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Abstract The follicular helper T cell (T FH) are established regulators of germinal center (GC) B cells, whether T FH have pathogenic potential independent of B cells is unknown. Based on in vitro T FH cell differentiation, in vivo T cell transfer animal colitis model, and intestinal tissues of inflammatory bowel disease (IBD) patients, T FH and its functions in colitis development were analyzed by FACS, ChIP, ChIP-sequencing, WB, ELISA and PCR. Herein we demonstrate that intestinal tissues of patients and colon tissues obtained from Rag1 −/− recipients of naïve CD4+ T cells with colitis, each over-express T FH -associated gene products. Adoptive transfer of naïve Bcl6 −/− CD4+ T cells into Rag1 −/− recipient mice abrogated development of colitis and limited T FH differentiation in vivo , demonstrating a mechanistic link. In contrast, T cell deficiency of interferon regulatory factor 8 (IRF8) resulted in augmentation of T FH induction in vitro and in vivo. Functional studies showed that adoptive transfer of IRF8 deficient CD4+ T cells into Rag1 −/− recipients exacerbated colitis development associated with increased gut T FH -related gene expression, while Irf8 −/− /Bcl6 −/− CD4+ T cells abrogated colitis, together indicating that IRF8-regulated T FH can directly cause colon inflammation. Molecular analyses revealed that IRF8 suppresses T FH differentiation by inhibiting transcription and transactivation of the TF IRF4, which is also known to be essential for T FH induction. Our documentation showed that IRF8-regulated T FH can function as B-cell-independent, pathogenic, mediators of colitis suggests that targeting T FH could be effective for treatment of IBD. Highlights • Our study reveals that T FH cells are critically involved in the development of T cell-mediated inflammatory diseases. • The study defines IRF8 as an important intrinsic suppressor of T FH differentiation. • Our studies are really novel and will lead to more exciting investigations concerning the contributions of T FH cells in the development of various T cell-mediated inflammatory diseases in future. [ABSTRACT FROM AUTHOR]

Abstract: The E3 ligase ARF-BP1 governs the balance of life and death decisions by directing the degradation of p53 and enhancing the transcriptional activity of MYC. We find B cells selectively deficient in ARF-BP1 have many defects in developing and mature B cells associated with increased expression of p53 and reduced expression of Myc. Overexpression of Myc results in suppression of p53 and complete reversal of defects induced by ARF-BP1 deficiency. These findings indicate that the dynamic balance between MYC and p53 required for normal B cell maturation and function is finely tuned and critically dependent on the activities of ARF-BP1. [Copyright &y& Elsevier]

Abstract: CDKN1B (p27) regulates cell-cycle progression at the G1-S transition by suppressing the cyclin E/CDK2 kinase complex. In normal lymphocytes and most human B cell non-Hodgkin lymphomas (NHL), there is an inverse correlation between proliferative activity and expression of p27; however, a subset of NHL with high mitotic indices expresses p27, which is inactive due to sequestration in nuclear protein complexes or due to cytoplasmic retention. Our studies of mouse B cell NHL also identified cases with high proliferative activity and high levels of p27 at a surprisingly high frequency. Here, p27 was complexed with D-type cyclins 1 and 3 and with the COPS9 protein, JAB1. In addition, we found cytoplasmic sequestration following phosphorylation by activated AKT. [Copyright &y& Elsevier]

In normal human germinal centre (GC) B-cells and post-GC B-cell lymphomas, a region in the first intron of the BCL6 gene, termed the major mutations cluster (MMC) exhibits somatic point mutations and deletions with patterns very similar to those seen in the variable regions of immunoglobulin (Ig) genes. In studies of mouse post-GC diffuse large cell lymphoma, Burkitt lymphomas, and plasmacytomas, direct sequencing or cold SSCP analyses revealed no mutations within a 686-bp region in Bcl6 intron 1 with 72% identity to the human MMC. The mouse Bcl6 locus must be inaccessible to the mutational machinery responsible for somatic mutations of Ig and BCL6 in humans. [Copyright &y& Elsevier]

