The present invention relates to TR18 polypeptides. In particular, isolated nucleic acid molecules are provided encoding human TR18 protein. TR18 polypeptides are also provided as are vectors, host cells and recombinant methods for producing the same. The invention further relates to screening methods for identifying agonists and antagonists of TR18 activity. The invention further relates to methods of treating, preventing, prognosing, or diagnosing an autoimmune disease or condition associated with an autoimmune disease, comprising administering to a patient an effective amount of polypeptides of the invention.