Search
Contact Us
HOME

  • Crossref logo
  • Crossref Similarity Check logo
Journal Search Engine

to

Search Advanced Search Adode Reader(link)
Download PDF Export Citaion korean bibliography PMC previewer
ISSN : 1226-7155(Print)
ISSN : 2287-6618(Online)
International Journal of Oral Biology Vol.50 No.3 pp.112-119
DOI : https://doi.org/10.11620/IJOB.2025.50.3.112

Filifactor alocis induces interleukin-1β secretion in THP-1 cells

So-Hee Kim, Jin Chung, In-Chol Kang*
Department of Oral Microbiology, School of Dentistry, Chonnam National University, Gwangju 61186, Republic of Korea
*Correspondence to: In-Chol Kang, E-mail: ickang@jnu.ac.krhttps://orcid.org/0000-0002-5993-8728
July 24, 2025 September 2, 2025 September 5, 2025

Abstract


While interleukin (IL)-1β is a well-established driver of periodontitis, the specific mechanisms by which the emerging pathogen Filifactor alocis induces this cytokine are largely unknown. We conducted a comprehensive investigation into how F. alocis stimulates IL-1β in THP-1 macrophages, analyzing the response at the mRNA (reverse transcription-polymerase chain reaction), cellular protein (Western blot), and secreted protein (enzymelinked immunosorbent assay) levels. Our results show a clear, dose-dependent increase in all measures, confirming its potent effect. To explore the underlying mechanisms, we first tested the contribution of the NLRP3 inflammasome using the specific inhibitor MCC950. This inhibitor almost completely blocked (~90%) a control response but only partially inhibited (~50%) the F. alocis -stimulated secretion. A similar result was observed with the pan-caspase inhibitor Z-VAD-FMK, which almost completely suppressed the control but only partially inhibited (~50%) the response to F. alocis . Moreover, we found a dominant role for mitogen-activated protein kinase signaling pathways. Specific inhibitors of extracellular signal-regulated kinase (ERK) and c-Jun N-terminal kinase (JNK) significantly attenuated both IL-1β mRNA expression and protein secretion, whereas the p38 inhibitor had no effect. These findings collectively demonstrate that F. alocis robustly induces IL-1β via ERK and JNK signaling with only partial dependence on canonical NLRP3 inflammasome and caspase-mediated pathways. This unique pattern suggests the involvement of other complementary pathways, underscoring the complex inflammatory processes involved in F. alocis -induced periodontitis.


Filifactor alocis , Interleukin-1β , Periodontal diseases , Inflammasomes , Caspases

초록

    © The Korean Academy of Oral Biology. All rights reserved.

    This is an open-access article distributed under the terms of the Creative Commons Attribution Non-Commercial License (http://creativecommons.org/licenses/bync/4.0/) which permits unrestricted non-commercial use, distribution, and reproduction in any medium, provided the original work is properly cited.

    Introduction

    Periodontal diseases, particularly periodontitis, are common infectious conditions in humans and have been increasingly implicated as contributors to various systemic diseases [1]. Periodontitis is a chronic, irreversible inflammatory disease that progressively destroys the periodontal connective tissue and alveolar bone, ultimately leading to tooth loss. The pathogenesis of periodontal disease is complex, involving a dysbiotic microbial community and a dysregulated host immune-inflammatory response [2]. Importantly, the tissue damage observed in periodontitis is largely attributable to the host’s immune response to microbial insult, rather than the direct effects of the bacteria themselves [3]. Thus, understanding the interactions between periodontal pathogens and host cells is crucial for elucidating the pathogenesis of the disease.

    Cytokines play a pivotal role in the development of periodontitis and have been suggested as potential biomarkers for its diagnosis and monitoring [4]. Among the numerous cytokines, interleukin (IL)-1β stands out as a critical proinflammatory cytokine associated with periodontitis. Studies have shown that patients with periodontitis exhibit increased levels of IL-1β in their gingival crevicular fluid, which correlates with clinical indicators such as attachment loss and probing depth [5,6]. In patients with periodontitis, non-surgical periodontal treatment led to a marked reduction in IL-1β levels, indicating that effective therapy may help prevent disease progression, at least partly, by inhibiting IL-1β activity [7].