Severe lupus often includes psychiatric and neurological sequelae, although the cellular contributors to CNS disease remain poorly defined. Using intravascular staining to discriminate tissue-localized from blood-borne cells, we find substantial accumulation of CD8+ T cells relative to other lymphocytes in brain tissue, which correlates with lupus disease and limited neuropathology. This is in contrast to all other affected organs, where infiltrating CD4+ cells are predominant. Brain-infiltrating CD8+ T cells represent an activated subset of those found in the periphery, having a resident-memory phenotype (CD69+CD122−PD1+CD44+CD62L−) and expressing adhesion molecules (VLA-4+LFA-1+) complementary to activated brain endothelium. Remarkably, infiltrating CD8+ T cells do not cause tissue damage in lupus-prone mice, as genetic ablation of these cells via β2 m deficiency does not reverse neuropathology, but exacerbates disease both in the brain and globally despite decreased serum IgG levels. Thus, lupus-associated inflammation disrupts the blood-brain barrier in a discriminating way biased in favor of non-pathogenic CD8+ T cells relative to other infiltrating leukocytes, perhaps preventing further tissue damage in such a sensitive organ. [ABSTRACT FROM AUTHOR]

Lupus nephritis is a severe organ manifestation in systemic lupus erythematosus leading to kidney failure in a subset of patients. In lupus-prone mice, controlled infection with Plasmodium parasites protects against the progression of autoimmune pathology including lethal glomerulonephritis. Here, we demonstrate that parasite-induced protection was not due to a systemic effect of infection on autoimmunity as previously assumed, but rather to specific alterations in immune cell infiltrates into kidneys and renal draining lymph nodes. Infection of lupus-prone mice with a Plasmodium parasite did not reduce the levels or specificities of autoreactive antibodies, vasculitis, immune complex-induced innate activation, or hypoxia. Instead, infection uniquely reduced kidney-infiltrating CCL17-producing bone marrow-derived type 2 inflammatory dendritic cells (iDC2s). Bone marrow reconstitution experiments revealed that infection with Plasmodium caused alterations in bone marrow cells that hindered the ability of DC2s to infiltrate the kidneys. The essential role for CCL17 in lupus nephritis was confirmed by in vivo depletion with a blocking antibody, which reduced kidney pathology and immune infiltrates, while bypassing the need for parasitic infection. Therefore, infiltration into the kidneys of iDC2s, with the potential to prime local adaptive responses, is an essential regulated event in the transition from manageable glomerulonephritis to lethal tubular injury. [ABSTRACT FROM AUTHOR]

Cerebral malaria (CM) is the deadliest form of severe Plasmodium infections. Currently, we have limited understanding of the mechanisms by which Plasmodium parasites induce CM. The mouse model of CM, experimental CM (ECM), induced by infection with the rodent parasite, Plasmodium berghei ANKA (PbANKA) has been extensively used to study the pathophysiology of CM. Recent genomic analyses revealed that the coding regions of PbANKA and the closely related Plasmodium berghei NK65 (PbNK65), that does not cause ECM, differ in only 21 single nucleotide polymorphysims (SNPs). Thus, the SNP-containing genes might contribute to the pathogenesis of ECM. Although the majority of these SNPs are located in genes of unknown function, one SNP is located in the DNA binding site of a member of the Plasmodium ApiAP2 transcription factor family, that we recently showed functions as a virulence factor alternating the host's immune response to the parasite. Here, we investigated the impact of this SNP on the development of ECM. Our results using CRISPR-Cas9 engineered parasites indicate that despite its immune modulatory function, the SNP is neither necessary nor sufficient to induce ECM and thus cannot account for parasite strain-specific differences in ECM phenotypes. [ABSTRACT FROM AUTHOR]

