A Pathogenic Th17/CD38+ Macrophage Feedback Loop Drives Inflammatory Arthritis through TNF-α.

The pathobiology of rheumatoid inflammatory diseases, including rheumatoid arthritis (RA) and psoriatic arthritis, involves the interplay between innate and adaptive immune components and resident synoviocytes. Single-cell analyses of patient samples and relevant mouse models have characterized many cellular subsets in RA. However, the impact of interactions between cell types is not fully understood. In this study, we temporally profiled murine arthritic synovial isolates at the single-cell level to identify perturbations similar to those found in human RA. Notably, murine macrophage subtypes like those found in RA patients were expanded in arthritis and linked to promoting the function of Th17 cells in the joint. In vitro experiments identified a capacity for murine macrophages to maintain the functionality and expansion of Th17 cells. Reciprocally, murine Th17 cell-derived TNF-α induced CD38+ macrophages that enhanced Th17 functionality. Murine synovial CD38+ macrophages were expanded during arthritis, and their depletion or blockade via TNF-α neutralization alleviated disease while reducing IL-17A-producing cells. These findings identify a cellular feedback loop that promotes Th17 cell pathogenicity through TNF-α to drive inflammatory arthritis.

A nondepleting anti-CD19 antibody impairs B cell function and inhibits autoimmune diseases.

B cells contribute to multiple aspects of autoimmune disorders, and B cell-targeting therapies, including B cell depletion, have been proven to be efficacious in treatment of multiple autoimmune diseases. However, the development of novel therapies targeting B cells with higher efficacy and a nondepleting mechanism of action is highly desirable. Here we describe a nondepleting, high-affinity anti-human CD19 antibody LY3541860 that exhibits potent B cell inhibitory activities. LY3541860 inhibits B cell activation, proliferation, and differentiation of primary human B cells with high potency. LY3541860 also inhibits human B cell activities in vivo in humanized mice. Similarly, our potent anti-mCD19 antibody also demonstrates improved efficacy over CD20 B cell depletion therapy in multiple B cell-dependent autoimmune disease models. Our data indicate that anti-CD19 antibody is a highly potent B cell inhibitor that may have potential to demonstrate improved efficacy over currently available B cell-targeting therapies in treatment of autoimmune conditions without causing B cell depletion.

STAT3 and STAT1 mediate IL-11-dependent and inflammation-associated gastric tumorigenesis in gp130 receptor mutant mice.

Deregulated activation of STAT3 is frequently associated with many human hematological and epithelial malignancies, including gastric cancer. While exaggerated STAT3 signaling facilitates an antiapoptotic, proangiogenic, and proproliferative environment for neoplastic cells, the molecular mechanisms leading to STAT3 hyperactivation remain poorly understood. Using the gp130(Y757F/Y757F) mouse model of gastric cancer, which carries a mutated gp130 cytokine receptor signaling subunit that cannot bind the negative regulator of cytokine signaling SOCS3 and is characterized by hyperactivation of the signaling molecules STAT1 and STAT3, we have provided genetic evidence that IL-11 promotes chronic gastric inflammation and associated tumorigenesis. Expression of IL-11 was increased in gastric tumors in gp130(Y757F/Y757F) mice, when compared with unaffected gastric tissue in wild-type mice, while gp130(Y757F/Y757F) mice lacking the IL-11 ligand-binding receptor subunit (IL-11Ralpha) showed normal gastric STAT3 activation and IL-11 expression and failed to develop gastric tumors. Furthermore, reducing STAT3 activity in gp130(Y757F/Y757F) mice, either genetically or by therapeutic administration of STAT3 antisense oligonucleotides, normalized gastric IL-11 expression and alleviated gastric tumor burden. Surprisingly, the genetic reduction of STAT1 expression also reduced gastric tumorigenesis in gp130(Y757F/Y757F) mice and coincided with reduced gastric inflammation and IL-11 expression. Collectively, our data have identified IL-11 as a crucial cytokine promoting chronic gastric inflammation and associated tumorigenesis mediated by excessive activation of STAT3 and STAT1.

IRAK4 kinase activity is required for Th17 differentiation and Th17-mediated disease.

