The invention provides methods of removing B7-H1-specific antibodies from a body fluid (e.g., blood), methods of diagnosing and treating diseases and pathological conditions mediated by activated T cells, methods for screening for compounds that inhibit binding of a B7-H1-specific antibody to B7-H1, and methods of designing compounds that inhibit binding of a B7-H1-specific antibody to B7-H1.