Follicular helper T cells (Tfh) support high-affinity Ab production by germinal center B cells through both membrane interactions and secretion of IL-4 and -21, two major cytokines implicated in B-cell survival and Ab class switch. Tfh-2 cells recently emerged in humans as a strong IL-4 producer Tfh cell subset implicated in both autoimmune and allergic diseases. Although the molecular mechanisms governing Tfh cell differentiation from naive T cells have been widely described, much less is known about the regulation of cytokine secretion by mouse Tfh-2 cells. The purpose of our study was to evaluate the role of dendritic cell-derived IL-6 in fine-tuning cytokine secretion by Tfh cells. Our results demonstrate that priming of Th cells by IL-6-deficient antigen-presenting dendritic cells preferentially leads to accumulation of a subset of Tfh cells characterized by high expression of GATA3 and IL-4, associated with reduced production of IL-21. STAT3-deficient Tfh cells also overexpress GATA3, suggesting that early IL-6/STAT3 signaling during Tfh cell development inhibits the expression of a set of genes associated with the Th2 differentiation program. Overall, our data indicate that IL-6/STAT3 signaling restrains the expression of Th2-like genes in Tfh cells, thus contributing to the control of IgE secretion in vivo.

The identification of DC-derived signals orchestrating activation of Th1 and Th17 immune responses has advanced our understanding on how these inflammatory responses develop. However, whether specific signals delivered by DCs also participate in the regulation of Th2 immune responses remains largely unknown. In this study, we show that administration of antigen-loaded, IL-6-deficient DCs to naïve mice induced an exacerbated Th2 response, characterized by the differentiation of GATA-3-expressing T lymphocytes secreting high levels of IL-4, IL-5, and IL-13. Coinjection of wild type and IL-6-deficient bone marrow-derived dendritic cells (BMDCs) confirmed that IL-6 exerted a dominant, negative influence on Th2-cell development. This finding was confirmed in vitro, where exogenously added IL-6 was found to limit IL-4-induced Th2-cell differentiation. iNKT cells were required for optimal Th2-cell differentiation in vivo although their activation occurred independently of IL-6 secretion by the BMDCs. Collectively, these observations identify IL-6 secretion as a major, unsuspected, mechanism whereby DCs control the magnitude of Th2 immunity.Keywords: Airway allergy r DCs r IL-6 r iNKT cells r Th2-cell differentiation Additional supporting information may be found in the online version of this article at the publisher's web-site IntroductionThe role of APCs, and in particular DCs, in regulating naïve Th-cell differentiation into the Th2 lineage remains poorly understood. Indeed, although DCs represent the major source of Th1-and Th17-polarizing cytokines (such as [1], these cells do not appear to produce the most efficient and best characterized pro-Th2 soluble factors (such as Correspondence: Dr. Fabienne Andris e-mail: fandris@ulb.ac.be or thymic stromal lymphopoietin) identified to date. Thus, although numerous studies have illustrated the role of several innate cell types, including basophils and DC subtypes (conventional CD8α − DCs, inflammatory monocyte-derived FcεRI + DCs, CD301b + , PDL2 + , and/or MGL2 + dermal DCs) in driving Th2-cell differentiation in vivo [2][3][4][5][6][7][8][9][10][11][12], the mechanisms by which APCs promote Th2-type responses in vivo remain ill-defined. * These authors contributed equally to this work as first authors. * * These authors contributed equally to this work as senior authors.C 2014 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim www.eji-journal.eu Eur. J. Immunol. 2014. 44: 3252-3262 Cellular immune response 3253The Th2 pathway has therefore been often considered as a "default pathway," mostly based on the observation that stimulation of naïve T cells in the absence of strong Th1-polarizing conditions (such as lack of APC-derived IL-12 [2,13]) favors the acquisition of a Th2 phenotype in several experimental models. This simple concept has been recently challenged, since several APC-derived, pro-Th2 instructing signals have been identified (OX40L, ICOS-L, the Notch family member Jagged-1, or the T-cell immunoglobulin and mucin domain molecule-4 [14-17]), although their relat...

Follicular T helper cells (Tfh) are crucial for effective antibody responses and long term T cell-dependent humoral immunity. Although many studies are devoted to this novel T helper cell population, the molecular mechanisms governing Tfh cell differentiation have yet to be characterized. MyoR/ABF-1 is a basic helix-loop-helix transcription factor that plays a role in the differentiation of the skeletal muscle and Hodgkin lymphoma. Here we show that MyoR mRNA is progressively induced during the course of Tfh-like cell differentiation in vitro and is expressed in Tfh responding to Alum-precipitated antigens in vivo. This expression pattern suggests that MyoR could play a role in the differentiation and/or function of Tfh cells. We tested this hypothesis using MyoR-deficient mice and found this deficiency had no impact on Tfh differentiation. Hence, MyoR-deficient mice developed optimal T-dependent humoral responses to Alum-precipitated antigens. In conclusion, MyoR is a transcription factor selectively up-regulated in CD4 T cells during Tfh cell differentiation in vitro and upon response to alum-protein vaccines in vivo, but the functional significance of this up-regulation remains uncertain.

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