Human antibodies in Mexico and Brazil neutralizing tick-borne flaviviruses.

Flaviviruses such as dengue virus (DENV), Zika virus (ZIKV), and yellow fever virus (YFV) are spread by mosquitoes and cause human disease and mortality in tropical areas. In contrast, Powassan virus (POWV), which causes severe neurologic illness, is a flavivirus transmitted by ticks in temperate regions of the Northern hemisphere. We find serologic neutralizing activity against POWV in individuals living in Mexico and Brazil. Monoclonal antibodies P002 and P003, which were derived from a resident of Mexico (where POWV is not reported), neutralize POWV lineage I by recognizing an epitope on the virus envelope domain III (EDIII) that is shared with a broad range of tick- and mosquito-borne flaviviruses. Our findings raise the possibility that POWV, or a flavivirus closely related to it, infects humans in the tropics.

Leishmania braziliensis enhances monocyte responses to promote anti-tumor activity.

Innate immune cells can undergo long-term functional reprogramming after certain infections, a process called trained immunity (TI). Here, we focus on antigens of Leishmania braziliensis, which induced anti-tumor effects via trained immunity in human monocytes. We reveal that monocytes exposed to promastigote antigens of L. braziliensis develop an enhanced response to subsequent exposure to Toll-like receptor (TLR)2 or TLR4 ligands. Mechanistically, the induction of TI in monocytes by L. braziliensis is mediated by multiple pattern recognition receptors, changes in metabolism, and increased deposition of H3K4me3 at the promoter regions of immune genes. The administration of L. braziliensis exerts potent anti-tumor capabilities by delaying tumor growth and prolonging survival of mice with non-Hodgkin lymphoma. Our work reveals mechanisms of TI induced by L. braziliensis in vitro and identifies its potential for cancer immunotherapy.

CD300f immune receptor contributes to healthy aging by regulating inflammaging, metabolism, and cognitive decline.

Emerging evidence suggests that immune receptors may participate in many aging-related processes such as energy metabolism, inflammation, and cognitive decline. CD300f, a TREM2-like lipid-sensing immune receptor, is an exceptional receptor as it integrates activating and inhibitory cell-signaling pathways that modulate inflammation, efferocytosis, and microglial metabolic fitness. We hypothesize that CD300f can regulate systemic aging-related processes and ultimately healthy lifespan. We closely followed several cohorts of two strains of CD300f-/- and WT mice of both sexes for 30 months and observed an important reduction in lifespan and healthspan in knockout mice. This was associated with systemic inflammaging, increased cognitive decline, reduced brain glucose uptake observed by 18FDG PET scans, enrichment in microglial aging/neurodegeneration phenotypes, proteostasis alterations, senescence, increased frailty, and sex-dependent systemic metabolic changes. Moreover, the absence of CD300f altered macrophage immunometabolic phenotype. Taken together, we provide strong evidence suggesting that myeloid cell CD300f immune receptor contributes to healthy aging.

SARS-CoV-2 Spike protein induces TLR4-mediated long-term cognitive dysfunction recapitulating post-COVID-19 syndrome in mice.

Cognitive dysfunction is often reported in patients with post-coronavirus disease 2019 (COVID-19) syndrome, but its underlying mechanisms are not completely understood. Evidence suggests that severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) Spike protein or its fragments are released from cells during infection, reaching different tissues, including the CNS, irrespective of the presence of the viral RNA. Here, we demonstrate that brain infusion of Spike protein in mice has a late impact on cognitive function, recapitulating post-COVID-19 syndrome. We also show that neuroinflammation and hippocampal microgliosis mediate Spike-induced memory dysfunction via complement-dependent engulfment of synapses. Genetic or pharmacological blockage of Toll-like receptor 4 (TLR4) signaling protects animals against synapse elimination and memory dysfunction induced by Spike brain infusion. Accordingly, in a cohort of 86 patients who recovered from mild COVID-19, the genotype GG TLR4-2604G>A (rs10759931) is associated with poor cognitive outcome. These results identify TLR4 as a key target to investigate the long-term cognitive dysfunction after COVID-19 infection in humans and rodents.

The ubiquitin E3 ligase TRIM10 promotes STING aggregation and activation in the Golgi apparatus.

STING is an endoplasmic reticulum-resident protein regulating innate immunity. After binding with cyclic guanosine monophosphate-AMP (cGAMP), STING translocates from the endoplasmic reticulum (ER) to the Golgi apparatus to stimulate TBK1 and IRF3 activation, leading to expression of type I interferon. However, the exact mechanism concerning STING activation remains largely enigmatic. Here, we identify tripartite motif 10 (TRIM10) as a positive regulator of STING signaling. TRIM10-deficient macrophages exhibit reduced type I interferon production upon double-stranded DNA (dsDNA) or cGAMP stimulation and decreased resistance to herpes simplex virus 1 (HSV-1) infection. Additionally, TRIM10-deficient mice are more susceptible to HSV-1 infection and exhibit faster melanoma growth. Mechanistically, TRIM10 associates with STING and catalyzes K27- and K29-linked polyubiquitination of STING at K289 and K370, which promotes STING trafficking from the ER to the Golgi apparatus, formation of STING aggregates, and recruitment of TBK1 to STING, ultimately enhancing the STING-dependent type I interferon response. Our study defines TRIM10 as a critical activator in cGAS-STING-mediated antiviral and antitumor immunity.

