Provided is an immunosuppressive peptide of 40 kDa molecular weight, isolated from the submandibular glands (SMG*) of rats, having the capacity to suppress immune reactions upon parenteral administration to rats and mice. The peptide was identified as glandular kallikrein (K1) by partial sequencing and by enzymatic activity. Also provided are methods and compositions for Using K1 peptides in the treatment of autoimmune diseases.
