ABSTRACT
Precise targeting of activation-induced cytidine deaminase (AID) to immunoglobulin (Ig) loci promotes antibody class switch recombination (CSR) and somatic hypermutation (SHM), whereas AID targeting of non-Ig loci can generate oncogenic DNA lesions. Here, we examined the contribution of G-quadruplex (G4) nucleic acid structures to AID targeting in vivo. Mice bearing a mutation in Aicda (AIDG133V) that disrupts AID-G4 binding modeled the pathology of hyper-IgM syndrome patients with an orthologous mutation, lacked CSR and SHM, and had broad defects in genome-wide AIDG133V chromatin localization. Genome-wide analyses also revealed that wild-type AID localized to MHCII genes, and AID expression correlated with decreased MHCII expression in germinal center B cells and diffuse large B cell lymphoma. Our findings indicate a crucial role for G4 binding in AID targeting and suggest that AID activity may extend beyond Ig loci to regulate the expression of genes relevant to the physiology and pathology of activated B cells.
Subject(s)
Chromatin/genetics , Chromatin/metabolism , Cytidine Deaminase/genetics , Cytidine Deaminase/metabolism , G-Quadruplexes , Hyper-IgM Immunodeficiency Syndrome/etiology , Hyper-IgM Immunodeficiency Syndrome/metabolism , Mutation , Animals , B-Lymphocytes/immunology , B-Lymphocytes/metabolism , Computational Biology/methods , Disease Models, Animal , Disease Susceptibility , Enzyme Activation , Fluorescent Antibody Technique , Gene Expression Profiling , Genome-Wide Association Study , Germinal Center/immunology , Germinal Center/metabolism , HLA Antigens/genetics , HLA Antigens/immunology , Humans , Hyper-IgM Immunodeficiency Syndrome/diagnosis , Immunoglobulin Class Switching/genetics , Immunoglobulin Class Switching/immunology , Immunophenotyping , Lymphocyte Activation/genetics , Lymphoma, Large B-Cell, Diffuse/etiology , Lymphoma, Large B-Cell, Diffuse/metabolism , Lymphoma, Large B-Cell, Diffuse/pathology , Mice , Mice, TransgenicABSTRACT
Bleeding and altered iron distribution occur in multiple gastrointestinal diseases, but the importance and regulation of these changes remain unclear. We found that hepcidin, the master regulator of systemic iron homeostasis, is required for tissue repair in the mouse intestine after experimental damage. This effect was independent of hepatocyte-derived hepcidin or systemic iron levels. Rather, we identified conventional dendritic cells (cDCs) as a source of hepcidin that is induced by microbial stimulation in mice, prominent in the inflamed intestine of humans, and essential for tissue repair. cDC-derived hepcidin acted on ferroportin-expressing phagocytes to promote local iron sequestration, which regulated the microbiota and consequently facilitated intestinal repair. Collectively, these results identify a pathway whereby cDC-derived hepcidin promotes mucosal healing in the intestine through means of nutritional immunity.
Subject(s)
Dendritic Cells/metabolism , Gastrointestinal Microbiome , Hepcidins/metabolism , Intestinal Diseases/microbiology , Intestinal Mucosa/microbiology , Intestinal Mucosa/physiology , Iron/metabolism , Animals , Cation Transport Proteins/metabolism , Fecal Microbiota Transplantation , Gene Deletion , Hepcidins/genetics , Homeostasis , Mice , Mice, Mutant Strains , Phagocytes/metabolismABSTRACT
The DNA damage response protein ATM has long been known to influence class switch recombination in ex vivo-cultured B cells. However, an assessment of B cell-intrinsic requirement of ATM in humoral responses in vivo was confounded by the fact that its germline deletion affects T cell function, and B:T cell interactions are critical for in vivo immune responses. In this study, we demonstrate that B cell-specific deletion of ATM in mice leads to reduction in germinal center (GC) frequency and size in response to immunization. We find that loss of ATM induces apoptosis of GC B cells, likely due to unresolved DNA lesions in cells attempting to undergo class-switch recombination. Accordingly, suboptimal GC responses in ATM-deficient animals are characterized by decreased titers of class-switched Abs and decreased rates of somatic hypermutation. These results unmask the critical B cell-intrinsic role of ATM in maintaining an optimal GC response following immunization.
