BACKGROUND: Norepinephrine (NE) is one of the primary catecholamines of the sympathetic nervous system released during a stress response and plays an important role in modulating immune function. NE binds to the adrenergic receptors on immune cells, including T cells, resulting in either suppressed or enhanced function depending on the type of cell, activation status of the cell, duration of NE exposure and concentration of NE. Here, we aim to analyze the effects of NE on the functionality of naive (Tn), central memory (Tcm) and effector memory (Tem) CD8 T cells.
METHODS: We isolated CD8 T cell subsets from healthy human adults and treated cells in vitro with NE (1 × 10−6 M) for 16 h; we then stimulated NE treated and untreated CD8 T cell subsets with antibodies for CD3 and CD28 for 24 and 72 h. We assessed the level of beta-2 adrenergic receptor (ADRB2) expression in these cells as well as global gene expression changes in NE treated Tcm cells by microarray analysis. Altered expressed genes after NE treatment were identified and further confirmed by RT-qPCR, and by ELISA for protein changes. We further determined whether the observed NE effects on memory CD8 T cells are mediated by ADRB2 using specific adrenergic receptor agonist and antagonists. Finally, we examined the levels of mRNA and protein of the NE-induced genes in healthy adults with high serum levels of NE (>150 pg/mL) compared to low levels (<150 pg/mL).
RESULTS: We found that memory (Tcm and Tem) CD8 T cells expressed a significantly higher level of ADRB2 compared to naïve cells. Consequently, memory CD8 T cells were significantly more sensitive than naive cells to NE induced changes in gene expressions in vitro. Global gene expression analysis revealed that NE induced an elevated expression of inflammatory cytokines and chemokines in resting and activated memory CD8 T cells in addition to a reduced expression of growth-related cytokines. The effects of NE on memory CD8 T cells were primarily mediated by ADRB2 as confirmed by the adrenergic receptor agonist and antagonist assays. Finally, individuals with high serum levels of NE had similar elevated gene expressions observed in vitro compared to the low NE group.
CONCLUSIONS: Our results demonstrate that NE preferentially modulates the functions of memory CD8 T cells by inducing inflammatory cytokine production and reducing activation-induced memory CD8 T cell expansion.
