The lipid globotriaosylceramide promotes germinal center B cell responses and antiviral immunity.

Influenza viruses escape immunity owing to rapid antigenic evolution, which requires vaccination strategies that allow for broadly protective antibody responses. We found that the lipid globotriaosylceramide (Gb3) expressed on germinal center (GC) B cells is essential for the production of high-affinity antibodies. Mechanistically, Gb3 bound and disengaged CD19 from its chaperone CD81, permitting CD19 to translocate to the B cell receptor complex to trigger signaling. Moreover, Gb3 regulated major histocompatibility complex class II expression to increase diversity of T follicular helper and GC B cells reactive with subdominant epitopes. In influenza infection, elevating Gb3, either endogenously or exogenously, promoted broadly reactive antibody responses and cross-protection. These data demonstrate that Gb3 determines the affinity and breadth of B cell immunity and has potential as a vaccine adjuvant.

Arctigenin inhibits abnormal germinal center reactions and attenuates murine lupus by inhibiting IFN-I pathway.

Interferon-I (IFN-I) signaling pathway plays a vital role in the differentiation of germinal center B cells and the pathogenesis of systemic lupus erythematosus (SLE). Therefore, targeting the IFN-I signaling pathway could serve as an effective treatment strategy in SLE. Arctigenin is an active ingredient present in the seeds of Arctium lappa L. It has been reported to act as a negative regulator of inflammatory responses. However, the role of arctigenin remains unknown in the regulation process of the IFN-I-mediated differentiation of germinal center B cells and the pathogenesis of SLE. In the present study, we demonstrated that arctigenin alleviated the progression of spontaneous lupus in MRL/lpr mice and imiquimod-mediated lupus mice. Especially, arctigenin significantly reduced the proportions of germinal center B cells (7.1%, vs. 5.12%, p < 0.01), follicular helper T cells (11.49%, vs. 5.53%, p < 0.05), and plasma cells (2.44%, vs. 1.39%, p < 0.01) in the lupus-prone mice. In vitro studies have shown that arctigenin significantly inhibited the IFN-α-induced CD69 and interferon-stimulated gene (ISG) expressions along with the phosphorylation of JAK1 and STAT1 by nearly half in murine B cells via activating PP2A. Overall, these data highlighted the role of arctigenin in regulating the IFN-I-mediated differentiation of germinal center B cells and the pathogenesis of SLE. Thus, arctigenin may be used as a potentially effective therapeutic target for the treatment of SLE.

BET-bromodomain and EZH2 inhibitor-treated chronic GVHD mice have blunted germinal centers with distinct transcriptomes.

Despite advances in the field, chronic graft-versus-host-disease (cGVHD) remains a leading cause of morbidity and mortality following allogenic hematopoietic stem cell transplant. Because treatment options remain limited, we tested efficacy of anticancer, chromatin-modifying enzyme inhibitors in a clinically relevant murine model of cGVHD with bronchiolitis obliterans (BO). We observed that the novel enhancer of zeste homolog 2 (EZH2) inhibitor JQ5 and the BET-bromodomain inhibitor JQ1 each improved pulmonary function; impaired the germinal center (GC) reaction, a prerequisite in cGVHD/BO pathogenesis; and JQ5 reduced EZH2-mediated H3K27me3 in donor T cells. Using conditional EZH2 knockout donor cells, we demonstrated that EZH2 is obligatory for the initiation of cGVHD/BO. In a sclerodermatous cGVHD model, JQ5 reduced the severity of cutaneous lesions. To determine how the 2 drugs could lead to the same physiological improvements while targeting unique epigenetic processes, we analyzed the transcriptomes of splenic GCB cells (GCBs) from transplanted mice treated with either drug. Multiple inflammatory and signaling pathways enriched in cGVHD/BO GCBs were reduced by each drug. GCBs from JQ5- but not JQ1-treated mice were enriched for proproliferative pathways also seen in GCBs from bone marrow-only transplanted mice, likely reflecting their underlying biology in the unperturbed state. In conjunction with in vivo data, these insights led us to conclude that epigenetic targeting of the GC is a viable clinical approach for the treatment of cGVHD, and that the EZH2 inhibitor JQ5 and the BET-bromodomain inhibitor JQ1 demonstrated clinical potential for EZH2i and BETi in patients with cGVHD/BO.

