The activation of pattern recognition receptors (PRRs) orchestrates inflammation and regulates adaptive immunity. To test whether tuning inflammation through PRR stimulation enhanced the efficacy of mRNA vaccines, we combined an mRNA-based vaccine generated against the ancestral spike protein of SARS-CoV-2 with mannadjuvant, a formulation of fungal mannan and aluminum hydroxide targeting the PRR dectin-2. In mice and non-human primates, mannadjuvant increased the magnitude and durability of the response elicited by the mRNA-based vaccine, and it also led to the induction of neutralizing antibodies directed against variants of concern with a high escape capacity, overcoming antigenic imprinting. Mechanistically, prolonged type I interferon (IFN) production and potentiated interleukin-1 (IL-1) signaling locally within the draining lymph node in mice or in human cells were necessary and sufficient to exert the effect of mannadjuvant. Our data indicate that antifungal PRRs can be harnessed to create more potent and durable mRNA-based vaccines.

Host-derived lipids undergoing enzymatic or nonenzymatic oxidation play critical roles in regulating inflammation. Polyunsaturated fatty acids, cholesterol, and cholesterol intermediates can be enzymatically oxidized and serve as signaling mediators controlling tissue homeostasis and immunity. Spontaneously generated oxidized lipids, including nonenzymatically oxidized phospholipids (oxPLs), result from oxidative stress and accumulate during inflammation, affecting cellular metabolism, immune cell functions, and cell fate. These distinct classes of oxidized lipids not only share overlapping inflammatory roles but also exhibit divergent effects depending on their molecular structures and cellular targets. This Review highlights the double-edged nature of oxPLs: Although their transient production triggers protective responses, their accumulation sustains inflammation, contributing to tissue damage. We also discuss the emerging roles of oxPLs in cell death programs, immune cell activation, and stromal cell functions, which are critical processes favoring tumor growth. Overall, we highlight how oxidized lipids orchestrate immune responses and explore their contribution to infectious diseases and cancer.

Type III interferons are essential immune mediators playing pleiotropic roles during health and disease. In this review, we highlight the molecular and cellular pathways that lead to the production of type III interferons. We also describe their exquisite capacity to act at primary barrier tissues such as those in the intestine, airways, urogenital tract, and skin, as well as to act in other organs such as the liver and thymus. We characterize the activity of type III interferons on distinct cell types in different tissues and organs and detail their impact for the host in the context of viral, bacterial, helminth, and fungal infections. Additionally, we illustrate roles of type III interferons during the development of inflammatory diseases such as inflammatory bowel disease, acute respiratory distress syndrome, asthma, solid tumors, and lupus. Overall, we summarize the dichotomous roles played by this class of interferons and highlight the knowledge gaps that must be addressed to harness type III interferons against multiple human diseases.

Type III IFNs, or IFNλ, are pleiotropic immune mediators that mostly work at mucosal surfaces by signaling in epithelial cells and selected immune cells. Zhou, Zhang, and colleagues (https://doi.org/10.1084/jem.20251858) demonstrate that IFNλ also signals in kidney fibroblasts sustaining renal fibrosis.

Inflammation is an essential defense response but operates at the cost of normal tissue functions. Whether and how the negative impact of inflammation is monitored remains largely unknown. Acidification of the tissue microenvironment is associated with inflammation. Here, we investigated whether macrophages sense tissue acidification to adjust inflammatory responses. We found that acidic pH restructured the inflammatory response of macrophages in a gene-specific manner. We identified mammalian BRD4 as an intracellular pH sensor. Acidic pH disrupts transcription condensates containing BRD4 and MED1 via histidine-enriched intrinsically disordered regions. Crucially, a decrease in macrophage intracellular pH is necessary and sufficient to regulate transcriptional condensates in vitro and in vivo, acting as negative feedback to regulate the inflammatory response. Collectively, these findings uncovered a pH-dependent switch in transcriptional condensates that enables environment-dependent control of inflammation, with a broader implication for calibrating the magnitude and quality of inflammation by the inflammatory cost.

