Salmonella SiiE prevents an efficient humoral immune memory by interfering with IgG+ plasma cell persistence in the bone marrow.

Serum IgG, which is mainly generated from IgG-secreting plasma cells in the bone marrow (BM), protects our body against various pathogens. We show here that the protein SiiE of Salmonella is both required and sufficient to prevent an efficient humoral immune memory against the pathogen by selectively reducing the number of IgG-secreting plasma cells in the BM. Attenuated SiiE-deficient Salmonella induces high and lasting titers of specific and protective Salmonella-specific IgG and qualifies as an efficient vaccine against Salmonella A SiiE-derived peptide with homology to laminin ß1 is sufficient to ablate IgG-secreting plasma cells from the BM, identifying laminin ß1 as a component of niches for IgG-secreting plasma cells in the BM, and furthermore, qualifies it as a unique therapeutic option to selectively ablate IgG-secreting plasma cells in autoimmune diseases and multiple myeloma.

Interleukin-36 receptor mediates the crosstalk between plasma cells and synovial fibroblasts.

The IL-1 family member IL-36α has proinflammatory and pathogenic properties in psoriasis. IL-36α binds to the IL-36 receptor leading to nuclear factor kappa B/mitogen activated protein kinase mediated cytokine release. The IL-36R antagonist prevents recruitment of IL-1 receptor accessory protein and therefore IL-36-dependent cell activation. In inflamed human tissue, we previously could show that resident B cells and plasma cells (PC) express IL-36α. Further, fibroblast-like synoviocytes (FLS) produced proinflammatory cytokines upon IL-36α-stimulation. We hypothesize an IL-36-specific crosstalk between B cells/PCs and FLS permitting a proinflammatory B cell niche. Here, we firstly demonstrated that B cell lines and B cells from healthy donors express IL-36α and stimulation increased IL-36α in B cells and primary plasmablasts/PCs. Moreover, FLS respond specifically to IL-36α by proliferation and production of matrix metalloproteinases via p38/HSP27 signaling. Importantly, IL-36R-deficiency abrogated IL-36α-induced production of inflammatory mediators in FLS and changed the intrinsic FLS-phenotype. Using an in vitro co-culture system, we could show that IL-36R-deficient FLS had a limited capacity to support PC survival compared to wild-type FLS. Hence, we demonstrated an IL-36R-dependent crosstalk between B cells/PCs and FLS. Our data support the concept of initiation and maintenance of a proinflammatory niche by B cells in the joints.

High Usability and Applicability Ratings for the New SmartClic®/ClicWise® Injection Device: Evidence from a Health Care Professional Opinion Study.

INTRODUCTION: The SmartClic®/ClicWise® autoinjector is a new reusable, multi-use, single-patient device for the administration of subcutaneously administered biologics in the treatment of chronic conditions, including rheumatoid arthritis. The device will be used in conjunction with a mobile application (app). The aim of this study was to collect feedback on the usability, functionality, and applicability of the device and the companion app from health care professionals (HCPs) who perform injections as part of their role and care for patients with rheumatic conditions. METHODS: The study was conducted from September to October 2020 in Germany. HCPs participated in a training session for the device and gained experience by performing simulated injections with water. Following the simulations, HCPs answered questions on the ease of use, feature design, effectiveness, and injection speed of the SmartClic/ClicWise device and estimate the patient training time required. They also answered questions on the functionality of the proposed app after attending a storyboard presentation. Responses were recorded as multiple-choice answers, Likert scale ratings (seven-point scale), or open-ended comments. The mean, median, and mode scores were recorded. RESULTS: Twenty-five HCPs (mean age, 38.2 years; females, n = 22 [88%]; registered nurses, n = 19 [76%]) participated in the study. HCP feedback on questions related to the SmartClic/ClicWise device was positive overall, with mean scores > 4.50 across questions; mean scores < 5.00 were reported on 2/40 questions. Twenty-four of 25 participants (96%) estimated that a training time of ≤ 20 min would suffice for patients learning to use the device. Positive feedback was also reported on questions related to the companion app, with mean scores > 5.70. CONCLUSIONS: Initial feedback from HCPs on the SmartClic/ClicWise device and proposed app was generally favorable, suggesting they will provide an acceptable alternative for self-administration of biologics for patients with rheumatoid arthritis and other chronic conditions.

Data-Driven Mathematical Model of Apoptosis Regulation in Memory Plasma Cells.

Memory plasma cells constitutively produce copious amounts of antibodies, imposing a critical risk factor for autoimmune disease. We previously found that plasma cell survival requires secreted factors such as APRIL and direct contact to stromal cells, which act in concert to activate NF-κB- and PI3K-dependent signaling pathways to prevent cell death. However, the regulatory properties of the underlying biochemical network are confounded by the complexity of potential interaction and cross-regulation pathways. Here, based on flow-cytometric quantification of key signaling proteins in the presence or absence of the survival signals APRIL and contact to the stromal cell line ST2, we generated a quantitative model of plasma cell survival. Our model emphasizes the non-redundant nature of the two plasma cell survival signals APRIL and stromal cell contact, and highlights a requirement for differential regulation of individual caspases. The modeling approach allowed us to unify distinct data sets and derive a consistent picture of the intertwined signaling and apoptosis pathways regulating plasma cell survival.

