To investigate long COVID-19 syndrome (LCS) pathophysiology, we performed an exploratory study with blood plasma derived from three groups: 1) healthy vaccinated individuals without SARS-CoV-2 exposure; 2) asymptomatic recovered patients at least three months after SARS-CoV-2 infection and; 3) symptomatic patients at least 3 months after SARS-CoV-2 infection with chronic fatigue syndrome or similar symptoms, here designated as patients with long COVID-19 syndrome (LCS). Multiplex cytokine profiling indicated slightly elevated pro-inflammatory cytokine levels in recovered individuals in contrast to patients with LCS. Plasma proteomics demonstrated low levels of acute phase proteins and macrophage-derived secreted proteins in LCS. High levels of anti-inflammatory oxylipins including omega-3 fatty acids in LCS were detected by eicosadomics, whereas targeted metabolic profiling indicated high levels of anti-inflammatory osmolytes taurine and hypaphorine, but low amino acid and triglyceride levels and deregulated acylcarnitines. A model considering alternatively polarized macrophages as a major contributor to these molecular alterations is presented.

T follicular helper (Tfh) cells are essential for the development of germinal center B cells and high-affinity antibody-producing B cells in humans and mice. Here, we identify the guanine nucleotide exchange factor (GEF) Rin-like (Rinl) as a negative regulator of Tfh generation. Loss of Rinl leads to an increase of Tfh in aging, upon in vivo immunization and acute LCMV Armstrong infection in mice, and in human CD4+ T cell in vitro cultures. Mechanistically, adoptive transfer experiments using WT and Rinl-KO naïve CD4+ T cells unraveled T cell–intrinsic GEF-dependent functions of Rinl. Further, Rinl regulates CD28 internalization and signaling, thereby shaping CD4+ T cell activation and differentiation. Thus, our results identify the GEF Rinl as a negative regulator of global Tfh differentiation in an immunological context and species-independent manner, and furthermore, connect Rinl with CD28 internalization and signaling pathways in CD4+ T cells, demonstrating for the first time the importance of endocytic processes for Tfh differentiation.

Arthropods are ancient vectors of infectious disease that alter the immune environment of the skin during feeding. The epidermis and its immune sentinels, including Langerhans cells, are critical for protection against ectoparasitic arthropods such as ticks. Here, we investigate how human Langerhans cells respond to clinical and experimental tick bites and concomitant infection with the tick-borne bacterium Borrelia burgdorferi. Using imaging, migration assays, immune spheroid models, and single-cell transcriptomic analysis of patient samples, we show that tick bites and tick saliva reprogram Langerhans cells to increase migration into lymphatic tissues, adopt a tolerogenic state marked by specific transcriptional programs, reduced ability to induce pro-inflammatory helper T cells, and enhanced promotion of type 2 and regulatory T cell responses. This shift dampens protective immunity and helps explain how ticks and their pathogens evade host defense and achieve efficient transmission.

First-generation vaccines against SARS-CoV-2 do not provide adequate immune protection. Therefore, we engineered a divalent gene construct combining the receptor-binding domain (RBD) of the spike protein and the immunodominant region of the viral nucleocapsid. This fusion protein was produced in either E. coli or a recombinant baculovirus system. Subsequently, the fusion protein was mixed with adjuvant and administered to mice in a prime-booster mode. Mice (72%) produced an IgG response against both proteins (titer: 10⁻⁴–10⁻⁵) 14 days after the first booster injection, which was increased to 100% by a second booster. Comparable IgG responses were detected against the delta, gamma and omicron variants of the RBD region. Durability testing revealed IgGs beyond 90 days. In addition, cytolytic effector cell molecules were increased in lymphocytes isolated from peripheral blood. Ex vivo stimulation of T cells by nucleocapsid and RBD peptides showed antigen-specific upregulation of CD44 among the CD4⁺ and CD8⁺ T cells of vaccinated mice. No side effect was documented in the central nervous system. Cumulatively, these data represent a proof-of-principle approach alternative to existing mRNA vaccination strategies.

In this study, we developed a customized high-resolution mass spectrometry metabolomics workflow integrating the dual sugar test employing lactulose and mannitol as test probes for intestinal permeability assessment with untargeted screening of small molecules. Urine samples were collected from patients with major depression and healthy controls as part of a clinical study at the psychiatric department. Using a dual injection/dual chromatography setup, the test probes were quantified by hydrophilic interaction liquid chromatography (HILIC) in a targeted assay, while drugs and their metabolites were profiled in an untargeted manner by reversed-phase separation. Rigorous method development and validation allowed for selective separation of sugar isomers and consequently accurate quantification of lactulose and mannitol in urine. Internal standardization with compound specific stable isotope-labeled standards enabled excellent analytical figures of merit such as high recoveries, precision (< 5%), and working range (5 orders of magnitude). Within one analytical run, intestinal permeability was assessed together with drugs and their metabolites, allowing to screen for confounding drugs and patient compliance to the therapeutic scheme. Graphical Abstract

FOXP3⁺ regulatory T cells (Treg cells) are key for immune homeostasis. Here, we reveal that nuclear receptor corepressor 1 (NCOR1) controls naïve and effector Treg cell states. Upon NCOR1 deletion in T cells, effector Treg cell frequencies were elevated in mice and in in vitro-generated human Treg cells. NCOR1-deficient Treg cells failed to protect mice from severe weight loss and intestinal inflammation associated with CD4⁺ T cell transfer colitis, indicating impaired suppressive function. NCOR1 controls the transcriptional integrity of Treg cells, since effector gene signatures were already upregulated in naïve NCOR1-deficient Treg cells while effector NCOR1-deficient Treg cells failed to repress genes associated with naïve Treg cells. Moreover, genes related to cholesterol homeostasis including targets of liver X receptor (LXR) were dysregulated in NCOR1-deficient Treg cells. However, genetic ablation of LXRβ in T cells did not revert the effects of NCOR1 deficiency, indicating that NCOR1 controls naïve and effector Treg cell subset composition independent from its ability to repress LXRβ-induced gene expression. Thus, our study reveals that NCOR1 maintains naïve and effector Treg cell states via regulating their transcriptional integrity. We also reveal a critical role for this epigenetic regulator in supporting the suppressive functions of Treg cells in vivo.