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. Author manuscript; available in PMC: 2023 Aug 10.
Published in final edited form as: J Immunol. 2021 May 5;206(10):2386–2392. doi: 10.4049/jimmunol.2001432

Local Sustained Delivery of Anti–IL-17A Antibodies Limits Inflammatory Bone Loss in Murine Experimental Periodontitis

Cinthia M F Pacheco *,1, Katia L M Maltos *,1, Mostafa S Shehabeldin *,†,‡,1, Laura L Thomas *, Zhe Zhuang *,§, Sayuri Yoshizawa *,†, Konstantinos Verdelis *, Sarah L Gaffen , Gustavo P Garlet ‖, Steven R Little #, Charles Sfeir *,†,‡,**
PMCID: PMC10415091  NIHMSID: NIHMS1735884  PMID: 33952619

Abstract

Periodontal disease (PD) is a chronic destructive inflammatory disease of the tooth-supporting structures that leads to tooth loss at its advanced stages. Although the disease is initiated by a complex organization of oral microorganisms in the form of a plaque biofilm, it is the uncontrolled immune response to periodontal pathogens that fuels periodontal tissue destruction. IL-17A has been identified as a key cytokine in the pathogenesis of PD. Despite its well documented role in host defense against invading pathogens at oral barrier sites, IL-17A–mediated signaling can also lead to a detrimental inflammatory response, causing periodontal bone destruction. In this study, we developed a local sustained delivery system that restrains IL-17A hyperactivity in periodontal tissues by incorporating neutralizing anti–IL-17A Abs in poly(lactic-coglycolic) acid microparticles (MP). This formulation allowed for controlled release of anti–IL-17A in the periodontium of mice with ligature-induced PD. Local delivery of anti–IL-17A MP after murine PD induction inhibited alveolar bone loss and osteoclastic activity. The anti–IL-17A MP formulation also decreased expression of IL-6, an IL-17A target gene known to induce bone resorption in periodontal tissues. This study demonstrates proof of concept that local and sustained release of IL-17A Abs constitutes a promising therapeutic strategy for PD and may be applicable to other osteolytic bone diseases mediated by IL-17A–driven inflammation.

periodontal disease (PD) is a chronic inflammatory condition that affects supporting tooth structures forming the periodontium. Although PD is triggered by keystone pathogens and pathobionts that colonize the tooth surface (1), it is the dysregulated host immune response against those pathogens that causes periodontal tissue destruction (2). This dysregulated host response is fueled by an array of mediators that induce inflammatory osteolysis in the periodontium (3). Among those mediators are proinflammatory cytokines such as IL-6 and TNF-α. These cytokines and others are released by both immune and structural cells (e.g., lymphocytes, macrophages, or fibroblasts and epithelial cells) in response to bacterial invasion in the periodontium. IL-6 and TNF-α have been associated with enhanced osteoclastic activity and progressive alveolar bone loss in animal models of PD (4).

IL-17A is a key driver of pathogenic host response in a number of chronic inflammatory conditions in which bone loss is a characteristic feature, such as psoriatic arthritis and PD (5–7). In both conditions, chronic expansion and activation of IL-17A–producing lymphocytes (broadly called “Type 17,” including CD4+ T cells, γδ-T cells, group 3 innate lymphoid cells [ILC3], and NKT cells) is triggered by locally upregulated IL-23, IL-1β, and IL-6 and results in progressive bone destruction (5, 8).

