C5a-licensed phagocytes drive sterilizing immunity during systemic fungal infection.

Systemic candidiasis is a common, high-mortality, nosocomial fungal infection. Unexpectedly, it has emerged as a complication of anti-complement C5-targeted monoclonal antibody treatment, indicating a critical niche for C5 in antifungal immunity. We identified transcription of complement system genes as the top biological pathway induced in candidemic patients and as predictive of candidemia. Mechanistically, C5a-C5aR1 promoted fungal clearance and host survival in a mouse model of systemic candidiasis by stimulating phagocyte effector function and ERK- and AKT-dependent survival in infected tissues. C5ar1 ablation rewired macrophage metabolism downstream of mTOR, promoting their apoptosis and enhancing mortality through kidney injury. Besides hepatocyte-derived C5, local C5 produced intrinsically by phagocytes provided a key substrate for antifungal protection. Lower serum C5a concentrations or a C5 polymorphism that decreases leukocyte C5 expression correlated independently with poor patient outcomes. Thus, local, phagocyte-derived C5 production licenses phagocyte antimicrobial function and confers innate protection during systemic fungal infection.

MCPIP1 Endoribonuclease Activity Negatively Regulates Interleukin-17-Mediated Signaling and Inflammation.

Interleukin-17 (IL-17) induces pathology in autoimmunity and infections; therefore, constraint of this pathway is an essential component of its regulation. We demonstrate that the signaling intermediate MCPIP1 (also termed Regnase-1, encoded by Zc3h12a) is a feedback inhibitor of IL-17 receptor signal transduction. MCPIP1 knockdown enhanced IL-17-mediated signaling, requiring MCPIP1's endoribonuclease but not deubiquitinase domain. MCPIP1 haploinsufficient mice showed enhanced resistance to disseminated Candida albicans infection, which was reversed in an Il17ra(-/-) background. Conversely, IL-17-dependent pathology in Zc3h12a(+/-) mice was exacerbated in both EAE and pulmonary inflammation. MCPIP1 degraded Il6 mRNA directly but only modestly downregulated the IL-6 promoter. However, MCPIP1 strongly inhibited the Lcn2 promoter by regulating the mRNA stability of Nfkbiz, encoding the IκBζ transcription factor. Unexpectedly, MCPIP1 degraded Il17ra and Il17rc mRNA, independently of the 3' UTR. The cumulative impact of MCPIP1 on IL-6, IκBζ, and possibly IL-17R subunits results in a biologically relevant inhibition of IL-17 signaling.

Stepping Up to the Plate(let) against Candida albicans.

Candida albicans is a pervasive commensal fungus that is the most common pathogen responsible for invasive fungal infection (IFI). With incidence of IFI on the rise due to increasing susceptible populations, it is imperative that we investigate how Candida albicans interacts with blood components. When stimulating either human or mouse whole blood with thrombin, we saw a significant decrease in C. albicans survival. We then repeated Candida killing assays with thrombin-stimulated or unstimulated washed platelets and saw a similar decrease in CFU. To investigate whether killing was mediated through surface components or releasable products, platelets were pretreated with an inhibitor of actin polymerization (cytochalasin D [CytoD]). CytoD was able to abrogate C. albicans killing. Moreover, dilution of releasates from thrombin-stimulated platelets showed that the toxicity of the releasates on C. albicans is concentration dependent. We then investigated C. albicans actions on platelet activation, granule release, and aggregation. While C. albicans does not appear to affect alpha or dense granule release, C. albicans exerts a significant attenuation of platelet aggregation to multiple agonists. These results illustrate for the first time that platelets can directly kill C. albicans through release of their granular contents. Additionally, C. albicans can also exert inhibitory effects on platelet aggregation.

CD4(+)CD25(+)Foxp3(+) regulatory T cells promote Th17 cells in vitro and enhance host resistance in mouse Candida albicans Th17 cell infection model.

Th17 cells and CD4(+)CD25(+)Foxp3(+) regulatory T (Treg) cells are thought to promote and suppress inflammatory responses, respectively. Here we explore why under Th17 cell polarizing conditions, Treg cells did not suppress, but rather upregulated, the expression of interleukin-17A (IL-17A), IL-17F, and IL-22 from responding CD4(+) T cells (Tresp cells). Upregulation of IL-17 cytokines in Tresp cells was dependent on consumption of IL-2 by Treg cells, especially at early time points both in vitro and in vivo. During an oral Candida albicans infection in mice, Treg cells induced IL-17 cytokines in Tresp cells, which markedly enhanced fungal clearance and recovery from infection. These findings show how Treg cells can promote acute Th17 cell responses to suppress mucosal fungus infections and reveal that Treg cells have a powerful capability to fight infections besides their role in maintaining tolerance or immune homeostasis.

