Epistatic Interactions Between Mutations of Deoxyribonuclease 1-Like 3 and the Inhibitory Fc Gamma Receptor IIB Result in Very Early and Massive Autoantibodies Against Double-Stranded DNA

Abstract

Autoantibodies against double-stranded DNA (anti-dsDNA) are a hallmark of systemic lupus erythematosus (SLE). It is well documented that anti-dsDNA reactive B lymphocytes are normally controlled by immune self-tolerance mechanisms operating at several levels. The evolution of high levels of IgG anti-dsDNA in SLE is dependent on somatic hypermutation and clonal selection, presumably in germinal centers from non-autoreactive B cells. Twin studies as well as genetic studies in mice indicate a very strong genetic contribution for the development of anti-dsDNA as well as SLE. Only few single gene defects with a monogenic Mendelian inheritance have been described so far that are directly responsible for the development of anti-dsDNA and SLE. Recently, among other mutations, rare null-alleles for the deoxyribonuclease 1 like 3 (DNASE1L3) and the Fc gamma receptor IIB (FCGR2B) have been described in SLE patients and genetic mouse models. Here, we demonstrate that double Dnase1l3- and FcgR2b-deficient mice in the C57BL/6 background exhibit a very early and massive IgG anti-dsDNA production. Already at 10 weeks of age, autoantibody production in double-deficient mice exceeds autoantibody levels of diseased 9-month-old NZB/W mice, a long established multigenic SLE mouse model. In single gene-deficient mice, autoantibody levels were moderately elevated at early age of the mice. Premature autoantibody production was accompanied by a spontaneous hyperactivation of germinal centers, early expansions of T follicular helper cells, and elevated plasmablasts in the spleen. Anti-dsDNA hybridomas generated from double-deficient mice show significantly elevated numbers of arginines in the CDR3 regions of the heavy-chain as well as clonal expansions and diversification of B cell clones with moderate numbers of somatic mutations. Our findings show a strong epistatic interaction of two SLE-alleles which prevent early and high-level anti-dsDNA autoantibody production. Both genes apparently synergize to keep in check excessive germinal center reactions evolving into IgG anti-dsDNA antibody producing B cells.

Plasma DNA Profile Associated with DNASE1L3 Gene Mutations: Clinical Observations, Relationships to Nuclease Substrate Preference, and In Vivo Correction

“…Hence, the autoantibodies may bind with the short DNA molecules and result in the increased frequency of both longer and shorter DNA in plasma of the patients with DNASE1L3 mutations. 26 , 33 …”

“… 27 , 32 Similarly, the loss of DNASE1L3 in mice causes an anti- ds DNA antibody response progressing to SLE-like disease. 26 , 33 , 34 In fact, DNASE1L3 and C1q (MIM: 120575 ) are the only genes associated with antibody-mediated monogenic SLE. Most of the others are associated with SLE-like interferonopathies such as Aicardi-Goutieres syndrome (e.g., TREX1 [MIM: 606609 ], DNASE2 [MIM: 126350 ], SAMHD1 [MIM: 606754 ], ADAR1 [MIM: 146920 ]).…”

Deoxyribonucleases and Their Applications in Biomedicine

“…DNase1L3 deletion in mice was found to lead to a much higher concentration of anti-DNA antibodies when Fc gamma receptor IIB was deleted too. Double deficient mice had overactivated germinal centers which could increase the number of anti-DNA antibody-producing B cells [42]. Further studies are required for better understanding of the physiological role and evolutionary development of these enzymes.…”

Germline Genetic Risk Variants for Progressive Multifocal Leukoencephalopathy

“…A list of candidate immune function genes was curated from the following main sources: genome-wide study of rare copy number variants in 70 PML cases (Dis cohort) that impact immune function genes (data not shown), genes from the ClinVar database (43) using search terms "immune deficiency" and "immunodeficiency, " IUIS and other immunodeficiency reviews (29,30,(44)(45)(46)(47)(48)(49)(50), type I interferon pathway genes (51)(52)(53)(54)(55)(56)(57)(58), complement pathway genes (59), and JCV or PML linked biology (23,26,33,(60)(61)(62)(63)(64). The full list of 711 unique genes were cross-checked against genes that were found with DV-called variants in the Dis and/or Rep cohorts.…”