There is provided the use of an antibody, antibody fragment or single chain antibody that selectively binds to a polypeptide comprising an amino acid sequence having at least 80% identity to an IL-20 polypeptide selected from the group consisting of SEQ ID NOs: 2, 4, 12, 13, 19, 20, 25, 26, 34 and 35 for the manufacture of a medicament for the prevention or treatment of an autoimmune disease or condition, or for the prevention or treatment of conditions characterised by improper cell proliferation, cell differentiation or cytokine production.