A number of studies have indicated that IL-17A mediates bone loss through a combination of osteoblast, osteocyte, and osteoclast functions. In osteoblast cultures, IL-17A stimulates the expression of the major osteoclast-differentiating factor RANKL in a dose-dependent manner (9). Similarly, the ability of IL-17A to upregulate RANKL extends to osteocytes in an animal model of hyperparathyroidism-induced bone loss (10). In osteoclasts, IL-17A can either promote the generation of osteoclasts from monocytes in the absence of RANKL (11) or enhance the sensitivity of osteoclasts precursors to RANKL by upregulating the expression of its receptor (12). In addition to acting on cells directly involved in the bone remodeling process, IL-17A indirectly influences bone loss by acting on stromal and epithelial cells to upregulate pro-osteoclastogenic cytokines, particularly IL-6 (13, 14). IL-17A also synergizes potently with other cytokines, especially TNF-α, thus serving as a rheostat for local inflammation (15, 16). Thus, on balance, the overall effect of IL-17A upregulation in chronic inflammatory conditions of bone is destructive, where it supports uncoupled bone remodeling by favoring osteoclastic activity through both direct and indirect mechanisms.

Interestingly, numerous studies have pointed out a protective role for IL-17A–mediated inflammation against pathogen-induced tissue damage, including in PD. In the oral environment, IL-17R signaling mediates host defense against Porphyromonas gingivalis–induced bone loss (17) as well as oral Candida albicans infection (18) in mice. In both models of oral infection, IL-17A–mediated tissue protection is explained by its vital role in orchestrating neutrophil expansion and recruitment to the infection site (19). This process contrasts with long-term PD or arthritic settings, in which the dominant effect of IL-17A seems to be as a key driver of hard tissue destruction. Collectively, the aforementioned reports indicate that the end result of IL-17A–driven inflammation depends on the nature of the inflammatory response produced in tissue and is dictated in part by the inflammatory setting.

In light of the reported roles of IL-17A in inflammatory diseases, systemic anti–IL-17A therapies have been investigated and have exhibited various degrees of success. In this respect, anti–IL-17A therapy is highly effective at improving clinical outcomes and quality of life in psoriatic arthritis patients (20). Although the clinical efficacy of IL-17A neutralizing Abs was reported for rheumatoid arthritis (RA) patients in some clinical trials (21, 22), other trials showed no clinical benefit of IL-17A blockade (23, 24). Therefore, anti–IL-17A therapy is not equally effective in all bone-destructive disease settings.

In this work, we investigated local, sustained release of IL-17A Abs as a therapeutic strategy for murine ligature PD as a model for chronic bone-destructive diseases driven by IL-17A. We hypothesized that modulating the activity of IL-17A locally by Ab neutralization would halt periodontal bone loss. To this end, poly(lactic-coglycolic) acid (PLGA) microparticles (MP) were used to encapsulate and sustainably release IL-17A Abs in diseased murine periodontium. This study demonstrated proof of principle that local anti–IL-17A therapy is a viable strategy for preventing bone loss in conditions associated with IL-17A–mediated pathology.

Materials and Methods

MP fabrication and characterization

PLGA MP, loaded with the anti–IL-17A Ab, were formulated using a standard water–oil–water double-emulsion procedure, as described previously (25). The aqueous phase contained 1 mg/ml of anti-mouse IL-17A mAb (16717385; eBioscience) in PBS, and the oil phase was made of PLGA dissolved in dichloromethane as an organic solvent. Blank MP (unloaded MP) were fabricated following the same procedure, except that the aqueous solution consisted only of PBS. MP were surface characterized using a scanning electron microscope (JSM-6330F; JEOL) and the release profile of the anti–IL-17A Ab was determined over 2 wk using an ELISA. The surface characterization of MP surface morphology was carried out using a scanning electron microscope (JSM-6330F; JEOL). The release profile of the Ab was determined by suspending the anti–IL-17A MP (~7 mg) in 1 ml of PBS. The suspension was placed on a tube rotator at 37°C, and the supernatants were collected and replaced daily for 2 wk. The amount (and structural integrity) of anti–IL-17A in the supernatant was quantified using a standard ELISA. In brief, a Recombinant Mouse IL-17A (ELISA Std.) (576009; BioLegend) was reconstituted in 1% BSA in PBS, then coated on an ELISA microplate (10 ng/100 μl/well). The plate was then incubated at room temperature overnight. Following overnight incubation, the plate was washed with PBS–Tween and then blocked with 3% BSA in PBS and incubated with the supernatants collected daily from the anti–IL-17A MP suspension for 2 h at room temperature. Serial dilutions of the stock anti-mouse IL-17A solution used for MP fabrication were used as standards for the assay. Next, the plate was washed, then incubated with a secondary Ab that consisted of goat anti-mouse IgG-AP (2047; Santa Cruz Biotechnology) at room temperature for 1 h. Finally, 100 μl of 1-Step PNPP (37621; Thermo Fisher Scientific) was added to each well, then incubated for 30 min at room temperature followed by the addition of 50 μl of 2N NaOH to stop the reaction. The absorbance was detected in a microplate reader at 405 nm, then the concentration of anti–IL-17A released at each timepoint was calculated using a standard curve.