Concomitant inhibition of PPARγ and mTORC1 induces the differentiation of human monocytes into highly immunogenic dendritic cells.

Monocytes can differentiate into macrophages (Mo-Macs) or dendritic cells (Mo-DCs). The cytokine granulocyte-macrophage colony-stimulating factor (GM-CSF) induces the differentiation of monocytes into Mo-Macs, while the combination of GM-CSF/interleukin (IL)-4 is widely used to generate Mo-DCs for clinical applications and to study human DC biology. Here, we report that pharmacological inhibition of the nuclear receptor peroxisome proliferator-activated receptor gamma (PPARγ) in the presence of GM-CSF and the absence of IL-4 induces monocyte differentiation into Mo-DCs. Remarkably, we find that simultaneous inhibition of PPARγ and the nutrient sensor mammalian target of rapamycin complex 1 (mTORC1) induces the differentiation of Mo-DCs with stronger phenotypic stability, superior immunogenicity, and a transcriptional profile characterized by a strong type I interferon (IFN) signature, a lower expression of a large set of tolerogenic genes, and the differential expression of several transcription factors compared with GM-CSF/IL-4 Mo-DCs. Our findings uncover a pathway that tailors Mo-DC differentiation with potential implications in the fields of DC vaccination and cancer immunotherapy.

Tissue-specific metabolic profile drives iNKT cell function during obesity and liver injury.

Invariant natural killer T (iNKT) cells are a distinct population of lymphocytes characterized by their reactivity to glycolipids presented by CD1d. iNKT cells are found throughout the body, and little is known about their tissue-specific metabolic regulation. Here, we show that splenic and hepatic iNKT cells are metabolically comparable and rely on glycolytic metabolism to support their activation. Deletion of the pyruvate kinase M2 (Pkm2) gene in splenic and hepatic iNKT cells impairs their response to specific stimulation and their ability to mitigate acute liver injury. In contrast, adipose tissue (AT) iNKT cells exhibit a distinctive immunometabolic profile, with AMP-activated protein kinase (AMPK) being necessary for their function. AMPK deficiency impairs AT-iNKT physiology, blocking their capacity to maintain AT homeostasis and their ability to regulate AT inflammation during obesity. Our work deepens our understanding on the tissue-specific immunometabolic regulation of iNKT cells, which directly impacts the course of liver injury and obesity-induced inflammation.

IgG targeting distinct seasonal coronavirus- conserved SARS-CoV-2 spike subdomains correlates with differential COVID-19 disease outcomes.

Despite SARS-CoV-2 being a "novel" virus, early detection of anti-spike IgG in severe COVID-19 patients may be caused by the amplification of humoral memory responses against seasonal coronaviruses. Here, we examine this phenomenon by characterizing anti-spike IgG responses in non-hospitalized convalescent individuals across a spectrum of COVID-19 severity. We observe that disease severity positively correlates with anti-spike IgG levels, IgG cross-reactivity against other betacoronaviruses (ß-CoVs), and FcγR activation. Analysis of IgG targeting ß-CoV-conserved and non-conserved immunodominant epitopes within the SARS-CoV-2 spike protein revealed epitope-specific relationships: IgG targeting the conserved heptad repeat (HR) 2 region significantly correlates with milder disease, while targeting the conserved S2'FP region correlates with more severe disease. Furthermore, a lower HR2-to-S2'FP IgG-binding ratio correlates with greater disease severity, with ICU-hospitalized COVID-19 patients showing the lowest HR2/S2'FP ratios. These findings suggest that HR2/S2'FP IgG profiles may predict disease severity and offer insight into protective versus deleterious humoral recall responses.

STING is an intrinsic checkpoint inhibitor that restrains the TH17 cell pathogenic program.

External and intrinsic factors regulate the transcriptional profile of T helper 17 (TH17) cells, thereby affecting their pathogenic potential and revealing their context-dependent plasticity. The stimulator of interferon genes (STING), a component of the intracellular DNA-sensing pathway, triggers immune responses but remains largely unexplored in T cells. Here, we describe an intrinsic role of STING in limiting the TH17 cell pathogenic program. We demonstrate that non-pathogenic TH17 cells express higher levels of STING than those activated under pathogenic conditions. Activation of STING induces interleukin-10 (IL-10) production in TH17 cells, decreasing IL-17A and IL-23R expression in a type I interferon (IFN)-independent manner. Mechanistically, STING-induced IL-10 production partially requires aryl hydrocarbon receptor (AhR) signaling, while the decrease of IL-17A expression occurs due to a reduction of Rorγt transcriptional activity. Our findings reveal a regulatory function of STING in the TH17 cell activation program, proposing it as a valuable target to limit TH17-cell-mediated inflammation.