Exposure of Human CD4 T Cells to IL-12 Results in Enhanced TCR-Induced Cytokine Production, Altered TCR Signaling, and Increased Oxidative Metabolism

Abstract

Human CD4 T cells are constantly exposed to IL-12 during infections and certain autoimmune disorders. The current paradigm is that IL-12 promotes the differentiation of naïve CD4 T cells into Th1 cells, but recent studies suggest IL-12 may play a more complex role in T cell biology. We examined if exposure to IL-12 alters human CD4 T cell responses to subsequent TCR stimulation. We found that IL-12 pretreatment increased TCR-induced IFN-γ, TNF-α, IL-13, IL-4 and IL-10 production. This suggests that prior exposure to IL-12 potentiates the TCR-induced release of a range of cytokines. We observed that IL-12 mediated its effects through both transcriptional and post-transcriptional mechanisms. IL-12 pretreatment increased the phosphorylation of AKT, p38 and LCK following TCR stimulation without altering other TCR signaling molecules, potentially mediating the increase in transcription of cytokines. In addition, the IL-12-mediated enhancement of cytokines that are not transcriptionally regulated was partially driven by increased oxidative metabolism. Our data uncover a novel function of IL-12 in human CD4 T cells; specifically, it enhances the release of a range of cytokines potentially by altering TCR signaling pathways and by enhancing oxidative metabolism.

Pretreatment of activated human CD8 T cells with IL-12 leads to enhanced TCR-induced signaling and cytokine production

“…Similarly, Raue and colleagues showed that murine memory CD8 T cells conditioned with IL-12 and IL-18 in vitro have enhanced cytokine production and cytotoxic activity upon TCR re-challenge [19]. Finally, we have recently found that IL-12 pretreatment in human CD4 T cells enhances the production of a range of cytokines following TCR induction [16]. Collectively, these studies suggest that the regulation of T cell responses by IL-12 is more complex than previously appreciated.…”

“…In murine CD4 and CD8 T cells, it was shown that exposure to pathogen-induced inflammation enhances T cell functions by increasing the activation of TCR signaling molecules [17, 18]. In addition, pretreatment of human T cells with IL-12, IL-7 and IL-15, or the TLR5 ligand bacterial flagellin, which all potentiated TCR-mediated functions, altered the activation of distinct sets of molecules downstream of the TCR [14-16]). Therefore, inflammatory stimuli that enhance subsequent TCR-induced downstream functions all regulate TCR signaling through distinct mechanisms.…”

“…In human CD8 T cells, IL-12 exposure for at least 24 h or longer amplified subsequent TCR-induced functions. In contrast, human CD4 T cells required only 1.5 h of IL-12 pretreatment to observe significant alterations in TCR function [16]. Furthermore, we observed that in human activated CD4 T cells the effects of IL-12 pretreatment in enhancing TCR-induced functions lasted for 3-6 hours [16].…”

“…In contrast, human CD4 T cells required only 1.5 h of IL-12 pretreatment to observe significant alterations in TCR function [16]. Furthermore, we observed that in human activated CD4 T cells the effects of IL-12 pretreatment in enhancing TCR-induced functions lasted for 3-6 hours [16]. In contrast, in human activated CD8 T cells the IL-12 mediated potentiation of TCR-induced responses lasted for 48-72 h. In addition, we found that, in human activated CD8 T cells, IL-12 pretreatment increases the mRNA expression of IFNG and TNF and the intracellular levels of these cytokines after 18 h of TCR stimulation.…”

“…To this end, prior exposure of human T cells to IL-7, IL-15, or the TLR5 ligand flagellin increases the responsiveness of these cells to TCR stimulation [14, 15]. Similarly, we have recently found that short exposure of human CD4 T cells to IL-12 enhances the TCR-induced production of a range of cytokines [16]. In addition, exposure to pathogen-induced inflammation alters the responsiveness of murine effector/memory CD8 T cells and secondary effector CD4 T cells to subsequent activation through the TCR [17-19].…”