Both IL-23- and IL-1-mediated signaling pathways play important roles in Th17 cell differentiation, cytokine production, and autoimmune diseases. The IL-1R-associated kinase 4 (IRAK4) is critical for IL-1/TLR signaling. We show here that inactivation of IRAK4 kinase in mice (IRAK4 KI) results in significant resistance to experimental autoimmune encephalomyelitis due to a reduction in infiltrating inflammatory cells into the CNS and reduced Ag-specific CD4(+) T cell-mediated IL-17 production. Adoptive transfer of myelin oligodendrocyte glycoprotein 35-55-specific IRAK4 KI Th17 cells failed to induce experimental autoimmune encephalomyelitis in either wild-type or IRAK4 KI recipient mice, indicating the lack of autoantigen-specific Th17 cell activities in the absence of IRAK4 kinase activity. Furthermore, the absence of IRAK4 kinase activity blocked induction of IL-23R expression, STAT3 activation by IL-23, and Th17 cytokine expression in differentiated Th17 cells. Importantly, blockade of IL-1 signaling by IL-1RA inhibited Th17 differentiation and IL-23-induced cytokine expression in differentiated Th17 cells. The results of these studies demonstrate that IL-1-mediated IRAK4 kinase activity in T cells is essential for induction of IL-23R expression, Th17 differentiation, and autoimmune disease.

Enhanced B cell expansion, survival, and humoral responses by targeting death receptor 6.

Targeted disruption of death receptor (DR)6 results in enhanced CD4(+) T cell expansion and T helper cell type 2 differentiation after stimulation. Similar to T cells, DR6 is expressed on resting B cells but is down-regulated upon activation. We examined DR6(-/-) B cell responses both in vitro and in vivo. In vitro, DR6(-/-) B cells undergo increased proliferation in response to anti-immunoglobulin M, anti-CD40, and lipopolysaccharide. This hyperproliferative response was due, at least in part, to both increased cell division and reduced cell apoptosis when compared with wild-type B cells. Consistent with these observations, increased nuclear levels and activity of nuclear factor kappaB transcription factor, c-Rel, and elevated Bcl-x(l) expression were observed in DR6(-/-) B cells upon stimulation. In addition, DR6(-/-) B cells exhibited higher surface levels of CD86 upon activation and were more effective as antigen-presenting cells in an allogeneic T cell proliferation response. DR6(-/-) mice exhibited enhanced germinal center formation and increased titers of immunoglobulins to T-dependent as well as T-independent type I and II antigens. This is the first demonstration of a regulatory role of DR6 in the activation and function of B cells.

Noncalcemic actions of vitamin D receptor ligands.

1alpha,25-Dihydroxyvitamin D(3) [1,25-(OH)(2)D(3)], the active metabolite of vitamin D(3), is known for the maintenance of mineral homeostasis and normal skeletal architecture. However, apart from these traditional calcium-related actions, 1,25-(OH)(2)D(3) and its synthetic analogs are being increasingly recognized for their potent antiproliferative, prodifferentiative, and immunomodulatory activities. These actions of 1,25-(OH)(2)D(3) are mediated through vitamin D receptor (VDR), which belongs to the superfamily of steroid/thyroid hormone nuclear receptors. Physiological and pharmacological actions of 1,25-(OH)(2)D(3) in various systems, along with the detection of VDR in target cells, have indicated potential therapeutic applications of VDR ligands in inflammation (rheumatoid arthritis, psoriatic arthritis), dermatological indications (psoriasis, actinic keratosis, seborrheic dermatitis, photoaging), osteoporosis (postmenopausal and steroid-induced osteoporosis), cancers (prostate, colon, breast, myelodysplasia, leukemia, head and neck squamous cell carcinoma, and basal cell carcinoma), secondary hyperparathyroidism, and autoimmune diseases (systemic lupus erythematosus, type I diabetes, multiple sclerosis, and organ transplantation). As a result, VDR ligands have been developed for the treatment of psoriasis, osteoporosis, and secondary hyperparathyroidism. Furthermore, encouraging results have been obtained with VDR ligands in clinical trials of prostate cancer and hepatocellular carcinoma. This review deals with the molecular aspects of noncalcemic actions of vitamin D analogs that account for the efficacy of VDR ligands in the above-mentioned indications.

The IL-23/Th(17) axis: therapeutic targets for autoimmune inflammation.