An orally available small molecule BCL6 inhibitor effectively suppresses diffuse large B cell lymphoma cells growth in vitro and in vivo.

The transcription factor B cell lymphoma 6 (BCL6) is an oncogenic driver of diffuse large B cell lymphoma (DLBCL) and mediates lymphomagenesis through transcriptional repression of its target genes by recruiting corepressors to its N-terminal broad-complex/tramtrack/bric-a-brac (BTB) domain. Blocking the protein-protein interactions of BCL6 and its corepressors has been proposed as an effective approach for the treatment of DLBCL. However, BCL6 inhibitors with excellent drug-like properties are rare. Hence, the development of BCL6 inhibitors is worth pursuing. We screened our internal chemical library by luciferase reporter assay and Homogenous Time Resolved Fluorescence (HTRF) assay and a small molecule compound named WK500B was identified. WK500B engaged BCL6 inside cells, blocked BCL6 repression complexes, reactivated BCL6 target genes, killed DLBCL cells and caused apoptosis as well as cell cycle arrest. In animal models, WK500B inhibited germinal center (GC) formation and DLBCL tumour growth without toxic and side effects. Moreover, WK500B displayed strong efficacy and favourable pharmacokinetics and presented superior druggability. Therefore, WK500B is a promising candidate that could be developed as an effective orally available therapeutic agent for DLBCL.

Negative feedback by NUR77/Nr4a1 restrains B cell clonal dominance during early T-dependent immune responses.

B cell clones compete for entry into and dominance within germinal centers (GCs), where the highest-affinity B cell receptors (BCRs) are selected. However, diverse and low-affinity B cells can enter and reside in GCs for extended periods. To reconcile these observations, we hypothesize that a negative feedback loop may operate within B cells to preferentially restrain high-affinity clones from monopolizing the early GC niche. Here, we report a role for the nuclear receptor NUR77/Nr4a1 in this process. We show that NUR77 expression scales with antigen stimulation and restrains B cell expansion. Although NUR77 is dispensable for regulating GC size when GCs are elicited in a largely clonal manner, it serves to curb immunodominance under conditions where diverse clonal populations must compete for a constrained niche. We propose that this is important to preserve early clonal diversity in order to limit holes in the post-immune repertoire and to optimize GC selection.

SMS2 deficiency impairs PKCδ-regulated B cell tolerance in the germinal center.

B cell tolerance prevents autoimmunity by deleting or deactivating autoreactive B cells that otherwise may cause autoantibody-driven disorders, including systemic lupus erythematosus (lupus). Lupus is characterized by immunoglobulin Gs carrying a double-stranded (ds)-DNA autospecificity derived mainly from somatic hypermutation in the germinal center (GC), pointing to a checkpoint breach of GC B cell tolerance that leads to lupus. However, tolerance mechanisms in the GC remain poorly understood. Here, we show that upregulated sphingomyelin synthase 2 (SMS2) in anti-dsDNA GC B cells induces apoptosis by directly activating protein kinase C δ (PKCδ)'s pro-apoptotic activity. This tolerance mechanism prevents lupus autoimmunity in C57/BL6 mice and can be stimulated pharmacologically to inhibit lupus pathogenesis in lupus-prone NZBWF1 mice. Patients with lupus consistently have substantially reduced SMS2 expression in B cells and to an even greater extent in autoimmune-prone, age-associated B cells, suggesting that patients with lupus have insufficient SMS2-regulated B cell tolerance.

Optimized immunofluorescence staining protocol for imaging germinal centers in secondary lymphoid tissues of vaccinated mice.

Location of immune cells that form the germinal center reaction within secondary lymphoid tissues can be characterized using confocal microscopy. Here, we present an optimized immunofluorescence staining protocol to image germinal center structures in fixed/frozen spleen sections from ChAdOx1 nCoV-19 immunized mice. This protocol can be adapted to identify other cell types within secondary lymphoid tissues. For complete information on the generation and use of this protocol to examine immune responses to the COVID vaccine ChAdOx1 nCoV-19, please refer to Silva-Cayetano et al. (2020).

BCL6 BTB-specific inhibitor reversely represses T-cell activation, Tfh cells differentiation, and germinal center reaction in vivo.

