Lactoferrin-derived chimeric peptide (LFch) strongly boosts TGFβ1-mediated inducible Treg differentiation possibly through downregulating TCR/CD28 signalling

We recently reported that lactoferrin (LF) induces Foxp3(+) Treg differentiation through binding to TGF beta receptor III (T beta RIII), and this activity was further enhanced by TGF beta 1. Generally, a low T-cell receptor (TCR) signal strength is favourable for Foxp3(+) Treg differentiation. In the present study, we explored the effect of lactoferrin chimera (LFch, containing lactoferricin [aa 17-30] and lactoferrampin [aa 265-2841), along with TGF beta 1 on Foxp3(+) Treg differentiation. LFch alone did not induce Foxp3 expression, yet LFch dramatically enhanced TGF beta 1-induced Foxp3 expression. LFch had little effect on the phosphorylation of Smad3, a canonical transcriptional factor of TGF beta 1. Instead, LFch attenuated the phosphorylation of S6 (a target of mTOR), I kappa B and PI3K. These activities of LFch were completely abrogated by pretreatment of LFch with soluble TGF beta 1 receptor III (sT beta RIII). Consistent with this, the activity of LFch on TGF beta 1-induced Foxp3 expression was also abrogated by treatment with sT beta RIII. Finally, the TGF beta 1/LFchinduced T cell population substantially suppressed the proliferation of responder CD4(+) T cells. These results indicate that LFch robustly enhances TGF beta 1-induced Foxp3(+) Treg differentiation by diminishing TCR/CD28 signal intensity.