Critical Role of Interleukin-34 in Gingival Crevicular Fluid as a Potential Markers of Inflammation in Patients With Periodontitis

A novel cytokine interleukin 34 (IL-34) is a second possible functional ligand of macrophage colony-stimulating factor-1 receptor (CSF-1R). IL-34 is secreted in different tissues including: heart, brain, lung, liver, kidney, thymus, testes, ovary, small intestine, prostate, colon and spleen . IL-34 shares vital functions of macrophage colony-stimulating factor -1(CSF-1), and manage myeloid cell survival, differentiation and proliferation. It is produced by synovial fluid, gingival fibroblast and human adipose tissue, and is controlled by the transcription factor RANK and activation of c-Jun N-terminal kinase (CJNK). Additionally, the pro-inflammatory cytokines tumornecrosis factor-alfa (TNF-α) and interleukin-1beta (IL-1β) arrange IL-34 release from gingival fibroblasts, by a mechanism including nuclear factor -kB (NF-kB) and mitogen activated protein kinase (MAPK).The targeting CSF-1 merely is not adequate to inhibit the effect via CSF-1R. Moreover, neither RANKL nor IL-34 solely can cause osteoclast formation which suggests that IL-34 is required but not enough. IL-34 plays a crucial role in RANKL-induced osteoclastogenesis; the osteoclasts differentiation is mediated by the same way with CSF-1.

Several studies evaluated the role of IL-34 in the pathogenesis of chronic periodontitis (CP). To the best of our knowledge, any of these studies reported the relationship between GCF IL-34 level and GCF RANKL/OPG ratio in other types of periodontitis before and after non-surgical periodontal therapy. This study highlights the influence of IL-34 in the pathogenesis of Chronic Periodontitis (CP) and Aggressive Periodontitis (AgP).

The objective of this study is to 1) identification of the impact of IL-34 on the pathogenesis of periodontal disease and determine whether any relationship among the existing levels of GCF IL-34 and GCF RANKL, OPG and RANKL/OPG ratio, as a mediator of bone resorption 2) analysis of the impact of non-surgical periodontal treatment on GCF IL-34 levels in patients with CP and AgP and 3) to correlate between biochemical markers and clinical recordings.

The study included 60 subjects: 20 who were periodontally healthy (CTRL), 20 with chronic periodontitis (CP)and 20 with aggressive periodontitis (AgP). Patients with periodontitis were treated with non-surgical periodontal therapy. GCF sampling procedures and clinical periodontal measures were investigated at the baseline and 6 weeks after treatment. Levels of IL-34, RANKL and OPG were analyzed with Enzyme-linked immunosorbent assay (ELISA).

Participants were periodontally assessed at baseline and after non-surgical periodontal therapy in accordance with the following criteria; plaque index (PI)(Silness and Loe, 1964), GI(Loe and Silness, 1963), PPD, clinical attachment level (CAL) and BOP (judged positive if it developed within 15 s following contact). Full-mouth periapical radiographs were used to determine the periodontal bone loss.The clinical measurement were taken in millimeters by a single calibrated examiner (ŞBD), who was blinded to the whole study composition, from six locations of each tooth (mesio-buccal, disto-buccal, mid-buccal, mesiolingual, disto-lingual, and mid-lingual), by the use of a periodontal probe (Hu-Friedy, Chicago, IL, USA).