The pentapetide thymopentin (TP5) corresponding to the aminoacids RKDVY rep
resents the residues 32 - 36 of thymopoietin (TP), which was originally iso
lated from bovine thymus. Both were observed to induce T-cell differentiati
on and maturation. Recently however it was shown, that TP represents the N-
terminal 49 aa of the human thymopoietin (TMPO) isoforms TMPO alpha, beta a
nd gamma, which are localized in the nucleus. TP5 was investigated in a var
iety of diseases and showed efficacy by improving the immune balance, where
by different cells increased in cell number or activity. Findings which sup
port 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 i
dentified monocytes and neutrophils as TP5-binding cells by displacing fluo
rescein-labelled TP5 with an excess of unlabelled TP5 in competition assays
. Binding of TP5 on cell surface proteins resulted in cellular signalling a
nd we report here that TP5 triggers signal transduction involving mitogen a
ctivated protein kinases p42/p44 (MAPKs) in monocytes.