Nida Meednu

Neutrophil-Mediated IFN Activation in the Bone Marrow Alters B Cell Development in Human and Murine Systemic Lupus Erythematosus

Inappropriate activation of type I IFN plays a key role in the pathogenesis of autoimmune disease, including systemic lupus erythematosus (SLE). In this study, we report the presence of IFN activation in SLE bone marrow (BM), as measured by an IFN gene signature, increased IFN regulated chemokines, and direct production of IFN by BM-resident cells, associated with profound changes in B cell development. The majority of SLE patients had an IFN signature in the BM that was more pronounced than the paired peripheral blood and correlated with both higher autoantibodies and disease activity. Pronounced alterations in B cell development were noted in SLE in the presence of an IFN signature with a reduction in the fraction of pro/pre-B cells, suggesting an inhibition in early B cell development and an expansion of B cells at the transitional stage. These B cell changes strongly correlated with an increase in BAFF and APRIL expression in the IFN-high BM. Furthermore, we found that BM neutrophils in SLE were prime producers of IFN-α and B cell factors. In NZM lupus-prone mice, similar changes in B cell development were observed and mediated by IFN, given abrogation in NZM mice lacking type-I IFNR. BM neutrophils were abundant, responsive to, and producers of IFN, in close proximity to B cells. These results indicate that the BM is an important but previously unrecognized target organ in SLE with neutrophil-mediated IFN activation and alterations in B cell ontogeny and selection.

T-Cell Activation under Hypoxic Conditions Enhances IFN-γ Secretion

Secondary lymphoid organs and peripheral tissues are characterized by hypoxic microenvironments, both in the steady state and during inflammation. Although hypoxia regulates T-cell metabolism and survival, very little is known about whether or how hypoxia influences T-cell activation. We stimulated mouse CD4(+) T cells in vitro with antibodies directed against the T-cell receptor (CD3) and CD28 under normoxic (20% O(2)) and hypoxic (1% O(2)) conditions. Here we report that stimulation under hypoxic conditions augments the secretion of effector CD4(+) T-cell cytokines, especially IFN-gamma. The enhancing effects of hypoxia on IFN-gamma secretion were independent of mouse strain, and were also unaffected using CD4(+) T cells from mice lacking one copy of the gene encoding hypoxia-inducible factor-1alpha. Using T cells from IFN-gamma receptor-deficient mice and promoter reporter studies in transiently transfected Jurkat T cells, we found that the enhancing effects of hypoxia on IFN-gamma expression were not due to effects on IFN-gamma consumption or proximal promoter activity. In contrast, deletion of the transcription factor, nuclear erythroid 2 p45-related factor 2 attenuated the enhancing effect of hypoxia on IFN-gamma secretion and other cytokines. We conclude that hypoxia is a previously underappreciated modulator of effector cytokine secretion in CD4(+) T cells.

Lpa2 Is a Negative Regulator of Both Dendritic Cell Activation and Murine Models of Allergic Lung Inflammation

Negative regulation of innate immune responses is essential to prevent excess inflammation and tissue injury and promote homeostasis. Lysophosphatidic acid (LPA) is a pleiotropic lipid that regulates cell growth, migration, and activation and is constitutively produced at low levels in tissues and in serum. Extracellular LPA binds to specific G protein-coupled receptors, whose function in regulating innate or adaptive immune responses remains poorly understood. Of the classical LPA receptors belonging to the Edg family, lpa2 (edg4) is expressed by dendritic cells (DC) and other innate immune cells. In this article, we show that DC from lpa2−/− mice are hyperactive compared with their wild-type counterparts and are less susceptible to inhibition by different LPA species. In transient-transfection assays, we found that lpa2 overexpression inhibits NF-κB–driven gene transcription. Using an adoptive-transfer approach, we found that allergen-pulsed lpa2−/− DC induced substantially more lung inflammation than did wild-type DC after inhaled allergen challenge. Finally, lpa2−/− mice develop greater allergen-driven lung inflammation than do their wild-type counterparts in models of allergic asthma involving both systemic and mucosal sensitization. Taken together, these findings identify LPA acting via lpa2 as a novel negative regulatory pathway that inhibits DC activation and allergic airway inflammation.

Production of RANKL by Memory B Cells: A Link Between B Cells and Bone Erosion in Rheumatoid Arthritis

Rheumatoid arthritis (RA) is a systemic autoimmune disease that often leads to joint damage. The mechanisms of bone damage in RA are complex, involving activation of bone‐resorbing osteoclasts (OCs) by synoviocytes and Th17 cells. This study was undertaken to investigate whether B cells play a direct role in osteoclastogenesis through the production of RANKL, the essential cytokine for OC development.

A link between B cells and bone erosion in rheumatoid arthritis: Receptor activator of nuclear factor kappa‐B ligand production by memory B cells

Rheumatoid arthritis (RA) is a systemic autoimmune disease that often leads to joint damage. The mechanisms of bone damage in RA are complex, involving activation of bone‐resorbing osteoclasts (OCs) by synoviocytes and Th17 cells. This study was undertaken to investigate whether B cells play a direct role in osteoclastogenesis through the production of RANKL, the essential cytokine for OC development.

