Avrion Mitchison Preis 2000
Dr. Anne Richter und Dr. Max Löhning
Deutsches Rheuma-Forschungszentrum Berlin
"Cytokine memory in T helper lymphocytes"
By selective expression of cytokines, T helper (Th) lymphocytes contribute to the pathology of many rheumatic disorders. Even the most advanced therapies fail in the durable modulation of the cytokine repertoire of established diseases because Th cells, upon restimulation by antigen, recall the expression of those cytokines for which they had been instructed in earlier activations, in the absence of cytokine-inducing or even in the presence of adverse factors. We show here that the molecular basis for this cytokine memory is an epigenetic and transcriptional imprinting of the Th cell.
Blocking the cell cycle of Th cells activated for the first time by antigen, costimulation, and cytokine-inducing signals, we could show that for the instruction to memorize expression of interleukin-4 (IL-4) and IL-10, Th cells have to enter the S phase of the first cell cycle after their primary activation. This points to a critical role of epigenetic DNA modifications during DNA replication in the induction of cytokine memory. For the induction of IL-4 memory, concomitant signaling through the T cell receptor and the IL-4 receptor is required. The signals are induced independently of progression into the S phase, can be stored for at least one day, and commit the cell for IL-4 memory when entering the initial S phase.
Induction of IL-4 memory can also occur independent of IL-4 receptor signaling, as can be shown in signal transducer and activator of transcription 6 (Stat6)-deficient Th cells. Using the cellular affinity matrix technology, we have isolated viable IL-4-secreting and non-secreting Th cells from Stat6-deficient mice. In contrast to the IL-4-negative T cells, the IL-4-positive T cells stably expressed high levels of the Th2-specific transcription factor GATA-3. Accordingly, retrovirally introduced expression of exogenous GATA-3 in Stat6-deficient Th cells induced their differentiation into IL-4-secreting Th2 cells. Furthermore, it induced expression of endogenous GATA-3, thus revealing an autoregulatory loop controling GATA-3 expression levels and stabilizing Th2 differentiation and memory.
This epigenetic and transcriptional stability may explain why it proved so difficult to redirect Th cell cytokine expression. Changing epigenetic modifications of cytokine genes and modulating GATA-3 expression levels may serve as future targets for redirecting an established cytokine memory in chronic immune reactions and immunopathology.