CD169⁺ macrophages promote periodontal bone repair via pathogen clearance and IL10 secretion

Periodontal bone regeneration remains a major challenge in in the treatment of periodontitis. This study we aimed to investigate whether there are CD169⁺ macrophages in periodontal tissues and the functions of these cells in the progressive and resolving phases of periodontitis.

Immunofluorescence staining was performed to localize CD169⁺ macrophages in human and murine periodontal tissues. Subsequently, CD169⁺ macrophages from mature bone marrow-derived macrophages (BMDMs) were isolated. To characterize their functional properties, we assessed the phagocytic capacity of CD169⁺ macrophages in vitro. Furthermore, CD169⁺ macrophages were co-cultured to evaluate their osteogenic-promoting effects by qPCR, alkaline phosphatase (ALP) staining, and alizarin red staining (ARS). For in vivo validation, ligature-induced periodontitis (LIP) mice were established and local bacterial inoculated to investigate phagocytic function of CD169⁺ macrophages. Anti-interferon-alpha/beta receptor (Anti-IFNAR1) was injected locally to inhibit the signaling of IFN Is. Bone repair was assessed using micro-computed tomography (micro-CT) and histological staining.

CD169 was primarily expressed on macrophages in periodontal tissues. In vitro CD169⁺ macrophages were positively induced by IFN Is. CD169⁺ macrophages exhibited robust phagocytic activity in clearing Porphyromonas gingivalis (P. gingivalis). Moreover, CD169⁺ macrophages promoted the osteogenic differentiation of BMSCs through the secretion of interleukin 10 (IL10), as evidenced by upregulated expression of osteogenesis-related genes (including Alpl, Sp7, Ibsp and Bglap), enhanced activity of ALP, and increased formation of mineralized nodules. In vivo results further demonstrated that CD169⁺ macrophages exhibited a high phagocytic capacity against P. gingivalis compared. During the resolving phase of periodontitis, a decrease in the number of CD169⁺ macrophages resulting from Anti-IFNAR1 application not only impaired alveolar bone repair, but also reduced expression of IL10 and osteogenesis-related proteins, such as OSX(Sp7) and OCN(Bglap).

CD169⁺ macrophages play a critical role in periodontitis by clearing of P. gingivalis during the progressive phase of periodontitis, and promoting bone repair via the secretion of IL10 during the resolving phase.