Stromal Cell-Contact Dependent PI3K and APRIL Induced NF-κB Signaling Prevent Mitochondrial- and ER Stress Induced Death of Memory Plasma Cells.

The persistence of long-lived memory plasma cells in the bone marrow depends on survival factors available in the bone marrow, which are provided in niches organized by stromal cells. Using an ex vivo system in which we supply the known survival signals, direct cell contact to stromal cells, and the soluble cytokine a proliferation-inducing ligand (APRIL), we have elucidated the critical signaling pathways required for the survival of long-lived plasma cells. Integrin-mediated contact of bone marrow plasma cells with stromal cells activates the phosphatidylinositol 3-kinase (PI3K) signaling pathway, leading to critical inactivation of Forkhead-Box-Protein O1/3 (FoxO1/3) and preventing the activation of mitochondrial stress-associated effector caspases 3 and 7. Accordingly, inhibition of PI3K signaling in vivo ablates bone marrow plasma cells. APRIL signaling, by the nuclear factor κB (NF-κB) pathway, blocks activation of the endoplasmic-reticulum-stress-associated initiator caspase 12. Thus, stromal-cell-contact-induced PI3K and APRIL-induced NF-κB signaling provide the necessary and complementary signals to maintain bone marrow memory plasma cells.

Discrete populations of isotype-switched memory B lymphocytes are maintained in murine spleen and bone marrow.

At present, it is not clear how memory B lymphocytes are maintained over time, and whether only as circulating cells or also residing in particular tissues. Here we describe distinct populations of isotype-switched memory B lymphocytes (Bsm) of murine spleen and bone marrow, identified according to individual transcriptional signature and B cell receptor repertoire. A population of marginal zone-like cells is located exclusively in the spleen, while a population of quiescent Bsm is found only in the bone marrow. Three further resident populations, present in spleen and bone marrow, represent transitional and follicular B cells and B1 cells, respectively. A population representing 10-20% of spleen and bone marrow memory B cells is the only one qualifying as circulating. In the bone marrow, all cells individually dock onto VCAM1+ stromal cells and, reminiscent of resident memory T and plasma cells, are void of activation, proliferation and mobility.

Transparent Substrates Prepared From Different Amorphous Polymers Can Directly Modulate Primary Human B cell functions.

Manipulation of B cell functions such as antibody and cytokine secretion, is of clinical and biotechnological interest and can be achieved by soluble ligands activating cell surface receptors. Alternatively, the exposure to suitable solid substrates would offer the possibility to transiently induced cell signaling, since the signaling is interrupted when the cells are removed from the substrate. Cell/substrate interactions are mediated by physical valences such as, hydrogen bonds or hydrophobic forces on the substrate surface. Therefore, in this study B cells were cultivated on polymeric substrates, differing in their chemical composition and thus their capacity to undergo physical interactions. Activated B cells cultivated on polystyrene (PS) showed an altered cytokine response indicated by increased IL-10 and decreased IL-6 secretion. Interestingly, B cells cultivated on polyetherurethane (PEU), which has among all tested polymers the highest potential to form strong hydrogen bonds showed an impaired activation, which could be restored by re-cultivation on tissue culture polystyrene. The results indicate that B cell behavior can transiently be manipulated solely by interacting with polymeric surface, which could be explained by receptor activation mediated by physical interaction with the substrate or by altering the availability of the soluble stimulatory reagents by adsorption processes.

Plasmablasts With a Mucosal Phenotype Contribute to Plasmacytosis in Systemic Lupus Erythematosus.

OBJECTIVE: To analyze the composition of known plasmacytosis in systemic lupus erythematosus (SLE) to obtain further insight into the nature of underlying mechanisms. METHODS: Plasmablasts from patients with active SLE, patients with inactive/treated SLE, and healthy controls were characterized by flow cytometry, enzyme-linked immunospot assay, and Transwell migration assays and compared to vaccination-induced plasmablasts. Serum cytokine levels were analyzed by Luminex assay, and histologic analysis of kidney biopsy specimens was performed. RESULTS: Circulating plasmablasts in SLE expressed markers of mucosal immune reactions. IgA, CCR10, and ß7 integrin were expressed by 48%, 40%, and 38% of plasmablasts, respectively, with varying coexpression patterns. Consistent with mucosal homing, some SLE plasmablasts migrated toward the mucosal chemokine CCL28 and secreted polymeric IgA. SLE plasmablasts shared phenotypic characteristics with antigen-specific plasmablasts induced by oral, but not parenteral, vaccinations. Autoreactive antibody-secreting cells of the IgG and IgA isotypes were detectable, but only the emergence of phenotypically mucosal plasmablasts was positively associated with serum interleukin-2 and platelet-derived growth factor BB levels. CONCLUSION: Our data suggest that distinct plasmablast differentiation pathways jointly contribute to peripheral plasmacytosis in SLE, i.e., a cytokine-amplified mucosal "steady-state" plasmablast response, and an autoreactive plasmablast response, representing conventional autoimmunity. Our results indicate an overly activated mucosal immune system in patients with SLE, with both immunologic and clinical implications.