Interferons (IFNs) are signaling proteins that play fundamental roles during health and disease. Although types I, II, and III IFNs are structurally and functionally different, all IFNs signal via an intricate network of Janus kinases, named after the Roman god of time and duality. IFNs are characterized by activities that vary over time and can lead to opposing outcomes. IFNs have protective roles during bacterial, viral, and fungal infections but can also drive numerous inflammatory and autoimmune diseases. In this review, we provide an overview of the cellular and molecular mechanisms governing IFN induction and responses, emphasizing their roles in infections, tumorigenesis, and inflammatory, autoimmune, and genetic diseases, with particular attention to mucosal tissues. Overall, we spotlight how the balanced production of distinct members of the IFN families over time is necessary to exert their protective functions and the detrimental consequences for the host when this balance is lost.

Activation of the NLRP3 inflammasome leads to the production of bioactive interleukin (IL)-1β fostering atherosclerosis. The current dogma is that NLRP3 must be first primed by microbial stimuli, known as pathogen-associated molecular patterns (PAMPs), and then activated by either microbial or host-derived inflammatory cues. The mechanism that controls NLRP3 functioning in the context of non-communicable diseases lacking overt microbial infections remains debated. Here, we show that chronic exposure to atherosclerosis-associated oxidized phospholipids (oxPLs) simultaneously primes and activates NLRP3 independently of microbial cues. Mechanistically, chronic exposure to host-derived oxPLs activate the transcription factor NRF2, which is necessary and sufficient to prime and activate NLRP3 in a PAMP-independent manner. NRF2 chronic activation drives oxidized mitochondrial DNA to activate NLRP3. Ex vivo analyses of atherosclerotic plaques in mice and humans identify a population of monocytes-derived macrophages which activates NRF2 and expresses IL-1β. Overall, our data point to oxPL-dependent NRF2 activation as an all-in-one signal necessary and sufficient to prime and activate NLRP3, sustaining atherogenesis.

Although solid organ transplant outcomes have dramatically improved over the last several decades, incomplete understanding of the immune interface between the donor organ and the recipient’s immune system has impaired our ability to induce immune tolerance in most transplant recipients. Since group 2 innate lymphoid cells (ILC2s) reside in all transplanted solid organs, participate in wound healing, and coordinate other immunoregulatory cell populations, we investigated their role in the alloimmune response. Using a mouse heterotopic cardiac transplant model, we show that recipient ILC2s replace donor’s ILC2s, upregulate MHCII without expressing costimulatory molecules. In addition, recipient derived ILC2s process and present alloantigen, inducing CD4+ T cell anergy via Caspase-3 pathway. When recipient-derived ILC2s are not present, we observed a significant increase in infiltrating donor reactive CD4+ T cells and worsened allograft survival. Additionally, expansion of ILC2s in vivo through IL33 administration prolonged the survival of murine heart allografts. Overall, these data highlight a critical and novel immunoregulatory role of host-derived ILC2s in solid organ transplant, where they induce anergy in alloreactive CD4+ T cells, promoting the induction of alloimmune tolerance. ### Competing Interest Statement The authors have declared no competing interest. Boston Children’s Hospital, https://ror.org/00dvg7y05, TRP Junior TIS

Macrophages detect invading microorganisms through pattern recognition receptors that recognize pathogen-associated molecular patterns or by sensing microbial activities. Tissue stress following pathogen encounters results in the release of host-derived factors that contribute to inflammation. The mechanisms by which these self-derived molecules are sensed by macrophages and their impact on immunity were not fully understood. Our research demonstrated that in both mice and humans, host-derived oxidized phospholipids (oxPLs) were generated upon microbial encounter. Blocking oxPLs limited inflammation and prevented host death without affecting pathogen load. Mechanistically, oxPLs bound and inhibited AKT, a central regulator of immunity and metabolism. AKT inhibition enhanced the methionine cycle and epigenetically suppressed Il10, a key anti-inflammatory cytokine. These findings revealed that host-derived inflammatory signals can drive immune responses, and targeting their activity may protect the host from excessive inflammation during microbial encounters. M.D.G. is supported by the Crohn’s and Colitis Foundation, award number 854391. Innate Immune Responses and Host Defense: Cellular Mechanisms (INC)

