ACE2 is the critical in vivo receptor for SARS-CoV-2 in a novel COVID-19 mouse model with TNF-and IFN?-driven immunopathology

Despite tremendous progress in the understanding of COVID-19, mechanistic insight into immunological, disease-driving factors remains limited. We generated maVie16, a mouse-adapted SARS-CoV-2, by serial passaging of a human isolate. In silico modeling revealed how only three Spike mutations of maVie16 enhanced interaction with murine ACE2. maVie16 induced profound pathology in BALB/c and C57BL/6 mice, and the resulting mouse COVID-19 (mCOVID-19) replicated critical aspects of human disease, including early lymphopenia, pulmonary immune cell infiltration, pneumonia, and specific adaptive immunity. Inhibition of the proinflammatory cyto-kines IFN? and TNF substantially reduced immunopathology. Importantly, genetic ACE2-deficiency completely prevented mCOVID-19 development. Finally, inhalation therapy with recombinant ACE2 fully protected mice from mCOVID-19, revealing a novel and efficient treatment. Thus, we here present maVie16 as a new tool to model COVID-19 for the discovery of new therapies and show that disease severity is determined by cytokine-driven immunopathology and critically dependent on ACE2 in vivo. © Gawish et al

The Triggering Receptor Expressed on Myeloid Cells 2 Inhibits Complement Component 1q Effector Mechanisms and Exerts Detrimental Effects during Pneumococcal Pneumonia

Phagocytosis and inflammation within the lungs is crucial for host defense during bacterial pneumonia. Triggering receptor expressed on myeloid cells (TREM)-2 was proposed to negatively regulate TLR-mediated responses and enhance phagocytosis by macrophages, but the role of TREM-2 in respiratory tract infections is unknown. Here, we established the presence of TREM-2 on alveolar macrophages (AM) and explored the function of TREM-2 in the innate immune response to pneumococcal infection in vivo. Unexpectedly, we found Trem-2(-/-) AM to display augmented bacterial phagocytosis in vitro and in vivo compared to WT AM. Mechanistically, we detected that in the absence of TREM-2, pulmonary macrophages selectively produced elevated complement component 1q (C1q) levels. We found that these increased C1q levels depended on peroxisome proliferator-activated receptor-δ (PPAR-δ) activity and were responsible for the enhanced phagocytosis of bacteria. Upon infection with S. pneumoniae, Trem-2(-/-) mice exhibited an augmented bacterial clearance from lungs, decreased bacteremia and improved survival compared to their WT counterparts. This work is the first to disclose a role for TREM-2 in clinically relevant respiratory tract infections and demonstrates a previously unknown link between TREM-2 and opsonin production within the lungs

A Dynamic Real Time In Vivo and Static Ex Vivo Analysis of Granulomonocytic Cell Migration in the Collagen-Induced Arthritis Model

<div><p>Neutrophilic granulocytes and monocytes (granulomonocytic cells; GMC) drive the inflammatory process at the earliest stages of rheumatoid arthritis (RA). The migratory behavior and functional properties of GMC within the synovial tissue are, however, only incompletely characterized. Here we have analyzed GMC in the murine collagen-induced arthritis (CIA) model of RA using multi-photon real time in vivo microscopy together with ex vivo analysis of GMC in tissue sections.</p> <p>GMC were abundant as soon as clinical arthritis was apparent. GMC were motile and migrated randomly through the synovial tissue. In addition, we observed the frequent formation of cell clusters consisting of both neutrophilic granulocytes and monocytes that actively contributed to the inflammatory process of arthritis. Treatment of animals with a single dose of prednisolone reduced the mean velocity of cell migration and diminished the overall immigration of GMC.</p> <p>In summary, our study shows that the combined application of real time in vivo microscopy together with elaborate static post-mortem analysis of GMC enables the description of dynamic migratory characteristics of GMC together with their precise location in a complex anatomical environment. Moreover, this approach is sensitive enough to detect subtle therapeutic effects within a very short period of time.</p> </div

Type I interferon promotes alveolar epithelial type II cell survival during pulmonary Streptococcus pneumoniae infection and sterile lung injury in mice.