Autoimmune inflammatory responses and the diseases that develop as a consequence are now thought to be driven through a novel non-Th(1) pathway. IL-23, together with additional factors including TGF-beta1 and IL-6, collectively generate and sustain a distinct CD4(+) 'Th(17) inflammation effector' T-cell subset characterized by its production of inflammatory chemokines and cytokines, including IL-17. With this paradigm shift in understanding of autoimmune inflammation pathogenesis comes exciting opportunities to identify and to target therapeutically molecules within the IL-23/Th(17) axis that are key to disease development.

Tumor necrosis factor receptor superfamily member 21: TNFR-related death receptor-6, DR6.

TNFRSF21 (death receptor-6, DR6) is an orphan TNF receptor superfamily member and belongs to a subgroup of receptors called death receptors. DR6 is expressed ubiquitously with high expression in lymphoid organs, heart, brain and pancreas. Ectopic expression of DR6 in some cell lines leads to apoptosis and activation of the JNK and NF-kappaB pathways. Some tumor cells overexpress DR6, typically in conjunction with elevated anti-apoptosis molecules. DR6 deficient mice (DR6(-/-)) show normal development with no gross pathology in any major organs. In the absence of DR6, ligation of the TCR results in enhanced T-cell proliferation, activation and skewed Th2 cytokine production. Similarly, B-cells lacking Dr6 show increased proliferation, cell division and cell survival upon mitogenic stimulation (anti-CD40 and LPS) or BCR ligation. As a result, DR6(-/-) mice show increased Th2 immune responses to both T-dependent and -independent antigens. All those data indicate that DR6 plays an important regulatory role for the generation of adaptive immunity. More importantly, DR6(-/-) mice are resistant to EAE and allergic airway hypersensitivity, possibly as a result of a deficiency in the migration of antigen specific T-cells. Therefore, DR6 is a potential therapeutic target for treating inflammatory and autoimmune disease by means of biological intervention. In addition, DR6 is highly expressed in many tumor cell lines and tumor samples. Interestingly, both of its transcriptional and cell surface expression are regulated by the NF-kappaB pathway and metalloproteinase in some tumor cell lines, respectively. The role of DR6 as an apoptosis-inducing receptor is less clear and perhaps cell type dependent. Therefore, in addition to its roles in regulating immune responses, DR6 may also be involved in tumor cell survival and immune evasion, which is subject to future investigations.

Comparison of baricitinib, upadacitinib, and tofacitinib mediated regulation of cytokine signaling in human leukocyte subpopulations.

BACKGROUND: The in vitro pharmacology of baricitinib, upadacitinib, and tofacitinib was evaluated to understand differences among these JAK inhibitors (JAKis) at the cellular level. METHODS: Peripheral blood mononuclear cells from healthy donors were incubated with different JAKis, levels of phosphorylated signal transducer and activator of transcription (pSTAT) were measured following cytokine stimulation, and half maximum inhibitory concentration (IC50) values were calculated in phenotypically gated leukocyte subpopulations. Therapeutic dose relevance of the in vitro analysis was assessed using calculated mean concentration-time profiles over 24 h obtained from JAKi-treated subjects. Time above IC50 and average daily percent inhibition of pSTAT formation were calculated for each JAKi, cytokine, and cell type. RESULTS: Distinct JAKis displayed different in vitro pharmacologic profiles. For example, tofacitinib and upadacitinib were the most potent inhibitors of the JAK1/3-dependent cytokines tested (interleukin [IL]-2, IL-4, IL-15, and IL-21) with lower IC50 values and increased time above IC50 translating to a greater overall inhibition of STAT signaling during the dosing interval. All JAKis tested inhibited JAK1/2-dependent cytokines (e.g., IL-6 and interferon [IFN]-γ), the JAK1/tyrosine kinase 2 (TYK2)-dependent cytokines IL-10 and IFN-α, the JAK2/2-dependent cytokines IL-3 and granulocyte-macrophage colony-stimulating factor (GM-CSF), and the JAK2/TYK2-dependent cytokine granulocyte colony-stimulating factor (G-CSF), but often to significantly differing degrees. CONCLUSIONS: Different JAKis modulated distinct cytokine pathways to varying degrees, and no agent potently or continuously inhibited an individual cytokine signaling pathway throughout the dosing interval. Notably, baricitinib inhibited JAK1/3 signaling to a lesser extent than upadacitinib and tofacitinib, while upadacitinib, baricitinib, and tofacitinib inhibited the signaling of JAK2/2-dependent cytokines, including GM-CSF and IL-3, as well as the signaling of the JAK2/TYK2-dependent cytokine G-CSF.

