Immunity
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Dendritic cells (DCs) are crucial for mounting allergic airway inflammation, but it is unclear which subset of DCs performs this task. By using CD64 and MAR-1 staining, we reliably separated CD11b(+) monocyte-derived DCs (moDCs) from conventional DCs (cDCs) and studied antigen uptake, migration, and presentation assays of lung and lymph node (LN) DCs in response to inhaled house dust mite (HDM). ⋯ The main function of moDCs was the production of proinflammatory chemokines and allergen presentation in the lung during challenge. Thus, we have identified migratory CD11b(+) cDCs as the principal subset inducing Th2 cell-mediated immunity in the LN, whereas moDCs orchestrate allergic inflammation in the lung.
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Toll-like receptor 11 (TLR11) recognizes T. gondii profilin (TgPRF) and is required for interleukin-12 production and induction of immune responses that limit cyst burden in Toxoplasma gondii-infected mice. However, TLR11 only modestly affects survival of T. gondii-challenged mice. We report that TLR12, a previously uncharacterized TLR, also recognized TgPRF. ⋯ TLR12-dependent induction of IL-12 and IFN-α in pDCs led to production of IFN-γ by NK cells. Consistent with this observation, the partial resistance of Tlr11(-/-) mice is lost upon pDC or NK cell depletion. Thus, TLR12 is critical for the innate immune response to T. gondii, and this TLR may promote host resistance by triggering pDC and NK cell function.
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7α,25-dihydroxycholesterol (7α,25-OHC) is a ligand for the G protein-coupled receptor EBI2; however, the cellular sources of this oxysterol are undefined. 7α,25-OHC is synthesized from cholesterol by the stepwise actions of two enzymes, CH25H and CYP7B1, and is metabolized to a 3-oxo derivative by HSD3B7. We showed that all three enzymes control EBI2 ligand concentration in lymphoid tissues. ⋯ CYP7B1, CH25H, and HSD3B7 deficiencies each resulted in defective T cell-dependent plasma cell responses. These findings establish that CYP7B1 and HSD3B7, as well as CH25H, have essential roles in controlling oxysterol production in lymphoid tissues, and they suggest that differential enzyme expression in stromal cell subsets establishes 7α,25-OHC gradients required for B cell responses.
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CD8(+) T cells undergo major metabolic changes upon activation, but how metabolism influences the establishment of long-lived memory T cells after infection remains a key question. We have shown here that CD8(+) memory T cells, but not CD8(+) T effector (Teff) cells, possessed substantial mitochondrial spare respiratory capacity (SRC). ⋯ We found that interleukin-15 (IL-15), a cytokine critical for CD8(+) memory T cells, regulated SRC and oxidative metabolism by promoting mitochondrial biogenesis and expression of carnitine palmitoyl transferase (CPT1a), a metabolic enzyme that controls the rate-limiting step to mitochondrial fatty acid oxidation (FAO). These results show how cytokines control the bioenergetic stability of memory T cells after infection by regulating mitochondrial metabolism.
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Pathogen and danger recognition by the inflammasome activates inflammatory caspases that mediate inflammation and cell death. The cellular inhibitor of apoptosis proteins (cIAPs) function in apoptosis and innate immunity, but their role in modulating the inflammasome and the inflammatory caspases is unknown. ⋯ Deficiency in cIAP1 (encoded by Birc2) or cIAP2 (Birc3) impaired caspase-1 activation after spontaneous or agonist-induced inflammasome assembly, and Birc2(-/-) or Birc3(-/-) mice or mice administered with an IAP antagonist had a dampened response to inflammasome agonists and were resistant to peritonitis. Our results describe a role for the cIAPs in innate immunity and further demonstrate the evolutionary conservation between cell death and inflammation mechanisms.