    IL-1β production typically requires two distinct signals. The first signal induces gene transcription and synthesis of the 33- kDa precursor pro-IL-1β, whereas the second activates the inflammasome, leading to caspase-1 activation and proteolytic cleavage of the precursor into the 17-kDa mature IL-1β, which is then secreted [8]. The NLRP3 inflammasome–caspase-1 pathway is the most widely studied and plays a critical role in IL-1β processing [9]. However, caspase-1-independent and even inflammasome-independent mechanisms of IL-1β maturation have also been reported [10,11]. Notably, stimulation of macrophages by various stimuli activates mitogen-activated protein (MAP) kinases―extracellular signal-regulated kinase (ERK), p38, and c-Jun N-terminal kinase (JNK)―which are key regulators of inflammatory responses and cytokine expression [12,13].

    The oral cavity is home to over 700 bacterial species, many of which are linked to the development of periodontal diseases [14]. While Porphyromonas gingivalis, Tannerella forsythia, and Treponema denticola are traditionally recognized as key periodontal pathogens, Filifactor alocis has emerged as a newly identified organism, demonstrating a higher prevalence in affected areas [15,16]. This gram-positive anaerobic rod is notably one of the most abundant bacteria found within the periodontal pockets of periodontitis patients [17]. Furthermore, F. alocis possesses distinct capabilities, including the invasion of periodontal cells, resistance to oxidative stress, and the stimulation of pro-inflammatory cytokine secretion [18].

    Although previous studies have reported IL-1β induction by F. alocis in host cells, these investigations primarily provided a broad overview of cytokine responses without specifically focusing on IL-1β [19,20]. Monocytes and macrophages are the principal cellular sources of this cytokine [21]. THP-1 cells, a widely used human monocytic cell line, can be differentiated into macrophage-like cells through treatment with phorbol 12-myristate 13-acetate (PMA) [22]. The present study aims to characterize IL-1β production and elucidate the underlying mechanisms in response to F. alocis stimulation in PMAdifferentiated THP-1 macrophage-like cells.

    Materials and Methods

    1. Reagents

    Z-VAD-FMK, MCC950, and monosodium urate (MSU) were purchased from InvivoGen. PD98059, SB203580, and SP600125 were obtained from Merck. Rabbit monoclonal antibody specific for cleaved (mature) IL-1β and a horseradish peroxidase (HRP)-conjugated goat anti-rabbit IgG secondary antibody were obtained from Cell Signaling Technology. An anti-GAPDH antibody was purchased from Santa Cruz Biotechnology.

    2. Bacterial culture

    F. alocis strain 35896 was obtained from the American Type Culture Collection (ATCC) and cultured in tryptic soy broth supplemented with 5 mg/mL yeast extract, 0.5 mg/mL cysteine, 5 μg/mL hemin, and 1 μg/mL menadione. Cultures were incubated anaerobically at 37℃ in an atmosphere of 85% N2, 10% H2, and 5% CO2. Bacteria cultured for 18–24 hours were used in all experiments.

    3. THP-1 culture

    Human monocytic THP-1 cells were obtained from ATCC and maintained in RPMI 1640 medium (Gibco) supplemented with 10% fetal bovine serum, 100 U/mL penicillin, and 100 μg/mL streptomycin at 37℃ in a humidified atmosphere containing 5% CO2. To induce macrophage-like differentiation, cells were treated with 100 ng/mL PMA for 24 hours in culture plates. After differentiation, adherent cells were washed twice with PMA-free medium prior to use in experiments.

    4. Infection protocol

    Bacteria were washed twice with phosphate-buffered saline and once with complete RPMI medium. After resuspension in complete RPMI, the optical density at 600 nm was measured and adjusted to 0.5, corresponding to approximately 5 × 108 CFU/mL. For enzyme-linked immunosorbent assay (ELISA), 1 × 106 THP-1 cells were seeded in 12-well plates and incubated with F. alocis at various multiplicities of infections (MOIs) in a final volume of 1 mL for 18 hours. For reverse transcription-polymerase chain reaction (RT-PCR), 1.5 × 106 THP-1 cells were seeded in 12-well plates and incubated with F. alocis for 3 hours. For Western blotting, 5 × 106 THP-1 cells were seeded in 6-well plates and incubated with F. alocis for 6 hours.

