Antigen-driven PD-1+ TOX+ BHLHE40+ and PD-1+ TOX+ EOMES+ T lymphocytes regulate juvenile idiopathic arthritis in situ

T lymphocytes accumulate in inflamed tissues of patients with chronic inflammatory diseases (CIDs) and express pro-inflammatory cytokines upon re-stimulation in vitro. Further, a significant genetic linkage to MHC genes suggests that T lymphocytes play an important role in the pathogenesis of CIDs including juvenile idiopathic arthritis (JIA). However, the functions of T lymphocytes in established disease remain elusive. Here we dissect the transcriptional and the clonal heterogeneity of synovial T lymphocytes in JIA patients by single-cell RNA sequencing combined with T cell receptor profiling on the same cells. We identify clonally expanded subpopulations of T lymphocytes expressing genes reflecting recent activation by antigen in situ. A PD-1⁺ TOX⁺ EOMES⁺ population of CD4⁺ T lymphocytes expressed immune regulatory genes and chemoattractant genes for myeloid cells. A PD-1⁺ TOX⁺ BHLHE40⁺ population of CD4⁺ , and a mirror population of CD8⁺ T lymphocytes expressed genes driving inflammation, and genes supporting B lymphocyte activation in situ. This analysis points out that multiple types of T lymphocytes have to be targeted for therapeutic regeneration of tolerance in arthritis.

B Cells Producing Type I IFN Modulate Macrophage Polarization in Tuberculosis

RATIONALE

In addition to their well-known function as antibody-producing cells, B lymphocytes can markedly influence the course of infectious or noninfectious diseases via antibody-independent mechanisms. In tuberculosis (TB), B cells accumulate in lungs, yet their functional contribution to the host response remains poorly understood.

OBJECTIVES

To document the role of B cells in TB in an unbiased manner.

METHODS

We generated the transcriptome of B cells isolated from Mycobacterium tuberculosis (Mtb)-infected mice and validated the identified key pathways using in vitro and in vivo assays. The obtained data were substantiated using B cells from pleural effusion of patients with TB.

MEASUREMENTS AND MAIN RESULTS

B cells isolated from Mtb-infected mice displayed a STAT1 (signal transducer and activator of transcription 1)-centered signature, suggesting a role for IFNs in B-cell response to infection. B cells stimulated in vitro with Mtb produced type I IFN, via a mechanism involving the innate sensor STING (stimulator of interferon genes), and antagonized by MyD88 (myeloid differentiation primary response 88) signaling. In vivo, B cells expressed type I IFN in the lungs of Mtb-infected mice and, of clinical relevance, in pleural fluid from patients with TB. Type I IFN expression by B cells induced an altered polarization of macrophages toward a regulatory/antiinflammatory profile in vitro. In vivo, increased provision of type I IFN by B cells in a murine model of B cell-restricted Myd88 deficiency correlated with an enhanced accumulation of regulatory/antiinflammatory macrophages in Mtb-infected lungs.

CONCLUSIONS

Type I IFN produced by Mtb-stimulated B cells favors macrophage polarization toward a regulatory/antiinflammatory phenotype during Mtb infection.

LAG-3 Inhibitory Receptor Expression Identifies Immunosuppressive Natural Regulatory Plasma Cells

B lymphocytes can suppress immunity through interleukin (IL)-10 production in infectious, autoimmune, and malignant diseases. Here, we have identified a natural plasma cell subset that distinctively expresses the inhibitory receptor LAG-3 and mediates this function in vivo. These plasma cells also express the inhibitory receptors CD200, PD-L1, and PD-L2. They develop from various B cell subsets in a B cell receptor (BCR)-dependent manner independently of microbiota in naive mice. After challenge they upregulate IL-10 expression via a Toll-like receptor-driven mechanism within hours and without proliferating. This function is associated with a unique transcriptome and epigenome, including the lowest amount of DNA methylation at the Il10 locus compared to other B cell subsets. Their augmented accumulation in naive mutant mice with increased BCR signaling correlates with the inhibition of memory T cell formation and vaccine efficacy after challenge. These natural regulatory plasma cells may be of broad relevance for disease intervention.

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LAG-3 expression identifies natural regulatory plasma cells

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LAG-3⁺CD138^hi plasma cells express IL-10 within hours of stimulation

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LAG-3⁺CD138^hi plasma cells have a unique epigenome poised to express IL-10

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LAG-3⁺CD138^hi plasma cells develop via an antigen-specific mechanism

B-type suppression: a role played by "regulatory B cells" or "regulatory plasma cells"?

