Discloses a therapeutic composition, comprising an isolated aminoacyl-tRNA synthetase (AARS) polypeptide of up to 300 amino acids in length that comprises SEQ ID NO: 16 or 14 or an amino acid sequence that is at least 90% identical to SEQ ID NO: 16 or 14, wherein the AARS polypeptide has an extracellular signalling activity and a solubility of at least about 5 mg/mL, and wherein the composition has a purity of at least about 95% on a protein basis and less than about 10 EU endotoxin / mg protein.