Modulating in vitro lung fibroblast activation via senolysis of senescent human alveolar epithelial cells.

Idiopathic pulmonary fibrosis (IPF) is an age-related disease with poor prognosis and limited therapeutic options. Activation of lung fibroblasts and differentiation to myofibroblasts are the principal effectors of disease pathology, but damage and senescence of alveolar epithelial cells, specifically type II (ATII) cells, has recently been identified as a potential trigger event for the progressive disease cycle. Targeting ATII senescence and the senescence-associated secretory phenotype (SASP) is an attractive therapeutic strategy; however, translatable primary human cell models that enable mechanistic studies and drug development are lacking. Here, we describe a novel system of conditioned medium (CM) transfer from bleomycin-induced senescent primary alveolar epithelial cells (AEC) onto normal human lung fibroblasts (NHLF) that demonstrates an enhanced fibrotic transcriptional and secretory phenotype compared to non-senescent AEC CM treatment or direct bleomycin damage of the NHLFs. In this system, the bleomycin-treated AECs exhibit classical hallmarks of cellular senescence, including SASP and a gene expression profile that resembles aberrant epithelial cells of the IPF lung. Fibroblast activation by CM transfer is attenuated by pre-treatment of senescent AECs with the senolytic Navitoclax and AD80, but not with the standard of care agent Nintedanib or senomorphic JAK-targeting drugs (e.g., ABT-317, ruxolitinib). This model provides a relevant human system for profiling novel senescence-targeting therapeutics for IPF drug development.

Utilizing a human TLR selective ligand in a humanized immune system mouse model to investigate human TLR4 signaling.

Mouse models with humanized immune systems are becoming increasingly prevalent in pharmaceutical research as a platform for preclinical testing with potential for greater translatability to clinical applications. However, the presence of both mouse and human cells that respond to TLR ligands poses a challenge for investigating therapeutic modalities targeting TLR signaling. AZ617 is a human TLR4 agonist, which has been shown in vitro to preferentially induce human cytokines via the TLR4 signaling pathway. We sought to examine the ability of AZ617 to preferentially induce human cytokines in CD34+ stem cell-engrafted NOG-EXL mice (huNOG-EXL), to determine its suitability as an in vivo human functional readout. AZ617 elicited a strong human TNFα and IL-6 response in vivo that demonstrated a 10- and 5-fold preference, respectively, over the mouse TNFα and IL-6. To assess efficacy of inhibiting a key protein in the TLR4 signaling pathway, PF-06650833, a small molecule inhibitor of IRAK4, was used as a tool molecule. PF-0660833 was found to effectively inhibit AZ617-induced human TNFα release in vitro. Likewise, PF-06650833 reduced AZ617-induced human TNFα in the huNOG-EXL mouse model, with a weaker effect on human IL-6. A longitudinal study tracking functionality of monocytes revealed that the ability of monocytes to respond to ex vivo stimuli was increased by 21 weeks after engraftment. Taken together, our data suggests that human selective TLR ligands could preferentially drive cytokine production from human cells in huNOG-EXL mice. This model will allow for investigation of pharmacological inhibition of human TLR signaling pathways in an in vivo model system.

Targeting the NLRP3 inflammasome reduces inflammation in hidradenitis suppurativa skin.

