Abstract: Provided are methods for production of cell surface receptor (CSR) and ligand isoforms. In particular, isoform fusions that a precursor sequence for secretion, processing and intracellular trafficking are provided. Nucleic acid molecules encoding the fusions are expressed in a host cell and the encoded and partially or completely processed encoded CSR or ligand isoforms is produced in the cell culture medium. The resulting polypeptide optionally includes an epitope tag for the detection and/or purification thereof.