Rapid and quantitative detection of p38 kinase pathway in mouse blood monocyte.

The p38 alpha mitogen-activated protein kinase (MAPK) is essential in controlling the production of many proinflammatory cytokines, and its specific inhibitor can effectively block their production for treating human diseases. To effectively identify highly specific p38 alpha inhibitors in vivo, we developed an ex vivo mouse blood cell-based assay by flow cytometry to measure the intracellular p38 alpha kinase activation. We first attempted to identify the individual blood cell population in which the p38 alpha kinase pathway is highly expressed and activated. Based on CD11b, combined with Ly-6G cell surface expression, we identified two distinct subsets of non-neutrophilic myeloid cells, CD11b(Med)Ly-6G(-) and CD11b(Lo)Ly-6G(-), and characterized them as monocytes and natural killer (NK) cells, respectively. Then, we demonstrated that only monocytes, not NK cells, expressed a high level of p38 alpha kinase, which was rapidly activated by anisomycin stimulation as evidenced by the phosphorylation of both p38 and its substrate, MAPKAP-K2 (MK2). Finally, the p38 alpha kinase pathway activation in monocytes was fully inhibited by a highly selective p38 alpha kinase inhibitor dose-dependently in vitro and in vivo. In conclusion, we demonstrated an effective method for separating blood monocytes from other cells and for detecting the expression level and activation of the p38 alpha kinase pathway in monocytes, which provided a new approach for the rapid identification of specific p38 alpha inhibitors.

The Initiation, but Not the Persistence, of Experimental Spondyloarthritis Is Dependent on Interleukin-23 Signaling.

IL-17A is a central driver of spondyloarthritis (SpA), its production was originally proposed to be IL-23 dependent. Emerging preclinical and clinical evidence suggests, however, that IL-17A and IL-23 have a partially overlapping but distinct biology. We aimed to assess the extent to which IL-17A-driven pathology is IL-23 dependent in experimental SpA. Experimental SpA was induced in HLA-B27/Huß2m transgenic rats, followed by prophylactic or therapeutic treatment with an anti-IL23R antibody or vehicle control. Spondylitis and arthritis were scored clinically and hind limb swelling was measured. Draining lymph node cytokine expression levels were analyzed directly ex vivo, and IL-17A protein was measured upon restimulation with PMA/ionomycin. Prophylactic treatment with anti-IL23R completely protected against the development of both spondylitis and arthritis, while vehicle-treated controls did develop spondylitis and arthritis. In a therapeutic study, anti-IL23R treatment failed to reduce the incidence or decrease the severity of experimental SpA. Mechanistically, expression of downstream effector cytokines, including IL-17A and IL-22, was significantly suppressed in anti-IL23R versus vehicle-treated rats in the prophylactic experiments. Accordingly, the production of IL-17A upon restimulation was reduced. In contrast, there was no difference in IL-17A and IL-22 expression after therapeutic anti-IL23R treatment. Targeting the IL-23 axis during the initiation phase of experimental SpA-but not in established disease-inhibits IL-17A expression and suppresses disease, suggesting the existence of IL-23-independent IL-17A production. Whether IL-17A can be produced independent of IL-23 in human SpA remains to be established.

Death receptor-6 regulates the development of pulmonary eosinophilia and airway inflammation in a mouse model of asthma.

Death receptor-6 (DR6), a member of the death domain-containing TNFR superfamily, is highly expressed in lymphoid tissues and regulated upon lymphocyte activation. Targeted disruption of DR6 results in enhanced CD4(+) T cell proliferation and T helper 2 (Th2) differentiation in vitro, whereas the in vivo role of DR6 in regulating Th2 cell differentiation and effector function remains largely unknown. In the current study, we used a Th2-skewed allergic airway inflammation model induced by ovalbumin (OVA) sensitization and challenge to compare the inflammatory response in the lung of both wild type (WT) and DR6(-/-) mice. DR6(-/-) mice were protected from the development of airway inflammation as evidenced by attenuated eosinophil accumulation and reduced mucus-producing cells in the lining airways of allergen-challenged animals. Consistent with these observations, a profound reduction of Th2 cytokine production (IL-5 and IL-13) was detected in the bronchoalveolar lavage fluid (BAL). Furthermore, a significant increase in the frequency of IFN-gamma secreting cells was observed in the DR6(-/-) mouse lungs after OVA challenge, which may account for the reduced pulmonary Th2 cytokine production. These data point to a critical role of DR6 in regulating airway inflammation in the OVA-induced mouse model of asthma.

