Influence of synthetic peptide corresponding to the ACTH-like sequence of human immunoglobulin G1 on activity of murine thymocytes and peritoneal macrophages.

The purpose of the present study was to investigate properties and mechanism of action of the synthetic adrenocorticotropin (ACTH)-like peptide VKKPGSSVKV, corresponding to the sequence 11-20 of the variable part of human immunoglobulin G1 (IgG1) heavy chain. The ACTH-like peptide was shown to act as an immunosuppressive agent in vitro: it inhibits the blast transformation of mouse thymocytes and reduces the spontaneous motility of mouse peritoneal macrophages as well as their bactericidal activity against Salmonella typhimurium 415 virulent strain bacteria. High affinity receptors for the ACTH-like peptide were found on thymocytes and macrophages and shown to be at the same time the receptors for ACTH. The kinetic characteristics of the ACTH-like peptide and 125I-labeled ACTH (13-24) (ACTH 'address segment') specific binding to the receptors were determined. It was found that the ACTH-like peptide binding to the receptors on target cells is accompanied by an increase in both adenylate cyclase activity and intracellular cAMP content.