BACKGROUND: Treatment for the debilitating disease hidradenitis suppurativa (HS) is inadequate in many patients. Despite an incidence of approximately 1%, HS is often under-recognized and underdiagnosed, and is associated with a high morbidity and poor quality of life. OBJECTIVES: To gain a better understanding of the pathogenesis of HS, in order to design new therapeutic strategies. METHODS: We employed single-cell RNA sequencing to analyse gene expression in immune cells isolated from involved HS skin vs. healthy skin. Flow cytometry was used to quantify the absolute numbers of the main immune populations. The secretion of inflammatory mediators from skin explant cultures was measured using multiplex and enzyme-linked immunosorbent assays. RESULTS: Single-cell RNA sequencing analysis identified a significant enrichment in the frequency of plasma cells, T helper (Th) 17 cells and dendritic cell subsets in HS skin, and the immune transcriptome was distinct and more heterogeneous than healthy skin. Flow cytometry revealed significantly increased numbers of T cells, B cells, neutrophils, dermal macrophages and dendritic cells in HS skin. Genes and pathways associated with Th17 cells, interleukin (IL)-17, IL-1ß and the NLRP3 inflammasome were enhanced in HS skin, particularly in samples with a high inflammatory load. Inflammasome constituent genes principally mapped to Langerhans cells and a subpopulation of dendritic cells. The secretome of HS skin explants contained significantly increased concentrations of inflammatory mediators, including IL-1ß and IL-17A, and culture with an NLRP3 inflammasome inhibitor significantly reduced the secretion of these, as well as other, key mediators of inflammation. CONCLUSIONS: These data provide a rationale for targeting the NLRP3 inflammasome in HS using small-molecule inhibitors that are currently being tested for other indications.

Synovial Inflammatory Pathways Characterize Anti-TNF-Responsive Rheumatoid Arthritis Patients.

OBJECTIVE: This study was undertaken to understand the mechanistic basis of response to anti-tumor necrosis factor (anti-TNF) therapies and to determine whether transcriptomic changes in the synovium are reflected in peripheral protein markers. METHODS: Synovial tissue from 46 rheumatoid arthritis (RA) patients was profiled with RNA sequencing before and 12 weeks after treatment with anti-TNF therapies. Pathway and gene signature analyses were performed on RNA expression profiles of synovial biopsies to identify mechanisms that could discriminate among patients with a good response, a moderate response, or no response, according to the American College of Rheumatology (ACR)/EULAR response criteria. Serum proteins encoded by synovial genes that were differentially expressed between ACR/EULAR response groups were measured in the same patients. RESULTS: Gene signatures predicted which patients would have good responses, and pathway analysis identified elevated immune pathways, including chemokine signaling, Th1/Th2 cell differentiation, and Toll-like receptor signaling, uniquely in good responders. These inflammatory pathways were correspondingly down-modulated by anti-TNF therapy only in good responders. Based on cell signature analysis, lymphocyte, myeloid, and fibroblast cell populations were elevated in good responders relative to nonresponders, consistent with the increased inflammatory pathways. Cell signatures that decreased following anti-TNF treatment were predominately associated with lymphocytes, and fewer were associated with myeloid and fibroblast populations. Following anti-TNF treatment, and only in good responders, several peripheral inflammatory proteins decreased in a manner that was consistent with corresponding synovial gene changes. CONCLUSION: Collectively, these data suggest that RA patients with robust responses to anti-TNF therapies are characterized at baseline by immune pathway activation, which decreases following anti-TNF treatment. Understanding mechanisms that define patient responsiveness to anti-TNF treatment may assist in development of predictive markers of patient response and earlier treatment options.

Safety and efficacy of elsubrutinib or upadacitinib alone or in combination (ABBV-599) in patients with rheumatoid arthritis and inadequate response or intolerance to biological therapies: a multicentre, double-blind, randomised, controlled, phase 2 trial.

