Krüppel-like factor 2 (KLF2) controls T lymphocyte egress from lymphoid organs by regulating sphingosin-1 phosphate receptor 1 (S1Pr1). Here we show that this is not the case for B cells. Instead, KLF2 controls homeostasis of B cells in peripheral lymphatic organs and homing of plasma cells to the bone marrow, presumably by controlling the expression of β 7 -integrin. In mice with a B cell-specific deletion of KLF2, S1Pr1 expression on B cells was only slightly affected. Accordingly, all splenic B cell subsets including B1 cells were present, but their numbers were increased with a clear bias for marginal zone (MZ) B cells. In contrast, fewer peyers patches harboring fewer B cells were found, and fewer B1 cells in the peritoneal cavity as well as recirculating B cells in the bone marrow were detected. Upon thymus-dependent immunization, IgG titers were diminished, and antigen-specific plasma cells were absent in the bone marrow, although numbers of antigen-specific splenic plasmablasts were normal. KLF2 plays also a role in determining the identity of follicular B cells, as KLF2-deficient follicular B cells showed calcium responses similar to those of MZ B cells and failed to down-regulate MZ B cell signature genes, such as CD21 and CXCR7.cell trafficking | S1P1 | LKLF | B cell development | knockout mouse M aturation of lymphocytes in primary lymphoid organs, controlled egress into the periphery, and proper positioning in lymphoid tissues are critical for efficient adaptive immune responses. Differential expression of Krüppel-like factor 2 (KLF2) promotes egress of T cells from lymphoid organs into the blood and T-cell migration to lymph nodes (1, 2). Accordingly, KLF2 is expressed in naive T cells, down-regulated upon activation, and reexpressed in memory T cells (1, 3-5). KLF2-deficient T cells inefficiently exit from the thymus and thus accumulate there; this is thought to be a consequence of a decrease in sphingosin-1 phosphate receptor 1 (S1Pr1) expression, which is regulated by KLF2 (2, 6). In addition, KLF2 increases the expression of β 7 -integrin (gene symbol: Itgb7) and CD62L (L-selectin) on T cells (1, 2). However, other downstream effects of KLF2 expression are less clear, although they very likely contribute to the migratory behavior of T cells. For example, vav-cre-and lck-cre-mediated deletion of KLF2 in T cells resulted in the up-regulation of the inflammatory chemokine receptors CCR3 and CCR5 (7) on thymocytes, whereas CD4-cre-mediated deletion led to the up-regulation of only CXCR3 and spontaneous IL4 production in naive T cells (8).Although the role of KLF2 in T-cell migration has been studied extensively, its function in B cells is not fully understood. KLF2 expression at the RNA and protein level is induced by pre-B cell receptor (pre-BCR) signals (9). Analogous to T cells, KLF2 transcripts are abundant in resting mature B cells, down-regulated upon mitogenic activation, and reexpressed in plasma and memory B cells (10)(11)(12). Because KLF2 controls the expression of β 7 -integrin and CD62...

