B-Lymphoid Cells with Attributes of Dendritic Cells Regulate T Cells via Indoleamine 2,3 Dioxygenase

Abstract

A rare subset of murine dendritic cells expressing the B cell marker CD19 are specialized to express the T cell regulatory enzyme indoleamine 2,3 dioxygenase (IDO-competent DCs). Here we show that IDO-competent DCs expressed Pax5, a transcription factor that maintains B cell lineage commitment, and drives expression of CD19 and surface immunoglobulin (slg). However IDO-competent DCs also exhibited multiple attributes of DCs including DC marker expression and potent T cell stimulatory properties when IDO was not induced. Unexpectedly, DCs expressing IDO were present in B cell deficient mice following TLR9 ligation, indication that B cell receptor (BCR) expression was not required for IDO function. Conversely, DCs from CD19 deficient mice did not express IDO after in vivo TLR9 ligation. This defect was not caused by blockade of IDO-competent DC development in CD19-deficient mice because IDO expression was incduced in these cells by in vitro interferon gamma treatment. Even though DCs from B cell deficient mice expressed IDO following TLR9 ligation, regulatory T cells (Tregs) from B cell deficient mice had impaired suppressor activity. IDO-competent DCs expressed high levels of CD1d-deficient mice. IDO-competent DCs also expressed IL-10 deficient mice to express IDO. Finally we demonstrated that DCs from draining lymph nodes (dLNs) of four week old prediabetic female non obese diabetic (NOD) mice expressed functional IDO following topical treatment with phorbol myristate acetate (PMA). However DCs from dLNs of six week old prediabetic NOD female mice did not express IDO following topical PMA treatment, indicating a critical defect in a specific immunosuppressive mechanism in NOD female mice that coincides with the appearance of insulitis. These data identify IDO competent DCs as a unique B lymphoid lineage cell type that has tightly controlled regulatory properties, and a DC subset whose acquired defect may contribute to autoimmune disease in NOD mice.