The Spindle Positioning Protein Kar9p Interacts With the Sumoylation Machinery in Saccharomyces cerevisiae

Accurate positioning of the mitotic spindle is important for the genetic material to be distributed evenly in dividing cells, but little is known about the mechanisms that regulate this process. Here we report that two microtubule-associated proteins important for spindle positioning interact with several proteins in the sumoylation pathway. By two-hybrid analysis, Kar9p and Bim1p interact with the yeast SUMO Smt3p, the E2 enzyme Ubc9p, an E3 Nfi1p, as well as Wss1p, a weak suppressor of a temperature-sensitive smt3 allele. The physical interaction between Kar9p and Ubc9p was confirmed by in vitro binding assays. A single-amino-acid substitution in Kar9p, L304P disrupted its two-hybrid interaction with proteins in the sumoylation pathway, but retained its interactions with the spindle positioning proteins Bim1p, Stu2p, Bik1p, and Myo2p. The kar9-L304P mutant showed defects in positioning the mitotic spindle, with the spindle located more distally than normal. Whereas wild-type Kar9p-3GFP normally localizes to only the bud-directed spindle pole body (SPB), Kar9p-L304P-3GFP was mislocalized to both SPBs. Using a reconstitution assay, Kar9p was sumoylated in vitro. We propose a model in which sumoylation regulates spindle positioning by restricting Kar9p to one SPB. These findings raise the possibility that sumoylation could regulate other microtubule-dependent processes.

The effects of EPA, DHA, and aspirin ingestion on plasma lysophospholipids and autotaxin.

Lysophophatidylcholine (LPC) and lysophosphatidic acid (LPA) are potent lysolipid mediators increasingly linked with atherosclerosis and inflammation. A current model proposing that plasma LPA is produced when LPC is hydrolyzed by the enzyme autotaxin has not been rigorously investigated in human subjects. We conducted a clinical trial of eicosapentaenoic acid/docosahexaenoic acid (EPA/DHA) and aspirin ingestion in normal volunteers. Fasting blood samples were drawn at baseline and after 4-week supplementation with EPA/DHA (3.4 g/d) with and without aspirin (650 mg). Plasma LPC and LPA species and autotaxin activity were measured. EPA-LPC and DHA-LPC concentrations increased significantly with EPA/DHA supplementation whereas EPA- and DHA-LPA did not. Autotaxin activity was unaffected by any treatment, and aspirin had no effect on any endpoint. Taken together, our data demonstrate that plasma LPC, but not LPA, species can be dynamically regulated by dietary supplementation, and argue against a simple model of LPA generation via LPC hydrolysis.

New insights into B cell biology in systemic lupus erythematosus and Sjögren's syndrome.

Purpose of reviewOur understanding of the physiological and pathogenic functions of B cells in systemic lupus erythematosus (SLE) and Primary Sjögrens syndrome (pSS) continues to expand. In this review, we discuss novel insights published in the last 18 months into the roles of B cells in systemic autoimmunity. Recent findingsData have continued to expand regarding the diverse mechanisms by which innate immune signals including Toll-like receptors (TLRs) regulate the B cell compartment. Localized B cells and long-lived plasma cells have been identified as playing an important role in target tissue including the development of ectopic lymphoid structures in kidney and salivary gland. In addition to pathogenic roles for B cells, there is mounting evidence for regulatory B cell subsets that play a protective role and new insights into the signals that regulate their development. SummaryThe past few years have provided insights into the multiple paths by which innate immune signals can lead to B cell activation in SLE and pSS and the increasingly diverse ways in which B cells contribute to disease expression. Further understanding the imbalance between protective and pathogenic functions for B cells in disease including in understudied target tissue should yield new treatment approaches.

The yeast homologue of the microtubule-associated protein Lis1 interacts with the sumoylation machinery and a SUMO-targeted ubiquitin ligase.

The two yeast members of the CLIP-170/Bik1p and Lis1/Pac1p families of microtubule-associated proteins are shown to interact with the sumoylation machinery and the STUbL complex Ris1p–Nis1p. Pac1p can be modified by both SUMO and ubiquitin. The She1 regulator of dynactin is identified as a novel inhibitor of Pac1p modification.

Effects of low-dose aspirin and fish oil on platelet function and NF-kappaB in adults with diabetes mellitus

INTRODUCTION Many diabetics are insensitive to aspirins platelet anti-aggregation effects. The possible modulating effects of co-administration of aspirin and fish oil in subjects with diabetes are poorly characterized. PARTICIPANTS AND METHODS Thirty adults with type 2 diabetes mellitus were treated with aspirin 81 mg/d for 7 days, then with fish oil 4 g/day for 28 days, then the combination of fish oil and aspirin for another 7 days. RESULTS Aspirin alone and in combination with fish oil reduced platelet aggregation in most participants. Five of 7 participants classified as aspirin insensitive 1 week after daily aspirin ingestion were sensitive after the combination. Although some platelet aggregation measures correlated positively after aspirin and fish oil ingestion alone and (in combination) in all individuals, correlation was only observed in those who were aspirin insensitive after ingestion of the combination. CONCLUSIONS Co-administration of aspirin and fish oil may reduce platelet aggregation more than aspirin alone in adults with diabetes mellitus.