Hematopoiesis occurs in different tissues during adult and
fetal life.
Splenic hematopoiesis arises in the
fetal period until the first weeks of life. We have analyzed the
hematopoietic progenitor content of the
fetal spleen (FS) at the
embryonic days 14.5-15.5. We first demonstrate that the
hematopoietic content of the FS differs largely from its
fetal liver (FL) counterpart. The difference mainly concerns the distribution of the different pool of progenitors, as most of the
splenic progenitors are comprised in the lineage(-)Sca1(-)cKit(lo) contrary to the FL. We have divided the
fetal hematopoietic pool into smaller fractions to enable characterization of the earliest
lymphoid progenitors. Among the
lymphoid progenitors that already represent a rare population, we were able to separate a population, respectively, enriched in B or T/NK progenitors. Lineage restriction of the different developmental intermediates was tested by clonal
assays. We propose a model for
fetal splenic hematopoietic progenitors and their distribution.
