Peptide, a method for its preparation and a pharmaceutical composition containing the peptide

A method of immunosuppressing the immune system in an animal comprising administering an effective amount of a peptide of a formula I:

• X-A-D-Trp-Y (I)
• wherein X is selected from the group comprising hydrogen, glycine, alanine, leucine, isoleucine, valine, N-valine, proline, tyrosine, phenylalanine, tryptophan, D-alanine, D-leucine, D-isoleucine, D-valine, D-N-valine, D-proline, D-tyrosine, D-phenylalanine, D-tryptophan, γ-aminobutyric acid, and ζ-aminocaproic acid;
• A is selected from the group comprising D-glutamic acid and D-iso-glutamic acid;
• and Y is selected from the group comprising glycine, alanine, leucine, isoleucine, valine, N-valine, proline, tyrosine, phenylalanine, tryptophan, D-alanine, D-leucine, D-isoleucine, D-valine, D-N-valine, D-proline, D-tyrosine, D-phenylalanine, D-tryptophan, γ-aminobutyric acid, ζ-aminocaproic acid, hydroxyl and an amide group, to an animal in need thereof.