THE IMMUNOMODULATORY PROPERTIES OF LOW-MOLECULAR TRIPEPTIDES AND TETRAPEPTIDES

Immunomodulatory effects of six linear tri- or tetrapeptides were stud ied. These peptides are physiologically inert precursors, which under the action of native proteases split into a C-terminal dipeptide ester , which is subsequently converted by spontaneous intramolecular cycliz ation to a biologically active compound, i.e., a spirocyclic dipeptide . The following biological activities were evaluated using human lymph ocytes: recovery of receptors for sheep red blood cells, test of activ e E-rosettes, and modulation of T-cell mitogen responses. All tested p eptides revealed significant inhibition in some assay, although none o f them induced significant inhibition in all assays. The compounds I, IV, and VI proved to be the best inhibitors in comparison with Alaptid e, i.e., cyclo(Ala-Acp).