The present invention relates to novel Tumor Necrosis Factor Receptor proteins. In particular, isolated nucleic acid molecules are provided encoding the human TNFR-6.alpha. & -6.beta. proteins. TNFR-6.alpha. & -6.beta. polypeptides and antibodies that bind TNFR-6.alpha. & -6.beta. 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 TNFR-6.alpha. & -6.beta. activity. Also provided are diagnostic methods for detecting immune system-related disorders and therapeutic methods for treating immune system-related disorders.