NFATc1 is a member of the nuclear factor of activated T cells (NFAT) family of transcription factors. NFAT is activated upon T-cell receptor activation followed by intracytoplasmatic Keywords: CD4+ T cells r EAE r NFAT r RORγT r Th17Additional supporting information may be found in the online version of this article at the publisher's web-site IntroductionNuclear factor of activated T cells (NFAT) was originally described as a transcription factor inducing the expression of interleukin 2 (IL-2) [1]. The NFAT family of transcription factors consists of five members, named NFAT1-5, and the main forms expressed in T cells are NFATc1 and NFATc2 [2]. NFATc2 is constitutively expressed in T cells [3], whereas NFATc1 is activated upon T-cell receptor stimulation [4]. NFATc1 is the only NFAT protein Correspondence: Prof. Susetta Finotto e-mail: susetta.finotto@uk-erlangen.de family member which acts in a positive autoregulatory loop [5] and thereby augments NFATc1 expression. NFAT proteins reside phosphorylated in the cytoplasm. Upon T-cell receptor activation the phospholipase C signaling pathway is activated, which leads to an induced influx of calcium into the cell. Intracytoplasmatic calcium signaling activates calmodulin, a calcium sensor protein that activates the phosphatase calcineurin. These phosphatase dephosphorylates NFAT proteins, so that they can shuttle into the nucleus where they act as transcription factors on the promoter of target * These authors contributed equally to this work. www.eji-journal.euThis is an open access article under the terms of the Creative Commons Attribution-NonCommercialNoDerivs License, which permits use and distribution in any medium, provided the original work is properly cited, the use is non-commercial and no modifications or adaptations are made.Eur. J. Immunol. 2015Immunol. . 45: 1426Immunol. -1440 Immunomodulation 1427 genes such as . Previous studies showed that NFAT proteins play regulatory roles during T-cell differentiation and effector functions. NFATc2 deficiency in T cells diminished Th1 differentiation and induced IL-4 production [7,8]. NFATc2 was also shown to contribute to IL-21 expression and to limit the immunosuppressive function of CD4 + CD25 + Foxp3 + GITR + T regulatory (Treg) cells [8,9]. The role of NFATc1 in T-cell differentiation processes is not fully understood, partially because NFATc1 total knockout mice die at the embryonic stage [10]. Previous analysis on Th1-and Th2-skewed T cells isolated from NFATc1−/− /Rag1 −/− chimeric mice revealed an involvement of NFATc1 in the induction of the Th2-cytokines IL-4 and IL-6, whereas it had no effect on interferon gamma (IFN-γ) and IL-2 expression in Th1 cells [11,12]. Other studies showed that NFATc1 induces IL-4 expression. In Th17 cells, NFAT transcription factors have been shown to be involved in the gene expression of RORγT (where ROR is RARrelated orphan receptor), . This has been shown mostly for other NFAT transcription factor family members than NFATc1. EAE is the murine model for the early in...

Maturation as well as antigen-dependent activation of B cells is accompanied by alternating phases of proliferation and quiescence. We and others have previously shown that Krüppel-like factor 2 (KLF2), a regulator of T cell quiescence and migration, is upregulated in small resting precursor (pre)-B cells after assembly of the immature pre-B cell receptor (pre-BCR) and is downregulated upon antigen-induced proliferation of mature B cells. These findings suggest that KLF2, besides its function in maintaining follicular B cell identity, peripheral B cell homeostasis and homing of antigen-specific plasma cells to the bone marrow, also controls clonal expansion phases in the B cell lineage. Here, we demonstrate that enforced expression of KLF2 in primary pre-B cells results in a severe block of pre-BCR-induced proliferation, upregulation of the cell cycle inhibitors p21 and p27 and downregulation of c-myc. Furthermore, retroviral KLF2 transduction of primary B cells impairs LPS-induced activation, favors apoptosis and results in reduced abundance of factors, such as AID, IRF4 and BLIMP1, that control the antigen-dependent phase of B cell activation and plasma cell differentiation. Hence, we conclude that KLF2 is not only a key player in terminating pre-B cell clonal expansion but also a potent suppressor of B cell activation.

The small adaptor protein growth factor receptor–bound protein 2 (Grb2) modulates and integrates signals from receptors on cellular surfaces in inner signaling pathways. In murine T cells, Grb2 is crucial for amplification of TCR signaling. T cell–specific Grb2fl/fl Lckcretg Grb2-deficient mice show reduced T cell numbers due to impaired negative and positive selection. In this study, we found that T cell numbers in Grb2fl/fl CD4cretg mice were normal in the thymus and were only slightly affected in the periphery. Ex vivo analysis of CD4+ Th cell populations revealed an increased amount of Th1 cells within the CD4+ population of Grb2fl/fl CD4cretg mice. Additionally, Grb2-deficient T cells showed a greater potential to differentiate into Th17 cells in vitro. To test whether these changes in Th cell differentiation potential rendered Grb2fl/fl CD4cretg mice more prone to inflammatory diseases, we used the murine Th1 cell– and Th17 cell–driven model of experimental autoimmune encephalomyelitis (EAE). In contrast to our expectations, Grb2fl/fl CD4cretg mice developed a milder form of EAE. The impaired EAE disease can be explained by the reduced proliferation rate of Grb2-deficient CD4+ T cells upon stimulation with IL-2 or upon activation by allogeneic dendritic cells, because the activation of T cells by dendritic cells and the subsequent T cell proliferation are known to be crucial factors for the induction of EAE. In summary, Grb2-deficient T cells show defects in T cell development, increased Th1 and Th17 cell differentiation capacities, and impaired proliferation after activation by dendritic cells, which likely reduce the clinical symptoms of EAE.