐22 and aryl hydrocarbon receptor (AhR), transcription factor master switch gene implicated in the differentiation and function of Th22 lymphocytes, have been detected in periodontal tissues of periodontitis‐affected patients. In addition, IL‐22 has been associated with osteoclast differentiation and their bone resorptive activity in vitro. However, the destructive potential of IL‐22–expressing AhR+ Th22 lymphocytes over periodontal tissues during periodontitis has not been demonstrated in vivo yet. Therefore, this study aimed to analyze whether IL‐22–expressing CD4+AhR+ T lymphocytes detected in periodontal lesions are associated with alveolar bone resorption during experimental periodontitis. Material and Methods Using a murine model of periodontitis, the expression levels of IL‐22 and AhR, as well as the Th1‐, Th2‐, Th17‐ and T regulatory‐associated cytokines, were analyzed in periodontal lesions using qPCR. The detection of CD4+IL‐22+AhR+ T lymphocytes was analyzed in periodontal lesions and cervical lymph nodes that drain these periodontal lesions using flow cytometry. In addition, the expression of the osteoclastogenic mediator called receptor activator of nuclear factor‐κB ligand (RANKL) was analyzed by qPCR, western blot, and immunohistochemistry. Finally, alveolar bone resorption was analyzed using micro‐computed tomography and scanning electron microscopy, and the bone resorption levels were correlated with IL‐22 and RANKL expression. Results Higher levels of IL‐22, AhR, and RANKL, as well as IL‐1β, IL‐6, IL‐12, IL‐17, IL‐23, and TNF‐α, were expressed in periodontal lesions of infected mice compared with periodontal tissues of sham‐infected and non‐infected controls. Similarly, high RANKL immunoreaction was observed in periodontal tissues of infected mice; however, few or absent RANKL immunoreaction was observed in controls. This association between RANKL and periodontal infection was ratified by western blot. Furthermore, a higher detection of CD4+IL‐22+AhR+ T lymphocytes was found in periodontal lesions and cervical lymph nodes that drain these periodontal lesions in infected mice compared with non‐infected controls. Finally, the increased IL‐22 and RANKL expression showed positive correlation between them and with the augmented alveolar bone resorption observed in experimental periodontal lesions. Conclusion This study demonstrates the increase of IL‐22–expressing CD4+AhR+ T lymphocytes in periodontitis‐affected tissues and shows a positive correlation between IL‐22, RANKL expression, and alveolar bone resorption.