Aluminum-based adjuvants (aluminum salts or alum) are widely used in human vaccination, although their mechanisms of action are poorly understood. Here we report that, in mice, alum causes cell death and the subsequent release of host cell DNA, which acts as a potent endogenous immunostimulatory signal mediating alum adjuvant activity. Furthermore, we propose that host DNA signaling differentially regulates IgE and IgG1 production after alum-adjuvanted immunization. We suggest that, on the one hand, host DNA induces primary B cell responses, including IgG1 production, through interferon response factor 3 (Irf3)-independent mechanisms. On the other hand, we suggest that host DNA also stimulates 'canonical' T helper type 2 (T(H)2) responses, associated with IgE isotype switching and peripheral effector responses, through Irf3-dependent mechanisms. The finding that host DNA released from dying cells acts as a damage-associated molecular pattern that mediates alum adjuvant activity may increase our understanding of the mechanisms of action of current vaccines and help in the design of new adjuvants.

The hygiene hypothesis postulates that the recent increase in allergic diseases such as asthma and hay fever observed in Western countries is linked to reduced exposure to childhood infections. Here we investigated how infection with a gammaherpesvirus affected the subsequent development of allergic asthma. We found that murid herpesvirus 4 (MuHV-4) inhibited the development of house dust mite (HDM)-induced experimental asthma by modulating lung innate immune cells. Specifically, infection with MuHV-4 caused the replacement of resident alveolar macrophages (AMs) by monocytes with regulatory functions. Monocyte-derived AMs blocked the ability of dendritic cells to trigger a HDM-specific response by the T2 subset of helper T cells. Our results indicate that replacement of embryonic AMs by regulatory monocytes is a major mechanism underlying the long-term training of lung immunity after infection.

Living in a microbe-rich environment reduces the risk of developing asthma. Exposure of humans or mice to unmethylated CpG DNA (CpG) from bacteria reproduces these protective effects, suggesting a major contribution of CpG to microbe-induced asthma resistance. However, how CpG confers protection remains elusive. We found that exposure to CpG expanded regulatory lung interstitial macrophages (IMs) from monocytes infiltrating the lung or mobilized from the spleen. Trafficking of IM precursors to the lung was independent of CCR2, a chemokine receptor required for monocyte mobilization from the bone marrow. Using a mouse model of allergic airway inflammation, we found that adoptive transfer of IMs isolated from CpG-treated mice recapitulated the protective effects of CpG when administered before allergen sensitization or challenge. IM-mediated protection was dependent on IL-10, given that Il10 CpG-induced IMs lacked regulatory effects. Thus, the expansion of regulatory lung IMs upon exposure to CpG might underlie the reduced risk of asthma development associated with a microbe-rich environment.

T cell exhaustion presents one of the major hurdles to cancer immunotherapy. Among exhausted CD8 + tumor-infiltrating lymphocytes (TILs), the terminally exhausted subset contributes directly to tumor cell killing owing to its cytotoxic effector function. However, this subset does not respond to immune checkpoint blockades and is difficult to be reinvigorated with restored proliferative capacity. Here, we show that a half-life–extended interleukin (IL)-10/Fc fusion protein directly and potently enhanced expansion and effector function of terminally exhausted CD8 + TILs by promoting oxidative phosphorylation (OXPHOS), a process independent of the progenitor exhausted T cells. IL-10/Fc was a safe and highly efficient metabolic intervention that synergized with adoptive T cell transfer immunotherapy, leading to eradication of established solid tumors and durable cures in a majority of treated mice. These findings show that metabolic reprogramming by upregulating mitochondrial pyruvate carrier-dependent OXPHOS can revitalize terminally exhausted T cells and enhance the response to cancer immunotherapy.

C.S. were involved in experimental design. C.R. and C.S. realized most experiments, compiled the data and contributed equally to this work. P.M., C.Ru. and J.S. were involved in (bone marrow-derived) dendritic cell-related experiments. M.T. and S.L.J. were involved in experiments aiming at detecting and inhibiting NETs. C.V., F.P., N.R. and D.C. contributed to experiments involving ozone exposure and invasive measurements of airway function. T.M. analysed single cell RNA sequencing data with the help of the GIGA Genomics Platform. C.R. and T.M. prepared the figures, and T.M. wrote the manuscript. All authors provided feedback on the manuscript.