Inhibition of the BCL6 BTB domain results in killing Diffuse Large B-cell Lymphoma (DLBL) cells, reducing the T-cell dependent germinal center (GC) reaction in mice, and reversing GC hyperplasia in nonhuman primates. The available BCL6 BTB-specific inhibitors are poorly water soluble, thus, limiting their absorption in vivo and our understanding of therapeutic strategy targeting GC. We synthesized a prodrug (AP-4-287) from a potent BCL6 BTB inhibitor (FX1) with improved aqueous solubility and pharmacokinetics (PK) in mice. We also evaluated its in vivo biological activity on humoral immune responses using the sheep red blood cells (SRBC)-vaccination mouse model. AP-4-287 had a significant higher aqueous solubility and was readily converted to FX1 in vivo after intraperitoneally (i.p.) administration, but a shorter half-life in vivo. Importantly, AP-4-287 treatment led to a reversible effect on (1) the reduction in the frequency of splenic Ki67+ CD4+ T cells, Tfh cells, and GC B cells; (2) lower GC formation following vaccination; and (3) a decrease in the titers of antigen-specific IgG and IgM antibodies. Our study advances the preclinical development of drug targeting BCL6 BTB domain for the treatment of diseases that are associated with abnormal BCL6 elevation.

Rap1 Is Essential for B-Cell Locomotion, Germinal Center Formation and Normal B-1a Cell Population.

Integrin regulation by Rap1 is indispensable for lymphocyte recirculation. In mice having B-cell-specific Rap1a/b double knockouts (DKO), the number of B cells in lymph nodes decreased to approximately 4% of that of control mice, and B cells were present in the spleen and blood. Upon the immunization with NP-CGG, DKO mice demonstrated the defective GC formation in the spleen, and the reduced NP-specific antibody production. In vitro, Rap1 deficiency impaired the movement of activated B cells along the gradients of chemoattractants known to be critical for their localization in the follicles. Furthermore, B-1a cells were almost completely absent in the peritoneal cavity, spleen and blood of adult DKO mice, and the number of B-cell progenitor/precursor (B-p) were reduced in neonatal and fetal livers. However, DKO B-ps normally proliferated, and differentiated into IgM+ cells in the presence of IL-7. CXCL12-dependent migration of B-ps on the VCAM-1 was severely impaired by Rap1 deficiency. Immunostaining study of fetal livers revealed defects in the co-localization of DKO B-ps and IL-7-producing stromal cells. This study proposes that the profound effects of Rap1-deficiency on humoral responses and B-1a cell generation may be due to or in part caused by impairments of the chemoattractant-dependent positioning and the contact with stromal cells.

Homotypic aggregates contribute to heterogeneity in B cell fates due to an intrinsic gradient of stimulant exposure.

Monocultures of several cell types result in the formation of robust clusters called homotypic aggregates (HAs). How this physical aggregation affects cell fates in immune cell cultures, is poorly understood. We studied anti-CD40-stimulated primary B cell cultures, where cells assembled into large three-dimensional LFA1-driven HAs by 72 h. The dense packing in these aggregates restricts the infiltration of stimulants, such as antibodies, to cells inside the clusters. This creates a concentration gradient of stimulant availability across the cross-section of HAs. We describe a method to retain this positional information even after the disruption of HAs, for analysis by flow cytometry. Comparison of stage-specific cell-surface markers showed that the extent of stimulant-binding affected multiple fates non-uniformly. While germinal center and lineage markers were moderately upregulated, immunoglobulins and markers associated with memory were more than doubled in the peripheral cells binding more anti-CD40. These cells also experienced a strong repression of the plasma cell regulator Prdm1 and an upregulation of the oncogene Myc. Thus, cells at different locations in HAs are subjected to unequal doses of stimulants, leading to a hitherto unreported source of heterogeneity in cell fates. These findings can be extrapolated to understand the dose-dependent effects of stimulants in other three-dimensional cell clusters.

Lycium barbarum Polysaccharide Ameliorates Sjögren's Syndrome in a Murine Model.

