ABSTRACT
Dendritic cells (DCs) as well as natural type I interferon-producing cells (IPCs, also called plasmacytoid dendritic cells, PDCs) are relatively recently described
cells of the hematopoietic system (1). With the exception of Langerhans cells (LCs) (10) and possibly some other non-lymphatic tissue DCs, most DCs and IPCs have a short in vivo turnover time of maximally two weeks (11,12). Thus, these cells need to be regenerated continuously from HSCs, a process that must be tightly regulated. Multiple DC types, differing in phenotype, localization, and function, were identified over the last few decades (13,14). With the recent phenotypic and functional identification of IPCs in both humans (15-17) and mice (18-20), and the finding that these cells are capable of differentiating to DCs, the heterogeneous group of DCs was further enlarged (21). Over the last few years we and others were able to elucidate some of the developmental pathways of these rare cells. Most of these findings are summarized in recent reviews (e.g., 14,21-24). Thus, I focus on our findings on DC and IPC development from mouse bone marrow or human cord-blood earlyprogenitor cells.
