Helios, and not FoxP3, is the marker of activated Tregs expressing GARP/LAP

// Eyad Elkord 1, 2, 3 , May Abd Al Samid 1, 2 , Belal Chaudhary 2, 4 1 College of Medicine & Health Sciences, United Arab Emirates University, Al Ain, United Arab Emirates 2 Biomedical Research Centre, School of Environment & Life Sciences, University of Salford, Manchester, United Kingdom 3 Institutes of Cancer, Inflammation & Repair, University of Manchester, Manchester, United Kingdom 4 University of Cambridge, Cambridge, United Kingdom Correspondence to: Eyad Elkord, e-mail: eelkord@uaeu.ac.ae , e.elkord@salford.ac.uk , eyad.elkord@manchester.ac.uk Keywords: Immunology and Microbiology Section, Immune response, Immunity, regulatory T cells, GARP/LAP, FoxP3, Helios Received: May 13, 2015      Accepted: July 17, 2015      Published: July 30, 2015 ABSTRACT Regulatory T cells (Tregs) are key players of immune regulation/dysregulation both in physiological and pathophysiological settings. Despite significant advances in understanding Treg function, there is still a pressing need to define reliable and specific markers that can distinguish different Treg subpopulations. Herein we show for the first time that markers of activated Tregs [latency associated peptide (LAP) and glycoprotein A repetitions predominant (GARP, or LRRC32)] are expressed on CD4 + FoxP3 − T cells expressing Helios (FoxP3 − Helios + ) in the steady state. Following TCR activation, GARP/LAP are up-regulated on CD4 + Helios + T cells regardless of FoxP3 expression (FoxP3 +/− Helios + ). We show that CD4 + GARP +/− LAP + Tregs make IL-10 immunosuppressive cytokine but not IFN-γ effector cytokine. Further characterization of FoxP3/Helios subpopulations showed that FoxP3 + Helios + Tregs proliferate in vitro significantly less than FoxP3 + Helios − Tregs upon TCR stimulation. Unlike FoxP3 + Helios − Tregs, FoxP3 + Helios + Tregs secrete IL-10 but not IFN-γ or IL-2, confirming they are bona fide Tregs with immunosuppressive characteristics. Taken together, Helios, and not FoxP3, is the marker of activated Tregs expressing GARP/LAP, and FoxP3 + Helios + Tregs have more suppressive characteristics, compared with FoxP3 + Helios − Tregs. Our work implies that therapeutic modalities for treating autoimmune and inflammatory diseases, allergies and graft rejection should be designed to induce and/or expand FoxP3 + Helios + Tregs, while therapies against cancers or infectious diseases should avoid such expansion/induction.