SCOPE: This study aims to evaluate the therapeutic efficacy and mechanisms of Lycium barbarum polysaccharide (LBP) in primary Sjögren's syndrome (pSS). METHODS AND RESULTS: Non-obese diabetic mice (the pSS model) are randomly divided into four groups: Low dose LBP (LBP.L, 5 mg kg-1  d-1 ), high dose LBP (10 mg kg-1  d-1 ), low dose interleukin (IL)-2 (25 000 IU/d), and control (saline water). Drugs were treated for 12 weeks. LBP.L significantly reduces the salivary gland inflammation compared with the control group (histological score p LBP.L vs Control  = 0.019; foci number: p LBP.L vs Control  = 0.038). LBP.L also remarkably reduces the effector follicular helper T (Tfh) cells and the CD4+ IL-17A+ helper T (Th17) cells in both spleen and cervical lymph node (cLN) cells. Additionally, the ratios of regulatory T cell (Treg)/Tfh cells and Treg/Th17 cells are substantially increased in mice treated with LBP.L in both spleen and cLNs. LBP also inhibits Th17 and Tfh cells and markedly increases the Treg/Tfh ratio in human peripheral blood mononuclear cells. CONCLUSION: LBP.L inhibits the progression of pSS in mice, associated with modulation of T cell differentiation.

IL-21 Receptor Blockade Shifts the Follicular T Cell Balance and Reduces De Novo Donor-Specific Antibody Generation.

Donor-specific antibodies (DSAs) play a key role in chronic kidney allograft injury. Follicular T helper (Tfh) cells trigger the humoral alloimmune response and promote DSA generation, while T-follicular regulatory (Tfr) cells inhibit antibody production by suppressing Tfh and B cells. Interleukin (IL)-21 exerts a distinct effect on Tfh and Tfr. Here, we studied whether blocking IL-21R with anti-IL-21R monoclonal antibody (αIL-21R) changes the Tfh/Tfr balance and inhibits DSA generation. First, we investigated the impact of αIL-21R on CD4+ T cell proliferation and apoptosis. The results showed that αIL-21R did not have cytotoxic effects on CD4+ T cells. Next, we examined Tfh and regulatory T cells (Tregs) in an in vitro conditioned culture model. Naïve CD4+ T cells were isolated from 3-month-old C57BL/6 mice and cultured in Tfh differentiation inducing conditions in presence of αIL-21R or isotype IgG and differentiation was evaluated by CXCR5 expression, a key Tfh marker. αIL-21R significantly inhibited Tfh differentiation. In contrast, under Treg differentiation conditions, FOXP3 expression was inhibited by IL-21. Notably, αIL-21R rescued IL-21-inhibited Treg differentiation. For in vivo investigation, a fully mismatched skin transplantation model was utilized to trigger the humoral alloimmune response. Consistently, flow cytometry revealed a reduced Tfh/Tfr ratio in recipients treated with αIL-21R. Germinal center response was evaluated by flow cytometry and lectin histochemistry. We observed that αIL-21R significantly inhibited germinal center reaction. Most importantly, DSA levels after transplantation were significantly inhibited by αIL-21R at different time points. In summary, our results demonstrate that αIL-21R shifts the Tfh/Tfr balance toward DSA inhibition. Therefore, αIL-21R may be a useful therapeutic agent to prevent chronic antibody mediated rejection after organ transplantation.

Follicular helper T cells: potential therapeutic targets in rheumatoid arthritis.

Rheumatoid arthritis (RA) is a chronic autoimmune disease with joint and systemic inflammation that is accompanied by the production of autoantibodies, such as rheumatoid factor and anti-cyclic citrullinated peptide (anti-CCP) antibodies. Follicular helper T (Tfh) cells, which are a subset of CD4+ T cells, facilitate germinal center (GC) reactions by providing signals required for high-affinity antibody production and the generation of long-lived antibody-secreting plasma cells. Uncontrolled expansion of Tfh cells is observed in various systemic autoimmune diseases. Particularly, the frequencies of circulating Tfh-like (cTfh-like) cells, their subtypes and synovial-infiltrated T helper cells correlate with disease activity in RA patients. Therefore, reducing autoantibody production and restricting excessive Tfh cell responses are ideal ways to control RA pathogenesis. The present review summarizes current knowledge of the involvement of Tfh cells in RA pathogenesis and highlights the potential of these cells as therapeutic targets.

