Instruction for Cytokine Expression in T Helper Lymphocytes in Relation to Proliferation and Cell Cycle Progression

Abstract

T helper (Th) lymphocytes, when reactivated, recall expression of those cytokines they had been instructed to express in earlier activations, even in the absence of specific cytokine-inducing factors. In cells that memorize their expression, the cytokine genes are modified by chromatin rearrangement and demethylation, suggesting that they have been somatically imprinted. Here we show, by using inhibitors blocking the cell cycle in various stages, that for the instruction of a Th cell to express interleukin (IL)-4 or IL-10 upon restimulation, entry of the cell into the S phase of the first cell cycle after initial activation is required. Separation of the IL-4 receptor (IL-4R) and T cell antigen receptor (TCR) signals in time, demonstrates that this instruction is dependent on concomitant signaling from both receptors. In Th cells, inhibited to progress into the first S phase after activation, the IL-4R and TCR signals can be memorized for at least 1 d, priming the T cell to become instructed for expression of IL-4 upon restimulation, when entering the S phase after release of the cell cycle block. The requirement of the initial S phase of T cell activation, for instruction of Th cells to express IL-4 or IL-10 upon restimulation points to the decisive role of epigenetic modification of cytokine genes as a molecular correlate of the memory to express particular cytokines.

Cell division curtails helper phenotype plasticity and expedites helper T‐cell differentiation

“…Using deterministic and stochastic models, we find that cell division expedites cell differentiation by shortening the time to achieve significant gene demethylation and cytokine expression in naive helper T cells. This finding is strongly supported by earlier observations reporting a correlation between cell division and the production of cytokines IL4 and IFNg, 22,23,60,61 without requiring a 'counting mechanism' in cells tracing the number of cell divisions they have completed. Furthermore, the expression of cytokines Il17A, Il17F and IL21, which are all related to the novel Th17 phenotype, is similarly found to correlate with cell division.…”

“…62 Our result underlines the fact that although the mean number of divisions required for high cytokine expression may be 3 or 4, the lowest number of divisions required for cytokine expression could be lower, including no cell division at all. 22 Contrary to naive helper T cells, our model finds that memory cells upregulate cytokine expression outright, without requiring cell division, as has also been shown experimentally. 63,64 One of the principle mechanisms that our model describes is derepression of cytokine loci through demethylation of CpG islets.…”

“…21 Cytokine expression seems to depend on the number of divisions cells have completed following antigenic activation, suggesting that cell division has a role in ensuing epigenetic changes required for derepression. 22,23 Here, we extend an established model for master transcription factors with epigenetic processes to investigate the differentiation, memory formation and plasticity of helper T cells. Helper T-cell differentiation has been studied extensively using mathematical models, 9,10,[24][25][26][27][28][29][30][31] but to the best of our knowledge, this is the first attempt to combine genetic and epigenetic levels of regulation in mechanistic models for cellular differentiation.…”

Immunological memories of the bone marrow

“…Most importantly, we and others have shown that imprinting of cytokine genes in activated naive T cells but not in memory T cells requires progression through the S phase of the first cell division. This is suggesting that imprinting is indeed linked to epigenetic modification of DNA and would explain why cytokine gene expression is faster in secondary than in primary immune reactions 90. Essentially everything that we think we know about memory T lymphocytes has been analyzed on T cells obtained from murine secondary lymphoid organs, mostly spleen, or human blood.…”

Stat Signals Release Activated Naive Th Cells from an Anergic Checkpoint

“…Requirements for DNA synthesis or cell division have been reported in some, but not all studies (3)(4)(5)(6)(7)(8)(9), and activation is proposed to enable cells to express cytokine genes instructed by polarizing environmental cytokines. Evidence supporting such a model includes the ease with which T cells expressing a fixed pattern of cytokines can be expanded in vitro using distinct types of exogenous cytokines and the phenotype of cells prepared from various cytokine, cytokine-receptor, and cytokine signal-transducing Stat knockout mice (1,2).…”