Immature dendritic cells convert anergic nonregulatory T cells into Foxp3- IL-10+ regulatory T cells by engaging CD28 and CTLA-4.

Katrien Pletinckx, Martin Vaeth, Theresa Schneider, Niklas Beyersdorf, Thomas Hünig, Friederike Berberich-Siebelt, Manfred B Lutz

Index: Eur. J. Immunol. 45(2) , 480-91, (2015)

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Abstract

Anergic T cells can survive for long time periods passively in a hyporesponsive state without obvious active functions. Thus, the immunological reason for their maintenance is unclear. Here, we induced peptide-specific anergy in T cells from mice by coculturing these cells with immature murine dendritic cells (DCs). We found that these anergic, nonsuppressive IL-10(-) Foxp3(-) CTLA-4(+) CD25(low) Egr2(+) T cells could be converted into suppressive IL-10(+) Foxp3(-) CTLA-4(+) CD25(high) Egr2(+) cells resembling type-1 Treg cells (Tr1) when stimulated a second time by immature DCs in vitro. Addition of TGF-β during anergy induction favored Foxp3(+) Treg-cell induction, while TGF-β had little effect when added to the second stimulation. Expression of both CD28 and CTLA-4 molecules on anergic T cells was required to allow their conversion into Tr1-like cells. Suppressor activity was enabled via CD28-mediated CD25 upregulation, acting as an IL-2 sink, together with a CTLA-4-mediated inhibition of NFATc1/α activation to shut down IL-2-mediated proliferation. Together, these data provide evidence and mechanistical insights into how persistent anergic T cells may serve as a resting memory pool for Tr1-like cells. © 2014 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.