Aspartate semialdehyde dehydrogenase inhibition suppresses the growth of the pathogenic fungus Candida albicans.

Potent inhibitors of an essential microbial enzyme have been shown to be effective growth inhibitors of Candida albicans, a pathogenic fungus. C. albicans is the main cause of oropharyngeal candidiasis, and also causes invasive fungal infections, including systemic sepsis, leading to serious complications in immunocompromised patients. As the rates of drug-resistant fungal infections continue to rise novel antifungal treatments are desperately needed. The enzyme aspartate semialdehyde dehydrogenase (ASADH) is critical for the functioning of the aspartate biosynthetic pathway in microbes and plants. Because the aspartate pathway is absent in humans, ASADH has the potential to be a promising new target for antifungal research. Deleting the asd gene encoding for ASADH significantly decreases the survival of C. albicans, establishing this enzyme as essential for this organism. Previously developed ASADH inhibitors were tested against several strains of C. albicans to measure their possible therapeutic impact. The more potent inhibitors show a good correlation between enzyme inhibitor potency and fungal growth inhibition. Growth curves generated by incubating different C. albicans strains with varying enzyme inhibitor levels show significant slowing of fungal growth by these inhibitors against each of these strains, similar to the effect observed with a clinical antifungal drug. The most effective inhibitors also demonstrated relatively low cytotoxicity against a human epithelial cell line. Taken together, these results establish that the ASADH enzyme is a promising new target for further development as a novel antifungal treatment against C. albicans and related fungal species.

IL-22 neutralizing autoantibodies impair fungal clearance in murine oropharyngeal candidiasis model.

Protection against mucocutaneous candidiasis depends on the T helper (Th)17 pathway, as gene defects affecting its integrity result in inability to clear Candida albicans infection on body surfaces. Moreover, autoantibodies neutralizing Th17 cytokines have been related to chronic candidiasis in a rare inherited disorder called autoimmune polyendocriopathy candidiasis ectodermal dystrophy (APECED) caused by mutations in autoimmune regulator (AIRE) gene. However, the direct pathogenicity of these autoantibodies has not yet been addressed. Here we show that the level of anti-IL17A autoantibodies that develop in aged Aire-deficient mice is not sufficient for conferring susceptibility to oropharyngeal candidiasis. However, patient-derived monoclonal antibodies that cross-react with murine IL-22 increase the fungal burden on C. albicans infected mucosa. Nevertheless, the lack of macroscopically evident infectious pathology on the oral mucosa of infected mice suggests that additional susceptibility factors are needed to precipitate a clinical disease.

The Kallikrein-Kinin System: A Novel Mediator of IL-17-Driven Anti-Candida Immunity in the Kidney.

The incidence of life-threatening disseminated Candida albicans infections is increasing in hospitalized patients, with fatalities as high as 60%. Death from disseminated candidiasis in a significant percentage of cases is due to fungal invasion of the kidney, leading to renal failure. Treatment of candidiasis is hampered by drug toxicity, the emergence of antifungal drug resistance and lack of vaccines against fungal pathogens. IL-17 is a key mediator of defense against candidiasis. The underlying mechanisms of IL-17-mediated renal immunity have so far been assumed to occur solely through the regulation of antimicrobial mechanisms, particularly activation of neutrophils. Here, we identify an unexpected role for IL-17 in inducing the Kallikrein (Klk)-Kinin System (KKS) in C. albicans-infected kidney, and we show that the KKS provides significant renal protection in candidiasis. Microarray data indicated that Klk1 was upregulated in infected kidney in an IL-17-dependent manner. Overexpression of Klk1 or treatment with bradykinin rescued IL-17RA-/- mice from candidiasis. Therapeutic manipulation of IL-17-KKS pathways restored renal function and prolonged survival by preventing apoptosis of renal cells following C. albicans infection. Furthermore, combining a minimally effective dose of fluconazole with bradykinin markedly improved survival compared to either drug alone. These results indicate that IL-17 not only limits fungal growth in the kidney, but also prevents renal tissue damage and preserves kidney function during disseminated candidiasis through the KKS. Since drugs targeting the KKS are approved clinically, these findings offer potential avenues for the treatment of this fatal nosocomial infection.

