Th1 and Th17 cells regulate innate immune responses and bacterial clearance during central nervous system infection.
ABSTRACT: Brain abscesses arise following parenchymal infection with pyogenic bacteria and are typified by inflammation and edema, which frequently results in a multitude of long-term health problems. The impact of adaptive immunity in shaping continued innate responses during late-stage brain abscess formation is not known but is important, because robust innate immunity is required for effective bacterial clearance. To address this issue, brain abscesses were induced in TCR ?? knockout (KO) mice, because CD4(+) and NKT cells represented the most numerous T cell infiltrates. TCR ?? KO mice exhibited impaired bacterial clearance during later stages of infection, which was associated with alterations in neutrophil and macrophage recruitment, as well as perturbations in cytokine/chemokine expression. Adoptive transfer of either Th1 or Th17 cells into TCR ?? KO mice restored bacterial burdens and innate immune cell infiltrates to levels detected in wild-type animals. Interestingly, adoptively transferred Th17 cells demonstrated plasticity within the CNS compartment and induced distinct cytokine secretion profiles in abscess-associated microglia and macrophages compared with Th1 transfer. Collectively, these studies identified an amplification loop for Th1 and Th17 cells in shaping established innate responses during CNS infection to maximize bacterial clearance and differentially regulate microglial and macrophage secretory profiles.
Project description:TLR2 plays a pivotal role in recognizing Staphylococcus aureus, a common etiologic agent of CNS parenchymal infections, such as brain abscess. We previously reported that brain abscesses of TLR2 knockout (KO) mice exhibited elevated IL-17 levels, suggesting the presence of an alternative pathway available to respond to S. aureus infection that may involve Th17 cells. Both CD4(+) and CD8(+) T cell infiltrates were elevated in brain abscesses of TLR2 KO mice at days 3, 7, and 14 postinfection compared with wild-type animals. Intracellular cytokine staining revealed a significant increase in the frequency of IL-17-producing Th17 cells in TLR2 KO mice with relatively few IFN-gamma-positive cells. gammadelta T cells were also a source of IL-17 in brain abscesses. Microglia, astrocytes, and macrophages were shown to express both IL-17RA and IL-17RC. Despite receptor expression, IL-17 was relatively ineffective at eliciting glial activation, whereas the cytokine augmented the ability of TNF-alpha to induce CXCL2 and CCL2 expression by macrophages. Based on the ability of IL-17 to elicit the release of chemokines and other proinflammatory mediators, we propose that the exaggerated IL-17 response that occurs in TLR2 KO mice functions in a compensatory manner to control brain abscess pathogenesis, with cells other than glia as targets for IL-17 action. This is supported by our findings in which innate immune infiltrates were not significantly different between TLR2 KO and wild-type mice in conjunction with the lack of prolonged alterations in the synthesis of other proinflammatory molecules during the course of infection.
Project description:Staphylococcus aureus is a common etiologic agent of brain abscesses and possesses numerous virulence factors that manipulate host immunity. One example is superantigens (SAG) that clonally expand T cell subsets bearing specific V? receptors. Toll-like receptor 2 (TLR2) is one receptor implicated in S. aureus recognition. However, the interplay between TLR2, SAG, and adaptive immunity during brain abscess formation has not yet been investigated and could reveal novel insights into host-pathogen interactions for regulating protective immunity. A comprehensive analysis of abscess-associated T cell populations in TLR2 KO and WT mice was performed following infection with a S. aureus clinical isolate. Both natural killer T (NKT) and ?? T cell infiltrates were increased in brain abscesses of TLR2 KO mice and produced more IL-17 and IFN-? compared to WT populations, which could have resulted from elevated bacterial burdens observed in these animals. Analysis of SAG-reactive T cells revealed a predominant V?(8.1,8.2) infiltrate reactive with staphylococcal enterotoxin B (SEB), whereas SEA-reactive V?(11) T cells were less numerous. Brain abscesses of TLR2 KO mice had fewer V?(8.1,8.2) and V?(11) T cells and produced less TNF-? and IFN-? compared to WT animals. Treatment of primary microglia with purified SEB augmented TNF-? production in response to the TLR2 ligand Pam3Cys, which may serve to amplify proinflammatory cascades during CNS S. aureus infection. Collectively, these studies demonstrate that TLR2 impacts adaptive immunity to S. aureus infection and modulates SAG responses.
