Autoreactive B cell tetramer analysis reveals a type I interferon-mediated marginal zone precursor B cell defect in autoimmune BXD2 mice (BA12P.102)

In human systemic lupus erythematosus and rheumatoid arthritis, development of self-reactive B cells has been associated with defective B-cell checkpoints prior to somatic hypermutation and class-switch recombination in germinal centers (GCs). To identify mechanisms leading to checkpoint defects in the periphery, sera from BXD2 autoimmune mice were screened on a PEPperPRINT Microarray. Highly specific autoepitopes were narrowed down via Discotope epitope analysis and high-throughput ELISA and ELISPOT analyses. Three peptides La, snRNP, and fibromodulin-citrulline (fib-cit) were used to make tetramers (tet) for characterization of B cell subsets in the spleen. Analysis of fib-cit tet+ B cells revealed an age-dependent 5 fold increase in tet+ B cells, especially within the marginal zone-precursor (MZ-P) (10.6% vs 4.85%) and GC (7.3% vs 0%) subsets, in BXD2 vs B6 mice. While the total frequency of La and snRNP tet+ B cells was not different in BXD2 vs B6, there was also an increase in the MZ-P (7.66% vs 1.51%) phenotype. Sorted tet+ B cells exhibited a >100-fold enhanced ability to secrete specific autoAb compared to tet- B cells. Additionally, there was significantly higher CD69 expression (75.5% vs 5.71%), a type I interferon (IFN)-induced protein in MZ-P B cells in BXD2 vs B6 mice. Together, these results establish a general method for characterization of autoAg specific B cells and suggest a checkpoint defect at the MZ-P stage as a result of type I IFN stimulation.