The ligation of Toll-like receptors (TLRs) leads to rapid activation of dendritic cells (DCs). However, the metabolic requirements that support this process remain poorly defined. We found that DC glycolytic flux increased within minutes of exposure to TLR agonists and that this served an essential role in supporting the de novo synthesis of fatty acids for the expansion of the endoplasmic reticulum and Golgi required for the production and secretion of proteins that are integral to DC activation. Signaling via the kinases TBK1, IKKε and Akt was essential for the TLR-induced increase in glycolysis by promoting the association of the glycolytic enzyme HK-II with mitochondria. In summary, we identified the rapid induction of glycolysis as an integral component of TLR signaling that is essential for the anabolic demands of the activation and function of DCs.

SUMMARY Due to the ongoing Zika virus (ZIKV) epidemic and unexpected clinical outcomes including Guillain-Barré syndrome and birth defects, there is an urgent need for animal model development. We evaluated infection and pathogenesis with contemporary and historical ZIKV strains in immunocompetent mice and transgenic mice lacking components of the innate antiviral response. Whereas 4 to 6 week-old wild-type, Irf3−/−, Irf5−/−, and Mavs−/−, mice showed no overt clinical illness, Irf3−/− Irf5−/− Irf7−/− TKO and Ifnar1−/− mice developed neurological disease and succumbed to ZIKV infection. Ifnar1−/− mice sustained high viral loads in the brain and spinal cord, consistent with evidence that ZIKV causes neurodevelopmental defects in human fetuses. The highest viral loads were detected in the testes of Ifnar1−/− mice, which is relevant to sexual transmission of ZIKV. This model of ZIKV pathogenesis will be valuable for evaluating vaccines and therapeutics, as well as understanding basic mechanisms of disease pathogenesis and immune evasion.

SUMMARY Zika virus (ZIKV) infection in pregnant women causes intrauterine growth restriction, spontaneous abortion, and microcephaly. Here, we describe two mouse models of placental and fetal disease associated with in utero transmission of ZIKV. Female mice lacking type I interferon signaling (Ifnar1−/−) crossed to wild-type (WT) males produced heterozygous fetuses resembling the immune status of human fetuses. Maternal inoculation at embryonic day 6.5 (E6.5) or E7.5 resulted in fetal demise that was associated with ZIKV infection of the placenta and fetal brain. We identified ZIKV within trophoblasts of the maternal and fetal placenta, consistent with a trans-placental infection route. Antibody blockade of Ifnar1 signaling in WT pregnant mice enhanced ZIKV trans-placental infection although it did not result in fetal death. These models will facilitate the study of ZIKV pathogenesis, in utero transmission, and testing of therapies and vaccines to prevent congenital malformations.

Alternative (M2) macrophage activation driven through interleukin 4 receptor α (IL-4Rα) is important for immunity to parasites, wound healing, the prevention of atherosclerosis and metabolic homeostasis. M2 polarization is dependent on fatty acid oxidation (FAO), but the source of fatty acids to support this metabolic program has not been clear. We show that the uptake of triacylglycerol substrates via CD36 and their subsequent lipolysis by lysosomal acid lipase (LAL) was important for the engagement of elevated oxidative phosphorylation (OXPHOS), enhanced spare respiratory capacity (SRC), prolonged survival and expression of genes that together define M2 activation. Inhibition of lipolysis suppressed M2 activation during infection with a parasitic helminth, and blocked protective responses against this pathogen. Our findings delineate a critical role for cell-intrinsic lysosomal lipolysis in M2 activation.

Macrophage-specific expression of Arginase-1 is commonly believed to promote inflammation, fibrosis, and wound healing by enhancing L-proline, polyamine, and Th2 cytokine production. Here, however, we show that macrophage-specific Arg1 functions as an inhibitor of inflammation and fibrosis following infection with the Th2-inducing pathogen Schistosoma mansoni. Although susceptibility to infection was not affected by the conditional deletion of Arg1 in macrophages, Arg1 −/flox ;LysMcre mice died at an accelerated rate. The mortality was not due to acute Th1/NOS2-mediated hepatotoxicity or endotoxemia. Instead, granulomatous inflammation, liver fibrosis, and portal hypertension increased in infected Arg1 −/flox ;LysMcre mice. Similar findings were obtained with Arg1 flox/flox ;Tie2cre mice, which delete Arg1 in all macrophage populations. Production of Th2 cytokines increased in the infected Arg1 −/flox ;LysMcre mice, and unlike alternatively activated wild-type macrophages, Arg1 −/flox ;LysMcre macrophages failed to inhibit T cell proliferation in vitro, providing an underlying mechanism for the exacerbated Th2 pathology. The suppressive activity of Arg1-expressing macrophages was independent of IL-10 and TGF-β1. However, when exogenous L-arginine was provided, T cell proliferation was restored, suggesting that Arg1-expressing macrophages deplete arginine, which is required to sustain CD4+ T cell responses. These data identify Arg1 as the essential suppressive mediator of alternatively activated macrophages (AAM) and demonstrate that Arg1-expressing macrophages function as suppressors rather than inducers of Th2-dependent inflammation and fibrosis.

Toll-like receptor (TLR) signaling in macrophages is required for antipathogen responses, including the biosynthesis of nitric oxide from arginine, and is essential for immunity to Mycobacterium tuberculosis, Toxoplasma gondii and other intracellular pathogens. Here we report a ‘loophole’ in the TLR pathway that is advantageous to these pathogens. Intracellular pathogens induced expression of the arginine hydrolytic enzyme arginase 1 (Arg1) in mouse macrophages through the TLR pathway. In contrast to diseases dominated by T helper type 2 (TH2) responses, TLR-mediated Arg1 induction was independent of the TH2-associated STAT6 pathway. Specific elimination of Arg1 in macrophages favored host survival in T. gondii infection and decreased lung bacterial load in tuberculosis infection.

Summary Generation of CD8+ memory T (TM) cells requires metabolic reprogramming that is characterized by enhanced mitochondrial fatty acid oxidation (FAO). However, where the fatty acids (FA) that fuel this process come from remains unclear. We found that while CD8+ TM cells engaged higher levels of FAO, they acquired substantially fewer long-chain FA from their external environment than CD8+ effector T (TE) cells. Rather than using extracellular FA directly, TM cells used extracellular glucose to support FAO and oxidative phosphorylation (OXPHOS), suggesting that lipids must be synthesized to generate the substrates needed for FAO. We have demonstrated that TM cells rely on cell intrinsic expression of the lysosomal hydrolase LAL (lysosomal acid lipase) to mobilize FA for FAO and TM cell development. Our observations link LAL to metabolic reprogramming in lymphocytes and show that cell intrinsic lipolysis is deterministic for TM cell fate.

Changes in metabolism can be initiated in response to signals received from other cells. An example of this is provided by macrophages that have been stimulated by IL-4 to become alternatively/M2 activated. In these cells, fatty acid oxidation is increased and this is critical for M2 activation. Compared to resting macrophages, M2 macrophages also exhibit changes in glucose metabolism that we have found are essential for activation. In other cell types, mTORC2 has been linked to enhanced glycolysis. We have found that mTORC2 operates in parallel with the IL-4Rα/Stat6 pathway to facilitate increased glycolysis during M2 activation. Our data strongly implicate PI3K and AKT signaling initiated by M-CSF as components in this pathway, and indicate that downstream induction of IRF4 expression plays a role in metabolic reprograming to support M2 activation. We show that loss of mTORC2 in macrophages suppresses tumor growth and decreases immunity to a parasitic nematode.