Murine ligature-induced PD

Six- to eight-week-old male BALB/c mice (The Jackson Laboratory, Bar Harbor, ME) were used in this study. Mice were maintained under a 12:12-h light/dark cycle at 23–25°C with free access to water and commercial food. The study was approved by Institutional Animal Care and Use Committee of the University of Pittsburgh (protocol identification number 15053781).

The murine ligature PD model employed in this study was previously described (26). Briefly, mice were anesthetized with a mixture of ketamine (80 mg/kg) and xylazine (8 mg/kg), then a sterile 6–0 silk suture (Henry Schein) was ligated around the maxillary second molar at the level of the gingival sulcus to induce plaque accumulation. The contralateral nonligated maxillary molar served as an internal control.

Experimental design, Anti–IL-17A MP local delivery, and samples collection

After ligature placement, the animals were divided into three experimental groups: 1) untreated, with ligature placement and no MP injection, 2) anti–IL-17A MP day 0, with ligature placement and anti–IL-17A MP injection on the same day, and 3) anti–IL-17A MP day 2, with ligature placement and anti–IL-17A MP injection after 48 h. All mice were sacrificed on the eighth day after ligation (n = 5 mice).

For the second and third groups, anti–IL-17A MP suspended in PBS with 2% carboxymethylcellulose (25 mg/ml) was locally delivered using a 28.5-gauge insulin syringe into four different sites (10–15 μl/site) in the buccal and palatal gingiva surrounding the ligated tooth under a stereomicroscope.

To rule out the possibility that PLGA may exert an effect on bone loss, we conducted an independent experiment in which alveolar bone loss was compared between mice with ligature placement only (no MP injection) and mice with ligature and local injection of unloaded (blank) MP (Supplementary Fig. 1).

At the end of the experiment, mice were euthanized, and the maxillae were harvested and placed in either 10% formaldehyde for fixation, then in alveolar bone loss and histological analysis, or in liquid nitrogen followed by storage at 80°C for RNA extraction and quantitative PCR (qPCR) analysis.

Alveolar bone loss quantification

To quantify alveolar bone loss, the fixed mice maxillae, were transferred to 70% ethanol for microcomputed tomography (microCT) scanning using a viva CT 40 microCT system (SCANCO Medical, Brüttisellen, Switzerland) at a resolution of 10.5 μm and 55 μA kVp. The scans were reoriented so that a horizontal line crossed the cementoenamel junction (CEJ) of the first and second molars in the sagittal plane, whereas a vertical line crossed the center of the pulp chamber of all molars in the transaxial plane. After reorientation, linear bone resorption was assessed by measuring the distance between the CEJ and the alveolar bone crest (ABC) using ImageJ software. On the buccal and palatal aspects, the ABC–CEJ distance was measured in 47 coronal sections spanning all molars, with 52.5-μm intervals between successive sections. On the interdental aspects, bone loss was assessed in 11 sagittal sections, with 52.5-μm intervals in between, on both the mesial and distal sides of the second molar. The interdental bone loss was calculated as the average of mesial and distal measurements. Measurements were performed on both the ligated (experimental) and nonligated (healthy) sides of the maxillae. For each aspect, data were presented as the differences between the average values on the ligated and nonligated sides. The investigator conducting the measurements was blinded from the treatment received in the experimental group being analyzed.

