Serine phosphorylation of the STAT1 transactivation domain promotes autoreactive B cell and systemic autoimmunity development

Although STAT1 tyrosine-701 phosphorylation (STAT1-pY701) is indispensable for STAT1 function, the requirement for STAT1 serine-727 phosphorylation (STAT1-pS727) during autoimmune and anti-pathogen responses remains unclear. Here we report that STAT1-pS727 promotes autoimmune antibody-forming cell (AFC) and germinal center (GC) responses, driving systemic lupus erythematosus (SLE) development. STAT1-pS727, however, is not required for GC and antibody responses to foreign-antigens including pathogens or gut microbiota. STAT1-pS727 plays an important B cell-intrinsic role in driving autoimmunity. Transcriptomic analysis of B cells from TLR7-accelerated SLE-prone mice reveals STAT1-pS727-mediated gene regulation of cellular pathways known to be involved in autoimmune GC and AFC responses. Mechanistically, TLR7 activation in B cells induces STAT1-pS727 and during autoimmune responses TLR7 signaling converges with IFNγ-STAT1 signaling in B cells by recruiting STAT1 into the MyD88 signaling complex. Together, we identify previously unappreciated differential regulation of autoimmune and anti-pathogen responses by STAT1-pS727, and implicate STAT1-pS727 as a therapeutic target for SLE.

B cell-intrinsic and lymphocyte extrinsic miR-21 drive optimal germinal center and antibody responses

Germinal centers (GCs) generate high affinity B cell responses that are protective against infection but can produce autoreactive responses when dysregulated. MicroRNAs (miRNAs) have been implicated in the regulation of GC fate, though the role of many individual miRNAs remains uncharacterized. Here, we demonstrate that within the GC, miR-21 promotes T follicular helper cell (Tfh), T follicular regulatory cell (Tfr), and GC B cell responses, as well as downstream antibody production. Regulation of the GC response by miR-21 requires multiple mechanisms, occurring in both B cells and innate cells. B cell-intrinsic miR-21 drives GC B cell expansion by promoting B cell activation and proliferation. MiR-21 target gene expression arrays have revealed several putative target genes in B cells, suggesting that miR-21 targets negative regulators of proliferative pathways to enhance B cell proliferation and GC responses. In contrast, Tfh and Tfr are driven by miR-21 in a B and T cell extrinsic manner, likely by innate cells. Our data suggest that miR-21 modifies the cytokine microenvironment, which impacts regulatory T cell expansion and Tfh programs. Therefore, the synergy of B cell intrinsic and lymphocyte extrinsic miR-21 activity is required to generate optimal GC and Ab responses. Of clinical relevance, we also found that upregulation of miR-21 in autoimmune-prone mice drives autoantibody responses, implicating miR-21 in both anti-pathogen responses and its dysregulation in autoimmunity. Therefore, dampening miR-21 function may provide a strategy for autoimmune therapeutics. Alternatively, boosting miR-21 activity in healthy individuals could allow more efficient generation of protective antibody following vaccination.

TLR7 and IFNγ signaling converge at STAT1 in B cells to control germinal center mediated autoimmunity

Toll like receptor 7 (TLR7) is required for the development of spontaneous germinal center (Spt-GC) mediated autoimmunity. Accordingly, autoimmune-prone B6.Sle1b mice carrying an extra copy of TLR7 in the Yaa locus (named B6.Sle1bYaa mice) exhibit significantly elevated Spt-GC responses that strongly correlate with exacerbation of lupus disease. However, the underlying molecular mechanisms in TLR7 driven autoimmunity are not clearly defined. Here we report that overexpression of TLR7 or stimulation with its agonist, imiquimod increases IFNγR and STAT1 expression, and the strength of IFNγR-STAT1 signaling in B cells. B6.Sle1bYaa mice deficient in IFNγR (Sle1bYaa.IFNγR−/−) fail to develop Spt-GCs, resulting in markedly reduced serum autoantibody (autoAb) titers and renal pathology. Further, B cell-intrinsic IFNgR or STAT1 deficient mice fail to generate Spt-GC responses upon imiquimod treatment. Interestingly, TLR7 stimulation induces STAT1 phosphorylation at serine-727 in B cells. Consistently, lupus-prone B6.Sle1b mice with alanine substitution for serine-727 in STAT1 (Sle1b.STAT1-S727A) show significantly reduced Spt-GC responses, resulting in decreased number of ANA-producing antibody forming cells and serum autoAb titers. Finally, using mixed bone marrow chimeras, we find that B cell-intrinsic STAT1-S727 phosphorylation is required for increased autoAb titers in B6.Sle1b mice. Mice with S727A mutation in STAT1, however, respond normally to T-dependent protein immunization. Together these data highlight the importance of a crosstalk between IFNγ and TLR7 signaling in B cells at STAT1 in Spt-GC responses and lupus-like autoimmunity.

