IL-2 Expression in Activated Human Memory FOXP3+ Cells Critically Depends on the Cellular Levels of FOXP3 as Well as of Four Transcription Factors of T Cell Activation

Hanna Bendfeldt,Andreas Radbruch,Manuela Benary,Kerstin Steinbrink,Tobias Scheel,Ria Baumgrass,Hanspeter Herzel

doi:10.3389/fimmu.2012.00264

Abstract

The human CD4+FOXP3+ T cell population is heterogeneous and consists of various subpopulations which remain poorly defined. Anergy and suppression are two main functional characteristics of FOXP3+Treg cells. We used the anergic behavior of FOXP3+Treg cells for a better discrimination and characterization of such subpopulations. We compared IL-2-expressing with IL-2-non-expressing cells within the memory FOXP3+ T cell population. In contrast to IL-2-non-expressing FOXP3+ cells, IL-2-expressing FOXP3+ cells exhibit intermediate characteristics of Treg and Th cells concerning the Treg cell markers CD25, GITR, and Helios. Besides lower levels of FOXP3, they also have higher levels of the transcription factors NFATc2, c-Fos, NF-κBp65, and c-Jun. An approach combining flow cytometric measurements with statistical interpretation for quantitative transcription factor analysis suggests that the physiological expression levels not only of FOXP3 but also of NFATc2, c-Jun, c-Fos, and NF-κBp65 are limiting for the decision whether IL-2 is expressed or not in activated peripheral human memory FOXP3+ cells. These findings demonstrate that concomitant high levels of NFATc2, c-Jun, c-Fos, and NF-κBp65 lead in addition to potential IL-2 expression in those FOXP3+ cells with low levels of FOXP3. We hypothesize that not only the level of FOXP3 expression but also the amounts of the four transcription factors studied represent determining factors for the anergic phenotype of FOXP3+ Treg cells.

Highlights

FOXP3-expressing Treg cells are essential for the maintenance of immunological self-tolerance and immune homeostasis
A detailed knowledge of human FOXP3+ cell subsets is essential for a better understanding of the regulation of human FOXP3 expression, the study of abnormalities among the FOXP3+ subpopulations in autoimmune diseases and allergies, and the selection and purification of the most promising subpopulation(s) of Treg cells for in vitro expansion and adoptive transfer (Fujii et al, 2011; Miyara and Sakaguchi, 2011)
UP TO ONE-FIFTH OF PERIPHERAL HUMAN MEMORY FOXP3+ CELLS ARE ABLE TO EXPRESS IL-2 Comparing transcription factor levels and cytokine expression within the memory CD4+ T cell population of healthy donors (Bendfeldt et al, 2012) we discovered that there are always 8–20% IL-2-expressing FOXP3+ Th cells, in spite of the fact that FOXP3+ cells are widely considered to be incapable of producing IL-2 and other effector cytokines (Hori et al, 2003)

Summary

Introduction

FOXP3-expressing Treg cells are essential for the maintenance of immunological self-tolerance and immune homeostasis. Not all peripheral human CD4+FOXP3+ cells are suppressive (Baecher-Allan et al, 2001). This high complexity of human FOXP3+ T cells causes some confusion in the field. Many efforts were undertaken to discriminate between suppressive and non-suppressive subpopulations among the ex vivo isolated CD4+FOXP3+ human T cells. Most promising so far is the division of FOXP3+ cells into three subpopulations based on FOXP3 and CD45RA or CD45RO expression: (i) naïve Treg cells (CD45RA+FOXP3low); (ii) memory effector Treg cells (CD45RA−FOXP3high); and (iii) memory non-suppressive Th cells (CD45RA−FOXP3low; Miyara et al, 2009)

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