Mouse SF20 is a secreted bone marrow stroma-derived growth factor. SF20 isnot only expressed in bone marrow and spleen stroma cells, It is expressed in resting mononuclear cells, resting CD8+ and CD19+ cells and activated CD8+ T cells. It has been shown only to bind to the surface of cells expressing the receptor TSA-1 (Thymic shared Ag-1). Reports show that SF20 stimulates the proliferation of FDCP2 (a mouse IL-3 factor-dependent hemopoietic cell line) cells and mouse lymphoid cells through TSA-1, but it does not show any myelopoietic activity. More research on SF20 and its receptor TSA-1 may help determine the role they play in the regulation of lymphocyte activation. Recombinant Mouse SF20 is a 15.8kD protein, consisting of 143 amino acid residues.