PU.1 Is Indispensable for Development of Mature Dendritic Cells and Their Function That Plays a Critical Role in Maintenance of Normal T Cell Pool.

Abstract 1471

Poster Board I-494

PU.1, a hematopoietic transcription factor, is indispensable for development of myelo-lymphoid cells from hematopoietic stem cells (HSCs). PU.1-deficient mice fail to develop common myeloid progenitors (CMPs) or common lymphoid progenitors (CLPs), resulting in complete loss of dendritic cells (DC) in addition to mature myeloid and lymphoid cells. By disrupting PU.1 specifically at the mature DC stage, we here show that PU.1 is necessary for maintenance of mature DC pool and their functions. We crossed PU.1 floxed/floxed mice with a mouse line harboring the Cre transgene driven by the CD11c-BAC. In these mice, PU.1 gene was disrupted in all conventional DCs but not in other hematopoietic cells, including lymphoid cells, myeloid cells and their progenitors. Development of DC precursors such as Lin⁻c-Kit^loFLT3⁺MCSFR⁺, FLT3⁺ CLP and FLT3⁺CMP were not affected. The number of CD11c⁺B220⁻ DCs, however, significantly reduced in all lymphoid tissues including the thymus, the spleen, the lymph node and the skin, down to <40%, <25%, <10% and <5% as compared with the wild-type control, respectively. Moreover, the number of mature T cells reduced to ∼60% in the spleen as compared to the control. PU.1-deficient DCs displayed impaired functions to induce antigen-driven T cell proliferation, and to produce inflammatory cytokines (TNFa, IL-6, IL-12) in response to Toll like receptor (TLR) stimulation. These results clearly show that PU.1 is required for development of the peripheral DC pool and for maintenance of their immunological functions, which might be required for maintenance of the peripheral T cell pool.