The regulation of autoreactive B cells during innate immune responses

The role of tolerogenic dendritic cells in systematic lupus erythematosus progression and remission

Systematic lupus erythematosus (SLE) is an autoimmune disease reflecting an imbalance between effector and regulatory immune responses. Dendritic cells (DC) are a link between innate and adaptive immunity. Inflammatory DCs (inflDC) can initiate and trigger lymphocyte responses in SLE with over-expression of surface molecules and pro-inflammatory cytokine, including Interferon (IFN) α, Interleukin (IL) 1α, IL-1β, and IL-6, resulting in the overreaction of T helper cells (Th), and B cells immune responses. On the opposite side, tolerogenic DCs (tolDC) express inhibitory interacting surface molecules and repressive mediators, such as IL-10, Transforming growth factor beta (TGF-β), and Indoleamine 2, 3-dioxygenase (IDO), which can maintain self-tolerance in SLE by induction of regulatory T cells (Treg), T cells deletion and anergy. Hence, tolDCs can be a therapeutic candidate for patients with SLE to suppress their systematic inflammation. Recent pre-clinical and clinical studies showed the efficacy of tolDCs therapy in autoimmune diseases. In this review, we provide a wide perspective on the effect of inflDCs in promoting inflammation and the role of tolDC in the suppression of immune cells' overreaction in SLE. Furthermore, we reviewed the finding of clinical trials and experimental studies related to autoimmune diseases, particularly SLE.

Myeloid cells limit production of antibody-secreting cells after immunization in the lymph node

Ab-secreting cell (ASC) expansion and survival are important processes in optimizing vaccines and controlling autoimmunity. The microenvironment of the medullary cords is positioned to control these key processes. Previously, we imaged and characterized ASC differentiation and migration by intravital microscopy in the lymph node (LN) by transferring and activating B cells expressing yellow fluorescent protein only in the ASC compartment. In this study, we observed that yellow fluorescent protein(+) ASCs in the medullary cords migrated along myelomonocytic cells and arrested in contact with them. Acute ablation of myeloid cells using the human diphtheria receptor system (diphtheria toxin receptor [DTR]) expressed in Lysmd1-cre-positive cells increased ASC and Ab production by 2-fold. Increases in ASC numbers were associated with cell proliferation based on Ki-67 staining, rather than reduced apoptosis, or changes in egress from the LN. Using DTR-mediated ablation targeted to Ccr2-expressing myeloid cells also generated increases in ASCs. In contrast, neither the depletion of Gr-1-positive cells with an Ab nor the ablation of cells using a cd11c-DTR resulted in any change in ASCs. IL-6 cytokine signaling can enhance ASC production and has been implicated in dampening ASCs in lupus mouse models through myeloid cells. Using mixed bone marrow chimeras, we observed that IL-6 enhances ASC production, but IL-6 production was not required by myeloid cells to dampen ASCs in the LN. Inhibition of ASCs by these myeloid cells in the LN provides a new regulatory mechanism with implications for tuning Ab responses.

Blimp-1 siRNA inhibits B cell differentiation and prevents the development of lupus in mice

Cumulative evidence suggest that B-lymphocytes play a role in the development of systemic lupus erythematosus (SLE). Thus, the therapeutic approach targeting specific B cells provides a promising way to treat SLE. Blimp-1 (B lymphocyte induced maturation protein), a transcriptional factor, controls the terminal differentiation of mature B cells to plasma cells. To explore the potential of Blimp-1 in the SLE development, we constructed the adenovirus encoding Blimp-1 siRNA, and injected it into BWF1 lupus mice. The results demonstrated that Blimp-1 siRNA decreased the Blimp-1 expression of B cells by regulating XBP-1 (X Box binding protein-1), BCMA (B-cell maturation antigen) expression through c-myc pathway. In addition, Blimp-1 siRNA eliminated anti-dsDNA antibody-producing plsma cells, reduced serum anti-dsDNA antibody levels and impeded the development of lupus. Therefore, our data provide the insight into the mechanism of Blimp-1 in SLE development and might represent a promising therapeutic strategy for autoantibody-mediated diseases.

Dendritic cells in systemic lupus erythematosus

Systemic lupus erythematosus (SLE) persists as a chronic inflammatory autoimmune disease and is characterized by the production of autoantibodies and immune complexes that affect multiple organs. The underlying mechanism that triggers and sustains disease are complex and involve certain susceptibility genes and environmental factors. There have been several immune mediators linked to SLE including cytokines and chemokines that have been reviewed elsewhere [ 1-3 ]. A number of articles have reviewed the role of B cells and T cells in SLE [ 4-10 ]. Here, we focus on the role of dendritic cells (DC) and innate immune factors that may regulate autoreactive B cells.

Innate pathways to B-cell activation and tolerance

B cells represent an important link between the adaptive and innate immune systems as they express both antigen-specific B-cell receptors (BCRs) as well as various Toll-like receptors (TLRs). Several checkpoints in B-cell development ensure that self-specific cells are eliminated from the mature B-cell repertoire to avoid harmful autoreactive responses. These checkpoints are controlled by BCR-mediated events but are also influenced by TLR-dependent signals from the innate immune system. Additionally, B-cell-intrinsic and extrinsic TLR signaling are critical for inflammatory events required for the clearance of microbial infections. Factors secreted by TLR-activated macrophages or dendritic cells directly influence the fate of protective and autoreactive B cells. Additionally, naive and memory B cells respond differentially to TLR ligands, as do different B-cell subsets. We review here recent literature describing intrinsic and extrinsic effects of TLR stimulation on the fate of B cells, with particular attention to autoimmune diseases.