    5. RT-PCR

    Total RNA was extracted using TRI Reagent (Molecular Research Center) according to the manufacturer’s instructions and quantified spectrophotometrically. First-strand cDNA was synthesized from 1 μg of total RNA using random primers (Promega) and Moloney murine leukemia virus reverse transcriptase (Invitrogen). One microliter of cDNA was amplified in a 20 μL reaction volume under a layer of mineral oil using a GeneAmp 2700 thermal cycler (Applied Biosystems). Each PCR mixture contained 50 mM KCl, 10 mM Tris-HCl, 1.5 mM MgCl2, 0.2 mM each dNTP, 1 U Taq DNA polymerase, and 0.5 μM of each primer. PCR conditions included denaturation at 94℃ for 30 seconds, annealing at 59℃ for 30 seconds, and extension at 72℃ for 60 seconds. The primer sequences were: IL-1β (548 bp), 5′-CAGTGAAATGATGGCTTATTAC-3′ (forward) and 5′-CTTTCAACACGCAGGACAGGT-3′ (reverse); β-actin (300 bp), 5′-AGCGGGAAATCGTGCGTG-3′ (forward) and 5′ -CAGGGTACATGGTGGTGCC-3′ (reverse). Ten microliters of each PCR product was separated by electrophoresis on 1.2% (w/v) agarose gels containing RedSafe (Intron Biotechnology), visualized under ultraviolet transillumination, and photographed.

    6. ELISA

    The culture supernatants from THP-1 cells were collected and centrifuged at 100 × g for 5 minutes to remove cellular debris. Levels of IL-1β and tumor necrosis factor-alpha (TNF-α) were quantified using commercial ELISA kits (R&D Systems). Although the IL-1β assay does not exclusively detect the mature form of IL-1β, it is calibrated against recombinant mature IL-1β and, according to the manufacturer’s instructions, provides a reliable estimate of active IL-1β levels in biological fluids.

    7. Western blot analysis

    Cells were harvested and lysed in 200 μL of Cell Lysis Buffer (Cell Signaling Technology). Equal amounts (50 μg) of each boiled lysate were resolved by 10% SDS-PAGE and transferred to a polyvinylidene difluoride membrane (Bio-Rad). The membrane was probed with rabbit primary antibodies against cleaved IL-1β (1:1,000 dilution), followed by incubation with HRP-conjugated goat anti-rabbit IgG secondary antibody (1:1,500). Immunoreactive bands were visualized using enhanced chemiluminescence (LumiGLO; Cell Signaling Technology). The membranes were subsequently stripped and reprobed with an anti-GAPDH antibody (1:1,500) as a loading control.

    8. Statistical analysis

    All experiments were independently performed at least three times to ensure reproducibility. Data are presented as mean ± standard deviation. Statistical analysis was conducted using GraphPad InStat (GraphPad Software). One-way analysis of variance was performed, followed by the Tukey–Kramer multiple comparisons test. Differences were considered statistically significant at p ＜ 0.05.

    Results

    1. IL-1β induction by F. alocis

    To determine the ability of F. alocis to induce IL-1β production in macrophages, PMA-differentiated THP-1 cells were stimulated with live F. alocis across a range of MOIs (1-100). IL-1β mRNA expression, cellular cleaved IL-1β, and secreted IL-1β were subsequently quantified using RT-PCR, Western blot, and ELISA, respectively. Results showed that IL-1β mRNA expression increased from an MOI of 5, with a more pronounced upregulation at an MOI of 50. Consistent with this, both cellular cleaved IL-1β and secreted IL-1β levels also demonstrated a dose-dependent increase, becoming evident from an MOI of 50 upon F. alocis stimulation (Fig. 1).

    2. NLRP3 inflammasome dependency

    To assess the contribution of NLRP3 inflammasome to F. alocis -induced IL-1β secretion, IL-1β levels were measured by ELISA in the presence or absence of the specific NLRP3 inhibitor, MCC950. For control purposes, we concurrently evaluated MSU-stimulated IL-1β secretion (as a positive control for NLRP3 inhibition) and F. alocis-stimulated TNF-α secretion (as a negative control, given that TNF-α production is not inflammasome-dependent). Consistent with its known inhibitory effect, MCC950 almost completely (~90%) suppressed MSU-induced IL-1β secretion. However, F. alocis -induced IL-1β secretion was only partially attenuated by MCC950 (less than 50% inhibition). Furthermore, MCC950 had no effect on F. alocis-stimulated TNF-α secretion (Fig. 2).

