Macrophage Depletion Abates Porphyromonas gingivalis–Induced Alveolar Bone Resorption in Mice

Abstract

The role of the macrophage in the immunopathology of periodontitis has not been well defined. In this study, we show that intraoral inoculation of mice with Porphyromonas gingivalis resulted in infection, alveolar bone resorption, and a significant increase in F4/80+ macrophages in gingival and submandibular lymph node tissues. Macrophage depletion using clodronate-liposomes resulted in a significant reduction in F4/80+ macrophage infiltration of gingival and submandibular lymph node tissues and significantly (p < 0.01) less P. gingivalis–induced bone resorption compared with controls in BALB/c and C57BL/6 mice. In both mouse strains, the P. gingivalis–specific IgG Ab subclass and serum cytokine [IL-4, IL-10, IFN-γ, and IL-12 (p70)] responses were significantly (p < 0.01) lower in the macrophage-depleted groups. Macrophage depletion resulted in a significant reduction in the level of P. gingivalis infection, and the level of P. gingivalis infection was significantly correlated with the level of alveolar bone resorption. M1 macrophages (CD86+), rather than M2 macrophages (CD206+), were the dominant macrophage phenotype of the gingival infiltrate in response to P. gingivalis infection. P. gingivalis induced a significant (p < 0.01) increase in NO production and a small increase in urea concentration, as well as a significant increase in the secretion of IL-1β, IL-6, IL-10, IL-12 (p70), eotaxin, G-CSF, GM-CSF, macrophage chemoattractant protein-1, macrophage inflammatory protein-α and -β, and TNF-α in isolated murine macrophages. In conclusion, P. gingivalis infection induced infiltration of functional/inflammatory M1 macrophages into gingival tissue and alveolar bone resorption. Macrophage depletion reduced P. gingivalis infection and alveolar bone resorption by modulating the host immune response.

Proinflammatory M1 Macrophages Inhibit RANKL-Induced Osteoclastogenesis

“…Although the regulation of osteoclastogenesis by macrophages has not previously been reported, macrophages and (pre)osteoclasts can colocalize in the context of inflammatory bone lesion, such as that seen in periodontal disease and arthritis (6,7). While identification of the major macrophage phenotype in human periodontal disease remains elusive (34), we showed that LPS from P. gingivalis, a keystone pathogen in periodontal tissue, can induce M1 macrophages, which suggested that polarization toward the M1 phenotype may occur in periodontal tissue.…”

“…While identification of the major macrophage phenotype in human periodontal disease remains elusive (34), we showed that LPS from P. gingivalis, a keystone pathogen in periodontal tissue, can induce M1 macrophages, which suggested that polarization toward the M1 phenotype may occur in periodontal tissue. Furthermore, it was reported that infiltration of both M1 and M2 macrophages increased in the P. gingivalis-induced mouse periodontitis lesion and that depletion of macrophages using clodronate liposomes prevented the bone resorption induced in the P. gingivalis-infected mice (7). However, since it must be noted that clodronate liposomes can also suppress osteoclastogenesis (35), further investigation may be required to establish the direct impact of either M1 or M2 macrophages on in vivo osteoclastogenesis induced in mice by P. gingivalis infection.…”

“…For instance, a recent study (4) revealed that ␥␦-T cells inhibit osteoclastogenesis by their production of interferon gamma (IFN-␥), whereas B and T cells can produce RANKL under inflammatory conditions, thus working toward the promotion of osteoclastogenesis (5). However, in the context of bone lytic diseases involving chronic inflammation, such as periodontitis and rheumatoid arthritis, infiltrations of not only B and T cells but also of macrophages are observed (6,7). It is true that macrophages are the most abundant immune cells found in the synovial membrane in osteoarthritis (8) and in synovial fluid in rheumatoid arthritis (9), outnumbering T and B cells.…”

Interrelationship Between Periapical Lesion and Systemic Metabolic Disorders

“…The number of NALP3 positive cells was also significantly associated with the level of inflammatory cell infiltration, ASC, caspase-1, IL-1β and IL-18 [172], suggesting that inflammasomes play an important role in production of IL-1 in periapical lesions. In a mouse P. gingivalis -induced periodontitis model, macrophage is an important source of proinflammatory mediators including nitric oxide (NO), IL-1β, IL-6, IL-10, IL-12 p70, eotaxin, G-CSF (granulocyte-colony stimulating factor), GM-CSF, MCP (monocyte chemoattractant protein)-1, MIP-α and -β, and TNF-α [173]. Depletion of macrophage using clodronate liposomes in this disease model resulted in suppression of P. gingivalis -induced immune response such as pathogen-specific IgG (immunoglobulin G) and serum cytokine levels [173].…”

Porphyromonas gingivalis Lipopolysaccharide Weakly Activates M1 and M2 Polarized Mouse Macrophages but Induces Inflammatory Cytokines

“…Investigating the activation of macrophage phenotypes in response to a periodontal pathogen may provide insights into important host-pathogen interactions. We have previously shown that macrophages in the gingival tissue of mice exhibiting alveolar bone resorption through infection with P. gingivalis expressed high levels of CD86 and lower levels of CD206, suggesting M1 macrophage polarization (27). The aim of this study was to investigate the response P. gingivalis LPS induces in pre-M1-M and pre-M2-M and the subsequent maturation of these macrophages.…”