Conventional dendritic cells (DCs) are considered to be the prime initiators of airway allergy. Yet, it remains unclear whether specific DC subsets are preferentially involved in allergic airway sensitization. Here, we systematically assessed the respective pro-allergic potential of individually sorted lung DC subsets isolated from house dust mite antigen (HDM)-treated donor mice, following transfer to naïve recipients. Transfer of lung CD11c+CD11b+ DCs, but not CD11c+CD11b−CD103+ DCs, was sufficient to prime airway allergy. The CD11c+CD11b+ DC subpopulation was composed of CD11c+CD11b+Ly6C+ inflammatory monocyte-derived cells, whose numbers increase in the lungs following HDM exposure, and of CD11c+CD11b+Ly6C− DCs, which remain stable. Counterintuitively, only CD11c+CD11b+Ly6C− DCs, and not CD11c+CD11b+Ly6C+ DCs, were able to convey antigen to the lymph nodes and induce adaptive T cell responses and subsequent airway allergy. Our results thus support that lung resident non-inflammatory CD11c+CD11b+Ly6C− DCs are the essential inducers of allergic airway sensitization to the common aeroallergen HDM in mice.

Allergic asthma is a chronic Th2 inflammatory disease of the lower airways affecting a growing number of people worldwide. The impact of infections and microbiota composition on allergic asthma has been investigated frequently. Until now, however, there have been few attempts to investigate the impact of asthma on the control of infectious microorganisms and the underlying mechanisms. In this work, we characterize the consequences of allergic asthma on intranasal (i.n.) infection by Brucella bacteria in mice. We observed that i.n. sensitization with extracts of the house dust mite Dermatophagoides farinae or the mold Alternaria alternata (Alt) significantly increased the number of Brucella melitensis, Brucella suis, and Brucella abortus in the lungs of infected mice. Microscopic analysis showed dense aggregates of infected cells composed mainly of alveolar macrophages (CD11c+ F4/80+ MHCII+) surrounded by neutrophils (Ly-6G+). Asthma-induced Brucella susceptibility appears to be dependent on CD4+ T cells, the IL-4/STAT6 signaling pathway and IL-10, and is maintained in IL-12- and IFN-γR-deficient mice. The effects of the Alt sensitization protocol were also tested on Streptococcus pneumoniae and Mycobacterium tuberculosis pulmonary infections. Surprisingly, we observed that Alt sensitization strongly increases the survival of S. pneumoniae infected mice by a T cell and STAT6 independent signaling pathway. In contrast, the course of M. tuberculosis infection is not affected in the lungs of sensitized mice. Our work demonstrates that the impact of the same allergic sensitization protocol can be neutral, negative, or positive with regard to the resistance of mice to bacterial infection, depending on the bacterial species.

IntroductionFor a safe and sustainable return to normal functioning of academic activities in higher education, objective-driven testing strategies that are flexible and rapidly adaptable are essential to effectively monitor and respond to new developments of the COVID-19 pandemic. To date, prospective longitudinal research on SARS-CoV-2 antibody testing in saliva and seroprevalence in higher education contexts is substantially lacking, limiting our understanding of COVID-19 prevalence, incidence and nature of the immune response to SARS-CoV-2 at various stages of the infection and vaccination. To address this lack of evidence, a prospective population-based cohort study (SARSSURV-ULiège) has recently been started.Methods and analysisStudents (n=1396) and staff members (n=1143) of the University of Liège are followed up over more than 1 year. All participants are required to complete anamnestic, clinical and vaccine hesitancy questionnaires for medical histories and undertaken treatments. Previous proven or suspected SARS-CoV-2 infection is also registered. In phase 1, weekly saliva samples to perform RT-qPCR to detect SARS-CoV-2 and monthly COVID-19 serological rapid test results are collected. Once being positive to either saliva RT-qPCR assay for SARS-CoV-2 presence or to serological test, the participant is invited to enter phase 2. If participants get vaccinated during the study period, they are invited to phase 2. In this second phase, besides weekly saliva self-test, depending on the participants’ profiles, both gargle and blood samples are collected to obtain various biological data to measure the presence of neutralising antibodies against SARS-CoV-2, determine the magnitude and the duration of antibody responses over time.Ethics and disseminationThe study has received the approval from the University Hospital of Liège Ethics Committee (reference number 2021/96, dated 26 March 2021). Potential protocol amendments will be presented to the Research Ethics Committee. The findings of the present study will be presented at scientific conferences and the results published in peer-review publications. Weekly reports will be submitted to the risk assessment group and the risk management group against COVID-19 of the university to enable a timely public health action if necessary.