BACKGROUND: ABBV-599 is a novel fixed-dose combination of the Bruton's tyrosine kinase (BTK) inhibitor elsubrutinib and the Janus kinase (JAK) inhibitor upadacitinib under investigation for the treatment of autoimmune diseases. We aimed to determine whether ABBV-599 could increase the treatment response for patients with active rheumatoid arthritis compared with inhibiting either pathway alone, while maintaining an acceptable safety profile. METHODS: We conducted a multicentre, double-blind, parallel-group, dose-exploratory, randomised, controlled, phase 2 trial at 75 community sites in eight countries in Europe and North America. We enrolled patients who were 18 years or older with rheumatoid arthritis and inadequate response or intolerance to biological disease-modifying antirheumatic drugs. Eligible patients were randomly assigned (3:2:2:2:2:1) via interactive response technology to receive daily, orally administered ABBV-599 (ie, upadacitinib 15 mg plus elsubrutinib 60 mg), elsubrutinib 60 mg, elsubrutinib 20 mg, elsubrutinib 5 mg, upadacitinib 15 mg, or placebo. Randomisation was stratified by the number of previous biological disease-modifying antirheumatic drugs. The investigator, study site personnel, and patients were masked throughout the study. The primary endpoint was change from baseline in disease activity score of 28 joints with C-reactive protein (DAS28-CRP) at week 12 for all patients who received a study drug. Pharmacokinetics and safety were also assessed. This study is registered with ClinicalTrials.gov, number NCT03682705. FINDINGS: Between Oct 8, 2018, and March 26, 2020, 242 patients were randomly assigned to receive ABBV-599 (n=62), elsubrutinib 60 mg (n=41), elsubrutinib 20 mg (n=39), elsubrutinib 5 mg (n=41), upadacitinib 15 mg (n=40), or placebo (n=19). Of the 242 patients, 204 (84%) were female, 38 (16%) were male, and 220 (91%) were White; the mean age at baseline was 58·0 years (SD 11·3). Compared with placebo, the least squares mean changes from baseline in DAS28-CRP were -1·44 (90% CI -2·03 to -0·85; p<0·0001) for ABBV-599, -0·40 (-1·03 to 0·23; p=0·29) for elsubrutinib 60 mg, -0·20 (-0·85 to 0·44; p=0·61) for elsubrutinib 20 mg, -0·21 (-0·84 to 0·41; p=0·57) for elsubrutinib 5 mg, and -1·75 (-2·38 to -1·13; p<0·0001) for upadacitinib. No significant improvements in efficacy measures for elsubrutinib alone (any dose) versus placebo were detected, despite adequate plasma exposure and target engagement. Treatment-emergent adverse events were observed in 113 (47%) of 242 patients, with similar proportions for all groups. INTERPRETATION: Significant improvements in disease activity metrics of rheumatoid arthritis with ABBV-599 were driven by the JAK inhibitor upadacitinib with no discernible effect by the BTK inhibitor elsubrutinib. FUNDING: AbbVie.

Myelin phagocytosis by astrocytes after myelin damage promotes lesion pathology.

Astrocytes are key players in the pathology of multiple sclerosis and can assume beneficial and detrimental roles during lesion development. The triggers and timing of the different astroglial responses in acute lesions remain unclear. Astrocytes in acute multiple sclerosis lesions have been shown previously to contain myelin debris, although its significance has not been examined. We hypothesized that myelin phagocytosis by astrocytes is an early event during lesion formation and leads to astroglial immune responses. We examined multiple sclerosis lesions and other central nervous system pathologies with prominent myelin injury, namely, progressive multifocal leukoencephalopathy, metachromatic leukodystrophy and subacute infarct. In all conditions, we found that myelin debris was present in most astrocytes at sites of acute myelin breakdown, indicating that astroglial myelin phagocytosis is an early and prominent feature. Functionally, myelin debris was taken up by astrocytes through receptor-mediated endocytosis and resulted in astroglial NF-κB activation and secretion of chemokines. These in vitro results in rats were validated in human disease where myelin-positive hypertrophic astrocytes showed increased nuclear localization of NF-κB and elevated chemokine expression compared to myelin-negative, reactive astrocytes. Thus, our data suggest that myelin uptake is an early response of astrocytes in diseases with prominent myelin injury that results in recruitment of immune cells. This first line response of astrocytes to myelin injury may exert beneficial or detrimental effects on the lesion pathology, depending on the inflammatory context. Modulating this response might be of therapeutic relevance in multiple sclerosis and other demyelinating conditions.

Differential Expression and Function of PDE8 and PDE4 in Effector T cells: Implications for PDE8 as a Drug Target in Inflammation.

