The present invention relates to in vitro methods for stimulating, or increasing a population of, immune cells comprising using compositions which comprise a substantially pure polypeptide comprising a first amino acid sequence having at least about 70% homology to a sequence selected from SEQ. ID. NOs:7, 8, 9, and 11； or a biologically active fragment of any of these, wherein said polypeptide or fragment thereof can stimulate the proliferation and differentiation of granulocytes, monocytes, or dendritic cells； and to the use of these polypeptides in methods of treatment
