Loss of interferon regulatory factor 8 (IRF-8) in B cells promotes the expansion of regulatory B cells (Bregs) and suppresses intraocular autoimmune disease

Abstract

Purpose : IRF-8 is implicated in the regulation of B-cell lineage commitment, activation, immunoglobulin gene recombination, and cytokine gene expression. In this study, we have generated mice with targeted deletion of IRF8 in B cells and have used the CD19-IRF-8KO (IRF-8KO) mice to investigated whether IRF-8 also plays a role in the development and/or expansion of regulatory B cells (Bregs) that regulate autoimmune diseases.

Methods : CD19-IRF-8KO mice were generated by cross-breeding CD19^CRE with IRF8^f/f mice. The conditional knockout mice were identified by tail DNA PCR. Targeted deletion of IRF8 in B cells of the IRF-8KO mice was ascertained by FACS, intracellular cytokine staining and Western blot analyses of peripheral CD19⁺ B cells. Immuno-phenotype of the IRF-8KO B cell was characterized by FACS analysis of B cell cell-surface proteins. We next examined whether loss of IRF8 in B cells would affect the generation/expansion of Breg cells during experimental autoimmune uveitis (EAU). We induced EAU by immunization with IRBP/CFA and established disease development by funduscopy and histology. Immune responses were analyzed by intracellular cytokine assay and ELISA. Lymphocyte proliferation was assessed by Thymidine incorporation.

Results : CD19-IRF-8KO mice exhibited marked reduction of follicular B cells (IgD^hiCD21^loCD23^hi) and the expansion of marginal zone B cells with cell surface markers characteristic of Breg cells. Consistent with expansion of IL-10/IL-35-producing IRF-8KO Breg cells, IRF8-deficient mice are relatively resistant to EAU induction compared to WT counterparts.

Conclusions : Marginal B cells have strong regulatory function, suppress autoimmune responses and have long been suspected to be a major source of Breg populations. Our data showing that mice with loss of IRF-8 in B cells exhibit marked reduction of follicular B cells with concomitant expansion of marginal B cells, suggest that IRF-8 might promote humoral immunity, follicular cell and plasma cell development by antagonizing the alternative immune-suppressive developmental pathway orchestrated by marginal zone cells.

This is an abstract that was submitted for the 2018 ARVO Annual Meeting, held in Honolulu, Hawaii, April 29 - May 3, 2018.