InVivoMAb anti-mouse CD317 (BST2, PDCA-1)

Following central nervous system injury, astrocytes form borders that were traditionally regarded as physical barriers. Emerging evidence demonstrates their capacity to regulate inflammation and repair; however, the specific characteristics of these border astrocytes and their interactions with immune cells remain insufficiently characterized. Using single-cell sequencing and spatial transcriptomics, we identified astrocytes expressing the interferon-inducible protein bone marrow stromal cell antigen 2 (BST2) enriched at injury boundaries that promote microglial recruitment via C3/C3aR signaling. Astrocyte-specific Bst2 knockout reduced astrocyte-microglia interactions and attenuated border formation, correlating with early neurological improvement after stroke. Mechanistically, BST2 enhanced C3 expression through protein kinase C-βII (PKCβII) phosphorylation. Moreover, treatment with a BST2 monoclonal antibody diminished astrocyte-microglia interactions and improved neurological function. Together, these findings highlight the pivotal role of astrocyte-microglia interactions in lesion border formation and suggest that BST2 may represent a therapeutic target to modulate these interactions and reduce early brain injury after stroke.

Mice lacking apolipoprotein E (APOE, Apoe-/- mice) on a high cholesterol (HC) diet are highly susceptible to infection with Mycobacterium tuberculosis (Mtb) but the underlying immune dysregulation has been unclear. While neutrophils are often the predominant cell type in the lungs of humans with severe tuberculosis (TB), they are relatively scarce in the lungs of some strains of mice that are used to study the disease. The neutrophil levels in the lungs of Mtb-infected Apoe-/- HC mice are very high, and thus studies in this model offer the opportunity to examine the role of specific neutrophil functions in the pathology of severe TB. We determined that depleting neutrophils, depleting plasmacytoid dendritic cells (pDCs), or blocking type I interferon signaling improved the outcome of TB in Apoe-/- HC mice. We also demonstrated that blocking the activation of peptidylarginine deiminase 4 (PAD4), an enzyme critical to NET formation, leads to fewer NETs in the lungs and dramatically improves the outcome of TB in Apoe-/- HC mice without affecting the number of neutrophils in the lung. We found that the transcriptional profile of neutrophils in Mtb-infected Apoe-/- HC mice is biased towards a state that resembles the "N2" phenotype that has been defined in cancer models and has been implicated in matrix degradation and tissue destruction. Our observations strongly suggest that the state of the neutrophil when it encounters the Mtb-infected lung is one of the main drivers of severe disease and implies that targeted interventions that alter specific states or functions, such as the production of NETs, may improve outcome while preserving sufficient capacity for host-defense.

Severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2)-induced impaired antiviral immunity and excessive inflammatory responses cause lethal pneumonia. However, the in vivo roles of key pattern recognition receptors that elicit protective antiviral and fatal inflammatory responses, specifically in the lungs, are not well described. Coronaviruses possess single-stranded RNA genome that activates TLR7/8 to induce an antiviral interferon (IFN) and robust inflammatory cytokine response. Here, using wild-type and TLR7-deficient (TLR7-/-) mice infected with mouse-adapted SARS-CoV-2 (MA-CoV-2), we examined the role of TLR7 in the lung antiviral and inflammatory response and severe pneumonia. We showed that TLR7 deficiency significantly increased lung virus loads and morbidity/mortality, which correlated with reduced levels of type I IFNs (Ifna/b), type III IFNs (Ifnl), and IFN-stimulated genes (ISGs) in the lungs. A detailed evaluation of MA-CoV-2-infected lungs revealed increased neutrophil accumulation and lung pathology in TLR7-/- mice. We further showed that blocking type I IFN receptor (IFNAR) signaling enhanced SARS-CoV-2 replication in the lungs and caused severe lung pathology, leading to 100% mortality compared to infected control mice. Moreover, immunohistochemical assessment of the lungs revealed increased numbers of SARS-CoV-2 antigen-positive macrophages, pneumocytes, and bronchial epithelial cells in TLR7-/- and IFNAR-deficient mice compared to control mice. In summary, we conclusively demonstrated that despite TLR7-induced robust lung inflammation, TLR7-induced IFN/ISG responses suppress lung virus replication and pathology and provide protection against SARS-CoV-2-induced fatal pneumonia. Additionally, given the similar disease outcomes in control, TLR7-/-, and IFNAR-deficient MA-CoV-2-infected mice and coronavirus disease 2019 (COVID-19) patients, we propose that MA-CoV-2-infected mice constitute an excellent model for studying COVID-19.IMPORTANCESevere coronavirus disease 2019 (COVID-19) is caused by a delicate balance between a strong antiviral and an exuberant inflammatory response. A robust antiviral immunity and regulated inflammation are protective, while a weak antiviral response and excessive inflammation are detrimental. However, the key host immune sensors that elicit protective antiviral and inflammatory responses to severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) challenge are poorly defined. Here, we examined the role of viral RNA-mediated TLR7 activation in the lung antiviral and inflammatory responses in SARS-CoV-2-infected mice. We demonstrate that TLR7 deficiency led to a high rate of morbidity and mortality, which correlated with an impaired antiviral interferon (IFN)-I/III response, enhanced lung virus replication, and severe lung pathology. Furthermore, we show that blocking IFN-I signaling using anti-IFN receptor antibody promoted SARS-CoV-2 replication in the lungs and caused severe disease. These results provide conclusive evidence that TLR7 and IFN-I receptor deficiencies lead to severe disease in mice, replicating clinical features observed in COVID-19 patients.

Photodynamic therapy (PDT) effectively kills cancer cells and initiates immune responses that promote anticancer effects locally and systemically. Primarily developed for local and regional cancers, the potential of PDT for systemic antitumor effects [in situ photo-vaccination (ISPV)] remains underexplored. This study investigates: (1) the comparative effectiveness of paclitaxel (PTX) prodrug [Pc-(L-PTX)2] for PDT and site-specific PTX effects versus its pseudo-prodrug [Pc-(NCL-PTX)2] for PDT combined with checkpoint inhibitors; (2) mechanisms driving systemic antitumor effects; and (3) the prophylactic impact on preventing cancer recurrence. A bilateral tumor model was established in BALB/c mice through subcutaneous injection of CT26 cells. Mice received the PTX prodrug (0.5 μmole kg-1, i.v.), and tumors were treated with a 690-nm laser (75 mW cm-2 for 30 min, drug-light interval 0.5 h, light does 135 J cm-1), followed by anti-CTLA-4 (100 μg dose-1, i.p.) on days 1, 4, and 7. Notable enhancement in both local and systemic antitumor effectiveness was observed with [Pc-(L-PTX)2] compared to [Pc-(NCL-PTX)2] with checkpoint inhibitor. Immune cell depletion and immunohistochemistry confirmed neutrophils and CD8+ T cells are effectors for systemic antitumor effects. Treatment-induced immune memory resisted newly rechallenged CT26, showcasing prophylactic benefits. ISPV with a PTX prodrug and anti-CTLA-4 is a promising approach for treating metastatic cancers and preventing recurrence.