CD5 dynamically calibrates basal NF-κB signaling in T cells during thymic development and peripheral activation

Abstract

Immature T cells undergo a process of positive selection in the thymus when their new T cell receptor (TCR) engages and signals in response to self-peptides. As the T cell matures, a slew of negative regulatory molecules, including the inhibitory surface glycoprotein CD5, are up-regulated in proportion to the strength of the self-peptide signal. Together these regulators dampen TCR-proximal signaling and help avoid any subsequent peripheral activation of T cells by self-peptides. Paradoxically, antigen-specific T cells initially expressing more CD5 (CD5hi) have been found to better persist as effector/memory cells after a peripheral challenge. The molecular mechanisms underlying such a duality in CD5 function is not clear. We found that CD5 alters the basal activity of the NF-κB signaling in resting peripheral T cells. When CD5 was conditionally ablated, T cells were unable to maintain higher expression of the cytoplasmic NF-κB inhibitor IκBα. Consistent with this, resting CD5hiT cells expressed more of the NF-κB p65 protein than CD5locells, without significant increases in transcript levels, in the absence of TCR signals. This posttranslationally stabilized cellular NF-κB depot potentially confers a survival advantage to CD5hiT cells over CD5loones. Taken together, these data suggest a two-step model whereby the strength of self-peptide–induced TCR signal lead to the up-regulation of CD5, which subsequently maintains a proportional reserve of NF-κB in peripheral T cells poised for responding to agonistic antigen-driven T cell activation.

Pre-existing chromatin accessibility and gene expression differences among naïve CD4+T cells influence effector potential

“…Further, our data imply that naïve CD4 + T cell heterogeneity is partly thymically imprinted and retained independent of interactions with self-pMHC in the periphery. Thus, our work reconciles prior studies that have described specific heterogeneous traits among naïve CD4 + T cells, not all of which were dependent on tonic TCR signals (Mandl et al, 2013;Matson et al, 2020;Persaud et al, 2014;Stefanová et al, 2002).…”

“…To define transcriptional differences among naïve CD4 + T cells with single cell resolution, we first performed scRNA-seq using CEL-Seq2 (Hashimshony et al, 2016) on a population of 1152 naïve CD4 + T cells (sorted from the spleen), of which 697 cells passed quality control tests (Table S1). During the cell sorts, we included measures of CD5 protein level expression for each individual T cell given prior studies implicating CD5 as a key read-out of diversity among naïve T cells (Bartleson et al, 2020;Fulton et al, 2015;Henderson et al, 2015;Mandl et al, 2013;Matson et al, 2020;Persaud et al, 2014;Vrisekoop et al, 2017). We verified that among cells in which Cd5 was detected, transcript counts correlated with measured CD5 protein levels, and drop-outs were more frequent in cells with lower CD5 mean fluorescent intensity (Figure S1), consistent with prior evidence for regulation of CD5 at the transcriptional level (Arman et al, 2004;Tung et al, 2001).…”

“…Importantly, not only does self-pMHC reactivity impact competition between T cells for homeostatic signals (Vrisekoop et al, 2017), it has also been shown to influence their responses to antigen in specific ways. CD5 hi naïve CD4 + T cells express higher basal levels of NFkB, phosphorylated TCR-z, and ERK, make more IL-2 post-activation, preferentially differentiate into regulatory T cells (Tregs), predominate in acute infections, and contribute disproportionately to the memory T cell pool (Fulton et al, 2015;Henderson et al, 2015;Mandl et al, 2013;Matson et al, 2020;Persaud et al, 2014). In contrast, CD5 lo naïve CD4 + T cells were recently shown to produce more IFN-g upon activation (Sood et al, 2019).…”

T cell self-reactivity during thymic development dictates the timing of positive selection

“…Specifically, there is another set of ion channel genes whose expression peaks at the late positive selection or CD8SP stage (Figure 6c, group 3). Interestingly, two of these genes, Kcna2 and Tmie (Figure 6-figure supplement 2b), are also upregulated in mature peripheral CD5 low CD8SP T cells relative to CD5 high CD8SP T cells, based on published data sets (Supplementary Files S3 and S4) (Fulton et al 2015;Matson et al 2020). Additionally, cells with low self-reactivity also have high expression of the sodium-dependent neutral amino acid transporter Slc6a19 (Figure 6-figure supplement 1 and 2b, Supplementary Files S3 and S4) (Fulton et al 2015;Matson et al 2020).…”

“…Altered ion flux in T cells with low self-reactivity may also impact ion-coupled transport of nutrients. In this regard, it is intriguing that the sodium-dependent neutral amino acid transporter gene Slc6a19 is also consistently upregulated in thymocytes and CD8 T cells with low self-reactivity (Figure 6c and d, Figure 6-figure supplement 1, Figure 6-figure supplement 2b, and Supplementary Files S3 and S4) (Fulton et al 2015;Matson et al 2020).…”