Innate immunity relies on pattern recognition receptors (PRRs) to detect threats, including pathogens and damage-associated molecular patterns (DAMPs) from damaged cells. IFI16 behaves as a DAMP and activates Toll-like receptor 4 (TLR4)-mediated inflammation. Here, we identify the N-terminal PYRIN domain (PYD) of IFI16 as critical for binding TLR4 and triggering inflammation, and we confirm this interaction through in vitro and in vivo assays. The inflammatory activity of IFI16PYD is unique to human and mouse PYHIN proteins, as PYDs in other proteins, such as NLRP3 or ASC, do not activate TLR4. Disrupting the IFI16-TLR4 interaction prevents pro-inflammatory cytokine production, reducing immune cell recruitment and skin fibrosis in mice. Elevated IFI16 and TLR4 levels in systemic sclerosis patients suggest a role in disease progression. These findings provide insight into DAMP recognition and inflammation propagation, highlighting the IFI16-TLR4 interaction as a potential therapeutic target for sterile inflammatory diseases.

Adjuvants are widely used to boost the immune response during vaccination protocols. Our group has previously reported that repeated intraperitoneal administration of alum in mice, known as adjuvant conditioning (AC), creates an immunosuppressive environment that delays allogeneic graft rejection through NLRP3-dependent MDSC expansion. However, little is known about the effects of AC on the reprogramming of peritoneal cavity cells, particularly the different peritoneal macrophage populations, and the impact on the adaptive immune response. We found a population-specific immune response to alum, with small peritoneal macrophages (SPMs) being more prone to inflammasome activation than large peritoneal macrophages (LPMs) in vitro. In vivo, alum exposure led to NLRP3-dependent macrophage disappearance reaction (MDR) of LPMs, which could be explained by aggregate formation and migration to the omentum. AC also induced the reprogramming of resident macrophages and infiltrating monocytes towards a less inflammatory state, making them more vulnerable to bacterial infections, but recruited neutrophils with enhanced killing ability. This suggests that AC may influence both innate and adaptive immunity in distinct ways, reprogramming cells to different profiles, and indicating its potential as an immunosuppressive treatment for autoimmune diseases and transplant rejection.

Non-immune cells contribute to induce an effective immune response and recent studies showed that platelets are major players in the modulation of the inflammation. Although platelets are anucleated cells, we recently found that the transcription factor NFAT modulates the activation of platelets and controls their hemostatic and inflammatory activity (Immunity, 2022). In particular, we showed that inhibition of NFAT activation in platelets boosts the anti-microbial functions of neutrophils and their capacity to release neutrophils extracellular traps in the context of sepsis. Mechanistically, we showed NFAT activation determine secondary granule release by platelets, the extent of their aggregation and activation, and a feed-forward loop with NET induction. Whether NFAT activation in platelets can regulate NETosis in the context of chronic inflammatory diseases remains a mystery. Here we focused on inflammatory bowel diseases (IBD), a group of diseases whose etiology is still a matter of debate. In the context of a mouse model of colitis, we investigated whether NFAT activation in platelets regulates NET induction during intestinal inflammation and its impact on disease progression. Crohn’s and colitis foundation research fellowship award Innate Immune Responses and Host Defense: Cellular Mechanisms (INC)