Selective role of PKCbeta enzymatic function in regulating cell survival mediated by B cell antigen receptor cross-linking.

Cross-linking of the B cell antigen receptor (BCR) results in the activation of several protein tyrosine kinases leading to phospholipase C-gamma2-dependent phospholipid hydrolysis and Ca2+ mobilization, followed by activation of the protein kinase C (PKC) family members. Sustained Ca2+ release in B lymphocytes is dependent on the membrane localization and activation of the protein tyrosine kinase BTK. Ca2+ release is a tightly regulated process involving BTK membrane localization through its phosphorylation by PKCbeta. A selective role of PKCbeta in B cell signaling was first revealed by the characterization of PKCbeta knockout mice, which displayed decreased B cell proliferation in response to various mitogenic stimuli. However, it is not clear whether the B cell defects displayed by the PKCbeta knockout mice are due a B cell developmental defect or the scaffolding function of PKCbeta, resulting in a defect in the recruitment or formation of signal transducing complex molecules. Thus, in this report we investigated the effects of pharmacologic inhibition of the catalytic function of PKCbeta on B cell survival and growth. Treatment of Daudi B lymphoma cell line with a selective PKCbeta inhibitor, LY333531, inhibited anti-IgM-induced phosphorylation of BTK on Ser180 in a concentration-dependent manner, which was concomitant with an increase in BTK activation, and Ca2+ mobilization. In primary splenic B cells, LY333531 inhibited BCR-induced B cell proliferation, but did not affect basal or LPS-induced proliferation. Finally, LY333531 treatment resulted in the induction of apoptosis of anti-IgM-activated B cells, which corroborated with their inability to up-regulate pro-survival factors, Bcl-X(L) and Bcl-2. These results support the important and selective role of the PKCbeta enzymatic function in controlling Ca2+ release during BCR signaling leading to B lymphocyte survival and growth.

Characterization of LY2228820 dimesylate, a potent and selective inhibitor of p38 MAPK with antitumor activity.

p38α mitogen-activated protein kinase (MAPK) is activated in cancer cells in response to environmental factors, oncogenic stress, radiation, and chemotherapy. p38α MAPK phosphorylates a number of substrates, including MAPKAP-K2 (MK2), and regulates the production of cytokines in the tumor microenvironment, such as TNF-α, interleukin-1ß (IL-1ß), IL-6, and CXCL8 (IL-8). p38α MAPK is highly expressed in human cancers and may play a role in tumor growth, invasion, metastasis, and drug resistance. LY2228820 dimesylate (hereafter LY2228820), a trisubstituted imidazole derivative, is a potent and selective, ATP-competitive inhibitor of the α- and ß-isoforms of p38 MAPK in vitro (IC(50) = 5.3 and 3.2 nmol/L, respectively). In cell-based assays, LY2228820 potently and selectively inhibited phosphorylation of MK2 (Thr334) in anisomycin-stimulated HeLa cells (at 9.8 nmol/L by Western blot analysis) and anisomycin-induced mouse RAW264.7 macrophages (IC(50) = 35.3 nmol/L) with no changes in phosphorylation of p38α MAPK, JNK, ERK1/2, c-Jun, ATF2, or c-Myc ≤ 10 µmol/L. LY2228820 also reduced TNF-α secretion by lipopolysaccharide/IFN-γ-stimulated macrophages (IC(50) = 6.3 nmol/L). In mice transplanted with B16-F10 melanoma, tumor phospho-MK2 (p-MK2) was inhibited by LY2228820 in a dose-dependent manner [threshold effective dose (TED)(70) = 11.2 mg/kg]. Significant target inhibition (>40% reduction in p-MK2) was maintained for 4 to 8 hours following a single 10 mg/kg oral dose. LY2228820 produced significant tumor growth delay in multiple in vivo cancer models (melanoma, non-small cell lung cancer, ovarian, glioma, myeloma, breast). In summary, LY2228820 is a p38 MAPK inhibitor, which has been optimized for potency, selectivity, drug-like properties (such as oral bioavailability), and efficacy in animal models of human cancer.