The interplay of type I and type II interferons in murine autoimmune cholangitis as a basis for sex-biased autoimmunity

We have reported on a murine model of autoimmune cholangitis, generated by altering the AU-rich element (ARE) by deletion of the interferon gamma (IFN-γ) 3' untranslated region (coined ARE-Del^-/- ), that has striking similarities to human primary biliary cholangitis (PBC) with female predominance. Previously, we suggested that the sex bias of autoimmune cholangitis was secondary to intense and sustained type I and II IFN signaling. Based on this thesis, and to define the mechanisms that lead to portal inflammation, we specifically addressed the hypothesis that type I IFNs are the driver of this disease. To accomplish these goals, we crossed ARE-Del^-/- mice with IFN type I receptor alpha chain (Ifnar1) knockout mice. We report herein that loss of type I IFN receptor signaling in the double construct of ARE-Del^-/- Ifnar1^-/- mice dramatically reduces liver pathology and abrogated sex bias. More importantly, female ARE-Del^-/- mice have an increased number of germinal center (GC) B cells as well as abnormal follicular formation, sites which have been implicated in loss of tolerance. Deletion of type I IFN signaling in ARE-Del^-/- Ifnar1^-/- mice corrects these GC abnormalities, including abnormal follicular structure.

CONCLUSION

Our data implicate type I IFN signaling as a necessary component of the sex bias of this murine model of autoimmune cholangitis. Importantly these data suggest that drugs that target the type I IFN signaling pathway would have potential benefit in the earlier stages of PBC. (Hepatology 2018;67:1408-1419).

Reciprocal regulation of germinal center and regulatory B cell responses by IFNγ receptor-STAT1 signaling in TLR7 mediated autoimmunity

Toll like receptor 7 (TLR7) plays a critical role in systemic autoimmunity. The mechanisms that fine-tune germinal center versus regulatory B cell response in TLR7 mediated autoimmunity remain unclear. Regulatory B cells that produce IL-10 (B10 cells) negatively regulate autoimmunity and infections. We report that TLR7 deficiency in non-autoimmune B6 and autoimmune prone B6.Sle1b mice showed increased IL-10 producing B10 cells. In contrast, B6.Yaa and B6.Sle1b.Yaa mice expressing an extra copy of TLR7 in the Yaa locus showed decreased percentage of B10 cells. TLR7 deficiency in B cells inhibited whereas an extra copy of TLR7 enhanced proliferation and cytokine expression of cocultured antigen specific CD4 T cells. Interestingly, B10 cells displayed highest IFNγR expression compared to other subsets of T and B cells. Whereas B6.Sle1b.Yaa mice lacked B10 cells and marginal zone compartment (MZ), B6.Sle1b.Yaa mice deficient in IFNγR (B6.Sle1b.Yaa/IFNγR−/−) restored these populations. Further, B6.Sle1b.Yaa/IFNγR−/− mice showed diminished spontaneous germinal center (Spt-GC) and serum autoantibody responses, and renal pathology compared to B6.Sle1b.Yaa control mice. Similar results were observed when B6.Sle1b and B6.Sle1b.IFNγR−/− mice were treated with TLR7 ligand, imiquimod. B10 and GC B cells exhibited higher STAT1 and T-bet expression than follicular B cells. Mice deficient in STAT1 and T-bet had significantly reduced GC and IgG2c Ab responses while retained intact B10 and MZ compartments upon imiquimod treatment, contrary to what was observed in wild type mice. Together, these data define the critical differential role of IFNγR, STAT1, and T-bet in GC B cell and B10 cell development in TLR7 mediated autoimmunity.