Histological analysis

The fixed maxillae were demineralized in 10% EDTA for 15 d at 4°C and processed for paraffin embedding histological analysis. Paraffin-embedded half-maxillae were sectioned in serial 4-μm-thick sections in a buccal-palatal direction. Sections were stained for tartrate-resistant acid phosphatase (TRAP; Sigma-Aldrich, Saint Louis, MO) and counterstained with hematoxylin for quantification of osteoclasts. Only the sections in which the pulp chamber and the two roots of the second molar could be visualized were selected for further analysis. For each sample, four maxillae sections at a distance of at least 16-μm intervals were used for identifying and counting of osteoclasts at ×400 magnification. In selected sections, the coronal two thirds of the mesial and distal ABC adjacent to the maxillary second molar and furcation area was demarcated using ImageJ software as regions of interest. Osteoclasts were identified as TRAP-positive, multinucleated cells with purple cytoplasm situated on the marginal alveolar bone of the demarcated areas. Results were presented as the average number of osteoclasts divided by the surface area of the regions of interest in mm2 in each experimental group.

qPCR

The frozen maxillae samples were first crushed in liquid nitrogen, then RNA extraction was performed using an RNeasy Mini Kit (QIAGEN, Valencia, CA). The gene expression of IL-17A, IL-6, TNF-α, and receptor activator of NF-κB ligand (RANKL) was assessed by qPCR using TaqMan probes (Applied Biosystems, Foster City, CA). Real-time PCR was performed using QuantStudioTM 6 Flex Real-Time PCR System (Thermo Fisher Scientific). Data were analyzed using the 2−ΔΔCT method and presented as the mean fold change normalized to the healthy control group.

Statistical analysis

Results were presented as means ± SD of 5–6 mice per group. Differences between means were evaluated using one-way ANOVA followed by Tukey (bone loss and osteoclastic activity) or Holm–Sidak (gene expression) post hoc multiple comparison tests. A p value <0.05 was considered statistically significant. Statistics were performed using GraphPad Prism.

Results

Sustained release profile of functionally active anti–IL-17A Abs from PLGA MP

Release of anti–IL-17A from PLGA MP included an initial burst release of 0.7 ng/ml, followed by a relatively steady release of additional 0.1 ng/ml per day, continuing until day 11. An increase in the anti–IL-17A release rate took place starting day 12, with 0.2 ng/ml being released until day 14 (Fig. 1A). Total loading of anti–IL-17A in PLGA was 20% of the amount initially used in the fabrication. Scanning electron microscope images revealed spherically shaped nonporous anti–IL-17A MP with an average diameter of 17.8 μm, which is within the known effective size range for PLGA MP intended for drug delivery (Fig. 1B, 1C). Although PLGA MP smaller than 10 μm are more susceptible to phagocytosis by immune cells, MP larger than 10 μm will remain in the extracellular matrix tissue, releasing encapsulated proteins locally at the site of the depot.

FIGURE 1.

FIGURE 1.

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Characterization of PLGA MP encapsulating IL-17A Ab. Cumulative fraction of anti–IL-17A released from PLGA MP for 14 d, determined by ELISA (A). Scanning electron microscope im- age of IL-17A Ab MP, ×2000 (B) and ×5500 (C).

It should be noted that these ELISA results confirm not only the quantity of IL-17A Abs released from the PLGA MP but also that the structural integrity of the Abs was maintained, given that this assay is based on the binding of functionally active IL-17A Ab to its epitope on IL-17A. Thus, it is likely that the released IL-17A Abs will exert neutralizing activity upon local delivery.

