T Cell Proliferation Is Induced by Chronically TLR2-Stimulated Gingival Fibroblasts or Monocytes

Abstract

During inflammation of the gums, resident cells of the periodontium, gingival fibroblasts (GFs), interact with heterogeneous cell populations of the innate and adaptive immune system that play a crucial role in protecting the host from pathogenic infectious agents. We investigated the effects of chronic inflammation, by exposing peripheral blood mononuclear cells (PBMCs), peripheral blood lymphocyte (PBL) cultures, and GF–PBMC cocultures to Toll-like receptor 2 (TLR2) and TLR4 activators for 21 days and assessed whether this influenced leukocyte retention, survival, and proliferation. Chronic stimulation of PBMC–GF cocultures with TLR2 and TLR4 agonists induced a reduction of NK (CD56+CD3−), T (CD3+), and B (CD19+) cells, whereas the number of TLR-expressing monocytes were unaffected. TLR2 agonists doubled the T cell proliferation, likely of a selective population, given the net decrease of T cells. Subsequent chronic exposure experiments without GF, using PBMC and PBL cultures, showed a significantly (p < 0.0001) increased proinflammatory cytokine production of TNF-α and IL-1β up to 21 days only in TLR2-activated PBMC with concomitant T cell proliferation, suggesting a role for monocytes. In conclusion, chronic TLR activation mediates the shift in cell populations during infection. Particularly, TLR2 activators play an important role in T cell proliferation and proinflammatory cytokine production by monocytes, suggesting that TLR2 activation represents a bridge between innate and adaptive immunity.

Chronic Exposure of Gingival Fibroblasts to TLR2 or TLR4 Agonist Inhibits Osteoclastogenesis but Does Not Affect Osteogenesis

“…We previously described, that TLR activation results in the production of inflammatory cytokines ( 24 ). We next measured TNF-α in the supernatant of GF-PBMC co-cultures ( Figure 3 ).…”

“…TLR2 and TLR4 are expressed in the periodontal tissues, and among them on GF ( 23 , 24 ). GF play an important role in processes associated with bone remodeling such as the induction and inhibition of osteoclast formation ( 25 , 26 ).…”

“…However, there is also evidence that shows that the in vitro activation of human osteoclast precursors with TLR agonists results in the inhibition of osteoclastogenesis ( 30 ). Besides inhibition of osteoclasts, chronic TLR2 activation plays a significant role in T cell proliferation, mediated by GF or monocytes, resulting in the production of proinflammatory cytokines by human monocytes ( 24 ).…”

Cells Derived from Human Long Bone Appear More Differentiated and More Actively Stimulate Osteoclastogenesis Compared to Alveolar Bone-Derived Cells

“…The next day (day 0), 0.5 × 10 6 peripheral blood mononuclear cells (PBMCs) were seeded on top. The PBMCs were isolated from the buffy coat (Sanquin, Amsterdam, The Netherlands) by a standard density gradient centrifugation with Ficoll-Paque [ 35 ]. Co-cultures of bone cells and PBMCs were cultured for up to 21 days in basic medium (same composition as the basic medium in the osteogenesis experiments) or the basic medium supplemented with 10 nM vitD 3 .…”

Molecular Mechanisms of Periodontal Disease

“…One of the vital recognition systems for microbial dysbiotic change is toll-like receptors (TLR). Moonen et al reported that activation of TLR2 in gingival fibroblasts or monocytes is responsible for the T cell proliferation [ 2 ]. Consistent with this study, it has long been demonstrated that the TLR-mediated innate immune system by pathogen-associated molecular patterns (PAMPs) activates T and B cells’ immune responses to produce inflammatory cytokines and elicits osteolytic pathways, promoting periodontal inflammation and bone resorption.…”