Females are more susceptible than males to many autoimmune diseases. The processes causing this phenomenon are incompletely understood. Here, we demonstrate that aged female mice acquire a previously uncharacterized population of B cells that we call age-associated B cells (ABCs) and that these cells express integrin ␣ X chain (CD11c). This unexpected population also appears in young lupus-

IgG2a is known to be the most efficient antibody isotype for viral clearance. Here, we demonstrate a unique pathway of B-cell activation, leading to IgG2a production, and involving synergistic stimulation via B-cell antigen receptors, toll-like receptor 7 (TLR7), and IFNγ receptors on B cells. This synergistic stimulation leads to induction of T-box transcription factor T-bet expression in B cells, which, in turn, drives expression of CD11b and CD11c on B cells. Tbet/CD11b/CD11c positive B cells appear during antiviral responses and produce high titers of antiviral IgG2a antibodies that are critical for efficient viral clearance. The results thus demonstrate a previously unknown role for T-bet expression in B cells during viral infections. Moreover, the appearance of T-bet + B cells during antiviral responses and during autoimmunity suggests a possible link between these two processes.interferon gamma | virus

No abstract

To test whether highly crossreactive alphabeta T cell receptors (TCRs) produced during limited negative selection best illustrate evolutionarily conserved interactions between TCR and major histocompatibility complex (MHC) molecules, we solved the structures of three TCRs bound to the same MHC II peptide (IAb-3K). The TCRs had similar affinities for IAb-3K but varied from noncrossreactive to extremely crossreactive with other peptides and MHCs. Crossreactivity correlated with a shrinking, increasingly hydrophobic TCR-ligand interface, involving fewer TCR amino acids. A few CDR1 and CDR2 amino acids dominated the most crossreactive TCR interface with MHC, including Vbeta8 48Y and 54E and Valpha4 29Y, arranged to impose the familiar diagonal orientation of TCR on MHC. These interactions contribute to MHC binding by other TCRs using related V regions, but not usually so dominantly. These data show that crossreactive TCRs can spotlight the evolutionarily conserved features of TCR-MHC interactions and that these interactions impose the diagonal docking of TCRs on MHC.

A newly discovered B cell subset, Age Associated B Cells, expresses the transcription factor T-bet, has a unique surface phenotype, and progressively accumulates with age. Moreover, B cells with these general features are associated with viral infections and autoimmunity in both mice and humans. Here we review current understanding of the characteristics, origins, and functions of these cells. We also suggest that the protective versus pathogenic actions of these cells reflect appropriate versus aberrant engagement of regulatory mechanisms that control the antibody responses to nucleic acid containing antigens.

Besides secretion of antigen-specific antibodies, B cells may play an important role in the generation of immune responses by efficiently presenting antigen to T cells. We and others recently described a subpopulation of CD11c+ B cells (Age/autoimmune associated B cells, ABCs) which appear with age, during virus infections and at the onset of some autoimmune diseases and which participate in autoimmune responses by secreting autoantibodies. Here we assessed the ability of these cells to present antigen and activate antigen-specific T cells. We demonstrated that ABCs present antigen to T cells, in vitro and in vivo, better than follicular B cells (FO cells) do. Our data indicate that ABCs express higher levels of the chemokine receptor, CCR7, and have higher responsiveness to CCL21 and CCL19 than FO cells and are localized at T/B cell border in spleen. Using multiphoton microscopy we show that, in vivo, CD11c+ B cells form significantly more stable interactions with T cells than Follicular B cells do. Together these data identify a previously undescribed role for ABCs as potent antigen-presenting cells and suggest another potential mechanism by which these cells can influence immune responses and/or the development of autoimmunity.

R e v i e w S e R i e S : A u t o i m m u n i t y 2 1 8 8jci.org Volume 125 Number 6 June 2015expression of IFN1 genes is controlled directly by sex hormones. On the other hand, sex hormones do affect expression of some of the PRRs (see below) and in this way might indirectly affect IFN1 levels. Thus, the abundance of IFN1s in lupus patients might be caused by female sex hormone-induced increases in PRR levels, which in turn increase production of IFN1s. One of the genes that controls expression of IFN1s is IFN regulatory factor 5 (IRF5). IRF5 has also been identified as a significant risk factor for lupus susceptibility (37,38). Expression of IRF5 in mice has been reported to be sex dependent (39). As demonstrated by Shen and colleagues (39), C57BL/6, NZB, Nba2, NZB/NZW F1, and NZM mouse strains express significantly higher levels of Irf5 mRNA in female than in male lymphocytes. Additionally, splenocytes from lupus-prone mice were shown to express higher levels of Irf5 mRNA compared with cells from the C57BL/6 strain, which is not prone to lupus. This group further demonstrated that Irf5 expression can be upregulated in vitro upon estrogen treatment, suggesting a potential mechanism for sex-biased expression of the gene and consequent overproduction of IFN1s (39).Absence of IFN-γ signaling protects NZB/NZW F1 mice against lupus-like disease (40). Expression of the IFNG gene, on the other hand, is regulated directly by estrogens (41)(42)(43)(44)(45). This finding suggests a positive feedback loop between the IFNs and estrogens, since activation of IFN1 or IFN-γ signaling upregulates the expression of ERα (46). Estrogen, in turn, promotes IFN-γ production by various lymphocytes. In addition, Panchanathan et al. demonstrated synergistic involvement of ERα and IFN signaling in activating the transcription of both IFN and estrogen-responsive target genes (46).Once produced, IFNs have many effects on the immune system that contribute to the sex bias of autoimmunity. For example, IFN1s increase class 1 MHC expression on cells, and IFN-γ induces class II MHC and changes the nature of the proteasome, thereby affecting the nature and quantity of self-peptides presented to T cells. Other examples are described below. Other immune-associated genes affected by sex hormonesMany genes with products that affect the immune system are controlled by sex hormones. As far as innate immunity is concerned, estrogens induce the expression of intracellular but not surface TLRs in both male and female PBMCs (23). Because intracellular TLRs have been shown to affect the development of autoimmunity (47-51), it is possible that the hormonal effect of the expression of intracellular TLRs contributes to female-biased autoimmunity.Unc-93 homolog B1 (UNC93B1) is an endoplasmic reticulum (ER) transmembrane protein that is essential for trafficking the TLRs that are expressed intracellularly (TLR3, TLR7, TLR8, TLR9, and probably other TLRs) from the ER to endosomes (52-54). UNC93B1 regulates the activity of these TLRs by mediating localization t...

Autoimmunity is controlled both by the environment and by genetic factors. One of the most well defined genetic factors is polymorphisms, with some alleles of particular genes promoting autoimmune diseases, whereas other alleles either not affecting susceptibility to disease or, in some cases actually inhibiting the appearance of such illnesses. Another genetically controlled factor, gender, also plays a profound role in the incidence of autoimmune diseases. For example, Systemic Lupus Erythematosus (SLE) occurs much more frequently in females than in males in both mice and man. The genetic differences that make some individuals susceptible to autoimmunity and protect others could act in many ways and affect many tissues. In this review we will discuss how gender may act on the cells of the immune system and thereby influence the predisposition of the host to autoimmune diseases.