IL-17A MP inhibited alveolar bone loss and reduced osteoclast counts in PD

To determine the impact of local sustained delivery of anti–IL-17A on periodontal bone loss, we employed a standard ligature-induced mouse model of PD (26). Anti–IL-17A MP were administered contemporaneously with or 2 d after the start of PD induction (anti–IL-17A day 0 or day 2). Compared with untreated controls, the anti–IL-17A MP day 2 group showed inhibition of alveolar bone loss on the buccal and interdental aspects of the ligated molar as determined by microCT analysis (Fig. 2). Additionally, the osteoclast count in the anti–IL-17A MP day 2 group was lower than the untreated group, which was particularly evident on the mesial aspect of the ligated molar as determined by TRAP staining (Fig. 3). Administration of unloaded PLGA MP did not alter the extent of bone loss or osteoclastic activity compared with the untreated/ligature control group (Supplemental Fig. 1), confirming that the PLGA delivery system does not impact alveolar bone loss in ligature PD.

FIGURE 2.

FIGURE 2.

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microCT evaluation of alveolar bone loss in mice. MP were injected into gingival tissue surrounding the ligated tooth on either day 0 or day 2 after ligature placement. Representative two-dimensional microCT images from sagittal and transaxial slices of mice hemimaxilla as follows: healthy group, untreated group, and groups treated with anti–IL-17A MP at day 0 and day 2. Quantification of alveolar bone loss represented by the linear bone loss between the CEJ and ABC (dashed lines) along the interdental (A), buccal (B), and palatal (C) sides. Values (mean ± SD) obtained from 5–6 animals per group. The p values were determined by one-way ANOVA, followed by a Tukey multiple comparisons test. *p < 0.05, **p < 0.005, ***p <0.0005, ****p < 0.0001.

FIGURE 3.

FIGURE 3.

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Effect of anti–IL-17A MP on the number of alveolar bone-associated osteoclasts. (A–D) Histological representation of healthy, untreated, and IL-17A MP in day 0 and day 2 groups. Hemimaxilla samples were stained for TRAP, as described in the Materials and Methods section. The arrows show TRAP-positive multinucleated osteoclasts associated with alveolar bone (original magnification ×400; scale bar, 100 μm). Quantification of TRAP-positive multinucleated alveolar bone-associated osteoclasts on the mesial aspect only (E), and on all aspects combined (mesial, distal, and furcation aspects) (F). Anti–IL-17A MP at day 2 significantly decreased the number of osteoclasts per mm2 in the alveolar bone in comparison with untreated group. Values (mean ± SD) obtained from six animals per group. The p values were determined by one-way ANOVA followed by Tukey multiple comparisons test. *p < 0.05, ***p < 0.0005.

Cytokine expression profiles following IL-17A MP administration

To determine the expression profile of Il17a and its dependent genes during ligature-induced PD, we extracted RNA from periodontal tissues at different time points days following ligature placement (Supplemental Fig. 2). We observed upregulation of Il17a mRNA expression starting at day 2 postligature placement, evident at day 4, and peaking at day 8 (Supplemental Fig. 2). The gradually increasing expression profile of Il17a during murine ligature-induced PD prompted us to deliver the anti–IL-17A MP 2 days after, instead of concurrently with, placing ligatures for all subsequent experiments.

Expression of Il6, Tnfa, and Tnfsf11 (RANKL) mRNA in periodontium was evaluated at either day 4 or day 8 after ligature placement. At day 4, the untreated/ligature–only group showed elevated Il6 and Tnfsf11 compared with controls. Anti–IL-17A MP administration reversed upregulation of Il6 but not Tnfsf11 (Fig. 4A, 4B). Tnfa was not different among experimental groups (Fig. 4C). At day 8, Tnfsf11 showed sustained upregulation in the untreated group compared with controls. Mice given anti–IL-17A MP exhibited no differences in the expression of Il6, Tnfa, and Tnfsf11 mRNA compared with the heathy controls or the untreated groups at day 8 (Fig. 4D–F). Collectively, these data show that local neutralization of IL-17A in diseased periodontium inhibits Il6 mRNA expression, recapitulating the previously reported effect of IL-17A on Il6 expression.

FIGURE 4.

FIGURE 4.

