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

Abstract

We recently reported that lactoferrin (LF) induces Foxp3 + Treg differentiation through binding to TGFβ receptor III (TβRIII), and this activity was further enhanced by TGFβ1. 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, and lactoferrampin [aa 265-284]), along with TGFβ1 on Foxp3 + Treg differentiation. LFch alone did not induce Foxp3 expression, yet LFch dramatically enhanced TGFβ1-induced Foxp3 expression. LFch had little effect on the phosphorylation of Smad3, a canonical transcriptional factor of TGFβ1. Instead, LFch attenuated the phosphorylation of S6 (a target of mTOR), IκB and PI3K. These activities of LFch were completely abrogated by pretreatment of LFch with soluble TGFβ1 receptor III (sTβRIII). Consistent with this, the activity of LFch on TGFβ1-induced Foxp3 expression was also abrogated by treatment with sTβRIII. Finally, the TGFβ1/LFchinduced T cell population substantially suppressed the proliferation of responder CD4 + T cells. These results indicate that LFch robustly enhances TGFβ1-induced Foxp3 + Treg differentiation by diminishing TCR/CD28 signal intensity.

Combined Treatment With TGF-β1, Retinoic Acid, and Lactoferrin Robustly Generate Inducible Tregs (iTregs) Against High Affinity Ligand

“…In the case of iTregs, it was shown that low doses of Ag or polyclonal TCR activators induce Foxp3 expression, whereas high doses of these stimuli ameliorate Foxp3 upregulation ( 9 ). Consistently, we and others have shown that inhibition of downstream mediators of TCR/CD28 signaling, such as PI3K, protein kinase B (Akt), and mTOR, significantly augments TGF-β1–induced Foxp3 expression ( 10 11 ). However, it is not known how TCR/CD28 signaling intensities (high or low) affect TGF-β-mediated Foxp3 expression in the presence of RA and LF.…”

“…However, the mechanism by which this combination might cause such synergistic iTreg generation remains unknown. It is well established that TGF-β/Smad3–dependent signaling induces Foxp3 + Treg differentiation ( 3 4 ), and TGF-β1–mediated iTreg generation is further enhanced by LF and its peptides ( 7 11 ). These studies reveal that LF promotes Foxp3 upregulation through two mechanisms: by phosphorylating Smad3 through activation of membrane-bound TGF-β and attenuating TCR/CD28 signaling, both of which occur via TGF-β type III receptor.…”