B-cell depletion can improve disease in some patients with rheumatoid arthritis or multiple sclerosis, indicating the pathogenic contribution of B cells to autoimmunity. However, studies in mice have demonstrated that B cells have immunosuppressive functions as well, with IL-10 being a critical mediator of B-cell-mediated suppression. IL-10-secreting B cells have been shown to promote disease remission in some mouse models of autoimmune disorders. Human B cells also produce IL-10, and evidence is accumulating that human IL-10-producing B cells might inhibit immunity. There is considerable interest in identifying the phenotype of B cells providing IL-10 in a suppressive manner, which would facilitate the analysis of the molecular mechanisms controlling this B-cell property. Here, we review current knowledge on the B-cell subpopulations found to provide suppressive functions in mice, considering both the pathological context in which they were identified and the signals that control their induction. We discuss the phenotype of B cells that have IL-10-dependent regulatory activities in mice, which leads us to propose that antibody-secreting cells are, in some cases at least, the major source of B-cell-derived regulatory IL-10 in vivo. Anti-inflammatory cytokine production by antibody-secreting cells offers a novel mechanism for the coordination of innate and humoral immune responses.

Interleukin-10-producing B cells and the regulation of immunity

B cells are usually considered primarily for their unique capacity to produce antibodies after differentiation into plasma cells. In addition to their roles as antibody-producing cells, it has become apparent during the last 10 years that B cells also perform important functions in immunity through the production of cytokines. In particular, it was shown that B cells could negatively regulate immunity through provision of interleukin (IL)-10 during autoimmune and infectious diseases in mice. Here, we review data on the suppressive functions of B cells in mice with particular emphasis on the signals controlling the acquisition of such suppressive functions by B cells, the phenotype of the B cells involved in the negative regulation of immunity, and the processes targeted by this inhibitory circuit. Finally, we discuss the possibility that human B cells might also perform similar inhibitory functions through the provision of IL-10, and review data suggesting that such B cell-mediated regulatory activities might be impaired in patients with autoimmune diseases.

Mannose phosphorylation in health and disease

Lysosomal hydrolases catalyze the degradation of a variety of macromolecules including proteins, carbohydrates, nucleic acids and lipids. The biogenesis of lysosomes or lysosome-related organelles requires a continuous substitution of soluble acid hydrolases and lysosomal membrane proteins. The targeting of lysosomal hydrolases depends on mannose 6-phosphate residues (M6P) that are recognized by specific receptors mediating their transport to an endosomal/prelysosomal compartment. The key role in the formation of M6P residues plays the GlcNAc-1-phosphotransferase localized in the Golgi apparatus. Two genes have been identified recently encoding the type III alpha/beta-subunit precursor membrane protein and the soluble gamma-subunit of GlcNAc-1-phosphotransferase. Mutations in these genes result in two severe diseases, mucolipidosis type II (MLII) and III (MLIII), biochemically characterized by the missorting of multiple lysosomal hydrolases due to impaired formation of the M6P recognition marker, and general lysosomal dysfunction. This review gives an update on structural properties, localization and functions of the GlcNAc-1-phosphotransferase subunits and improvements of pre- and postnatal diagnosis of ML patients. Further, the generation of recombinant single-chain antibody fragments against M6P residues and of new mouse models of MLII and MLIII will have considerable impact to provide deeper insight into the cell biology of lysosomal dysfunctions and the pathomechanisms underlying these lysosomal disorders.

The Rho GDI Rdi1 regulates Rho GTPases by distinct mechanisms

The small guanosine triphosphate (GTP)-binding proteins of the Rho family are implicated in various cell functions, including establishment and maintenance of cell polarity. Activity of Rho guanosine triphosphatases (GTPases) is not only regulated by guanine nucleotide exchange factors and GTPase-activating proteins but also by guanine nucleotide dissociation inhibitors (GDIs). These proteins have the ability to extract Rho proteins from membranes and keep them in an inactive cytosolic complex. Here, we show that Rdi1, the sole Rho GDI of the yeast Saccharomyces cerevisiae, contributes to pseudohyphal growth and mitotic exit. Rdi1 interacts only with Cdc42, Rho1, and Rho4, and it regulates these Rho GTPases by distinct mechanisms. Binding between Rdi1 and Cdc42 as well as Rho1 is modulated by the Cdc42 effector and p21-activated kinase Cla4. After membrane extraction mediated by Rdi1, Rho4 is degraded by a novel mechanism, which includes the glycogen synthase kinase 3beta homologue Ygk3, vacuolar proteases, and the proteasome. Together, these results indicate that Rdi1 uses distinct modes of regulation for different Rho GTPases.