Murine SF20 is a bone marrow stroma-derived growth factor. SF20 is expressed in bone marrow, spleen stroma cells, resting mononuclear cells, resting CD8 and CD19 cells and activated CD8 T cells and has been shown to bind to the surface of cells expressing the receptor TSA-1 (Thymic shared Ag-1). Among its biological activities, SF20 stimulates the proliferation of FDCP2 cells (a mouse factor-dependent hemopoietic cell line) and mouse lymphoid cells. Recombinant murine SF20 is a 15.8 kDa protein containing 143 amino acid residues.