Negative regulation of B cell responses and self-tolerance to RNA-related lupus self-antigen

T-bet+ B cells are activated by and control endogenous retroviruses through TLR-dependent mechanisms

Endogenous retroviruses (ERVs) are an integral part of the mammalian genome. The role of immune control of ERVs in general is poorly defined as is their function as anti-cancer immune targets or drivers of autoimmune disease. Here, we generate mouse-strains where Moloney-Murine Leukemia Virus tagged with GFP (ERV-GFP) infected the mouse germline. This enables us to analyze the role of genetic, epigenetic and cell intrinsic restriction factors in ERV activation and control. We identify an autoreactive B cell response against the neo-self/ERV antigen GFP as a key mechanism of ERV control. Hallmarks of this response are spontaneous ERV-GFP+ germinal center formation, elevated serum IFN-γ levels and a dependency on Age-associated B cells (ABCs) a subclass of T-bet+ memory B cells. Impairment of IgM B cell receptor-signal in nucleic-acid sensing TLR-deficient mice contributes to defective ERV control. Although ERVs are a part of the genome they break immune tolerance, induce immune surveillance against ERV-derived self-antigens and shape the host immune response.

An Exploratory Gene Expression Study of the Intestinal Mucosa of Patients with Non-Celiac Wheat Sensitivity

Non-celiac wheat sensitivity (NCWS) is a recently recognized syndrome triggered by a gluten-containing diet. The pathophysiological mechanisms engaged in NCWS are poorly understood and, in the absence of laboratory markers, the diagnosis relies only on a double-blind protocol of symptoms evaluation during a gluten challenge. We aimed to shed light on the molecular mechanisms governing this disorder and identify biomarkers helpful to the diagnosis. By a genome-wide transcriptomic analysis, we investigated gene expression profiles of the intestinal mucosa of 12 NCWS patients, as well as 7 controls. We identified 300 RNA transcripts whose expression differed between NCWS patients and controls. Only 37% of these transcripts were protein-coding RNA, whereas the remaining were non-coding RNA. Principal component analysis (PCA) and receiver operating characteristic curves showed that these microarray data are potentially useful to set apart NCWS from controls. Literature and network analyses indicated a possible implication/dysregulation of innate immune response, hedgehog pathway, and circadian rhythm in NCWS. This exploratory study indicates that NCWS can be genetically defined and gene expression profiling might be a suitable tool to support the diagnosis. The dysregulated genes suggest that NCWS may result from a deranged immune response. Furthermore, non-coding RNA might play an important role in the pathogenesis of NCWS.

CD72 is a Negative Regulator of B Cell Responses to Nuclear Lupus Self-antigens and Development of Systemic Lupus Erythematosus

Systemic lupus erythematosus (SLE) is the prototypic systemic autoimmune disease characterized by production of autoantibodies to various nuclear antigens and overexpression of genes regulated by IFN-I called IFN signature. Genetic studies on SLE patients and mutational analyses of mouse models demonstrate crucial roles of nucleic acid (NA) sensors in development of SLE. Although NA sensors are involved in induction of anti-microbial immune responses by recognizing microbial NAs, recognition of self NAs by NA sensors induces production of autoantibodies to NAs in B cells and production of IFN-I in plasmacytoid dendritic cells. Among various NA sensors, the endosomal RNA sensor TLR7 plays an essential role in development of SLE at least in mouse models. CD72 is an inhibitory B cell co-receptor containing an immunoreceptor tyrosine-based inhibition motif (ITIM) in the cytoplasmic region and a C-type lectin like-domain (CTLD) in the extracellular region. CD72 is known to regulate development of SLE because CD72 polymorphisms associate with SLE in both human and mice and CD72^−/− mice develop relatively severe lupus-like disease. CD72 specifically recognizes the RNA-containing endogenous TLR7 ligand Sm/RNP by its extracellular CTLD, and inhibits B cell responses to Sm/RNP by ITIM-mediated signal inhibition. These findings indicate that CD72 inhibits development of SLE by suppressing TLR7-dependent B cell response to self NAs. CD72 is thus involved in discrimination of self-NAs from microbial NAs by specifically suppressing autoimmune responses to self-NAs.