A Nonsecosteroidal Vitamin D Receptor Modulator Ameliorates Experimental Autoimmune Encephalomyelitis without Causing Hypercalcemia.

Vitamin D receptor (VDR) agonists are currently the agents of choice for the treatment of psoriasis, a skin inflammatory indication that is believed to involve an autoimmune component. 1,25-dihydroxyvitamin D3 [1,25-(OH)(2)D(3)], the biologically active metabolite of vitamin D, has shown efficacy in animal autoimmune disease models of multiple sclerosis, rheumatoid arthritis, inflammatory bowel disease, and type I diabetes. However, the side effect of 1,25-(OH)(2)D(3) and its synthetic secosteroidal analogs is hypercalcemia, which is a major impediment in their clinical development for autoimmune diseases. Hypercalcemia develops as a result of the action of VDR agonists on the intestine. Here, we describe the identification of a VDR modulator (VDRM) compound A that was transcriptionally less active in intestinal cells and as a result exhibited less calcemic activity in vivo than 1,25-(OH)(2)D(3). Cytokine analysis indicated that the VDRM not only modulated the T-helper cell balance from Th1 to Th2 effector function but also inhibited Th17 differentiation. Finally, we demonstrate that the oral administration of compound A inhibited the induction and progress of experimental autoimmune encephalomyelitis in mice without causing hypercalcemia.

Resistance to experimental autoimmune encephalomyelitis and impaired IL-17 production in protein kinase C theta-deficient mice.

The protein kinase C theta (PKC theta) serine/threonine kinase has been implicated in signaling of T cell activation, proliferation, and cytokine production. However, the in vivo consequences of ablation of PKC theta on T cell function in inflammatory autoimmune disease have not been thoroughly examined. In this study we used PKC theta-deficient mice to investigate the potential involvement of PKC theta in the development of experimental autoimmune encephalomyelitis, a prototypic T cell-mediated autoimmune disease model of the CNS. We found that PKC theta-/- mice immunized with the myelin oligodendrocyte glycoprotein (MOG) peptide MOG(35-55) were completely resistant to the development of clinical experimental autoimmune encephalomyelitis compared with wild-type control mice. Flow cytometric and histopathological analysis of the CNS revealed profound reduction of both T cell and macrophage infiltration and demyelination. Ex vivo MOG(35-55) stimulation of splenic T lymphocytes from immunized PKC theta-/- mice revealed significantly reduced production of the Th1 cytokine IFN-gamma as well as the T cell effector cytokine IL-17 despite comparable levels of IL-2 and IL-4 and similar cell proliferative responses. Furthermore, IL-17 expression was dramatically reduced in the CNS of PKC theta-/- mice compared with wild-type mice during the disease course. In addition, PKC theta-/- T cells failed to up-regulate LFA-1 expression in response to TCR activation, and LFA-1 expression was also significantly reduced in the spleens of MOG(35-55)-immunized PKC theta-/- mice as well as in in vitro-stimulated CD4+ T cells compared with wild-type mice. These results underscore the importance of PKC theta in the regulation of multiple T cell functions necessary for the development of autoimmune disease.

Dicer is required for embryonic angiogenesis during mouse development.

Dicer is a multi-domain protein responsible for the generation of short interfering RNAs (siRNAs) from long double-stranded RNAs during RNA interference. It is also involved in the maturation of microRNAs, some of which are transcriptional regulators of developmental timing in nematodes. To assess the role of Dicer in mammals, we generated Dicerex1/2 mice with a deletion of the amino acid sequences corresponding to the first and second exons of the dicer gene via homologous recombination. We found that Dicerex1/2 homozygous embryos displayed a retarded phenotype and died between days 12.5 and 14.5 of gestation. Thus, these results show that dicerex1/2 is severely hypomorphic and that Dicer is essential for normal mouse development. Interestingly, we also found that blood vessel formation/maintenance in dicerex1/2 embryos and yolk sacs were severely compromised, suggesting a possible role for Dicer in angiogenesis. This finding is consistent with the altered expression of vegf, flt1, kdr, and tie1 in the mutant embryos. Taken together, the results of this study indicate that Dicer exerts its function on mouse embryonic angiogenesis probably through its role in the processing of microRNAs that regulate the expression levels of some critical angiogenic regulators in the cell.