Project description:Regulation of Th17 and Th1 cell responses against intracellular pathogens, including Listeria monocytogenes (L. m), is critical to limit inflammation-induced tissue damage. We recently demonstrated the ability of P. UF1 bacterium derived from the intestinal bacterial commensals of preterm infants fed human breast milk to significantly mitigate pathogen-induced inflammation limiting colonic tissue damage. Here we further elucidated the potential of P. UF1 to also regulate innate and T cells, particularly Th17 and Th1 cells, against systemic L. m infection. Data demonstrate that P. UF1 not only robustly regulated protective Th17 and Th1 cells, but also sustained regulatory T cells (Treg cells) resulting in accelerated L. m clearance. Together, regulation of pathogenic inflammation by a novel probiotic bacterium such as P. UF1 may illuminate a new strategy to specifically control Th17-Th1 cells via IL-10+ Treg cells to limit systemic tissue damage induced by intracellular pathogens, including L. m.
Project description:Abscesses are a hallmark of invasive staphylococcal infections and the site of a dynamic struggle between pathogen and host. However, the precise host and bacterial factors that contribute to abscess formation and maintenance have not been completely described. In this work, we define the Staphylococcus aureus abscess proteome from both wild-type and neutropenic mice to elucidate the host response to staphylococcal infection and uncover novel S. aureus virulence factors. Among the proteins identified, the mouse protein histone H4 was enriched in the abscesses of wild-type compared with neutropenic animals. Histone H4 inhibits staphylococcal growth in vitro demonstrating a role for this protein in the innate immune response to staphylococcal infection. These analyses also identified staphylococcal proteins within the abscess, including known virulence factors and proteins with previously unrecognized roles in pathogenesis. Within the latter group was the universal stress protein Usp2, which was enriched in kidney lesions from neutropenic mice and required for the S. aureus response to stringent stress. Taken together, these data describe the S. aureus abscess proteome and lay the foundation for the identification of contributors to innate immunity and bacterial pathogenesis.
Project description:IL-17-producing CD4 T cells play a key role in immune responses against extracellular bacteria and autoimmunity. Nuclear factor ?B (NF-?B) is required for T-cell activation and selected effector functions, but its role in Th17 differentiation is controversial. Using genetic mouse models that impede T-cell-NF-?B signaling either downstream of the T-cell receptor (TCR) or of I?B kinase ? (IKK?), we demonstrate that NF-?B signaling controls not only survival and proliferation of activated T cells, but, if cell survival and cell-cycle progression are enabled, has an additional role in promoting completion of Th17 differentiation. CARD-containing MAGUK protein 1 (CARMA1), an adapter required for TCR/NF-?B signaling, was necessary for acquisition of IL-17A, IL-17F, IL-21, IL-22, IL-23R, and CCR6 expression in T cells cultured under Th17 conditions. In proliferating cells, lack of CARMA1 selectively prevented Th17, but not Th1 or Th2 differentiation, in a cell-intrinsic manner. Consistent with these data, CARMA1-KO mice were resistant to experimental autoimmune encephalomyelitis. Surprisingly, transcription factors essential for Th17 differentiation such as ROR?t, AHR, and IRF4 were normally induced in CARMA1-KO T cells activated under Th17 conditions, suggesting that the Th17 differentiation program was initiated normally. Instead, chromatin loci of Th17 effector molecules failed to acquire an open conformation in CARMA1-KO T cells. Our results demonstrate that TCR/CARMA1/NF-?B controls completion of Th17 differentiation by enabling chromatin accessibility of Th17 effector molecule loci.
Project description:MyD88 KO (knockout) mice are exquisitely sensitive to CNS (central nervous system) infection with Staphylococcus aureus, a common aetiological agent of brain abscess, exhibiting global defects in innate immunity and exacerbated tissue damage. However, since brain abscesses are typified by the involvement of both activated CNS-resident and infiltrating immune cells, in our previous studies it has been impossible to determine the relative contribution of MyD88-dependent signalling in the CNS compared with the peripheral immune cell compartments. In the present study we addressed this by examining the course of S. aureus infection in MyD88 bone marrow chimaera mice. Interestingly, chimaeras where MyD88 was present in the CNS, but not bone marrow-derived cells, mounted pro-inflammatory mediator expression profiles and neutrophil recruitment equivalent to or exceeding that detected in WT (wild-type) mice. These results implicate CNS MyD88 as essential in eliciting the initial wave of inflammation during the acute response to parenchymal infection. Microarray analysis of infected MyD88 KO compared with WT mice revealed a preponderance of differentially regulated genes involved in apoptotic pathways, suggesting that the extensive tissue damage characteristic of brain abscesses from MyD88 KO mice could result from dysregulated apoptosis. Collectively, the findings of the present study highlight a novel mechanism for CNS-resident cells in initiating a protective innate immune response in the infected brain and, in the absence of MyD88 in this compartment, immunity is compromised.
