Marginal zone precursor B cells as cellular agents for type I IFN-promoted antigen transport in autoimmunity

The pathogenic connection of type I IFN and its role in regulating the migration response of Ag delivery by B cells into lymphoid follicles in an autoimmune condition has not been well-identified. Here, we show that there was a significantly larger population of marginal zone precursor (MZ-P) B cells, defined as being IgM(hi)CD1d(hi)CD21(hi)CD23(hi) in the spleens of autoimmune BXD2 mice compared with B6 mice. MZ-P B cells were highly proliferative compared with marginal zone (MZ) and follicular (FO) B cells. The intrafollicular accumulation of MZ-P B cells in proximity to germinal centers (GCs) in BXD2 mice facilitated rapid Ag delivery to the GC area, whereas Ag-carrying MZ B cells, residing predominantly in the periphery, had a lower ability to carry Ag into the GCs. IFN-alpha, generated by plasmacytoid dendritic cells, induced the expression of CD69 and suppressed the sphingosine-1-phosphate-induced chemotactic response, promoting FO-oriented Ag transport by MZ-P B cells. Knockout of type I IFN receptor in BXD2 (BXD2-Ifnalphar(-/-)) mice substantially diffused the intrafollicular MZ-P B cell conglomeration and shifted their location to the FO-MZ border near the marginal sinus, making Ag delivery to the FO interior less efficient. The development of spontaneous GCs was decreased in BXD2-Ifnalphar(-/-) mice. Together, our results suggest that the MZ-P B cells are major Ag-delivery B cells and that the FO entry of these B cells is highly regulated by type I IFN-producing plasmacytoid dendritic cells in the marginal sinus in the spleens of autoimmune BXD2 mice.