Poster Tour: Friday

Formation of highly dynamic and spatially organized granulomas is a common feature of inflammation in response to tissue invading pathogens. However, the intricate interplay between immune cells and fibroblastic stromal cells during the formation of intestinal granulomas has remained largely elusive. Here, we show that the induction of the nuclear alarmin interleukin-33 (IL-33) in lamina propria fibroblasts during the granulomatous immune response to the intestinal helminth Heligmosomoides polygyrus bakeri (Hpb) favorably affects granuloma formation and worm clearance. Ablation of IL-33 in intestinal fibroblasts targeted by the Cxcl13-Cre-transgene led to impaired immune cell recruitment and protective properties of granulomas. Thereby, IL-33-mediated activation of interleukin 1 receptor like 1 (IL1RL1)-positive myeloid cells initiated the upregulation of discrete singling pathways to support macrophage attraction and fibroblast activation within granulomas. Consequently, IL-33-dependent regulatory circuits led to the induction of the eosinophil chemotactic chemokine CCL11 in granuloma-associated fibroblasts, facilitating the accumulation of eosinophils within granulomas. Collectively, these findings highlight the pivotal role of fibroblast-derived IL-33 as a key mediator in controlling local immunological processes within intestinal granulomas, providing insights into tissue-specific immunity and host defense.

Aim: Endosomal nucleic acid sensing by Toll-like receptors (TLRs) is central to antimicrobial immunity and several autoimmune conditions such as systemic lupus erythematosus (SLE). The innate immune adaptor TASL mediates, via the interaction with solute carrier SLC15A4 on endolysosome, the activation of interferon regulatory factor 5 (IRF5) downstream of human TLR7, TLR8 and TLR9, but the pathophysiological functions of this axis remain unexplored. 

Methods: Using the whole body knock-out mouse models we addressed ex vivo and in vivo immune responses triggered by TLR7/9 activation.

Results: Our work shows that SLC15A4 deficiency results in a selective block of TLR7/9-induced IRF5 activation, while loss of TASL leads to a strong but incomplete impairment, which depends on the cell type and TLR engaged. This residual IRF5 activity is ascribed to a previously uncharacterized paralogue, Gm6377, named here TASL2. Double knockout of TASL and TASL2 (TASL^DKO) phenocopies SLC15A4-deficient feeble mice showing comparable impairment of innate and humoral responses. Consequently, TASL^DKO mice fail to control chronic LCMV infection, while being protected in chemically (pristane) and genetically (Fas^lpr) induced SLE disease models. 

Conclusion: Our study thus demonstrates the critical pathophysiological role of SLC15A4 and TASL/TASL2 for TLR7/9-driven inflammatory responses, further supporting the therapeutic potential of targeting this complex in SLE and related autoimmune diseases.

Upon lung tissue migration, hookworm larvae cause extensive host damage. Short-term, this results in pulmonary hemorrhage; long-term, mice develop emphysema resembling COPD. While many immune cells involved in repair are known to limit emphysema, mechanisms underlying its development remain unclear.
To address this, we used digital cytometry to study the impact of Nippostrongylus brasiliensis infection on lung structure. From 3 to at least 12 days post-infection, ciliated, alveolar type I (ATI) epithelial cells, and capillary endothelial cells were reduced in favor of alveolar type II (ATII) cells. The ATI/ATII balance is critical for lung architecture, with imbalance linked to fibrosis. We thus investigated ATII cells upon infection with N. brasiliensis in vivo and in vitro and confirmed infection's sustained impact on ATII numbers up to 40 days. Purified epithelial cells from infected mice lacked typical cobblestone morphology, were prone to death, expressed high SMA levels, and showed impaired alveolosphere formation in 3D cultures. In co-culture assays, we observed that ATII cells recognized and bound N. brasiliensis larvae, with binding enhanced both short and long-term (2 and 40 days post-infection) compared to naïve ATII cells. Larval recognition by epithelial cells was TGF-β and Yap/Taz dependent, suggesting a mechanosensory mechanism. Finally, stimulation of ATII cells with larvae enhanced IL-4-activated macrophage recognition, and blockade of ATII cells activation with TGF-β inhibitor during re-infection limited macrophage trapping and killing of N. brasiliensis.

Rhinovirus (RV) infection of airway epithelial cells from patients with asthma results in an abnormal engagement of retinoic-acid inducible gene I (RIG-I) into RIG-I inflammasome formation, which subsequently delays RIG-I dependent interferon responses and enhances proinflammatory signaling in asthma. The exacerbation-prone asthma has been linked with metabolic dysfunctions, however, the metabolic regulation of antiviral responses during those pathogenic viral infections in asthma is not well understood. Therefore, bronchial epithelium from patients with asthma and healthy controls upon in vitro and in vivo RV infection were used to analyze the metabolic regulation of RIG-I-dependent signaling. Bronchial epithelium of patients with asthma upon RV infection demonstrated increased glycolytic ATP and decreased mitochondrial ATP production. We also observed a broad downregulation of mitochondrial proteins, related to the electron transport chain (ETC), TCA cycle, reactive oxygen species (ROS) removal, and mitochondrial structure in asthma. Moreover, inhibition of ETC complex I with rotenone reduced IFNB and DDX58 (RIG-I) expression while increasing the release of mature IL-1β protein upon RV infection. Conversely, blocking glycolysis with 2-deoxy-D-glucose (2-DG) reduced both viral replication and IL-1β release, demonstrating a clear metabolic regulation of RIG-I-dependent proinflammatory/antiviral responses in bronchial epithelium. In summary, abnormal metabolic reprogramming in the bronchial epithelium affects impaired RIG-I signaling and subsequent antiviral response in asthma.

Antifungal resistance is increasing worldwide and development of alternative therapeutic strategies for fungal infections is imperative. Aspergillus niger infection induces lung damage via oxalic acid secretion and accumulation of calcium oxalate cristals (CaOx). Oxalotrophic bacteria (C. oxalaticus) degrade CaOx and inhibit fungal growth via environmental interference. Here we provide a proof-of-concept study for the use of biocontrol bacteria against respiratory fungal infections.

Human bronchial epithelial cells (hBECs) were cultured on Air-Liquid Interface for 28 days before exposure to A.niger conidia, C.oxalaticus, or a combination for 72h. Transepithelial electrical resistance, cell morphology, pH and calcium levels were assessed in vitro. Immunosuppressed adult BalbC/J mice were exposed (i.n.) to A.niger, C.oxalaticus, or a combination. Immune cell influx and hyphal development were assessed after 72h in BALf and lung tissue.

Infection of hBECs with A. niger modified pH and Ca2+ concentrations and impaired barrier integrity. This effect was rescued by co-exposure with C.oxalaticus. Coadministration of C.oxalaticus with A.niger in mice led to improved clinical scoring and reduced hyphae formation compared to control (A.niger alone). Interestingly, smaller CaOx crystals were observed following administration of both C.oxalaticus and A. niger, compared to control.

We successfully demonstrated the potential of environmental interference as a biocontrol strategy against Aspergillus infections. Overall, this provides novel treatment avenues for respiratory fungal infections.