    3. Caspase dependency of IL-1β secretion

    To determine the role of caspases in F. alocis-induced IL-1β secretion, IL-1β levels were assessed by ELISA in the presence or absence of Z-VAD-FMK, a pan-caspase inhibitor. For control purposes, MSU-stimulated IL-1β secretion served as a positive control. F. alocis-stimulated TNF-α secretion was included as a caspase-independent negative control. Z-VADFMK almost completely inhibited MSU-induced IL-1β secretion. However, F. alocis-induced IL-1β secretion was only partially inhibited by Z-VAD-FMK (approximately 50% inhibition). Furthermore, F. alocis-stimulated TNF-α secretion remained unaffected by Z-VAD-FMK treatment (Fig. 3).

    4. Involvement of MAP kinases

    The role of MAP kinases in F. alocis-stimulated IL-1β production was examined using specific pharmacological inhibitors. THP-1 macrophages were pretreated with indicated concentrations of PD98059 (ERK inhibitor), SB203580 (p38 inhibitor), or SP600125 (JNK inhibitor) before stimulating them with F. alocis. We then assessed IL-1β production at multiple levels: mRNA expression by RT-PCR, cellular cleaved IL-1β by Western blot, and secreted IL-1β by ELISA. Pretreatment with PD98059 and SP600125 significantly attenuated F. alocis-induced IL-1β production at both mRNA and protein levels. Conversely, SB203580 showed no inhibitory effect on F. alocisinduced IL-1β mRNA expression or protein levels (Fig. 4).

    Discussion

    Limited information is available regarding F. alocis induction of IL-1β. One study reported that F. alocis induces secretion of IL-1β, IL-6, and TNF-α from gingival epithelial cells [19]. In another study, 14 cytokines, including IL-1β, were detected in the culture supernatants of F. alocis-stimulated THP-1 monocytes using a human cytokine antibody array kit [20]. However, these findings represented only minor parts of broader investigations. Therefore, our study aimed to specifically focus on IL-1β induction by F. alocis in THP-1 macrophages.

    Our initial findings demonstrate that relatively low doses of F. alocis potently induce IL-1β production in PMA-differentiated THP-1 macrophages. Both IL-1β mRNA expression and levels of cellular cleaved and secreted IL-1β showed dosedependent increases with rising MOIs. These results indicate that F. alocis not only stimulates transcriptional upregulation of pro-IL-1β but also promotes its subsequent processing and release, which is indicative of inflammasome activation. The ability of F. alocis to elicit such a robust IL-1β response underscores its potential role as a significant inflammatory trigger in the oral cavity.

    Given the well-established role of the NLRP3 inflammasome in IL-1β processing, we investigated its involvement using the specific inhibitor MCC950. We measured secreted IL-1β to assess the final outcome of IL-1β processing. MSU-induced IL-1β secretion served as a positive control for MCC950 inhibition, as MSU is known to stimulate IL-1β secretion via NLRP3 inflammasome and caspase-1 activity in THP-1 cells [23]. While MCC950 almost completely suppressed MSU-induced IL-1β secretion, its inhibitory effect on F. alocis-induced IL-1β was only partial (less than 50% inhibition). The absence of TNF-α inhibition by MCC950 further confirmed its specificity. These observations suggest that while the NLRP3 inflammasome contributes to F. alocis-induced IL-1β production, it is neither the sole nor predominant pathway. This points toward the potential involvement of other inflammasomes, such as NLRC4 or AIM2, in IL-1β maturation in response to F. alocis. For instance, Streptococcus mutans has been shown to activate AIM2, NLRP3, and NLRC4 inflammasomes in THP-1 macrophages [24].