IL-17-Mediated Immunity to the Opportunistic Fungal Pathogen Candida albicans.

IL-17 (IL-17A) has emerged as a key mediator of protection against extracellular microbes, but this cytokine also drives pathology in various autoimmune diseases. Overwhelming data in both humans and mice reveal a clear and surprisingly specific role for IL-17 in protection against the fungus Candida albicans, a commensal microbe of the human oral cavity, gastrointestinal tract, and reproductive mucosa. The IL-17 pathway regulates antifungal immunity through upregulation of proinflammatory cytokines, including IL-6, neutrophil-recruiting chemokines (e.g., CXCL1 and CXCL5), and antimicrobial peptides (e.g., defensins), which act in concert to limit fungal overgrowth. This review focuses on diseases caused by C. albicans, the role of IL-17-mediated immunity in candidiasis, and the implications for clinical therapies for both autoimmune conditions and fungal infections.

Role of neutrophils in IL-17-dependent immunity to mucosal candidiasis.

Oropharyngeal candidiasis (OPC), caused by the commensal fungus Candida albicans, is an opportunistic infection associated with infancy, AIDS, and IL-17-related primary immunodeficiencies. The Th17-associated cytokines IL-23 and IL-17 are crucial for immunity to OPC, but the mechanisms by which they mediate immunity are poorly defined. IL-17RA-deficient humans and mice are strongly susceptible to OPC, with reduced levels of CXC chemokines and concomitantly impaired neutrophil recruitment to the oral mucosa. Paradoxically, humans with isolated neutropenia are typically not susceptible to candidiasis. To determine whether immunity to OPC is mediated via neutrophil recruitment, mice lacking CXCR2 were subjected to OPC and were found to be highly susceptible, although there was no dissemination of fungi to peripheral organs. To assess whether the entire neutrophil response is IL-17 dependent, IL-17RA(-/-) and IL-23(-/-) mice were administered neutrophil-depleting Abs and subjected to OPC. These mice displayed increased oral fungal burdens compared with IL-17RA(-/-) or IL-23(-/-) mice alone, indicating that additional IL-17-independent signals contribute to the neutrophil response. WT mice treated with anti-Gr-1 Abs exhibited a robust infiltrate of CD11b(+)Ly-6G(low)F4/80(-) cells to the oral mucosa but were nonetheless highly susceptible to OPC, indicating that this monocytic influx is insufficient for host defense. Surprisingly, Ly-6G Ab treatment did not induce the same strong susceptibility to OPC in WT mice. Thus, CXCR2(+) and Gr-1(+) neutrophils play a vital role in host defense against OPC. Moreover, defects in the IL-23/17 axis cause a potent but incomplete deficiency in the neutrophil response to oral candidiasis.

The adaptor CARD9 is required for adaptive but not innate immunity to oral mucosal Candida albicans infections.

Oropharyngeal candidiasis (OPC [thrush]) is an opportunistic infection caused by the commensal fungus Candida albicans. OPC is common in individuals with HIV/AIDS, infants, patients on chemotherapy, and individuals with congenital immune defects. Immunity to OPC is strongly dependent on the interleukin-23 (IL-23)/IL-17R axis, as mice and humans with defects in IL-17R signaling (IL17F, ACT1, IL-17RA) or in genes that direct Th17 differentiation (STAT3, STAT1, CARD9) are prone to mucocutaneous candidiasis. Conventional Th17 cells are induced in response to C. albicans infection via signals from C-type lectin receptors, which signal through the adaptor CARD9, leading to production of Th17-inducing cytokines such as IL-6, IL-1ß, and IL-23. Recent data indicate that IL-17 can also be made by numerous innate cell subsets. These innate "type 17" cells resemble conventional Th17 cells, but they can be activated without need for prior antigen exposure. Because C. albicans is not a commensal organism in rodents and mice are thus naive to this fungus, we had the opportunity to assess the role of CARD9 in innate versus adaptive responses using an OPC infection model. As expected, CARD9(-/-) mice failed to mount an adaptive Th17 response following oral Candida infection. Surprisingly, however, CARD9(-/-) mice had preserved innate IL-17-dependent responses to Candida and were almost fully resistant to OPC. Thus, CARD9 is important primarily for adaptive immunity to C. albicans, whereas alternate recognition systems appear to be needed for effective innate responses.

Immunity to pathogenic mucosal C. albicans infections mediated by oral megakaryocytes activated by IL-17 and candidalysin.