Accumulating evidence suggests granulocyte macrophage-colony stimulating factor (GM-CSF) can function as an inflammatory mediator, but whether GM-CSF-producing CD4+ T cells (T H -GM-CSF) are a distinct T helper cell subset is lacking. Herein we demonstrate that interleukin (IL)-1β exclusively drives differentiation of naïve CD4+ T cells into T H -GM-CSF cells via inducing ubiquitination of IL-1 receptor-associated kinase 1 (IRAK1) and subsequent activation of the transcription factor NF-kappaB (NF-κB), independent of RAR-related orphan receptor gamma (RORγt) required for T H 17 differentiation. In vivo, T H -GM-CSF cells are present in murine Citrobacter Rodentium infections and mediate colitis following adoptive transfer of CD4+ T cells into Rag1 −/− mice via GM-CSF-induced macrophage activation. The T H -GM-CSF cell phenotype is stable and distinct from the T H 17 genetic program, but IL-1β can convert pre-formed T H 17 cells into T H -GM-CSF cells, thereby accounting for previously reported associations between IL-17 and GM-CSF. Together, our results newly identify IL-1β/NF-κB-dependent T H -GM-CSF cells as a unique T helper cell subset and highlight the importance of CD4+ T cell-derived GM-CSF induced macrophage activation as a previously undescribed T cell effector mechanism. • Our study newly identifies GM-‐CSF-‐single producing T helper cells (TH-‐GM-‐CSF) as a unique T helper subset. • Our study reveals that IL-‐1® directly programs TH-‐GM-‐CSF differentiation via IRAK1/NF-‐κB axis and that IL-‐1® induces conversion of TH17 into TH-‐GM-‐CSF. • Our study shows that TH-‐GM-‐CSF cells are critically involved in the development of T cell transfer induced colitis. These novel findings will lead to more exciting investigations concerning the contributions of TH-‐GM-‐CSF in various T cell-‐ mediated inflammatory diseases. [ABSTRACT FROM AUTHOR]

TREX1/DNASE III, the most abundant 3′-5′ DNA exonuclease in mammalian cells, is tail-anchored on the endoplasmic reticulum (ER). Mutations at the N-terminus affecting TREX1 DNase activity are associated with autoimmune and inflammatory conditions such as Aicardi-Goutières syndrome (AGS). Mutations in the C-terminus of TREX1 cause loss of localization to the ER and dysregulation of oligosaccharyltransferase (OST) activity, and are associated with retinal vasculopathy with cerebral leukodystrophy (RVCL) and in some cases with systemic lupus erythematosus (SLE). Here we investigate mice with conditional expression of the most common RVCL mutation, V235fs, and another mouse expressing a conditional C-terminal mutation, D272fs, associated with a case of human SLE. Mice homozygous for either mutant allele express the encoded human TREX1 truncations without endogenous mouse TREX1, and both remain DNase active in tissues. The two mouse strains are similar phenotypically without major signs of retinal, cerebral or renal disease but exhibit striking elevations of autoantibodies in the serum. The broad range of autoantibodies is primarily against non-nuclear antigens, in sharp contrast to the predominantly DNA-related autoantibodies produced by a TREX1-D18N mouse that specifically lacks DNase activity. We also found that treatment with an OST inhibitor, aclacinomycin, rapidly suppressed autoantibody production in the TREX1 frame-shift mutant mice. Together, our study presents two new mouse models based on TREX1 frame-shift mutations with a unique set of serologic autoimmune-like phenotypes. [ABSTRACT FROM AUTHOR]

Summary Receptor CD300b is implicated in regulating the immune response to bacterial infection by an unknown mechanism. Here, we identified CD300b as a lipopolysaccharide (LPS)-binding receptor and determined the mechanism underlying CD300b augmentation of septic shock. In vivo depletion and adoptive transfer studies identified CD300b-expressing macrophages as the key cell type augmenting sepsis. We showed that CD300b, and its adaptor DAP12, associated with Toll-like receptor 4 (TLR4) upon LPS binding, thereby enhancing TLR4-adaptor MyD88- and TRIF-dependent signaling that resulted in an elevated pro-inflammatory cytokine storm. LPS engagement of the CD300b-TLR4 complex led to the recruitment and activation of spleen tyrosine kinase (Syk) and phosphatidylinositol-4,5-bisphosphate 3-kinase (PI3K). This resulted in an inhibition of the ERK1/2 protein kinase- and NF-κB transcription factor-mediated signaling pathways, which subsequently led to a reduced interleukin-10 (IL-10) production. Collectively, our data describe a mechanism of TLR4 signaling regulated by CD300b in myeloid cells in response to LPS. [ABSTRACT FROM AUTHOR]