Abolishing the inhibitory signal of intracellular cAMP is a prerequisite for effector T (Teff) cell function. The regulation of cAMP within leukocytes critically depends on its degradation by cyclic nucleotide phosphodiesterases (PDEs). We have previously shown that PDE8A, a PDE isoform with 40-100-fold greater affinity for cAMP than PDE4, is selectively expressed in Teff vs. regulatory T (Treg) cells and controls CD4(+) Teff cell adhesion and chemotaxis. Here, we determined PDE8A expression and function in CD4(+) Teff cell populations in vivo. Using magnetic bead separation to purify leukocyte populations from the lung draining hilar lymph node (HLN) in a mouse model of ovalbumin-induced allergic airway disease (AAD), we found by Western immunoblot and quantitative (q)RT-PCR that PDE8A protein and gene expression are enhanced in the CD4(+) T cell fraction over the course of the acute inflammatory disease and recede at the late tolerant non-inflammatory stage. To evaluate PDE8A as a potential drug target, we compared the selective and combined effects of the recently characterized highly potent PDE8-selective inhibitor PF-04957325 with the PDE4-selective inhibitor piclamilast (PICL). As previously shown, PF-04957325 suppresses T cell adhesion to endothelial cells. In contrast, we found that PICL alone increased firm T cell adhesion to endothelial cells by ~20% and significantly abrogated the inhibitory effect of PF-04957325 on T cell adhesion by over 50% when cells were co-exposed to PICL and PF-04957325. Despite its robust effect on T cell adhesion, PF-04957325 was over two orders of magnitude less efficient than PICL in suppressing polyclonal Teff cell proliferation, and showed no effect on cytokine gene expression in these cells. More importantly, PDE8 inhibition did not suppress proliferation and cytokine production of myelin-antigen reactive proinflammatory Teff cells in vivo and in vitro. Thus, targeting PDE8 through PF-04957325 selectively regulates Teff cell interactions with endothelial cells without marked immunosuppression of proliferation, while PDE4 inhibition has partially opposing effects. Collectively, our data identify PF-04957325 as a novel function-specific tool for the suppression of Teff cell adhesion and indicate that PDE4 and PDE8 play unique and non-redundant roles in the control of Teff cell functions.

The Response in Twitter to an Assisted Suicide in a Television Soap Opera.

BACKGROUND: Concern has been expressed about the potentially contagious effect of television soap opera suicides and suicidal language in social media. AIMS: Twitter content was analyzed during the week in which a fictional assisted suicide was broadcast on a British television soap opera, "Coronation Street." METHOD: Tweets were collected if they contained language indicating possible suicidal intent or used the word suicide. The modified Thompson tau method was used to test for any differences in the volume of tweets in both categories on the day of screening. Content analysis broke down the use of the word suicide into six thematic categories. RESULTS: There was no evidence on the day of screening of an increase in tweets expressing possible suicidal intent but there was an increase in tweets containing the word suicide. Content analysis found the most common thematic category to be information or support, followed by the raising of moral issues in relation to suicide. CONCLUSION: It is possible that for certain high-profile media events Twitter may be used more as a civic reactive forum than as a medium for introspection or disclosure of distress.

Biomarkers in multiple sclerosis.

Substantial effort has been made over the last six decades to identify biomarkers for multiple sclerosis that can improve disease diagnosis, predict disease progression, and improve clinical outcomes. However, to date, few of these findings have proven clinically useful. In this review, we address the current state of MS biomarker research. We start by discussing biomarkers currently in clinical use including Oligoclonal bands, MRI, and JC viral titers. We go on to discuss other potential biomarkers from MS serum and cerebrospinal fluid including Markers of neurodegeneration including neurofilament and GFAP, the monocyte macrophage marker CD163, the glial activation marker YKL-40, the B cell chemoattractant CXCL13, miRNA and mRNA, myelin reactive t cells, Kir4.1 antibodies, osteopontin, and microbiome associated lipopeptides. Finally, we discuss the current state of MS genetic studies and how genetics may offer simple, reliable testing for MS susceptibility and progression.

Genetic basis of autoimmunity.

