Novel tumor necrosis factor receptor (TNFR) polypeptides, polynucleotides encoding the polypeptides, antibodies and related compositions and methods are disclosed. The polypeptides may be used for detecting ligand, as well as agonists and antagonists. The polypeptides, polynucleotides and antibodies may also be used in methods that modulate tumor growth, metastasis, and immunity such as separating resting from stimulated immune cells.