Novel secreted and membrane bound 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 ligands, agonists and antagonists. The polypeptides, polynucleotides and antibodies may also be used in methods that modulate inflammation, tumor growth and metastasis, infection, immunity, and cellular maturation.