Autoimmune diseases affect up to approximately 10% of the population. While rare Mendelian autoimmunity syndromes can result from monogenic mutations disrupting essential mechanisms of central and peripheral tolerance, more common human autoimmune diseases are complex disorders that arise from the interaction between polygenic risk factors and environmental factors. Although the risk attributable to most individual nucleotide variants is modest, genome-wide association studies (GWAS) have the potential to provide an unbiased view of biological pathways that drive human autoimmune diseases. Interpretation of GWAS requires integration of multiple genomic datasets including dense genotyping, cis-regulatory maps of primary immune cells, and genotyped studies of gene expression in relevant cell types and cellular conditions. Improved understanding of the genetic basis of autoimmunity may lead to a more sophisticated understanding of underlying cellular phenotypes and, eventually, novel diagnostics and targeted therapies.

Genetic variants associated with autoimmunity drive NFκB signaling and responses to inflammatory stimuli.

The transcription factor nuclear factor κB (NFκB) is a central regulator of inflammation, and genome-wide association studies in subjects with autoimmune disease have identified a number of variants within the NFκB signaling cascade. In addition, causal variant fine-mapping has demonstrated that autoimmune disease susceptibility variants for multiple sclerosis (MS) and ulcerative colitis are strongly enriched within binding sites for NFκB. We report that MS-associated variants proximal to NFκB1 and in an intron of TNFRSF1A (TNFR1) are associated with increased NFκB signaling after tumor necrosis factor-α (TNFα) stimulation. Both variants result in increased degradation of inhibitor of NFκB α (IκBα), a negative regulator of NFκB, and nuclear translocation of p65 NFκB. The variant proximal to NFκB1 controls signaling responses by altering the expression of NFκB itself, with the GG risk genotype expressing 20-fold more p50 NFκB and diminished expression of the negative regulators of the NFκB pathway: TNFα-induced protein 3 (TNFAIP3), B cell leukemia 3 (BCL3), and cellular inhibitor of apoptosis 1 (CIAP1). Finally, naïve CD4 T cells from patients with MS express enhanced activation of p65 NFκB. These results demonstrate that genetic variants associated with risk of developing MS alter NFκB signaling pathways, resulting in enhanced NFκB activation and greater responsiveness to inflammatory stimuli. As such, this suggests that rapid genetic screening for variants associated with NFκB signaling may identify individuals amenable to NFκB or cytokine blockade.

Genetic and epigenetic fine mapping of causal autoimmune disease variants.

Genome-wide association studies have identified loci underlying human diseases, but the causal nucleotide changes and mechanisms remain largely unknown. Here we developed a fine-mapping algorithm to identify candidate causal variants for 21 autoimmune diseases from genotyping data. We integrated these predictions with transcription and cis-regulatory element annotations, derived by mapping RNA and chromatin in primary immune cells, including resting and stimulated CD4(+) T-cell subsets, regulatory T cells, CD8(+) T cells, B cells, and monocytes. We find that ∼90% of causal variants are non-coding, with ∼60% mapping to immune-cell enhancers, many of which gain histone acetylation and transcribe enhancer-associated RNA upon immune stimulation. Causal variants tend to occur near binding sites for master regulators of immune differentiation and stimulus-dependent gene activation, but only 10-20% directly alter recognizable transcription factor binding motifs. Rather, most non-coding risk variants, including those that alter gene expression, affect non-canonical sequence determinants not well-explained by current gene regulatory models.

Regulatory T-cells and cAMP suppress effector T-cells independently of PKA-CREM/ICER: a potential role for Epac.

cAMP signalling is both a major pathway as well as a key therapeutic target for inducing immune tolerance and is involved in Treg cell (regulatory T-cell) function. To achieve potent immunoregulation, cAMP can act through several downstream effectors. One proposed mechanism is that cAMP-mediated suppression, including immunosuppression by Treg cells, results from activation of PKA (protein kinase A) leading to the induction of the transcription factor ICER (inducible cAMP early repressor). In the present study, we examined CD4(+)CD25(-) Teff cell (effector T-cell) and CD4(+)CD25(+) Treg cell immune responses in Crem (cAMP-response-element modulator) gene-deficient mice which lack ICER (Crem(-/-)/ICER-deficient mice). ICER deficiency did not significantly alter the frequency or number of Treg cells and Teff cells. Treg cells or a pharmacological increase in cAMP suppressed Teff cells from Crem(+/+) and Crem(-/-)/ICER-deficient mice to an equivalent degree, demonstrating that ICER is dispensable in these functions. Additionally, activating the cAMP effector Epac (exchange protein directly activated by cAMP) suppressed Teff cells. Treg cells expressed low levels of all cyclic nucleotide Pde (phosphodiesterase) genes tested, but high levels of Epac. These data identify ICER as a redundant mediator of Treg cells and cAMP action on Teff cells and suggest that Epac may function as an alternative effector to promote cAMP-dependent Teff cell suppression.