The fungus Candida albicans can cause mucosal infections including oropharyngeal candidiasis (OPC) in immunocompromised patients. In humans, an increased risk of fungal infections correlates with thrombocytopenia. However, our understanding of platelets and megakaryocytes (Mks) in mucosal fungal infections is almost entirely unknown. When megakaryocyte- and platelet-depleted mice were infected with OPC, the tongue showed higher fungal burden, due to decreased neutrophil accumulation. Protection depended on a distinct population of oral-resident Mks. Interleukin-17, important in antifungal immunity, was required since mice lacking the IL-17 receptor had decreased circulating platelets and their oral Mks did not expand during OPC. The secretion of the peptide toxin candidalysin activated human Mks to release platelets with antifungal capacity. Infection with a candidalysin-deficient strain resulted in decreased expansion of tongue Mks during OPC. This is the first time that a distinct megakaryocyte population was identified in the oral mucosa which is critical for immunity against fungal infection.

IκBζ is an essential mediator of immunity to oropharyngeal candidiasis.

Fungal infections are a global threat; yet, there are no licensed vaccines to any fungal pathogens. Th17 cells mediate immunity to Candida albicans, particularly oropharyngeal candidiasis (OPC), but essential downstream mechanisms remain unclear. In the murine model of OPC, IκBζ (Nfkbiz, a non-canonical NF-κB transcription factor) was upregulated in an interleukin (IL)-17-dependent manner and was essential to prevent candidiasis. Deletion of Nfkbiz rendered mice highly susceptible to OPC. IκBζ was dispensable in hematopoietic cells and acted partially in the suprabasal oral epithelium to control OPC. One prominent IκBζ-dependent gene target was ß-defensin 3 (BD3) (Defb3), an essential antimicrobial peptide. Human oral epithelial cells required IκBζ for IL-17-mediated induction of BD2 (DEFB4A, human ortholog of mouse Defb3) through binding to the DEFB4A promoter. Unexpectedly, IκBζ regulated the transcription factor Egr3, which was essential for C. albicans induction of BD2/DEFB4A. Accordingly, IκBζ and Egr3 comprise an antifungal signaling hub mediating mucosal defense against oral candidiasis.

Histatin 5 uptake by Candida albicans utilizes polyamine transporters Dur3 and Dur31 proteins.

Histatin 5 (Hst 5) is a salivary gland-secreted cationic peptide with potent fungicidal activity against Candida albicans. Hst 5 kills fungal cells following intracellular translocation, although its selective transport mechanism is unknown. C. albicans cells grown in the presence of polyamines were resistant to Hst 5 due to reduced intracellular uptake, suggesting that this cationic peptide may enter candidal cells through native yeast polyamine transporters. Based upon homology to known Saccharomyces cerevisiae polyamine permeases, we identified six C. albicans Dur polyamine transporter family members and propose a new nomenclature. Gene deletion mutants were constructed for C. albicans polyamine transporters Dur3, Dur31, Dur33, Dur34, and were tested for Hst 5 sensitivity and uptake of spermidine. We found spermidine uptake and Hst 5 mediated killing were decreased significantly in Δdur3, Δdur31, and Δdur3/Δdur31 strains; whereas a DUR3 overexpression strain increased Hst 5 sensitivity and higher spermidine uptake. Treatment of cells with a spermidine synthase inhibitor increased spermidine uptake and Hst 5 killing, whereas protonophores and cold treatment reduced spermidine uptake. Inhibition assays showed that Hst 5 is a competitive analog of spermidine for uptake into C. albicans cells, and that Hst 5 Ki values were increased by 80-fold in Δdur3/Δdur31 cells. Thus, Dur3p and Dur31p are preferential spermidine transporters used by Hst 5 for its entry into candidal cells. Understanding of polyamine transporter-mediated internalization of Hst 5 provides new insights into the uptake mechanism for C. albicans toxicity, and further suggests design for targeted fungal therapeutic agents.

IL-17RC is required for immune signaling via an extended SEF/IL-17R signaling domain in the cytoplasmic tail.