Project description:Oropharyngeal candidiasis (OPC) is an opportunistic infection caused by Candida albicans. Despite its prevalence, little is known about C. albicans-specific immunity in the oral mucosa. Vaccines against Candida generate both T helper type 1 (Th1) and Th17 responses, and considerable evidence implicates interleukin (IL)-17 in immunity to OPC. However, IL-17 is also produced by innate immune cells that are remarkably similar to Th17 cells, expressing the same markers and localizing to similar mucosal sites. To date, the relative contribution(s) of Th1, Th17, and innate IL-17-producing cells in OPC have not been clearly defined. Here, we sought to determine the nature and function of adaptive T-cell responses to OPC, using a new recall infection model. Mice subjected to infection and re-challenge with Candida mounted a robust and stable antigen-specific IL-17 response in CD4+ but not CD8+ T cells. There was little evidence for Th1 or Th1/Th17 responses. The Th17 response promoted accelerated fungal clearance, and Th17 cells could confer protection in Rag1-/- mice upon adoptive transfer. Surprisingly, CD4 deficiency did not cause OPC but was instead associated with compensatory IL-17 production by Tc17 and CD3+CD4-CD8- cells. Therefore, classic CD4+Th17 cells protect from OPC but can be compensated by other IL-17-producing cells in CD4-deficient hosts.
Project description:The development of Sjögren's syndrome (SjS) is a dynamic and temporal process with a female predilection. Following the initial influx of immune cells, T cell clusters develop, accelerating the pathology in the salivary glands. Proinflammatory cytokines, IFN-? and IL-17A, produced by T cells contribute synergistically to the disease. In this study, we examined the sexual dimorphism in cellular infiltrates of the salivary glands by using functional single-cell microengraving analysis. Using high-throughput sequencing, we investigated the clonal diversity of the T cell receptors (TCRs) of infiltrating IFN-? and IL-17A-producing T cells in male and female SjS-susceptible (SjSs) C57BL/6.NOD-Aec1Aec2 mice. There were elevated frequencies of IFN-? and IL-17A-producing effector T cell populations in female SjSS mice compared to male SjSS mice. MEME analysis shows high frequency and unique, sexually dimorphic motifs in the TCR hypervariable regions in the SjSS mice. Male mice selected for TRAV8/TRAJ52 (CATDLNTGANTGKLTFG) TCR genes in Th1 cells and TRBV16/(TRBD1/2)TRBJ1-7 (CGGKRRLESIFR) in Th1 and Th17 cells. Female SjSS mice selected for TRAV8/TRAJ52 (CATDLNTGANTGKLTFG), TRAV13D-2/TRAJ23 (CVYLEHHFE), and TRBV23/(TRBD2)TRBJ2-2 (CRKLHSCATCALNFL) in Th1 cells. These findings suggest that there is an elevated prevalence of pathogenic effector T cells in the glands with a sexually dimorphic selection bias of TCR repertoires.
Project description:Citrobacter koseri (C. koseri) is a Gram-negative bacterium that can cause a highly aggressive form of neonatal meningitis, which often progresses to establish multi-focal brain abscesses. The roles of Toll-like receptor 4 (TLR4) and its signaling adaptor MyD88 during CNS C. koseri infection have not yet been examined, which is important since recent evidence indicates that innate immune responses are tailored towards specific pathogen classes. Here TLR4 WT (C3H/FeJ) and TLR4 mutant (C3H/HeJ) mice as well as MyD88 KO animals were infected intracerebrally with live C. koseri, resulting in meningitis and ventriculitis with accompanying brain abscess formation. MyD88 KO mice were exquisitely sensitive to C. koseri, demonstrating enhanced mortality rates and significantly elevated bacterial burdens compared to WT animals. Interestingly, although early proinflammatory mediator release (i.e. 12 h) was MyD88-dependent, a role for MyD88-independent signaling was evident at 24 h, revealing a compensatory response to CNS C. koseri infection. In contrast, TLR4 did not significantly impact bacterial burdens or proinflammatory mediator production in response to C. koseri. Similar findings were obtained with primary astrocytes, where MyD88-dependent pathways were essential for chemokine release in response to intact C. koseri, whereas TLR4 was dispensable; implicating the involvement of alternative TLRs since highly enriched astrocytes did not produce IL-1 upon bacterial exposure, which also signals via MyD88. Collectively, these findings demonstrate the importance of MyD88-dependent mechanisms in eliciting maximal proinflammatory responses, astrocyte activation, and bacterial containment during CNS C. koseri infection, as well as a late-phase MyD88-independent signaling pathway for cytokine/chemokine production.
Project description:Nocardia cerebral abscess is rare, constituting approximately 1-2% of all cerebral abscesses. Mortality for a cerebral abscess of Nocardia is three times higher than that of other bacterial cerebral abscesses, therefore, early diagnosis and therapy is important. Nocardia cerebral abscess is generally occur among immunocompromised patients, and critical infection in immunocompetent patients is extremely rare. We report on a case of a brain abscess by Nocardia farcinica in an immunocompetent patient who received treatment with surgery and antibiotics. This is the second case of a brain abscess caused by N. farcinica in an immunocompetent patient in Korea.