InVivoPlus anti-mouse IL-4

Loss of host-microbiota balance promotes gut inflammation, colitis and inflammatory bowel disease. Yet, whether host or microbial factors are the critical driver of the pathology remains unclear. Here, we investigate how cardiolipin maintains metabolic fitness of regulatory T (Treg) cells to preserve gut-immune homeostasis. We discover that deleting the cardiolipin-synthesizing enzyme protein tyrosine phosphatase mitochondrial 1 (PTPMT1) in T cells predisposes mice to colitis due to impaired Treg cell function in the absence of dysbiosis. Subsequent pathobiont infections accelerate the progression and severity of gut inflammation. Mechanistically, the absence of cardiolipin impairs Treg cell metabolic fitness and triggers a maladaptive integrated stress response, which can be reversed pharmacologically or genetically, restoring gut homeostasis and extending lifespan in PTPMT1 ΔT mice. Barth syndrome, a genetic disorder marked by severe cardiolipin deficiency, also exhibits gastrointestinal symptoms and inflammation associated with helper T cell imbalance and an active integrated stress response signature. Overall, these results suggest that a cardiolipin-mediated mitonuclear axis in T cells preserves gut-immune homeostasis and dictates outcome in pathobiont infections.

IL-4 can have significant therapeutic benefit in many injury settings, but its mechanism of action is unclear. Using a model of carbon tetrachloride (CCl4)-mediated acute liver injury, we find that exogenous IL-4 causes a dramatic shift from recruited Ly6Chi monocytes to an abundance of monocyte-derived macrophages (MoMFs) within the injured tissue that is accompanied by reduced indices of hepatic damage and enhanced hepatic regeneration. Rather than altering the recruitment or differentiation of monocytes, treatment with IL-4 triggers monocyte apoptosis alongside proliferation of MoMFs. Single-cell RNA sequencing reveals injury and cell-type-specific responses to IL-4 treatment across hepatic myeloid lineages and a largely pro-reparative gene signature in the expanded pool of MoMFs. IL-4 treatment fails to enhance hepatic repair when the accrual of MoMFs is limited using Ccr2-deficient monocytopenic mice. Together, these data reveal a pathway through which therapeutic IL-4 alters the composition, number, and function of injury-associated myeloid cells to resolve liver injury.

The pathology of severe COVID-19 is due to a hyperinflammatory immune response persisting after viral clearance. To understand how the immune response to SARS-CoV-2 is regulated to avoid severe COVID-19, we tested relevant immunoregulatory cytokines. Transforming growth factor β (TGF-β), interleukin (IL)-10, and IL-4 were neutralized upon infection with mouse-adapted SARS-CoV-2 (CMA3p20), a model of mild disease; lung inflammation was quantified by histology and flow cytometry at early and late time points. Mild weight loss and lung inflammation including consolidation and alveolar thickening were evident 3 d postinfection (dpi), and inflammation persisted to 7 dpi. Coinciding with early monocytic infiltrates, CCL2 and granulocyte colony-stimulating factor were transiently produced 3 dpi, while IL-12 and CCL5 persisted to 7 dpi, modeling viral and inflammatory phases of disease. Neutralization of TGF-β, but not IL-10 or IL-4, significantly increased lung inflammatory monocytes and elevated serum but not lung IL-6. Neutralization of IL-4 prolonged weight loss and increased early perivascular infiltration without changing viral titer. Anti-IL-4 reduced expression of Arg1, a gene associated with alternative activation of macrophages. Neutralizing TGF-β and IL-4 had differential effects on pathology after virus control. Lung perivascular infiltration was reduced 7 dpi by neutralization of IL-4 or TGF-β, and periairway inflammation was affected by anti-TGF-β, while alveolar infiltrates were not affected by either. Anti-IL-4 prolonged IL-12 to 7 dpi along with reduced IL-10 in lungs. Overall, the immunoregulatory cytokines TGF-β and IL-4 dampen initial inflammation in this mouse-adapted SARS-CoV-2 infection, suggesting that promotion of immunoregulation could help patients in early stages of disease.

Imbalanced effector and regulatory CD4+ T cell subsets drive many inflammatory diseases. These T cell subsets rely on distinct metabolic programs, modulation of which differentially affects T cell fate and function. Lipid metabolism is fundamental yet remains poorly understood across CD4+ T cell subsets. Therefore, we performed targeted in vivo CRISPR/Cas9 screens to identify lipid metabolism genes and pathways essential for T cell functions. These screens established mitochondrial fatty acid synthesis genes Mecr, Mcat, and Oxsm as key metabolic regulators. Of these, the inborn error of metabolism gene Mecr was most dynamically regulated. Mecrfl/fl; Cd4cre mice had normal naïve CD4+ and CD8+ T cell numbers, demonstrating that MECR is not essential in homeostatic conditions. However, effector and memory T cells were reduced in Mecr knockout and MECR-deficient CD4+ T cells and proliferated, differentiated, and survived less well than control T cells. Interestingly, T cells ultimately showed signs of mitochondrial stress and dysfunction in the absence of MECR. Mecr-deficient T cells also had decreased mitochondrial respiration, reduced tricarboxylic acid intermediates, and accumulated intracellular iron, which appeared to contribute to increased cell death and sensitivity to ferroptosis. Importantly, MECR-deficient T cells exhibited fitness disadvantages and were less effective at driving disease in an in vivo model of inflammatory bowel disease. Thus, MECR-mediated metabolism broadly supports CD4+ T cell proliferation and survival in vivo. These findings may also provide insight to the immunological state of MECR- and other mitochondrial fatty acid synthesis-deficient patients.