Resistance to myelin oligodendrocyte glycoprotein-induced experimental autoimmune encephalomyelitis by death receptor 6-deficient mice.

Genetic disruption of death receptor 6 (DR6) results in enhanced CD4+ T cell expansion, Th2 differentiation, and humoral responses after stimulation. However, the in vivo consequences of DR6 targeting (DR6-/-) during the initiation and progression of inflammatory autoimmune disease are unclear. Using a myelin oligodendrocyte glycoprotein (MOG(35-55))-induced model of experimental autoimmune encephalomyelitis, DR6-/- mice were found to be highly resistant to both the onset and the progression of CNS disease compared with wild-type (WT) littermates. DR6-/- mice exhibited fewer inflammatory foci along with minimal demyelination and perivascular cuffing of inflammatory cells. Consistent with these observations, mononuclear cell infiltration, including CD4+ T cells and macrophages, in the spinal cord of DR6-/- mice was dramatically reduced. Furthermore, CD4+ T cells from DR6-/- mice exhibited profoundly reduced cell surface expression of VLA-4 before and after stimulation. Compared with WT mice, DR6-/- mice exhibited significantly increased autoantigen-induced T cell proliferative responses along with greater numbers of IL-4-producing and similar or slightly higher numbers of IFN-gamma-producing CD4+ T cells. DR6-/- CD4+ T cells secreted higher levels of the Th2 cytokine, IL-4, and similar levels of the Th1 cytokine, IFN-gamma, compared with WT cells. Taken together, our data demonstrate that DR6 plays an important role in regulating leukocyte infiltration and function in the induction and progression of experimental autoimmune encephalomyelitis.

Environmental chemical-induced bone marrow B cell apoptosis: death receptor-independent activation of a caspase-3 to caspase-8 pathway.

Programmed cell death is a critical process in B lymphocyte development. Premature apoptosis in developing B cells could affect the repertoire and number of mature B cells produced. Of particular concern is the ability of environmentally ubiquitous polycyclic aromatic hydrocarbons (PAH) to induce B cell apoptosis within the bone marrow microenvironment in a clonally nonspecific way. Here, models of bone marrow B cell development were used to assess the role of the "extrinsic" apoptosis pathway in PAH-induced apoptosis and to compare PAH-induced apoptosis with that induced during clonal deletion. As demonstrated previously with a nontransformed pro-/pre-B cell line, primary pro-B cells cultured on bone marrow stromal cells underwent apoptosis after exposure to a prototypic PAH, 7,12-dimethylbenz[a]anthracene (DMBA). Apoptosis was preceded by cleavage of caspase-3 (4-6 h) and caspase-8 (6-8 h) and their respective substrates, alpha-fodrin and Bid. Inhibition of caspase-3 blocked caspase-8 activation and apoptosis. Furthermore, a pan-caspase inhibitor blocked apoptosis and activation of both caspases-3 and -8. Cells from mice defective in tumor necrosis factor (TNF)-alpha, TNF-beta, lymphotoxin-beta, or TNFR1, TNFR2, Fas, or death receptor 6 were as susceptible to apoptosis signaling as wild-type cells. These results suggest a complex death receptor-independent B cell apoptosis pathway in which caspase-8 is activated downstream of caspase-3.

Adoptive transfer of in vitro-stimulated CD4+CD25+ regulatory T cells increases bacterial clearance and improves survival in polymicrobial sepsis.

Regulatory CD4(+)CD25(+) T cells (Tregs) suppress autoimmune and inflammatory diseases through mechanisms that are only partly understood. Previous studies suggest that Tregs can suppress bacterially triggered intestinal inflammation and respond to LPS through TLRs with enhanced suppressive activity. In this study, we have used murine cecal ligation and puncture as a model of polymicrobial sepsis to explore the effects of adoptive transfer of Tregs on septic outcome. Adoptive transfer of in vitro-stimulated Tregs in both prevention and therapeutic modes significantly improved survival of cecal ligation and puncture mice. Furthermore, the effect was dependent on both the number of Tregs adoptively transferred and the presence of host T cells. Animals that received stimulated Tregs had significantly increased peritoneal mast cells and peritoneal TNF-alpha production. More importantly, adoptive transfer of in vitro-stimulated Tregs significantly improved bacterial clearance, which resulted in improved survival. Our results suggest a novel role for Tregs in sepsis.