IL-17 mediates essential inflammatory responses in host defense and autoimmunity. The IL-17A-IL-17F signaling complex is composed of IL-17RA and IL-17RC, both of which are necessary for signal transduction. To date, the specific contribution of IL-17RC to downstream signaling remains poorly understood. To define the regions within the IL-17RC cytoplasmic tail required for signal transduction, we assayed signaling by a panel of IL-17RC deletion mutants. These findings reveal that IL-17RC inducibly associates with a specific glycosylated IL-17RA isoform, in a manner independent of the IL-17RC cytoplasmic tail. Using expression of the IL-17 target genes IL-6 and 24p3/lipocalin-2 as a readout, functional reconstitution of signaling in IL-17RC(-/-) fibroblasts required the SEF/IL-17R signaling domain (SEFIR), a conserved motif common to IL-17R family members. Unexpectedly, the IL-17RC SEFIR alone was not sufficient to reconstitute IL-17-dependent signaling. Rather, an additional sequence downstream of the SEFIR was also necessary. We further found that IL-17RC interacts directly with the adaptor/E3 ubiquitin ligase Act1, and that the functional IL-17RC isoforms containing the extended SEFIR region interact specifically with a phosphorylated isoform of Act1. Finally, we show that IL-17RC is required for in vivo IL-17-dependent responses during oral mucosal infections caused by the human commensal fungus Candida albicans. These results indicate that IL-17RC is vital for IL-17-dependent signaling both in vitro and in vivo. Insight into the mechanisms by which IL-17RC signals helps shed light on IL-17-dependent inflammatory responses and may ultimately provide an avenue for therapeutic intervention in IL-17-mediated diseases.

Understanding the Protective Role of IL-17 During Oropharyngeal Candidiasis.

Oropharyngeal candidiasis is an opportunistic mucosal infection caused predominantly by Candida albicans. While healthy individuals are protected, susceptibility is associated with immunodeficiency. In particular, patients with defects related to T helper-17 (Th17) cells and interleukin (IL)-17 signaling are highly susceptible to mucocutaneous forms of candidiasis. Since mice are naïve to Candida albicans, induction of oropharyngeal candidiasis enables a thorough understanding of IL-17 and its related immune components during acute infection. Here we describe a murine model of oropharyngeal candidiasis. This protocol allows for translatable and reproducible infection with results that can be obtained between 2 and 5 days following infection.

Radiation Exposure Perturbs IL-17RA-Mediated Immunity Leading to Changes in Neutrophil Responses That Increase Susceptibility to Oropharyngeal Candidiasis.

Fungal infections caused by Candida albicans are a serious problem for immunocompromised individuals, including those undergoing radiotherapy for head and neck cancers. Targeted irradiation causes inflammatory dysregulation and damage to the oral mucosa that can be exacerbated by candidiasis. Post-irradiation the cytokine interleukin-17 (IL-17) protects the oral mucosae by promoting oral epithelial regeneration and balancing the oral immune cell populations, which leads to the eventual healing of the tissue. IL-17 signaling is also critical for the antifungal response during oropharyngeal candidiasis (OPC). Yet, the benefit of IL-17 during other forms of candidiasis, such as vulvovaginal candidiasis, is not straightforward. Therefore, it was important to determine the role of IL-17 during OPC associated with radiation-induced inflammatory damage. To answer this question, we exposed Il17ra-/- and wild-type mice to head-neck irradiation (HNI) and OPC to determine if the IL-17 signaling pathway was still protective against C. albicans. HNI increased susceptibility to OPC, and in Il17ra-/- mice, the mucosal damage and fungal burden were elevated compared to control mice. Intriguingly, neutrophil influx was increased in Il17ra-/- mice, yet these cells had reduced capacity to phagocytose C. albicans and failed to clear OPC compared to immunocompetent mice. These findings suggest that radiotherapy not only causes physical damage to the oral cavity but also skews immune mediators, leading to increased susceptibility to oropharyngeal candidiasis.

Tissue Damage in Radiation-Induced Oral Mucositis Is Mitigated by IL-17 Receptor Signaling.

Oral mucositis (OM) is a treatment-limiting adverse side effect of radiation and chemotherapy. Approximately 80% of patients undergoing radiotherapy (RT) for head and neck cancers (HNC) develop OM, representing a major unmet medical condition. Our understanding of the immunopathogenesis of OM is limited, due in part to the surprising paucity of information regarding healing mechanisms in the oral mucosa. RNAseq of oral tissue in a murine model that closely mimics human OM, showed elevated expression of IL-17 and related immune pathways in response to head and neck irradiation (HNI). Strikingly, mice lacking the IL-17 receptor (IL-17RA) exhibited markedly more severe OM. Restoration of the oral mucosa was compromised in Il17ra-/- mice and components associated with healing, including matrix metalloproteinase 3, 10 and IL-24 were diminished. IL-17 is typically associated with recruitment of neutrophils to mucosal sites following oral infections. Unexpectedly, in OM the absence of IL-17RA resulted in excessive neutrophil recruitment and immunopathology. Instead, neutrophil activation was IL-1R-driven in Il17ra-/- mice. Blockade of IL-1R and depletion of neutrophils lessened the severity of damage in these mice. Overall, we show IL-17 is protective in OM through multiple mechanisms including restoration of the damaged epithelia and control of the neutrophil response. We also present a clinically relevant murine model of human OM to improve mechanistic understanding and develop rational translational therapeutics.

