Spleen as a distinct site for dendritic cell haematopoiesis

This article addresses haematopoiesis and specifically the development of dendritic cells (DC) in the mouse spleen. Evidence is presented that the spleen microenvironment makes a distinct contribution to haematopoiesis and supports the differentiation of haematopoietic progenitors to give a novel type of dendritic-like myeloid cell not previously reported. This novel subset appears to be unique in terms of cell surface marker phenotype and immune function. It was discovered in response to our search for an in vivo equivalent of a novel dendritic-like antigen presenting cell type that develops in long-term stroma-dependent spleen cultures which was pioneered in this lab. These cultures maintain self-renewing haematopoietic progenitor or stem cells (HPC/HSC), and support the development of this novel cell type and no other haematopoietic cells. We have now shown that infusion of isolated HSC/HPC from spleen into blood results in increased production of these cells over the more commonly described DC and myeloid subsets in spleen. While bone marrow is the primary site for haematopoiesis in adult mice, we now question the importance of spleen in haematopoiesis, particularly in regard to development of this novel antigen presenting cell type. The work described here relates to the differentiation of DC, and also to the concept of tissue-specific haematopoiesis leading to cells which mediate inflammation and immune responses.