TP5 triggers signal transduction involving mitogen activated protein kinases in monocytes

The pentapetide thymopentin (TP5) corresponding to the aminoacids RKDVY represents the residues 32-36 of thymopoietin (TP), which was originally isolated from bovine thymus. Both were observed to induce T-cell differentiation and maturation. Recently however it was shown, that TP represents the N-terminal 49 aa of the human thymopoietin (TMPO) isoforms TMPO alpha, beta and gamma, which are localized in the nucleus. TP5 was investigated in a variety of diseases and showed efficacy by improving the immune balance, whereby different cells increased in cell number or activity. Findings which support the assumption of multifunctional efficacy and a description of TP and TP5 modulating T cells lack any interpretation on molecular level. In the present study we investigated the binding of TP5 on white blood cells. We identified monocytes and neutrophils as TP5-binding cells by displacing fluorescein-labelled TP5 with an excess of unlabelled TP5 in competition assays. Binding of TP5 on cell surface proteins resulted in cellular signalling and we report here that TP5 triggers signal transduction involving mitogen activated protein kinases p42/p44 (MAPKs) in monocytes.