Targeting macrophages by an aza-anthrapyrazole to ameliorate experimental autoimmune encephalomyelitis.

BACKGROUND: Multiple sclerosis (MS) is an immune-mediated neurodegenerative disease in the central nerve system, in which both innate and adaptive immune cells are involved. BBR3378, an aza-anthrapyrazole prevents experimental autoimmune encephalomyelitis (EAE), an inflammatory condition similar to MS, by antagonizing T cell autoimmune responses. Here, we report BBR3378's regulatory effect on macrophages. METHODS: EAE was induced in ten-week-old female C57BL/6 mice by immunization with myelin oligodendrocyte glycoprotein peptides followed by BBR3378 or sham treatment administered intraperitoneally, and clinical signs were assessed using a 0-5 scoring system. These mice were subjected to serum ELISA for cytokine IFNγ and TNFα levels, RT qPCR analysis of macrophage markers in isolated monocytes, and flow cytometry analysis for macrophage infiltration in the brain. Macrophages derived from primary monocytes and macrophage cell line RAW 264.7 were used to investigate BBR3378's effect on LPS-stimulated pro-inflammatory cytokine induction. RAW 264.7 cells expressing NF-κB-driven luciferase reporter were treated with LPS with or without BBR3378, and luciferase assays performed to assess the inhibition on NF-κB activation. LPS-induced activation of mitogen-activated protein kinases (MAPKs) with or without the presence of BBR3378 was also investigated by Western blot analysis. RESULTS: BBR3378 down-regulated cytokine-induced macrophage differentiation and activation in EAE mice, contributing to protection against macrophage infiltration in the brain and clinical symptoms from EAE. Treating macrophages with BBR3378 counteracted LPS-induced cytokine production via blocking activation of key signal molecules mediating inflammatory responses, such as NF-κB and MAPKs. CONCLUSIONS: These data suggest that in addition to T cells, BBR3378 can also target macrophages to attenuate the inflammation associated with EAE.

The interleukin-17 receptor plays a gender-dependent role in host protection against Porphyromonas gingivalis-induced periodontal bone loss.

Interleukin-17 (IL-17) is a proinflammatory cytokine secreted by the newly described CD4(+) Th17 subset, which is distinct from classic Th1 and Th2 lineages. IL-17 contributes to bone destruction in rheumatoid arthritis but is essential in host defense against pathogens that are susceptible to neutrophils. Periodontal disease (PD) is a chronic inflammatory condition initiated by anaerobic oral pathogens such as Porphyromonas gingivalis, and it is characterized by host-mediated alveolar bone destruction due primarily to the immune response. The role of IL-17 in PD is controversial. Whereas elevated IL-17 levels have been found in humans with severe PD, we recently reported that female C57BL/6J mice lacking the IL-17 receptor (IL-17RA(KO)) are significantly more susceptible to PD bone loss due to defects in the chemokine-neutrophil axis (J. J. Yu, M. J. Ruddy, G. C. Wong, C. Sfintescu, P. J. Baker, J. B. Smith, R. T. Evans, and S. L. Gaffen, Blood 109:3794-3802, 2007). Since different mouse strains exhibit differences in susceptibility to PD as well as Th1/Th2 cell skewing, we crossed the IL-17RA gene knockout onto the BALB/c background and observed a similar enhancement in alveolar bone loss following P. gingivalis infection. Unexpectedly, in both strains IL-17RA(KO) female mice were much more susceptible to PD bone loss than males. Moreover, female BALB/c-IL-17RA(KO) mice were defective in producing anti-P. gingivalis immunoglobulin G and the chemokines KC/Groalpha and MIP-2. In contrast, male mice produced normal levels of chemokines and anti-P. gingivalis antibodies, but they were defective in granulocyte colony-stimulating factor upregulation. This study demonstrates a gender-dependent effect of IL-17 signaling and indicates that gender differences should be taken into account in the preclinical and clinical safety testing of anti-IL-17 biologic therapies.