Phenotypic characterization of B1a cells releasing mitochondrial DNA induced by phosphorothioate-linked GpC-based stem-loop oligonucleotide stimulation

We have previously shown that phosphorothioate-linked GpC-based stem-loop oligonucleotides (GC-SL ODN) induce the release of extracellular mitochondria DNA (mtDNA) from peritoneal B1a cells. Since B1a cells play immunoregulatory roles in the peritoneal cavity, we decided to investigate further which phenotype of B1a cells secrete mtDNA and what factors are involved in the mtDNA secretion by B1a cells. We found that the CD11b⁺ subpopulation among peritoneal B cells is the primary producer of mtDNA upon GC-SL ODN stimulation. Moreover, reactive oxygen species signaling negatively regulated mtDNA release from B1a cells, suggesting that mtDNA secretion might be correlated with anti-inflammatory function. In addition, we found that the mtDNA-releasing phenotype of subset B cells displayed higher levels of CD9 and TIM1, anti-inflammatory markers, in the presence or absence of GC-SL ODN treatment. Furthermore, stimulation of B1a cells with recombinant IL5 and CD40 ligands resulted in more mtDNA production than unstimulated B1a cells under GC-SL ODN stimulation. Overall, our results suggest that mtDNA-releasing B1a cells might be effector B cells with potent regulatory functions.