B-cell-intrinsic DNase1L3 is essential for T-cell-independent type II response in mice

T-cell independent type II (TI-II) antigens, such as capsular polysaccharides, have multivalent epitope, which induce B cell activation, plasma cell differentiation and antibody production by strongly cross-linking B cell receptors. However, the mechanism of B cell activation by TI-II antigens remains unclear. In this study, we demonstrate that DNA endonuclease DNase1L3 (also termed DNase g) is required for the TI-II response. The production of antigen-specific antibodies was severely diminished in DNase1L3-deficient mice upon immunization with TI-II antigens, but not with TD antigens. Bone-marrow chimeric mice and B cell transfer experiments revealed that B-cell-intrinsic DNase1L3 was required for the TI-II response. DNase1L3-deficient B cells were defective in cell proliferation and plasma cell differentiation in the TI-II response in vivo as well as in vitro, which was not rescued by co-culture with DNase1L3-sufficient B cells in vitro, disproving an involvement of a secretory DNase1L3. In vitro stimulation with TI-II antigen transiently increased expression of DNase1L3 and its translocation into the nucleus. RNA-seq analysis of ex-vivo B cells having been responded to TI-II antigen in vivo revealed a marked reduction of Myc-target gene sets in DNase1L3-deficient B cells. Expression of IRF4, the gene of which is a target of Myc, was diminished in the ex-vivo DNase1L3-deficient B cells, in which forced expression of IRF4 restored the TI-II response in vivo. These data revealed an unexpected role of DNase1L3 in a missing link between B cell receptor signaling and B cell activation in the TI-II response, giving a valuable clue to molecularly dissect this response. Marginal zone B cells purified from pooled spleens of CD45.1+ VHB1-8 knock-in gene (B1-8f/+), Dnase1l3+/+ (WT) or Dnase1l3-/- (KO) mice were intravinously(i.v.) transferred into C57BL/6NCrSlc mice, which were immunized i.v. with 4-hydroxy-3-nitrophenyl acetyl (NP)-Ficoll on the following day. Two days later, donor cells (CD45.1+ B220+ CD138- FSChi) were sorted by cell sorter. RNA-sequencing was performed to identify the difference of gene expression between Dnase1l3+/+ and Dnase1l3-/- marginal zone B cells.