For example, in one embodiment where one is assaying for the ability to bind or compete with complete (full-length) or mature TNFR-6?? and/or TNFR-6?? polypeptide for binding to anti-TNFR-6?? and/or anti-TNFR-6?? antibody, various immunoassays known in the art can be used, including but not limited to, competitive and non-competitive assay systems using techniques such as radioimmunoassays, ELISA