The immunosuppressive effect of glucocorticoids in human primary T cells is mainly mediated via a rapid inhibition of the IL-2/IL-2R signaling axis

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BACKGROUND: Glucocorticoids (GCs) are highly effective anti-inflammatory drugs that suppress T-cell activation, cytokine production, and T-cell proliferation. Nevertheless, at which molecular level and how fast GCs exert their immunosuppressive effect in T cells still remains elusive, as inconsistent genomic and non-genomic mechanisms of action have been proposed. One model postulates that GCs quickly inhibit proximal T-cell receptor (TCR) signaling via a non-genomic mechanism, whereas others have shown a strong inhibition of interleukin-2 (IL-2) transcription at later stages of T-cell activation. Due to their therapeutic significance, we have decided to shed light onto this issue and investigated how fast and at which level GCs inhibit T-cell activation by analyzing TCR and IL-2 signaling. METHODS: We utilized primary human T cells isolated from healthy donors, which were stimulated with immobilized CD3/CD28 antibodies. These cells were treated with three different GCs, diflorasone, dexamethasone, and prednisolone. RESULTS: influx. Conversely, we found that GCs strongly and rapidly suppressed the activation of the Janus kinase (Jak)/ signal transducer and activator of transcription (STAT) pathway within 4-6 h upon CD3/CD28 stimulation in primary human T cells. This observation was in line with a strong inhibition of cytokine production and with the impaired upregulation of the IL-2 receptor (IL-2R) upon GC treatment, thus resulting in the abrogation of T-cell proliferation. CONCLUSIONS: Our study, by showing that GCs rapidly suppress the IL-2/IL-2R expression and signaling without significantly affecting proximal TCR signaling, has highlighted a clear mechanism of action of GCs that contributes to their therapeutic efficacy.