Chemokine Receptor CCR7 in Ectopic Lymphoid-cluster Formation During Periodontitis

Objectives: Periodontitis is a chronic inflammatory disease that arise from polymicrobial dysbiosis in which periodontal-pathogenic bacteria residing in the subgingival biofilm trigger a complex immuno-inflammatory response. In this context, the formation of a dense inflammatory infiltrate composed by a wide variety of leukocytes, matrix metalloproteinases, and bone pro-resorptive factors results in the destruction of tooth-supporting tissues. Chemokine receptor CCR7 and its ligands play a key role during lymphocyte and dendritic cell homing towards secondary lymphoid organs, regulating the antigen presentation process. Its ectopic expression alters the location of immune cell infiltrates by promoting naïve cell migration, activation and differentiation in peripheral inflamed-tissues, inducing formation of ectopic lymphoid-like clusters. However, the role of CCR7 during aetio-pathogenia of periodontitis remains unknown; therefore, this study aimed to analyze the CCR7, CXCR4, CXCL12, CCL19, and CCL21 mRNA expression, along with CCR7⁺ T-helper lymphocyte detection, in periodontal tissues from healthy or periodontitis affected individuals.
Methods: From gingival samples obtained from healthy or periodontitis individuals, total cells were isolated by enzymatic digestion. The expression of CD4/CD25α/CD45RA/ CD45RO/RORC2/Foxp3/T-bet/CCR7 was analyzed by flow cytometry. Additionally, mRNA expression for CCR7, CXCR4, CXCL12, CCL19 and CCL21 was quantified by qPCR along with the quantification of CCL19, CCL21 and CXCL12 secretion from gingival crevicular fluid samples by ELISA. Finally, CD4 and CCR7 were localized in periodontal tissues by immunofluorescence.
Results: Higher levels of CCR7, CXCR4, CCL19, CCL21, and CXL12 were detected in periodontitis compared with healthy individuals. Additionally, the number of CD45RA⁺CCR7⁺ (naïve) and RORC2⁺CCR7⁺ (Th17) T-lymphocytes increased in periodontitis. All CCR7⁺ cells were localized in the sub-epithelial connective tissue.
Conclusions: The upregulation of CCR7⁺ naïve and Th17 lymphocytes in periodontitis was correlated with local CCL19, CCL21, and CXCL12 production. Hence, CCR7 may play a chemotactic role in the formation of periodontal ectopic lymphoid clusters during periodontitis.