CQMUH-011 mitigates autoimmune hepatitis via inhibiting the function of T lymphocytes.

CQMUH-011 is a modified adamantane sulfonamide compound, that inhibits macrophage proliferation and possesses anti-inflammatory properties. Here, fresh mouse splenocytes were obtained and stimulated with concanavalin A (ConA, 5 µg/ml) in vitro; and experimental autoimmune hepatitis (AIH) was induced by ConA (20 mg/kg, iv) in vivo, to clarify the protective effects of CQMUH-011 against AIH and its possible mechanisms. Our results demonstrated that CQMUH-011 pretreatment can dose-dependently inhibit the proliferation of splenocytes in vitro. In vivo, CQMUH-011 administration reduced the hepatic histopathological score and the infiltration of lymphocytes in the liver parenchyma; additionally, it downregulated the levels of alanine aminotransferase (ALT), aspartate aminotransferase (AST) and pro-inflammatory cytokines interferon (IFN)-γ, tumor necrosis factor (TNF)-α, and interleukin (IL)-6 in serum, as well as those of methane dicarboxylic aldehyde and myeloperoxidase in the liver tissues. It also down-regulated the expression of p-NF-κB and related proteins in the liver tissues. Furthermore, CQMUH-011 could maintain the balance of CD3+ CD4+ /CD3+ CD8+ and decrease the percentages of CD8+ CD69+ and CD4+ CD25+/- CD69+ T-cells in the splenocytes of ConA-challenged mice. Moreover, we found thatCD4+ CD25+/- CD69+ T-cells were significantly correlated with ALT levels, especially CD4+ CD25- CD69+ T-cells. In conclusion, CQMUH-011 exerts potential protective effects against ConA-induced hepatitis, which may be partially attributed to its inhibition of T cells, especially the suppression of the proliferation of CD4+ CD25- CD69+ and CD8+ CD69+ subsets in the spleen. CQMUH-011 also reduced the early apoptosis of lymphocytes in the thymus.

Epstein-Barr virus latent membrane protein-1 upregulates autophagy and promotes viability in Hodgkin lymphoma: Implications for targeted therapy.

Hodgkin lymphoma (HL) is composed of neoplastic Hodgkin and Reed-Sternberg cells in an inflammatory background. The neoplastic cells are derived from germinal center B cells that, in most cases, are infected by Epstein-Barr virus (EBV), which may play a role in tumorigenesis. Given that EBV-latent membrane protein 1 (LMP1) regulates autophagy in B cells, we explored the role of autophagy mediated by EBV or LMP1 in HL. We found that EBV-LMP1 transfection in HL cells induced a modest increase in autophagy signals, attenuated starvation-induced autophagic stress, and alleviated autophagy inhibition- or doxorubicin-induced cell death. LMP1 knockdown leads to decreased autophagy LC3 signals. A xenograft mouse model further showed that EBV infection significantly increased expression of the autophagy marker LC3 in HL cells. Clinically, LC3 was expressed in 15% (19/127) of HL samples, but was absent in all cases of nodular lymphocyte-predominant and lymphocyte-rich classic HL cases. Although expression of LC3 was not correlated with EBV status or clinical outcome, autophagic blockade effectively eradicated LMP1-positive HL xenografts with better efficacy than LMP1-negative HL xenografts. Collectively, these results suggest that EBV-LMP1 enhances autophagy and promotes the viability of HL cells. Autophagic inhibition may be a potential therapeutic strategy for treating patients with HL, especially EBV-positive cases.

CTLA4-Ig-Based Bifunctional Costimulation Inhibitor Blocks CD28 and ICOS Signaling to Prevent T Cell Priming and Effector Function.