Although adjuvants typically enhance immune responses, we show that repeated alum administration-termed adjuvant conditioning (AC)-induces an immunosuppressive environment that delays allogeneic graft rejection by expanding myeloid-derived suppressor cells (MDSCs). AC-induced MDSCs suppress antigen-specific adaptive responses both in vitro and in vivo, a process dependent on NLRP3 and IL-1 signaling. Allogeneic pancreatic islets transplanted into AC-treated NLRP3-/- mice are not protected, confirming the necessity of NLRP3. Moreover, AC-induced MDSCs cultured with LPS exhibit reduced pro-inflammatory and increased immunosuppressive cytokine production. Similarly, prolonged alum exposure blunts inflammatory cytokine production in human cells. Together, these findings reveal that AC establishes an immunosuppressive milieu via the NLRP3/IL-1 axis. This work suggests that targeting this pathway could promote allograft tolerance in transplant recipients.

Phagocytes initiate immunity to invading microorganisms by detecting pathogen-associated molecular patterns via pattern recognition receptors. Pathogen encounter and consequent activation of the immune system cause tissue damage and the release of host-derived damage-associated molecular patterns, contributing to shape immunity. However, how self-derived factors are sensed by phagocytes and impact the immune response remains poorly understood. Here, we demonstrated that host-derived oxidized phospholipids (oxPLs) are formed after microbial encounter in both mice and humans. oxPLs exacerbated inflammation without affecting pathogen burden. Mechanistically, oxPLs bound and inhibited AKT, potentiating the methionine cycle and the activity of the epigenetic writer EZH2. EZH2 epigenetically dampened the pluripotent anti-inflammatory cytokine IL-10, contributing to the death of the host. Overall, we found that host-derived oxPLs set the balance between protective and detrimental antimicrobial responses and that they can be prophylactically or therapeutically targeted to protect the host against deranged inflammation and immunopathology.

Tissue damage and repair are hallmarks of inflammation. Despite a wealth of information on the mechanisms that govern tissue damage, mechanistic insight into how inflammation affects repair is lacking. Here, we investigated how interferons influence tissue repair after damage to the intestinal mucosa. We found that type III, not type I or type II, interferons delay epithelial cell regeneration by inducing the upregulation of Z-DNA-binding protein 1 (ZBP1). Z-nucleic acids formed following intestinal damage are sensed by ZBP1, leading to caspase-8 activation and the cleavage of gasdermin C (GSDMC). Cleaved GSDMC drives epithelial cell death by pyroptosis and delays repair of the large or small intestine after colitis or irradiation, respectively. The type III interferon/ZBP1/caspase-8/GSDMC axis is also active in patients with inflammatory bowel disease (IBD). Our findings highlight the capacity of type III interferons to delay gut repair, which has implications for IBD patients or individuals exposed to radiation therapies.

Mycobacterium tuberculosis (Mtb)-specific γ9δ2 T cells secrete granzyme A (GzmA) protective against intracellular Mtb growth. However, GzmA-enzymatic activity is unnecessary for pathogen inhibition, and the mechanisms of GzmA-mediated protection remain unknown. We show that GzmA homodimerization is essential for opsonization of mycobacteria, altered uptake into human monocytes, and subsequent pathogen clearance within the phagolysosome. Although monomeric and homodimeric GzmA bind mycobacteria, only homodimers also bind cluster of differentiation 14 (CD14) and Toll-like receptor 4 (TLR4). Without access to surface-expressed CD14 and TLR4, GzmA fails to inhibit intracellular Mtb. Upregulation of Rab11FIP1 was associated with inhibitory activity. Furthermore, GzmA colocalized with and was regulated by protein disulfide isomerase AI (PDIA1), which cleaves GzmA homodimers into monomers and prevents Mtb inhibitory activity. These studies identify a previously unrecognized role for homodimeric GzmA structure in opsonization, phagocytosis, and elimination of Mtb in human monocytes, and they highlight PDIA1 as a potential host-directed therapy for prevention and treatment of tuberculosis, a major human disease.

Age is the single greatest risk factor driving mortality after encounter with SARS-CoV-2. A new study shows that the composition of nasal epithelial cells varies across ages, facilitating SARS-CoV-2 growth and spread in older people.