Free lipid A isolated from Porphyromonas gingivalis lipopolysaccharide is contaminated with phosphorylated dihydroceramide lipids: recovery in diseased dental samples.

Recent reports indicate that Porphyromonas gingivalis mediates alveolar bone loss or osteoclast modulation through engagement of Toll-like receptor 2 (TLR2), though the factors responsible for TLR2 engagement have yet to be determined. Lipopolysaccharide (LPS) and lipid A, lipoprotein, fimbriae, and phosphorylated dihydroceramides of P. gingivalis have been reported to activate host cell responses through engagement of TLR2. LPS and lipid A are the most controversial in this regard because conflicting evidence has been reported concerning the capacity of P. gingivalis LPS or lipid A to engage TLR2 versus TLR4. In the present study, we first prepared P. gingivalis LPS by the Tri-Reagent method and evaluated this isolate for contamination with phosphorylated dihydroceramide lipids. Next, the lipid A prepared from this LPS was evaluated for the presence of phosphorylated dihydroceramide lipids. Finally, we characterized the lipid A by the matrix-assisted laser desorption ionization mass spectrometry (MALDI-MS) and electrospray-MS methods in order to quantify recovery of lipid A in lipid extracts from diseased teeth or subgingival plaque samples. Our results demonstrate that both the LPS and lipid A derived from P. gingivalis are contaminated with phosphorylated dihydroceramide lipids. Furthermore, the lipid extracts derived from diseased teeth or subgingival plaque do not contain free lipid A constituents of P. gingivalis but contain substantial amounts of phosphorylated dihydroceramide lipids. Therefore, the free lipid A of P. gingivalis is not present in measurable levels at periodontal disease sites. Our results also suggest that the TLR2 activation of host tissues attributed to LPS and lipid A of P. gingivalis could actually be mediated by phosphorylated dihydroceramides.

Peroxisome proliferator-activated receptor gamma is required for CD4+ T cell-mediated lymphopenia-associated autoimmunity.

The nuclear hormone receptor peroxisome proliferator-activated receptor γ (PPARγ) was shown to play an immunoregulatory role in many immune-related cell types, and activation of PPARγ was reported to be an effective therapeutic approach in murine and human autoimmune disease. However, despite an association between lymphopenia and autoimmunity, there has been no study on the role of T cell PPARγ in lymphopenia-associated autoimmunity. In the present studies, we examined the role of PPARγ in CD4(+) T cells in two murine models of lymphopenia-associated autoimmunity. Surprisingly, we found that PPARγ expression in CD4(+) CD25(-) T cells (T effector cells [Teffs]) is actually required for development of autoimmunity under lymphopenic conditions. Mechanistically, the inability of PPARγ-deficient (T-PPAR) Teffs to mediate lymphopenic autoimmunity is associated with a significant decrease in accumulation of Teffs in the spleen, lymph nodes, and tissues after adoptive transfer. This abnormal accumulation of T-PPAR Teffs was associated with defects in both in vivo proliferation and survival. Additionally, T-PPAR Teffs demonstrated decreased cytokine production in inflammatory sites and decreased expression of the homing receptor α4ß7. Finally, these abnormalities in T-PPAR Teff function were not elicited by lymphopenia alone but also required the additional activation involved in the mediation of autoimmunity. Thus, in contrast to its documented immunosuppressive role, we identified an unexpected function for PPARγ in Teffs: a role in Teff proliferation and survival in lymphopenia-associated autoimmunity. These findings highlight both the multifunctional role of PPARγ in T cells and the complexity of PPARγ as a potential therapeutic target in autoimmunity.

