The present invention generally features therapeutic and diagnostic compositions and methods for increasing or decreasing the binding of a lysozyme polypeptide to a Treponema pallidum P17 polypeptide (Tp17) or a Tp17-like polypeptide. More particularly, the invention relates to compositions and methods for detecting, treating, or preventing a pathogen infection or a chronic disorder; and to binding assays using a Tp17-like polypeptide and a lysozyme polypeptide.