Mer receptor tyrosine kinase signaling prevents TLR-mediated self-ligand sensing and aberrant selection in germinal centers

Mer receptor tyrosine kinase (Mer) signaling maintains immune tolerance by clearing apoptotic cells and inducing immunoregulatory signaling cascades. We previously showed that Mer-deficient mice on a mixed B6 and 129 background (B6129F2.Mer−/−) have increased germinal center (GC) responses, T cell activation, and apoptotic cell accumulation within GCs. Whereas B6129F2.Mer−/− mice accumulate apoptotic cells in GCs, B6.Mer−/− mice do not accumulate apoptotic cells, resembling B6 mice. Therefore, we used these two models to mechanistically separate the effects of debris released from secondary necrotic cells as a result of apoptotic cell accumulation from those driven by the loss of immune regulation by Mer. Through the study of global and cell-type intrinsic TLR and MyD88 deficiency in B6129F2.Mer−/− mice, we found that GC B cell-intrinsic sensing of self-RNA, but not self-DNA, released from secondary necrotic cells drives self-antigen induced GC responses. While self-ligands drive the magnitude of GC response, the loss of Mer immunoregulatory signaling bolsters antigen presentation and APC-intrinsic TLR activation drives pro-inflammatory cytokine production. Further, the loss of Mer immunoregulatory signaling accelerates the onset of autoimmunity when B6.Mer−/− mice are crossed to autoimmune-prone B6.Sle1b mice (Sle1b.Mer−/−) due to the retention of autoreactive B cells in GCs. Collectively, Mer prevents the cell-intrinsic activation of GC B cells and APCs to regulate the magnitude of GC response and T cell activation, in addition to regulating GC selection events to prevent the development of autoimmunity.

Mer tyrosine kinase (MerTK) deficiency drives the loss of marginal zone macrophages with subsequent accumulation of apoptotic cells and dysregulation of germinal centers

MerTK is a scavenger receptor involved in anti-inflammatory efferocytosis. We previously reported that MerTK deficiency on a mixed B6 and 129 background (B6-129.MerKO) led to dysregulated germinal center (GC) responses and accumulation of apoptotic cells (ACs), primarily in the GCs. Here we report that the dysregulation of GCs in B6-129.MerKO mice strongly correlates with the loss of marginal zone macrophages (MZMs) starting at two months of age. In addition to MerTK, MZMs also express other AC-scavenger receptors like SIGNR1, MARCO and Tim-4, which are also lost from the splenic MZ of B6-129.MerKO mice. We do not observe a loss or translocation of marginal zone B cells (MZBs) or marginal zone metallophillic macrophages (MMMs) from the marginal zone, indicating the exclusive role of MZMs in deregulated GC responses observed in this model. Preliminary results using splenic and bone marrow derived macrophages show reduced expression of a pro-survival heat shock protein Hsp27 and its phosphorylation through p38 and MAPKAPK-2 in the absence of MerTK. We also observe increased cell death in MerTK deficient macrophages vs. WT macrophages, when challenged with ACs. Our data indicate that reduced Hsp27 expression due to MerTK deficiency may lead to cell death of MZMs.

We are further investigating if the increased availability of self-antigens through AC accumulation, due to the loss of MZMs can lead to positive selection of self-reactive B cells in the GCs, causing autoimmunity. Our data indicate that MerTK deficiency and ACs enhance antigen presentation by macrophages, DCs and B cells. In accordance, we observe an increase in activated T cells in MerTK deficient mice, which may promote dysregulation of GC responses observed in this model.

Community-based programs for safe disposal of used needles and syringes

OBJECTIVES

To review issues related to discarded syringes in the community and to describe community-based programs for the safe disposal of used needles and syringes.

METHODS

We used the medical literature and chain referral to identify community-based syringe disposal programs other than syringe exchange programs (SEPs). We held a workshop in June 1996 involving staff from disposal programs; manufacturers of syringes, sharps containers, and other disposal devices; solid waste companies; public health staff; and researchers.

RESULTS

Fifteen programs for the safe disposal of syringes were identified in the United States, Canada, and Australia. Of these, 12 primarily served persons with diabetes who use insulin, and 3 primarily served injection drug users (IDUs). The programs used three major strategies: puncture-resistant containers discarded in trash, community drop boxes, and sharps containers turned in for biohazard disposal at community sites, hospitals, or pharmacies. Participants in the workshop described key points in developing syringe disposal programs. Programs should involve pharmacists, physicians, waste disposal companies, public health departments, hospitals, diabetes educators, persons with diabetes who use insulin, and IDUs. For IDUs, criminal penalties for possession of syringes are a substantial deterrent to participation in community efforts to safely dispose of used syringes. The multiple and sometimes conflicting local, state, and federal laws and regulations concerning medical waste hinder development of multistate or national approaches to the safe disposal of syringes. More information is needed on community-based syringe disposal programs.

CONCLUSION

Communities in the United States, Canada, and Australia have developed different approaches to achieve safe disposal of used syringes.