Recognition of microbial components by APCs and their activation through Toll-like receptors (TLR) leads to the induction of adaptive immune responses. In this study, we show that activation of TLR2 by its synthetic ligand Pam3Cys, in contrast to activation of TLR9 by immunostimulatory DNA (ISS-ODN), induces a prominent Th2-biased immune response. Activation of APCs by Pam3Cys resulted in the induction of Th2-associated effector molecules like IL-13, and IL-1β, GM-CSF and up-regulation of B7RP-1, but low levels of Th1-associated cytokines (IL-12, IFNα, IL-18, IL-27). Accordingly, TLR2 ligands aggravated experimental asthma. These data indicate that the type of TLR stimulation during the initial phase of immune activation determines the polarization of the adaptive immune response and may play a role in the initiation of Th2-mediated immune disorders, such as asthma.

The underlying pathology of atopic dermatitis (AD) includes impaired skin barrier function, susceptibility to Staphylococcus aureus skin infection, immune dysregulation, and cutaneous dysbiosis. Our recent investigation into the potential role of Gram-negative skin bacteria in AD revealed that isolates of one particular commensal, Roseomonas mucosa , collected from healthy volunteers (HVs) improved outcomes in mouse and cell culture models of AD. In contrast, isolates of R . mucosa from patients with AD worsened outcomes in these models. These preclinical results suggested that interventions targeting the microbiome could provide therapeutic benefit for patients with AD. As a first test of this hypothesis in humans, 10 adult and 5 pediatric patients were enrolled in an open-label phase I/II safety and activity trial (the Beginning Assessment of Cutaneous Treatment Efficacy for Roseomonas in Atopic Dermatitis trial; BACTE R iAD I/II). Treatment with R . mucosa was associated with significant decreases in measures of disease severity, topical steroid requirement, and S . aureus burden. There were no adverse events or treatment complications. We additionally evaluated differentiating bacterial metabolites and topical exposures that may contribute to the skin dysbiosis associated with AD and/or influence future microbiome-based treatments. These early results support continued evaluation of R . mucosa therapy with a placebo-controlled trial.

Dendritic cells (DCs) are capable of cross-presenting exogenous Ag to CD8⁺ CTLs. Detection of microbial products by Toll-like receptors (TLRs) leads to activation of DCs and subsequent orchestration of an adaptive immune response. We hypothesized that microbial TLR ligands could activate DCs to cross-present Ag to CTLs. Using DCs and CTLs in an in vitro cross-presentation system, we show that a subset of microbial TLR ligands, namely ligands of TLR3 (poly(inosinic-cytidylic) acid) and TLR9 (immunostimulatory CpG DNA), induces cross-presentation. In contrast to presentation of Ag to CD4⁺ T cells by immature DCs, TLR-induced cross-presentation is mediated by mature DCs, is independent of endosomal acidification, and relies on cytosolic Ag processing machinery.

Mechanisms underlying modern increases in prevalence of human inflammatory diseases remain unclear. The hygiene hypothesis postulates that decreased microbial exposure has, in part, driven this immune dysregulation. However, dietary fatty acids also influence immunity, partially through modulation of responses to microbes. Prior reports have described the direct effects of high-fat diets on the gut microbiome and inflammation, and some have additionally shown metabolic consequences for offspring. Our study sought to expand on these previous observations to identify the effects of parental diet on offspring immunity using mouse models to provide insights into challenging aspects of human health. To test the hypothesis that parental dietary fat consumption during gestation and lactation influences offspring immunity, we compared pups of mice fed either a Western diet (WD) fatty acid profile or a standard low-fat diet. All pups were weaned onto the control diet to specifically test the effects of early developmental fat exposure on immune development. Pups from WD breeders were not obese or diabetic, but still had worse outcomes in models of infection, autoimmunity, and allergic sensitization. They had heightened colonic inflammatory responses, with increased circulating bacterial LPS and muted systemic LPS responsiveness. These deleterious impacts of the WD were associated with alterations of the offspring gut microbiome. These results indicate that parental fat consumption can leave a “lard legacy” impacting offspring immunity and suggest inheritable microbiota may contribute to the modern patterns of human health and disease.

Candida is the most common human fungal pathogen and causes systemic infections that require neutrophils for effective host defense. Humans deficient in the C-type lectin pathway adaptor protein CARD9 develop spontaneous fungal disease that targets the central nervous system (CNS). However, how CARD9 promotes protective antifungal immunity in the CNS remains unclear. Here, we show that a patient with CARD9 deficiency had impaired neutrophil accumulation and induction of neutrophil-recruiting CXC chemokines in the cerebrospinal fluid despite uncontrolled CNS Candida infection. We phenocopied the human susceptibility in Card9^-/- mice, which develop uncontrolled brain candidiasis with diminished neutrophil accumulation. The induction of neutrophil-recruiting CXC chemokines is significantly impaired in infected Card9^-/- brains, from both myeloid and resident glial cellular sources, whereas cell-intrinsic neutrophil chemotaxis is Card9-independent. Taken together, our data highlight the critical role of CARD9-dependent neutrophil trafficking into the CNS and provide novel insight into the CNS fungal susceptibility of CARD9-deficient humans. CARD9 is a molecule expressed by mammalian immune cells and is centrally positioned downstream of several C-type lectin receptors, which sense fungi. The critical role of CARD9 in the activation of antifungal host defense has been highlighted by the demonstration that human mutations that disrupt the function of CARD9 are associated with the development of spontaneous life-threatening fungal infections, many of which target the central nervous system (CNS). However, why CARD9-deficient patients develop fungal disease in the CNS remained unclear. Here, we show that CARD9 is required for the recruitment of neutrophils, an immune cell critical for antifungal host defense, to the fungal-infected CNS in both mice and humans. Furthermore, we show that CARD9-deficient mice and humans are unable to produce the molecules (chemoattractants) needed to recruit neutrophils to the site of infection, thus identifying the mechanism for the striking absence of these cells in the infected CNS. Our work helps explain why CARD9 deficiency associates with CNS fungal disease, and furthers our understanding of how antifungal immunity operates in this complex tissue.