YY1 has been implicated as a master regulator of germinal center B cell development as YY1 binding sites are frequently present in promoters of germinal center-expressed genes. YY1 is known to be important for other stages of B cell development including the pro-B and pre-B cells stages. To determine if YY1 plays a critical role in germinal center development, we evaluated YY1 expression during B cell development, and used a YY1 conditional knock-out approach for deletion of YY1 in germinal center B cells (CRE driven by the immunoglobulin heavy chain γ1 switch region promoter; γ1-CRE). We found that YY1 is most highly expressed in germinal center B cells and is increased 3 fold in splenic B cells activated by treatment with anti-IgM and anti-CD40. In addition, deletion of the yy1 gene by action of γ1-CRE recombinase resulted in significant loss of GC cells in both un-immunized and immunized contexts with corresponding loss of serum IgG1. Our results show a crucial role for YY1 in the germinal center reaction.

Environmental factors including drugs, mineral oils and heavy metals such as lead, gold and mercury are triggers of autoimmune diseases in animal models or even in occupationally exposed humans. After exposure to subtoxic levels of mercury (Hg), genetically susceptible strains of mice develop an autoimmune disease characterized by the production of highly specific anti-nucleolar autoantibodies, hyperglobulinemia and nephritis. However, mice can be tolerized to the disease by a single low dose administration of Hg. Lymphocyte Activation Gene-3 (LAG-3) is a CD4-related, MHC-class II binding molecule expressed on activated T cells and NK cells which maintains lymphocyte homeostatic balance via various inhibitory mechanisms. In our model, administration of anti-LAG-3 monoclonal antibody broke tolerance to Hg resulting in autoantibody production and an increase in serum IgE level. In addition, LAG-3-deficient B6.SJL mice not only had increased susceptibility to Hg-induced autoimmunity but were also unresponsive to tolerance induction. Conversely, adoptive transfer of wild-type CD4+ T cells was able to partially rescue LAG-3-deficient mice from the autoimmune disease. Further, in LAG-3-deficient mice, mercury elicited higher amounts of IL-6, IL-4 and IFN-γ, cytokines known to play a critical role in mercury-induced autoimmunity. Therefore, we conclude that LAG-3 exerts an important regulatory effect on autoimmunity elicited by a common environmental pollutant.

Key Points Transcription factor YY1 regulates the IgH Eμ-3′RR long-distance DNA loop without the YY1 transcriptional activation domain. YY1 constructs that rescue the Eμ-3′RR DNA loop also restore CSR strongly arguing for the necessity of this long-distance DNA loop for CSR.

Although immune infiltrates in ovarian cancer are associated with improved survival, the ovarian tumor environment has been characterized as immunosuppressive, due in part to functional shifts among dendritic cells with disease progression. We hypothesized that flux in dendritic cell subpopulations with cancer progression were responsible for observed differences in antitumor immune responses in early and late-stage disease. Here we identify three dendritic cell subsets with disparate functions in the ovarian tumor environment. CD11c+CD11b(-)CD103(+) dendritic cells are absent in the peritoneal cavity of healthy mice but comprise up to 40% of dendritic cells in tumor-bearing mice and retain T cell stimulatory capacity in advanced disease. Among CD11c+CD11b+ cells, Lair-1 expression distinguishes stimulatory and immunoregulatory DC subsets, which are also enriched in the tumor environment. Notably, PD-L1 is expressed by Lair-1(hi) immunoregulatory dendritic cells, and may contribute to local tumor antigen-specific T cell dysfunction. Using an adoptive transfer model, we find that PD-1 blockade enables tumor-associated CD103(+) dendritic cells to promote disease clearance. These data demonstrate that antitumor immune capacity is maintained among local dendritic cell subpopulations in the tumor environment with cancer progression. Similar dendritic cell subsets are present in malignant ascites from women with ovarian cancer, supporting the translational relevance of these results.