Mechanism underlying the induction of Foxp3+ regulatory T cells by lactoferrin

Abstract

Abstract Lactoferrin (LF) is multifunctional in the immune response. We have previously demonstrated that LF acts like TGF-β in IgA B cell differentiation. Therein, we explored whether LF affects peripheral regulatory T cell (Treg) differentiation. Indeed, LF induced Foxp3+ Treg differentiation by itself and in combination with TGF-β1 synergized to express Foxp3. It was conceivable that LF may increase Foxp3 expression through secretion of active TGF-β or facilitating latent TGF-β to active form. There was little active TGF-β in the supernatant from LF-stimulated T cells. Surprisingly, however, pan anti-TGFβ Ab completely abolished the LF-induced Foxp3 expression, suggesting that membrane-bound TGF-β may be involved. In this, we found that both LF and TGF-β1 increase latency-associated peptide negative (LAP−)TGF-β on the surface of Foxp3+T cells, and this increase was more dramatic when treated with LF plus TGF-β1. As was the case in B cells, LF-induced Foxp3 expression was virtually disappeared by pretreatment with soluble TβRIII. Collectively, these results suggest that LF induces Foxp3+Treg through TβRIII and subsequent expression of membrane-bound/LAP-negative TGF-β.