Muthusamy Thiruppathi

Ischemic tissue damage activates hematopoietic stem and progenitor cells (HSPCs) in the bone marrow (BM)-generating myeloid cells, and persistent HSPC activity may drive chronic inflammation and impair tissue recovery. Although increased reactive oxygen species in the BM regulate HSPC functions, their roles in myelopoiesis of activated HSPCs and subsequent tissue recovery during ischemic damage are not well understood. In this paper, we report that deletion of Nox2 NADPH oxidase in mice results in persistent elevations in BM HSPC activity and levels of inflammatory monocytes/macrophages in BM and ischemic tissue in a model of hindlimb ischemia. Ischemic tissue damage induces oxidants in BM such as elevations of hydrogen peroxide and oxidized phospholipids, which activate redox-sensitive Lyn kinase in a Nox2-dependent manner. Moreover, during tissue recovery after ischemic injury, this Nox2-ROS–Lyn kinase axis is induced by Nox2 in neutrophils that home to the BM, which inhibits HSPC activity and inflammatory monocyte generation and promotes tissue regeneration after ischemic damage. Thus, oxidant signaling in the BM mediated by Nox2 in neutrophils regulates myelopoiesis of HSPCs to promote regeneration of damaged tissue.

Alternative NF-κB signaling is crucial for B cell activation and Ig production, and it is mainly regulated by the inhibitor of κ B kinase (IKK) regulatory complex. Dysregulation of alternative NF-κB signaling in B cells could therefore lead to hyperactive B cells and Ig overproduction. In our previous, study we found that deleted in breast cancer 1 (DBC1) is a suppressor of the alternative NF-κB pathway to attenuate B cell activation. In this study, we report that loss of DBC1 results in spontaneous overproduction of Ig in mice after 10 mo of age. Using a double mutant genetic model, we confirm that DBC1 suppresses B cell activation through RelB inhibition. At the molecular level, we show that DBC1 interacts with alternative NF-κB members RelB and p52 through its leucine zipper domain. In addition, phosphorylation of DBC1 at its C terminus by IKKα facilitates its interaction with RelB and IKKα, indicating that DBC1-mediated suppression of alternative NF-κB is regulated by IKKα. Our results define the molecular mechanism of DBC1 inhibition of alternative NF-κB activation in suppressing B cell activation.

Granulocyte macrophage colony stimulating factor (GM-CSF) is generally recognized as an inflammatory cytokine. Its inflammatory activity is primarily due its role as a growth and differentiation factor for granulocyte and macrophage populations. In this capacity, among other clinical applications, it has been used to bolster anti-tumor immune responses. GM-CSF-mediated inflammation has also been implicated in certain types of autoimmune diseases, including rheumatoid arthritis and multiple sclerosis. Thus, agents that can block GM-CSF or its receptor have been used as anti-inflammatory therapies. However, a review of literature reveals that in many situations GM-CSF can act as an anti-inflammatory/regulatory cytokine. We and others have shown that GM-CSF can modulate dendritic cell differentiation to render them "tolerogenic," which, in turn, can increase regulatory T-cell numbers and function. Therefore, the pro-inflammatory and regulatory effects of GM-CSF appear to depend on the dose and the presence of other relevant cytokines in the context of an immune response. A thorough understanding of the various immunomodulatory effects of GM-CSF will facilitate more appropriate use and thus further enhance its clinical utility.

CD40 and BAFFR signaling play important roles in B cell proliferation and Ig production. In this study, we found that B cells from mice with deletion of Dbc1 gene (Dbc1^−/−) show elevated proliferation, and IgG1 and IgA production upon in vitro CD40 and BAFF, but not BCR and LPS stimulation, indicating that DBC1 inhibits CD40/BAFF-mediated B cell activation in a cell-intrinsic manner. Microarray analysis and chromatin immunoprecipitation experiments reveal that DBC1 inhibits B cell function by selectively suppressing the transcriptional activity of alternative NF-κB members RelB and p52 upon CD40 stimulation. As a result, when immunized with nitrophenylated-keyhole limpet hemocyanin, Dbc1^−/− mice produce significantly increased levels of germinal center B cells, plasma cells, and Ag-specific Ig. Finally, loss of DBC1 in mice leads to higher susceptibility to experimental autoimmune myasthenia gravis. Our study identifies DBC1 as a novel regulator of B cell activation by suppressing the alternative NF-κB pathway.

Forkhead box P3 (FOXP3) is a transcription factor necessary for the function of regulatory T cells (T_reg cells). T_reg cells maintain immune homeostasis and self‐tolerance and play an important role in the prevention of autoimmune disease. Here, we discuss the role of T_reg cells in the pathogenesis of myasthenia gravis (MG) and review evidence indicating that a significant defect in T_reg cell in vitro suppressive function exists in MG patients, without an alteration in circulating frequency. This functional defect is associated with a reduced expression of key functional molecules, such as FOXP3 on isolated T_reg cells, and appears to be more pronounced in immunosuppression‐naive MG patients. In vitro administration of granulocyte macrophage–colony‐stimulating factor (GM‐CSF) enhanced the suppressive function of T_reg cells and upregulated FOXP3 expression. These findings indicate a clinically relevant T_reg cell–intrinsic defect in immune regulation in MG that may reveal a novel therapeutic target.

Introduction: In this study we describe a patient with a prolonged myasthenic crisis refractory to conventional immunomodulatory therapy who was treated with GM‐CSF (granulocyte macrophage colony‐stimulating factor, sargramostim). Methods: T‐regulatory cell (Treg) suppressive function and Foxp3 expression were evaluated before and after treatment with GM‐CSF. Results: Treatment with GM‐CSF was associated with clinical improvement, expansion in the circulating numbers of Foxp3⁺ cells, increase in Foxp3 expression levels in Tregs, early improvement in Treg suppressive capacity for AChR‐α–induced T‐cell proliferation, and subsequent enhancement in Treg suppression of polyclonal T‐cell proliferation. Conclusion: Although definitive conclusions cannot be drawn from a single case, the correlation with similar findings in GM‐CSF–treated animals with experimental autoimmune myasthenia gravis suggests further exploration of the effects of GM‐CSF in myasthenia gravis should be studied in a clinical trial setting. Muscle Nerve 46: 449–453, 2012