Mouse SF20 is a bone marrow stroma-derived growth factor. SF20 is expressed in the bone marrow,spleen stroma cells,resting mononuclear cells,resting CD8+ and CD19+ cells and activated CD8+ T cells. SF20 has been shown to bind to the surface of cells expressing the receptor TSA-1 (Thymic shared Ag-1). Among SF20’s biological activities is stimulation of the proliferation of FDCP2 cells (a mouse factor-dependent hemopoietic cell line) and mouse lymphoid cells.