The present invention relates to the use of alpha (2) macroglobulin (".alpha.2M") receptor as a heat shock protein receptor, cells that express the .alpha.2M receptor bound to an HSP, and antibodies and other molecules that bind the .alpha.2M receptor-HSP complex. The invention also relates to screening assays to identify compounds that modulate the interaction of an HSP with the .alpha.2M receptor, and methods for using compositions comprising .alpha.2M-receptor sequences for the diagnosis and treatment of immune disorders, proliferative disorders, and infectious diseases.