Compositions and methods relating to soluble dimeric proteins are disclosed. The dimeric proteins comprise first and second polypeptide fusions linked via a dimerizing domain, each polypeptide fusion comprising first and second monomer domains corresponding to a cytokine or an extracellular domain of a cell-surface receptor. The monomer domains may be positioned amino terminal and carboxyl terminal to the dimerizing domain. Alternatively, the monomer domains may be positioned in tandem, either carboxyl terminal or amino terminal to the dimerizing domain. The dimeric proteins are useful in methods for therapy, diagnosis, and research.