    To further dissect the enzymatic steps involved in IL-1β maturation, we examined the role of caspases, using the pan-caspase inhibitor Z-VAD-FMK. Z-VAD-FMK potently inhibits human caspase-1 through -10, with the exception of caspase-2 [25]. The caspases-1, -4, and -5 are grouped as inflammatory caspases, whereas caspases-3, -6, -7, -8, -9, and -10 are apoptotic caspases, and caspase-2 has cellcycle related functions [26]. Similar to the MCC950 results, ZVAD- FMK almost completely inhibited MSU-induced IL-1β secretion; however, F. alocis -induced IL-1β secretion was only partially inhibited (approximately 50%). The partial inhibition of IL-1β secretion by the pan-caspase inhibitor following F. alocis stimulation indicates the involvement of both caspasedependent and -independent pathways. Previous studies have identified neutrophil- and macrophage-derived serine proteases such as proteinase 3, elastase, and cathepsin G, as enzymes capable of processing pro-IL-1β into its bioactive form [11]. Metalloproteinases can also process pro-IL-1β [27]. Although the exact caspase-independent mechanisms remain to be elucidated, the partial resistance to caspase inhibition suggests the existence of additional pathways contributing to F. alocis-induced IL-1β secretion.

    Activation of MAP kinases triggers the expression of numerous genes that control the inflammatory response, including IL-1β production [12]. Our results revealed the involvement of ERK and JNK–but not p38–in F. alocis-induced IL-1β mRNA expression and protein secretion. Such differential involvement of MAP kinases is not uncommon. For example, the Escherichia coli effector EspT induced IL-1β secretion via ERK and JNK pathways but independently of p38 [28]. Notably, ERK and JNK pathways have been shown to mediate the osteogenic inhibition caused by extracellular vesicles derived from F. alocis [29]. The transcription factor activating protein-1 (AP- 1) promotes IL-1β gene transcription and serves as a major substrate of multiple MAP kinase pathways [30,31]. Since activated ERK can stimulate the expression of c-Fos, a component of AP-1, and activated JNK phosphorylates c-Jun, the second component of AP-1 [32,33], it is plausible that F. alocis activates ERK and JNK pathways, leading to AP-1-mediated promotion of IL-1β gene expression.

    In conclusion, our study demonstrates that F. alocis is a potent inducer of IL-1β in THP-1 macrophages. While NLRP3 inflammasome and caspase-dependent mechanisms are partially involved, our data strongly suggest the presence of yetto- be-identified caspase-independent mechanisms contributing to IL-1β secretion. Moreover, ERK and JNK MAP kinase pathways play critical roles in F. alocis-induced IL-1β production. These findings enhance our understanding of F. alocis pathogenesis and may provide novel targets for therapeutic intervention in periodontal disease.

    Funding

    This study was financially supported by Chonnam National University (grant number: 2022-0195).

    Conflicts of Interest

    Jin Chung is an editorial board member of the journal but was not involved in the review process of this manuscript. Otherwise, there is no conflict of interest to declare.

    Figure

    IJOB-50-3-112_F1.jpg

    Effect of Filifactor alocis on IL-1β mRNA expression and protein secretion in THP-1 macrophagic cells. PMA-differentiated THP-1 cells were stimulated with increasing MOIs of F. alocis . (A) After 3 hours, RNA was isolated, and the relative levels of IL-1β mRNA expression were determined by RT-PCR. (B) After 6 hours, cell lysates were prepared, and Western blot analysis was performed to assess the levels of cleaved IL-1β. (C) After 18 hours, culture supernatants were collected, and concentrations of IL-1β were determined by ELISA. Data are presented as means ± SD of a representative experiment performed in triplicate. Statistical significance between medium only and F. alocis -treated samples was evaluated.

    *Significant differences (p < 0.05).

    IJOB-50-3-112_F2.jpg

    Effect of MCC950 (MCC) on Filifactor alocis -induced IL-1β secretion in THP-1 macrophagic cells. (A, C) PMA-differentiated THP-1 cells were pretreated with 5 μM MCC for 1 hour and the cells were incubated with F. alocis (MOI 50) for 18 hours. (B) PMA-differentiated THP-1 cells were pretreated with MCC for 1 hour and the cells were incubated with 200 μg/mL MSU for 18 hours. Culture supernatants were collected, and concentrations of IL-1β or TNF-α were determined by ELISA. Data are presented as means ± SD of a representative experiment performed in triplicate.