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Expression of proinflammatory markers in periodontal tissues of mice. The mRNA expression of genes encoding the proinflammatory markers IL-6, TNF-α, and RANKL in the periodontal tissues was compared by the value of 2(−ΔΔCt) (n = 5 mice). MPs were injected into the maxillary gingiva on day 2 (buccal and palatal sides) after ligation, and the biochemical markers were assessed at fourth and eighth day after ligature placement. Periodontal tissues from untreated group showed an increase in the expression of genes encoding IL-6 and RANKL at 4 d (A and B). Anti–IL-17A MP injection decreased the level of the gene encoding IL-6 when evaluated at the fourth but not at the eighth day after ligature placement (A and D). Expression of Tnfsf11, which encodes RANKL, did not change by anti–IL-17A MP delivery at 4 or 8 d (B and E). Ligature placement and anti–IL-17A MP injection did not affect TNF-α expression in the periodontal tissues at both timepoints (C and F). The p values were determined by one-way ANOVA followed by Holm–Sidak multiple comparisons test. *p < 0.05, **p < 0.005, ****p < 0.0001.

Discussion

A healthy periodontium depends on an intricate balance between the host response and the periodontal microbiota. In PD, changes in the periodontal microbial load or composition (dysbiosis) provokes inflammation-driven tissue destruction (1). Because periodontal damage is primarily caused by an uncontrolled host inflammatory response to a dysbiotic microbiota (27), host modulation has become an attractive therapeutic approach for PD in recent years. In this regard, our group previously demonstrated that recruitment of regulatory T cells (28) or induction of proresolving M2 macrophages (29) in murine periodontium can protect against inflammatory bone loss.

IL-17A is the signature cytokine of Th17 cells, as well as innate lymphocytes, such as γδ T cells, NKT, and ILC3s (30). In the current study, we evaluated the therapeutic efficacy of modulating IL-17A in murine ligature PD as an exemplar for chronic osteolytic diseases. Our goal was to provide a proof of concept for the application of this therapeutic strategy to ameliorate bone-destructive diseases involving IL-17A. To that end, we developed a formulation that sustainably releases functionally active IL-17A Abs to suppress the destructive effects of IL-17A in murine periodontium. This formulation was intended for local administration as a single-dose therapy over the course of murine PD. This translational approach builds on an earlier report pointing to a protective effect of daily local administration of an IL-17A mAb against inflammatory bone loss in mice undergoing experimental periodontitis (31).

In the current study, we observed an inhibition in alveolar bone loss when anti–IL-17A MP were delivered 2 days after but not simultaneously with PD induction. One possible explanation for this observation is the difference in timing between the secretion of IL-17A in the inflamed periodontium and the release of the IL-17A Abs from the MP (Fig. 1A). Our qPCR data showed that Il17a mRNA expression in murine periodontal tissues following PD induction is modest at day 2, then sharply increases at day 4, remaining elevated up to day 8 (Supplemental Fig. 2). We speculate that the rise in Il17a from day 2 to day 4 marks the emergence of a pathogenic rather than homeostatic subset of IL-17A–producing cells in the inflamed periodontal environment, denoting a switch from a protective to a destructive IL-17A–driven inflammation. This switch to a destructive IL-17A–driven inflammation could explain the previously reported acceleration in bone loss three to five days after ligature placement in the murine ligature-induced PD model (26, 32). Thus, it is expected that a therapeutic strategy that targets IL-17A activity would be most effective as IL-17A is produced in the periodontium (2 days after ligature placement). To that end, we designed our experiment so that the anti–IL-17A burst release takes place just before the emergence of pathogenic IL-17A–producing cells. This temporal synchrony between the anti–IL-17A burst release and the hypothesized window for IL-17A hyperactivity may explain the protective effect of delivering anti–IL-17A MP 2 days after ligature placement and not earlier.

