ICOS maintains the T follicular helper cell phenotype by down-regulating Krüppel-like factor 2.
Bottom Line: While CD28 regulated early expression of the master transcription factor Bcl-6, ICOS co-stimulation was essential to maintain the phenotype by regulating the novel TFH transcription factor Klf2 via Foxo1.Klf2 directly binds to Cxcr5, Ccr7, Psgl-1, and S1pr1, and low levels of Klf2 were essential to maintain this typical TFH homing receptor pattern.Our study describes for the first time the exclusive role of ICOS and its downstream signaling in the maintenance of TFH cells by controlling their anatomical localization in the B cell follicle.
Affiliation: Chronic Immune Reactions, Cell Biology, and Bioinformatics, German Rheumatism Research Centre, a Leibniz Institute, 10117 Berlin, Germany Molecular Immunology, Robert Koch Institute, 13353 Berlin, Germany.Show MeSH
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Mentions: To gain a deeper understanding of this phenotype reversion, TFH cells were analyzed 20 h after blocking ICOS-L, while conversion was still in progress. After this short period, the intensity of CXCR5 and PD-1 staining was already diminished on TFH cells (Fig. 5 A). At the same time, the expression of the T cell zone homing receptors CCR7 and P-selectin glycoprotein ligand-1 (PSGL-1; Haynes et al., 2007; Veerman et al., 2007; Poholek et al., 2010) increased (Fig. 5 B). Importantly, expression of the transcription factors Bcl-6 and c-Maf by TFH cells was unchanged. Ascl2 was slightly reduced by only 16%, which is unlikely to have any biological significance (Fig. 5, B and C). This demonstrates that ICOS primarily regulates the expression of TFH homing markers and not TFH-related transcription factors. However, expression of Tbx21 and Gata3 significantly increased upon blocking ICOS-L, indicating the conversion of TFH cells into other Th subsets.
Affiliation: Chronic Immune Reactions, Cell Biology, and Bioinformatics, German Rheumatism Research Centre, a Leibniz Institute, 10117 Berlin, Germany Molecular Immunology, Robert Koch Institute, 13353 Berlin, Germany.