    *Significant differences (p < 0.05) compared to cell stimulation without MCC.

    IJOB-50-3-112_F3.jpg

    Effect of Z-VAD-FMK (ZVAD) on Filifactor alocis -induced IL-1β secretion in THP-1 macrophagic cells. (A, C) PMA-differentiated THP-1 cells were pretreated with 20 μg/mL ZVAD for 1 hour and the cells were incubated with F. alocis (MOI 50) for 18 hours. (B) PMA-differentiated THP-1 cells were pretreated with ZVAD for 1 hour and the cells were incubated with 200 μg/mL MSU for 18 hours. Culture supernatants were collected, and concentrations of IL-1β or TNF-α were determined by ELISA. Data are presented as means ± SD of a representative experiment performed in triplicate.

    *Significant differences (p < 0.05) compared to cell stimulation without ZVAD.

    IJOB-50-3-112_F4.jpg

    Effect of inhibitors of MAP kinases on Filifactor alocis -induced IL-1β mRNA expression and protein secretion in THP-1 macrophagic cells. PMAdifferentiated THP-1 cells were pretreated for 1 hour with specific pharmacological inhibitors: PD98059 (PD, 50 μM), SB203580 (SB, 50 μM), or SP600125 (SP, 50 μM). Subsequently, the cells were stimulated with F. alocis (MOI 50). (A) After 3 hours, RNA was isolated, and the relative levels of IL-1β mRNA expression were determined by RT-PCR. (B) After 6 hours, cell lysates were prepared, and Western blot analysis was performed to assess the levels of cleaved IL- 1β. (C) After 18 hours, culture supernatants were collected, and concentrations of IL-1β were determined by ELISA. Data are presented as means ± SD of a representative experiment performed in triplicate.

    *Significant differences (p < 0.05) compared to F. alocis stimulation without inhibitors.