CTLA4-Ig/abatacept dampens activation of naive T cells by blocking costimulation via CD28. It is an approved drug for rheumatoid arthritis but failed to deliver efficacy in a number of other autoimmune diseases. One explanation is that activated T cells rely less on CD28 signaling and use alternate coreceptors for effector function. ICOS is critical for activation of T-dependent humoral immune responses, which drives pathophysiology of IgG-mediated autoimmune diseases. In this study, we asked whether CD28 and ICOS play nonredundant roles for maintenance of T-dependent responses in mouse models. Using a hapten-protein immunization model, we show that during an ongoing germinal center response, combination treatment with CTLA4-Ig and ICOS ligand (ICOSL) blocking Ab completely dissolves ongoing germinal center responses, whereas single agents show only partial activity. Next, we took two approaches to engineer a therapeutic molecule that blocks both pathways. First, we engineered CTLA4-Ig to enhance binding to ICOSL while retaining affinity to CD80/CD86. Using a library approach, binding affinity of CTLA4-Ig to human ICOSL was increased significantly from undetectable to 15-42 nM; however, the affinity was still insufficient to completely block binding of ICOSL to ICOS. Second, we designed a bispecific costimulation inhibitor with high-affinity CTLA4 extracellular domains fused to anti-ICOSL Ab termed bifunctional costimulation inhibitor. With this bispecific approach, we achieved complete inhibition of CD80 and CD86 binding to CD28 as well as ICOS binding to ICOSL. Such bispecific molecules may provide greater therapeutic benefit in IgG-mediated inflammatory diseases compared with CTLA4-Ig alone.

Double-hit Signature with TP53 Abnormalities Predicts Poor Survival in Patients with Germinal Center Type Diffuse Large B-cell Lymphoma Treated with R-CHOP.

PURPOSE: We performed detailed genomic analysis on 87 cases of de novo diffuse large B-cell lymphoma of germinal center type (GCB DLBCL) to identify characteristics that are associated with survival in those treated with R-CHOP (rituximab, cyclophosphamide, doxorubicin, vincristine, and prednisone). EXPERIMENTAL DESIGN: The cases were extensively characterized by combining the results of IHC, cell-of-origin gene expression profiling (GEP; NanoString), double-hit GEP (DLBCL90), FISH cytogenetic analysis for double/triple-hit lymphoma, copy-number analysis, and targeted deep sequencing using a custom mutation panel of 334 genes. RESULTS: We identified four distinct biologic subgroups with different survivals, and with similarities to the genomic classifications from two large retrospective studies of DLBCL. Patients with the double-hit signature, but no abnormalities of TP53, and those lacking EZH2 mutation and/or BCL2 translocation, had an excellent prognosis. However, patients with an EZB-like profile had an intermediate prognosis, whereas those with TP53 inactivation combined with the double-hit signature had an extremely poor prognosis. This latter finding was validated using two independent cohorts. CONCLUSIONS: We propose a practical schema to use genomic variables to risk-stratify patients with GCB DLBCL. This schema provides a promising new approach to identify high-risk patients for new and innovative therapies.

D-mannose ameliorates autoimmune phenotypes in mouse models of lupus.

BACKGROUND: Systemic lupus erythematosus is an autoimmune disease characterized by an overproduction of autoantibodies resulting from dysregulation in multiple immune cell types. D-mannose is a C- 2 epimer of glucose that exhibits immunoregulatory effects in models of autoimmune diseases, such as type 1 diabetes, induced rheumatoid arthritis, and airway inflammation. This study was conducted to evaluate the efficacy of D-mannose treatment in mouse models of lupus. RESULTS: Firstly, the effect of D-Mannose was evaluated by flow cytometry on the in vitro activation of non-autoimmune C57BL/6 (B6) bone marrow-derived dendritic cells (BMDCs) and their ability to induce antigen-specific CD4+ T cell proliferation and activation. D-mannose inhibited the maturation of BMDCs and their induction of antigen-specific T cell proliferation and activation. In vivo, D-mannose increased the frequency of Foxp3+ regulatory T cells in unmanipulated B6 mice. To assess the effect of D-mannose in mouse models of lupus, we used the graft-versus-host disease (cGVHD) induced model and the B6.lpr spontaneous model. In the cGVHD model, D-mannose treatment decreased autoantibody production, with a concomitant reduction of the frequency of effector memory and follicular helper T cells as well as germinal center B cells and plasma cells. These results were partially validated in the B6.lpr model of spontaneous lupus. CONCLUSION: Overall, our results suggest that D-mannose ameliorates autoimmune activation in models of lupus, at least partially due to its expansion of Treg cells, the induction of immature conventional dendritic cells and the downregulation of effector T cells activation. D-Mannose showed however a weaker immunomodulatory effect in lupus than in other autoimmune diseases.