Natural but not inducible regulatory T cells require TNF-alpha signaling for in vivo function.

TNF-α has a multifunctional role in autoimmune diseases as reflected in the variable responses of different human diseases to anti-TNF-α therapy. Recent studies have suggested that TNF-α modulates autoimmunity partially via effects on regulatory T cells (Tregs) and that these effects are mediated through the type II TNFR (TNFR2). We have investigated the requirement for TNFR2-expression on murine natural Tregs (nTregs) and induced Tregs (iTregs) in mediating suppression of colitis. Surprisingly, we find that TNFR2-expression is required for both spleen- and thymus-derived nTreg-mediated suppression, but is not required for iTreg-mediated suppression. Abnormal TNFR2(-/-) nTreg function was not associated with an in vivo decrease in accumulation, stability, or expression of markers known to be relevant in Treg function. Because iTregs are generated in the presence of TGF-ß, we investigated whether activation in the presence of TGF-ß could overcome the functional defect in TNFR2(-/-) nTregs. Although preactivation alone did not restore suppressive function of nTregs, preactivation in the presence of TGF-ß did. These results identify potentially critical differences in activation requirements for nTregs versus iTregs. Furthermore, our findings are consistent with reports suggesting that nTregs are activated in sites of inflammation while iTregs are activated in lymph nodes. Finally, by demonstrating that nTregs require TNF-α for optimal function whereas iTregs do not, our results suggest that the enigma of variable responses of different human diseases to anti-TNF-α therapy may relate to whether nTregs or iTregs have the predominant regulatory role in a given disease.

Phosphorylated dihydroceramides from common human bacteria are recovered in human tissues.

Novel phosphorylated dihydroceramide (PDHC) lipids produced by the periodontal pathogen Porphyromonas gingivalis include phosphoethanolamine (PE DHC) and phosphoglycerol dihydroceramides (PG DHC) lipids. These PDHC lipids mediate cellular effects through Toll-like receptor 2 (TLR2) including promotion of IL-6 secretion from dendritic cells and inhibition of osteoblast differentiation and function in vitro and in vivo. The PE DHC lipids also enhance (TLR2)-dependent murine experimental autoimmune encephalomyelitis (EAE), a model for multiple sclerosis. The unique non-mammalian structures of these lipids allows for their specific quantification in bacteria and human tissues using multiple reaction monitoring (MRM)-mass spectrometry (MS). Synthesis of these lipids by other common human bacteria and the presence of these lipids in human tissues have not yet been determined. We now report that synthesis of these lipids can be attributed to a small number of intestinal and oral organisms within the Bacteroides, Parabacteroides, Prevotella, Tannerella and Porphyromonas genera. Additionally, the PDHCs are not only present in gingival tissues, but are also present in human blood, vasculature tissues and brain. Finally, the distribution of these TLR2-activating lipids in human tissues varies with both the tissue site and disease status of the tissue suggesting a role for PDHCs in human disease.

PDE8 regulates rapid Teff cell adhesion and proliferation independent of ICER.

BACKGROUND: Abolishing the inhibitory signal of intracellular cAMP by phosphodiesterases (PDEs) is a prerequisite for effector T (Teff) cell function. While PDE4 plays a prominent role, its control of cAMP levels in Teff cells is not exclusive. T cell activation has been shown to induce PDE8, a PDE isoform with 40- to 100-fold greater affinity for cAMP than PDE4. Thus, we postulated that PDE8 is an important regulator of Teff cell functions. METHODOLOGY/PRINCIPAL FINDINGS: We found that Teff cells express PDE8 in vivo. Inhibition of PDE8 by the PDE inhibitor dipyridamole (DP) activates cAMP signaling and suppresses two major integrins involved in Teff cell adhesion. Accordingly, DP as well as the novel PDE8-selective inhibitor PF-4957325-00 suppress firm attachment of Teff cells to endothelial cells. Analysis of downstream signaling shows that DP suppresses proliferation and cytokine expression of Teff cells from Crem-/- mice lacking the inducible cAMP early repressor (ICER). Importantly, endothelial cells also express PDE8. DP treatment decreases vascular adhesion molecule and chemokine expression, while upregulating the tight junction molecule claudin-5. In vivo, DP reduces CXCL12 gene expression as determined by in situ probing of the mouse microvasculature by cell-selective laser-capture microdissection. CONCLUSION/SIGNIFICANCE: Collectively, our data identify PDE8 as a novel target for suppression of Teff cell functions, including adhesion to endothelial cells.

