CCR7⁺ T Lymphocytes and Their Association With Formation of Periodontal Lymphoid-like Clusters

Objectives: The formation of periodontal lymphoid-like clusters has been proposed as associated with pathogenesis of periodontitis. In these lymphoid-like clusters, dendritic cells could locally present bacterial antigens to naïve and/or memory T lymphocytes, promoting resorption of tooth-supporting alveolar bone in a periodontal site-specific manner. In other inflammatory diseases, the expression of CCR7, CXCR4, CCL19, CCL21, and CXCL12 have been associated with formation of ectopic lymphoid-like structures. This study was aimed to analyze the CCR7, CXCR4, CCL19, CCL21, and CXCL12 production, as well as the CCR7⁺ T-lymphocyte detection, in periodontal tissues from healthy and periodontitis individuals.
Methods: Gingival biopsies and crevicular fluid samples were obtained from healthy or moderate-to-severe chronic periodontitis individuals. Total gingival cells were isolated using enzymatic-digestion and then analyzed by flow cytometry using the following monoclonal-antibodies: anti-CD4, CD25, CD45RA, CD45RO, RORC2, Foxp3, and CD197. The mRNA expression for CCR7, CXCR4, CCL19, CCL21, and CXCL12 was quantified by qPCR. In addition, CCR7 was detected by western-blot and localized by immuno-fluorescence. Finally, the secretion of CCL19, CCL21, and CXCL12 was quantified by ELISA.
Results: Higher levels of CCR7, CXCR4, CCL19, CCL21, and CXCL12 were expressed in samples of periodontitis patients as compared with healthy individuals. Similarly, an increased number of CCR7⁺ naïve and CCR7⁺RORC2⁺ memory T lymphocytes was detected in periodontitis patients as compared with healthy individuals. In periodontitis patients, CCR7 was broadly localized in gingival connective tissue, mainly clustered around blood vessels.
Conclusions: An increment in the number of infiltrating CCR7⁺ naïve and memory Th17 lymphocytes was detected in periodontal tissues from periodontitis patients as compared with healthy individuals. This increment was associated with local production of CXCR4, CCL19, CCL21, and CXCL12. Thus, CCR7 could play a role in the pathogenesis of periodontitis by inducing the formation of periodontal lymphoid-like clusters. Funded by grants FONDECYT 1140904 and FONDEQUIP EQM150010.