Identification of BLNK and BTK as mediators of rituximab-induced programmed cell death by CRISPR screens in GCB-subtype diffuse large B-cell lymphoma.

Diffuse large B-cell lymphoma (DLBCL) is characterized by extensive genetic heterogeneity, and this results in unpredictable responses to the current treatment, R-CHOP, which consists of a cancer drug combination supplemented with the humanized CD20-targeting monoclonal antibody rituximab. Despite improvements in the patient response rate through rituximab addition to the treatment plan, up to 40% of DLBCL patients end in a relapsed or refractory state due to inherent or acquired resistance to the regimen. Here, we employ a lentiviral genome-wide clustered regularly interspaced short palindromic repeats library screening approach to identify genes involved in facilitating the rituximab response in cancerous B cells. Along with the CD20-encoding MS4A1 gene, we identify genes related to B-cell receptor (BCR) signaling as mediators of the intracellular signaling response to rituximab. More specifically, the B-cell linker protein (BLNK) and Bruton's tyrosine kinase (BTK) genes stand out as pivotal genes in facilitating direct rituximab-induced apoptosis through mechanisms that occur alongside complement-dependent cytotoxicity (CDC). Our findings demonstrate that rituximab triggers BCR signaling in a BLNK- and BTK-dependent manner and support the existing notion that intertwined CD20 and BCR signaling pathways in germinal center B-cell-like-subtype DLBCL lead to programmed cell death.

miR-146a in Myasthenia Gravis Thymus Bridges Innate Immunity With Autoimmunity and Is Linked to Therapeutic Effects of Corticosteroids.

Toll-like receptor (TLR)-mediated innate immune responses are critically involved in the pathogenesis of myasthenia gravis (MG), an autoimmune disorder affecting neuromuscular junction mainly mediated by antiacetylcholine receptor antibodies. Considerable evidence indicate that uncontrolled TLR activation and chronic inflammation significantly contribute to hyperplastic changes and germinal center (GC) formation in the MG thymus, ultimately leading to autoantibody production and autoimmunity. miR-146a is a key modulator of innate immunity, whose dysregulation has been associated with autoimmune diseases. It acts as inhibitor of TLR pathways, mainly by targeting the nuclear factor kappa B (NF-κB) signaling transducers, interleukin 1 receptor associated kinase 1 (IRAK1) and tumor necrosis factor (TNF) receptor associated factor 6 (TRAF6); miR-146a is also able to target c-REL, inducible T-cell costimulator (ICOS), and Fas cell surface death receptor (FAS), known to regulate B-cell function and GC response. Herein, we investigated the miR-146a contribution to the intrathymic MG pathogenesis. By real-time PCR, we found that miR-146a expression was significantly downregulated in hyperplastic MG compared to control thymuses; contrariwise, IRAK1, TRAF6, c-REL, and ICOS messenger RNA (mRNA) levels were upregulated and negatively correlated with miR-146a levels. Microdissection experiments revealed that miR-146a deficiency in hyperplastic MG thymuses was not due to GCs, but restricted to the GC-surrounding medulla, characterized by IRAK1 overexpression. We also showed higher c-REL and ICOS mRNA levels, and lower FAS mRNA levels, in GCs than in the remaining medulla, according to the contribution of these molecules in GC formation. By double immunofluorescence, an increased proportion of IRAK1-expressing dendritic cells and macrophages was found in hyperplastic MG compared to control thymuses, along with GC immunoreactivity for c-REL. Interestingly, in corticosteroid-treated MG patients intrathymic miR-146a and mRNA target levels were comparable to those of controls, suggesting that immunosuppressive therapy may restore the microRNA (miRNA) levels. Indeed, an effect of prednisone on miR-146a expression was demonstrated in vitro on peripheral blood cells. Serum miR-146a levels were lower in MG patients compared to controls, indicating dysregulation of the circulating miRNA. Our overall findings strongly suggest that defective miR-146a expression could contribute to persistent TLR activation, lack of inflammation resolution, and hyperplastic changes in MG thymuses, thus linking TLR-mediated innate immunity to B-cell-mediated autoimmunity. Furthermore, they unraveled a new mechanism of action of corticosteroids in inducing control of autoimmunity in MG via miR-146a.