Investigation of Murine Spleen as a Niche for Hematopoiesis

BACKGROUND: Spleen as a lymphoid tissue is specialized for monitoring blood and mounting immunity against blood-borne antigens. Antigen-presenting cells present in spleen commonly develop from bone marrow-derived precursors that enter blood circulation. However, a distinct splenic myeloid antigen-presenting cell subset described in this laboratory, namely "dendritic-like cells" (L-DC), has been hypothesized not to share a bone marrow origin. METHODS: In this study, the presence of endogenous hematopoietic progenitors in spleen was investigated by transplanting intact spleen into allotype-distinct recipients and monitoring development of progeny cells in grafted tissues. RESULTS: Successful engraftment of donor spleens was achieved for up to 4 weeks. After 2 weeks, donor-type myeloid cells, dendritic cells (DC) and few B cells were observed in spleen grafts indicative of spleen-endogenous hematopoiesis. An influx of host-type hematopoietic stem cell, as well as host-type lymphoid and myeloid cells, was also observed. CONCLUSION: Evidence for the maintenance of donor-type myeloid cells after 2 to 4 weeks reflected development from hematopoietic progenitors endogenous to spleen. L-DC were also detected in spleen grafts; however, within the graft microenvironment they were one of the several DC and myeloid subsets, including activated DC, resembling L-DC. Overall, this study adds further evidence that spleen can support endogenous myelopoiesis.