    Table

    Reference

    1. Genco RJ, Sanz M. Clinical and public health implications of periodontal and systemic diseases: an overview. Periodontol 2000 2020;83:7-13.
    2. Hajishengallis G. Periodontitis: from microbial immune subversion to systemic inflammation. Nat Rev Immunol 2015;15: 30-44.
    3. Van Dyke TE, Bartold PM, Reynolds EC. The nexus between periodontal inflammation and dysbiosis. Front Immunol 2020; 11:511.
    4. Neurath N, Kesting M. Cytokines in gingivitis and periodontitis: from pathogenesis to therapeutic targets. Front Immunol 2024;15:1435054.
    5. Stadler AF, Angst PD, Arce RM, Gomes SC, Oppermann RV, Susin C. Gingival crevicular fluid levels of cytokines/chemokines in chronic periodontitis: a meta-analysis. J Clin Periodontol 2016;43:727-45.
    6. Becerik S, Öztürk VÖ, Atmaca H, Atilla G, Emingil G. Gingival crevicular fluid and plasma acute-phase cytokine levels in different periodontal diseases. J Periodontol 2012;83:1304-13.
    7. Reis C, DA Costa AV, Guimarães JT, Tuna D, Braga AC, Pacheco JJ, Arosa FA, Salazar F, Cardoso EM. Clinical improvement following therapy for periodontitis: association with a decrease in IL-1 and IL-6. Exp Ther Med 2014;8:323-7.
    8. Dinarello CA. Immunological and inflammatory functions of the interleukin-1 family. Annu Rev Immunol 2009;27:519-50.
    9. Paik S, Kim JK, Silwal P, Sasakawa C, Jo EK. An update on the regulatory mechanisms of NLRP3 inflammasome activation. Cell Mol Immunol 2021;18:1141-60.
    10. Russo AJ, Behl B, Banerjee I, Rathinam VAK. Emerging insights into noncanonical inflammasome recognition of microbes. J Mol Biol 2018;430:207-16.
    11. Netea MG, van de Veerdonk FL, van der Meer JW, Dinarello CA, Joosten LA. Inflammasome-independent regulation of IL-1-family cytokines. Annu Rev Immunol 2015;33:49-77.
    12. Arthur JS, Ley SC. Mitogen-activated protein kinases in innate immunity. Nat Rev Immunol 2013;13:679-92.
    13. Rao KM. MAP kinase activation in macrophages. J Leukoc Biol 2001;69:3-10.
    14. Zhang M, Whiteley M, Lewin GR. Polymicrobial interactions of oral microbiota: a historical review and current perspective. mBio 2022;13:e0023522.
    15. Lamont RJ, Koo H, Hajishengallis G. The oral microbiota: dynamic communities and host interactions. Nat Rev Microbiol 2018;16:745-59.
    16. Aruni AW, Mishra A, Dou Y, Chioma O, Hamilton BN, Fletcher HM. Filifactor alocis--a new emerging periodontal pathogen. Microbes Infect 2015;17:517-30.
    17. Razooqi Z, Höglund Åberg C, Kwamin F, Claesson R, Haubek D, Oscarsson J, Johansson A. Aggregatibacter actinomycetemcomitans and Filifactor alocis as associated with periodontal attachment loss in a cohort of ghanaian adolescents. Microorganisms 2022;10:2511.
    18. Aja E, Mangar M, Fletcher HM, Mishra A. Filifactor alocis: recent insights and advances. J Dent Res 2021;100:790-7.
    19. Moffatt CE, Whitmore SE, Griffen AL, Leys EJ, Lamont RJ. Filifactor alocis interactions with gingival epithelial cells. Mol Oral Microbiol 2011;26:365-73.
    20. Kim HY, Lim Y, An SJ, Choi BK. Characterization and immunostimulatory activity of extracellular vesicles from Filifactor alocis. Mol Oral Microbiol 2020;35:1-9.
    21. Garlanda C, Dinarello CA, Mantovani A. The interleukin-1 family: back to the future. Immunity 2013;39:1003-18.
    22. Auwerx J. The human leukemia cell line, THP-1: a multifacetted model for the study of monocyte-macrophage differentiation. Experientia 1991;47:22-31.
    23. Martinon F, Pétrilli V, Mayor A, Tardivel A, Tschopp J. Goutassociated uric acid crystals activate the NALP3 inflammasome. Nature 2006;440:237-41.
    24. Song Y, Na HS, Park E, Park MH, Lee HA, Chung J. Streptococcus mutans activates the AIM2, NLRP3 and NLRC4 inflammasomes in human THP-1 macrophages. Int J Oral Sci 2018;10:23.
    25. Chauvier D, Ankri S, Charriaut-Marlangue C, Casimir R, Jacotot E. Broad-spectrum caspase inhibitors: from myth to reality? Cell Death Differ 2007;14:387-91.
    26. Van Opdenbosch N, Lamkanfi M. Caspases in cell death, inflammation, and disease. Immunity 2019;50:1352-64.
    27. Herzog C, Haun RS, Kaushal GP. Role of meprin metalloproteinases in cytokine processing and inflammation. Cytokine 2019;114:18-25.
    28. Raymond B, Crepin VF, Collins JW, Frankel G. The WxxxE effector EspT triggers expression of immune mediators in an Erk/JNK and NF-κB-dependent manner. Cell Microbiol 2011; 13:1881-93.
    29. Song MK, Kim HY, Choi BK, Kim HH. Filifactor alocis-derived extracellular vesicles inhibit osteogenesis through TLR2 signaling. Mol Oral Microbiol 2020;35:202-10.
    30. Abe M, Tanaka Y, Saito K, Shirakawa F, Koyama Y, Goto S, Eto S. Regulation of interleukin (IL)-1beta gene transcription induced by IL-1beta in rheumatoid synovial fibroblast-like cells, E11, transformed with simian virus 40 large T antigen. J Rheumatol 1997;24:420-9.
    31. Whitmarsh AJ, Davis RJ. Transcription factor AP-1 regulation by mitogen-activated protein kinase signal transduction pathways. J Mol Med (Berl) 1996;74:589-607.
    32. Iles KE, Forman HJ. Macrophage signaling and respiratory burst. Immunol Res 2002;26:95-105.
    33. Johnson GL, Lapadat R. Mitogen-activated protein kinase pathways mediated by ERK, JNK, and p38 protein kinases. Science 2002;298:1911-2.
    Copyright © Korean of Oral Biology and the UCLA Dental Research Institute. All rights reserved.