Background: The role of intracellular radical oxygen species (ROS) in pathogenesis of cerebral malaria (CM) remains incompletely understood. Methods and Findings: We undertook testing Tempol—a superoxide dismutase (SOD) mimetic and pleiotropic intracellular antioxidant—in cells relevant to malaria pathogenesis in the context of coagulation and inflammation. Tempol was also tested in a murine model of CM induced by Plasmodium berghei Anka infection. Tempol was found to prevent transcription and functional expression of procoagulant tissue factor in endothelial cells (ECs) stimulated by lipopolysaccharide (LPS). This effect was accompanied by inhibition of IL-6, IL-8, and monocyte chemoattractant protein (MCP-1) production. Tempol also attenuated platelet aggregation and human promyelocytic leukemia HL60 cells oxidative burst. In dendritic cells, Tempol inhibited LPS-induced production of TNF-α, IL-6, and IL-12p70, downregulated expression of co-stimulatory molecules, and prevented antigen-dependent lymphocyte proliferation. Notably, Tempol (20 mg/kg) partially increased the survival of mice with CM. Mechanistically, treated mice had lowered plasma levels of MCP-1, suggesting that Tempol downmodulates EC function and vascular inflammation. Tempol also diminished blood brain barrier permeability associated with CM when started at day 4 post infection but not at day 1, suggesting that ROS production is tightly regulated. Other antioxidants—such as α-phenyl N-tertiary-butyl nitrone (PBN; a spin trap), MnTe-2-PyP and MnTBAP (Mn-phorphyrin), Mitoquinone (MitoQ) and Mitotempo (mitochondrial antioxidants), M30 (an iron chelator), and epigallocatechin gallate (EGCG; polyphenol from green tea) did not improve survival. By contrast, these compounds (except PBN) inhibited Plasmodium falciparum growth in culture with different IC50s. Knockout mice for SOD1 or phagocyte nicotinamide adenine dinucleotide phosphate (NADPH) oxidase (gp91phox–/–) or mice treated with inhibitors of SOD (diethyldithiocarbamate) or NADPH oxidase (diphenyleneiodonium) did not show protection or exacerbation for CM. Conclusion: Results with Tempol suggest that intracellular ROS contribute, in part, to CM pathogenesis. Therapeutic targeting of intracellular ROS in CM is discussed. [ABSTRACT FROM AUTHOR]

Abstract: Six cases of megakaryocytic leukemia (MKL) were identified and analyzed for morphology and molecular features. MKL were composed of megakaryocyte lineage cells ranging from immature to quite mature cells. VWF, GATA1 and RUNX1 were strongly expressed in megakaryocytes in both normal spleen and MKL as analyzed by immunohistochemistry (IHC). Altered expression of Meis1, Pbx1 and Psen2 and Lef1 in MKL detected with oligonucleotide microarrays was confirmed by qPCR and IHC. This is the first report of spontaneous MKL in mice, defining VWF as a biomarker for diagnosis and suggesting possible involvement of a series of genes in disease pathogenesis. [Copyright &y& Elsevier]

The cytokine interleukin-21 (IL-21) is closely related to IL-2 and IL-15, and their receptors all share the common cytokine receptor γ chain, γ[subc], which is mutated in humans with X-linked severe combined immunodeficiency disease (XSCID). We demonstrate that, although mice deficient in the receptor for IL-21 (IL-21R) have normal lymphoid development, after immunization, these animals have higher production of the immunoglobulin IgE, but lower lgG1, than wild-type animals. Mice lacking both IL-4 and IL-21 R exhibited a significantly more pronounced phenotype, with dysgammagtobulinemia, characterized primarily by a severely impaired IgG response. Thus, IL-21 has a significant influence on the regulation of B cell function in vivo and cooperates with IL-4. This suggests that these γ[subc]-dependent cytokines may be those whose inactivation is primarily responsible for the B cell defect in humans with XSCID. [ABSTRACT FROM AUTHOR]