Cbl-b(-/-) T cells demonstrate in vivo resistance to regulatory T cells but a context-dependent resistance to TGF-beta.

Cbl-b is an E3 ubiquitin ligase that negatively regulates T cell activation. Cbl-b(-/-) mice develop spontaneous autoimmunity, and Cbl-b dysregulation has been described in both murine and human autoimmune diseases. Although the mechanisms underlying the development of autoimmunity in Cbl-b(-/-) mice are not yet clear, we have reported that Cbl-b(-/-) CD4(+)CD25(-) effector T cells (Teffs) are resistant to CD4(+)CD25(+) regulatory T cell (Treg)-mediated suppression in vitro and have suggested that this may be an important mechanism in the development of autoimmunity. To confirm the relevance of this resistance to autoimmune disease, we now show that Cbl-b(-/-) Teffs are resistant to suppression by Tregs in vivo and that this involves a resistance of truly naive Cbl-b(-/-) Teffs. Additionally, we show that Cbl-b(-/-) Tregs are fully functional in vivo, further suggesting that the regulatory abnormalities in Cbl-b(-/-) mice are related to defects in Teff, not Treg, function. To characterize the relevance of TGF-beta sensitivity in Treg resistance, we examined in vivo Th17 generation and report that Cbl-b(-/-) mice are able to mount a normal Th17 response in vivo. As Cbl-b(-/-) Teffs have been shown to be insensitive to the suppressive effects of TGF-beta in other in vivo models, the present results suggest that Cbl-b(-/-) Teffs demonstrate a context-dependent sensitivity to TGF-beta in vivo. Overall, our results suggest that resistance to Tregs may be a bona fide mechanism underlying autoimmunity and that Cbl-b(-/-) mice offer unique approaches for studying the interrelationships between Treg function, TGF-beta-mediated responses, and the development of autoimmunity.

Unique lipids from a common human bacterium represent a new class of Toll-like receptor 2 ligands capable of enhancing autoimmunity.

Recent reports suggest that commensal bacteria may play a down-regulatory role in autoimmune disease. In the present studies, we demonstrate that phosphorylated dihydroceramides, uniquely structured lipids derived from the common human oral bacterium Porphyromonas gingivalis and from bacteria commonly found in the gastrointestinal tract and other organs, are capable of enhancing autoimmunity. We have previously reported that these lipids have proinflammatory effects on human fibroblasts in vitro and, in preliminary studies, have recovered these lipids from surgically removed human carotid atheroma, suggesting that they may play a role in human inflammatory disease. To investigate whether these lipids have functional effects on autoimmunity, we administered phosphorylated dihydroceramides to mice with the murine model of multiple sclerosis, experimental allergic encephalomyelitis (EAE). We find that these lipids, and particularly the phosphoethanolamine dihydroceramide (PE DHC) fraction, significantly enhanced EAE. Mechanistically, PE DHC enhances EAE in mice lacking natural killer T cells, fails to enhance EAE in Toll-like receptor 2 (TLR2)-deficient mice and, in vitro, induces dendritic cell interleukin-6 secretion in a TLR2-dependent manner. Finally, PE DHC-treated mice with EAE demonstrate a decreased percentage of spinal cord Foxp3+ T cells, suggesting that these lipids may affect regulatory aspects of adaptive immune responses. Overall, our results suggest that phosphorylated dihydroceramides derived from common human bacteria function as TLR2 ligands and may play a previously unrecognized role in human autoimmune diseases.