Comprehensive Profiling of an Aging Immune System Reveals Clonal GZMK+ CD8+ T Cells as Conserved Hallmark of Inflammaging.

Systematic understanding of immune aging on a whole-body scale is currently lacking. We characterized age-associated alterations in immune cells across multiple mouse organs using single-cell RNA and antigen receptor sequencing and flow cytometry-based validation. We defined organ-specific and common immune alterations and identified a subpopulation of age-associated granzyme K (GZMK)-expressing CD8+ T (Taa) cells that are distinct from T effector memory (Tem) cells. Taa cells were highly clonal, had specific epigenetic and transcriptional signatures, developed in response to an aged host environment, and expressed markers of exhaustion and tissue homing. Activated Taa cells were the primary source of GZMK, which enhanced inflammatory functions of non-immune cells. In humans, proportions of the circulating GZMK+CD8+ T cell population that shares transcriptional and epigenetic signatures with mouse Taa cells increased during healthy aging. These results identify GZMK+ Taa cells as a potential target to address age-associated dysfunctions of the immune system.

Comparative evaluation of itaconate and its derivatives reveals divergent inflammasome and type I interferon regulation in macrophages.

Following activation, macrophages undergo extensive metabolic rewiring1,2. Production of itaconate through the inducible enzyme IRG1 is a key hallmark of this process3. Itaconate inhibits succinate dehydrogenase4,5, has electrophilic properties6 and is associated with a change in cytokine production4. Here, we compare the metabolic, electrophilic and immunologic profiles of macrophages treated with unmodified itaconate and a panel of commonly used itaconate derivatives to examine its role. Using wild-type and Irg1-/- macrophages, we show that neither dimethyl itaconate, 4-octyl itaconate nor 4-monoethyl itaconate are converted to intracellular itaconate, while exogenous itaconic acid readily enters macrophages. We find that only dimethyl itaconate and 4-octyl itaconate induce a strong electrophilic stress response, in contrast to itaconate and 4-monoethyl itaconate. This correlates with their immunosuppressive phenotype: dimethyl itaconate and 4-octyl itaconate inhibited IκBζ and pro-interleukin (IL)-1ß induction, as well as IL-6, IL-10 and interferon-ß secretion, in an NRF2-independent manner. In contrast, itaconate treatment suppressed IL-1ß secretion but not pro-IL-1ß levels and, surprisingly, strongly enhanced lipopolysaccharide-induced interferon-ß secretion. Consistently, Irg1-/- macrophages produced lower levels of interferon and reduced transcriptional activation of this pathway. Our work establishes itaconate as an immunoregulatory, rather than strictly immunosuppressive, metabolite and highlights the importance of using unmodified itaconate in future studies.