The magnitude of inflammatory bone loss inhibition achieved with delivery of anti–IL-17A MP ranged from 25% on the interdental aspect to 50% on the buccal aspect, compared with the untreated group. A similar range of efficacy/bone loss protection is of clinical significance in terms of human disease, in which a 20–30% difference in bone loss marks the transition from mild/moderate to severe disease, based on the newly introduced classification (33). This further supports the clinical translation potential of anti–IL-17A therapeutics for PD. Moreover, it is likely that a larger magnitude of bone loss inhibition can be achieved by delivering higher doses of anti–IL-17A using our delivery system. This is because Il17a expression has been shown to correlate with the severity of bone loss in previous studies employing the murine ligature PD model (31, 32).

The IL-17A–targeted approach outlined in this study is of clinical significance because IL-17A–producing cells present at periodontal sites are not always pathogenic in nature. On one hand, one study suggested that a homeostatic subset of Th17 cells arise in the gingiva as a result of physiological forces of mastication, and this population is essential for immune surveillance and host defense at oral barrier sites (34). On the other hand, a pathogenic Th17 cell subset expands locally in response to microbial dysbiosis and drives inflammatory damage in murine ligature PD (5). The latter report suggested that the destructive inflammatory response in murine PD is induced by IL-17A–dependent signaling. Thus, it is evident that the effects of IL-17A and its producing cells in tissue can be context dependent. Therefore, an understanding of the IL-17A dynamic and divergent functions should form the basis for deploying IL-17A–targeted therapies in a specific clinical setting.

Osteoclastic bone resorption is a hallmark of PD and is regulated by diverse signals within the bone microenvironment (9, 35–37). In line with the findings of alveolar bone loss suppression, we observed a reduction in the number of osteoclasts in the ABC area in the group that received local anti–IL-17A MP 2 days after ligature placement. Indeed, IL-17A can upregulate the pro-osteoclastogenic cytokines IL-6 and IL-8, either alone or in synergy with other cytokines, such as IL-1β and TNF-α (38). The synergistic interaction between IL-17A and TNF-α was suggested as a predictor of early joint damage in RA patients (39). Similarly, IL-1β was shown to potentiate the IL-17A effect on bone destruction in explants from RA patients (40). Therefore, blockade of IL-17A may indirectly inhibit the effects of other inflammatory cytokines by mitigating their synergistic interactions (41).

IL-6 has been shown to be indispensable for pathogenic Th17 cell expansion, leading to IL-17A overproduction and bone loss in ligature-induced periodontitis (5). Moreover, IL-6 is a signature gene induced by IL-17A signaling in many cell types, thus establishing a feed-forward amplification cycle of local inflammation (42). Consistent with this, we saw that the local delivery of anti–IL-17A MP downregulated Il6 mRNA expression in periodontal tissues, which may be central to its efficacy, interfering with this inflammatory loop in the periodontal tissues.

In conclusion, the current work demonstrates that local and sustained release of IL-17A Abs can halt inflammatory bone loss in murine PD, which served as a model for chronic osteolytic diseases. Accordingly, this approach may represent a promising therapeutic strategy for conditions in which inflammatory bone loss is driven by IL-17A–mediated inflammation.

Supplementary Material

Supplementary Material

Acknowledgments

This work was supported by the Center for Craniofacial Regeneration at the University of Pittsburgh, the National Institutes of Health (DE022550, to S.L.G.), the National Council for the Improvement of Higher Education (Brazil) (to C.M.F.P.), and the National Research Center of Egypt (M.S.S.).

Abbreviations used in this article:

ABC

alveolar bone crest

CEJ

cementoenamel junction

ILC3

group 3 innate lymphoid cell

microCT

microcomputed tomography

MP

PLGA microparticle

PD

periodontal disease

PLGA

poly(lactic-coglycolic) acid

qPCR

quantitative PCR

RA

rheumatoid arthritis

RANKL

receptor activator of NF- κB ligand

TRAP

tartrate-resistant acid phosphatase

Footnotes

The online version of this article contains supplemental material.

Disclosures

The authors have no financial conflicts of interest.

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