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 interact with the .alpha.2M receptor, and modulate the interaction of the .alpha.2M receptor with its ligand, such as HSPs, and methods for using compositions comprising .alpha.2M-receptor sequences for the diagnosis and treatment of immune disorders, proliferative disorders, and infectious diseases.