Stromal cell-derived factor 1 (SDF-1) and antenatal human B cell lymphopoiesis: Expression of SDF-1 by mesothelial cells and biliary ductal plate epithelial cells

The chemokine stromal cell-derived factor 1 (SDF-1) stimulates the growth o f pre-B cells in vitro, and mice with a disrupted SDF-1 gene have abnormal fetal liver B cell lymphopoiesis. The origin of SDF-1 production has not be en determined yet. Using an anti-SDF-1 mAb, we performed immunohistochemica l studies in four human embryos and five fetuses to define which cells expr ess the SDF-1 protein at sites of antenatal B cell lymphopoiesis. All mesot helial cells contained SDF-1 at all stages of development, including in the intraembryonic splanchnopleuric mesoderm early into gestation. In fetal lu ngs and kidneys, SDF-1 was expressed by epithelial cells, and a few B lymph oid precursor, expressing V pre-B chains, were also detected. In the fetal liver, in addition to mesothelial cells, biliary epithelial cells were the only cells to contain SDF-1, Pre-B cells expressing V chains were abundant and exclusively located around the edge of portal spaces, in close contact with biliary ductal plate epithelial cells. They did not colocalize with bi liary collecting ducts. Biliary ductal plate epithelial cells and liver B c ell lymphopoiesis display a parallel development and disappearance during f etal life. These results indicate that early B cell lymphopoiesis in the sp lanchnopleura may be triggered by mesothelial cells producing SDF-1, Later into gestation, biliary ductal plate epithelial cells may support B cell ly mphopoiesis, thus playing a role similar to that of epithelial cells in the avian bursa of Fabricius, and of thymic epithelial cells for T cell lympho poiesis.