Protecting the integrity of the lung epithelial barrier is essential to ensure respiration and proper oxygenation in patients suffering from various types of lung inflammation. Type I interferon (IFN-I) has been associated with pulmonary epithelial barrier function, however, the mechanisms and involved cell types remain unknown. We aimed to investigate the importance of IFN-I with respect to its epithelial barrier strengthening function to better understand immune-modulating effects in the lung with potential medical implications. Using a mouse model of pneumococcal pneumonia, we revealed that IFN-I selectively protects alveolar epithelial type II cells (AECII) from inflammation-induced cell death. Mechanistically, signaling via the IFN-I receptor on AECII is sufficient to promote AECII survival. The net effects of IFN-I are barrier protection, together with diminished tissue damage, inflammation, and bacterial loads. Importantly, we found that the protective role of IFN-I can also apply to sterile acute lung injury, in which loss of IFN-I signaling leads to a significant reduction in barrier function caused by AECII cell death. Our data suggest that IFN-I is an important mediator in lung inflammation that plays a protective role by antagonizing inflammation-associated cell obstruction, thereby strengthening the integrity of the epithelial barrier

Combined Vaccination with B Cell Peptides Targeting Her-2/neu and Immune Checkpoints as Emerging Treatment Option in Cancer

The application of monoclonal antibodies (mAbs), targeting tumor-associated (TAAs) or tumor-specific antigens or immune checkpoints (ICs), has shown tremendous success in cancer therapy. However, the application of mAbs suffers from a series of limitations, including the necessity of frequent administration, the limited duration of clinical response and the emergence of frequently pronounced immune-related adverse events. However, the introduction of mAbs has also resulted in a multitude of novel developments for the treatment of cancers, including vaccinations against various tumor cell-associated epitopes. Here, we reviewed recent clinical trials involving combination therapies with mAbs targeting the PD-1/PD-L1 axis and Her-2/neu, which was chosen as a paradigm for a clinically highly relevant TAA. Our recent findings from murine immunizations against the PD-1 pathway and Her-2/neu with peptides representing the mimotopes/B cell peptides of therapeutic antibodies targeting these molecules are an important focus of the present review. Moreover, concerns regarding the safety of vaccination approaches targeting PD-1, in the context of the continuing immune response, as a result of induced immunological memory, are also addressed. Hence, we describe a new frontier of cancer treatment by active immunization using combined mimotopes/B cell peptides aimed at various targets relevant to cancer biology

Analysis of GMC migration and histomorphological assessment of arthritis in animals with CIA.

<p>A) Paraffin sections were stained with HE and anti-Ly-6B.2 mAb. In contrast to healthy animals GMC cells can be detected in animals with CIA at the earliest time-points (paw swelling day 1) of clinical signs of arthritis and are abundant at later (paw swelling day 10) time-points. Scale bars represent 50 µm. Representative pictures are shown from experiments that were performed in three healthy animals and three animals with CIA. B) Representative samples of paraffin sections from hind paws of three healthy control animals and three animals with CIA stained for HE, TRAP and TB are shown. Arrows point to areas of bone erosions. Scale bars represent 500 µm. C) Histomorphological signs of arthritis were quantified in three CIA subjects (day 11±6 of paw swelling) as compared to three healthy control subjects. Areas of inflammation, bone erosions, osteoclasts and cartilage degradation can be detected in CIA subjects but not in healthy control animals. Graph bars represent mean values ± s.e.m.</p

GMC cluster formation.

<p>A) Real time in vivo cell cluster formation (arrow) during a 2 h time interval. Individual pictures were taken at the indicated time points (Green channel: EGFP⁺ GMC cells, magenta channel: SHG of collagen structures). Scale bars represent 100 µm. Representative pictures are shown from movies that were made in three healthy control subjects and three subjects with CIA. B) Real time in vivo cell cluster formation during a 30 min time interval at higher magnification. Individual pictures of EGFP⁺ cells were taken at the indicated time points. Arrows point at individual cells with high EGFP fluorescence expression intensity. Scale bars represent 15 µm. Representative pictures are shown from movies that were made in three subjects with CIA. Quantification of cell velocity, displacement over time and the motility index (total displacement/cumulative path length) are shown for EGFP^high (defined as 30% of EGFP⁺ cells with highest mean fluorescence intensity of EGFP) and EGFP^low (defined as 30% of EGFP⁺ cells with lowest mean fluorescence intensity of EGFP) cells. Data points represent individual cells (EGFP^high: n = 216; EGFP^low: n = 202) compiled from three independent imaging session from individual joints of three CIA animals. Graph bars show mean±s.e.m. from the same experiments. Asterisks (*) indicate significant p values (p<0.05). Cumulative cell tracks are shown from one representative experiment for EGFP^high, EGFP^low and both (merged) cell populations. Scale bars represent 15 µm.</p

Kinetics of cell migration.

<p>A) Comparative real time in vivo analysis of cell migration in healthy versus CIA subjects were performed in C57BL/6 lysM-EGFP animals. GMC cells with the expression of EGFP (green) are rarely found in healthy tissue, whereas they are abundant in the synovial tissue of CIA subjects. The magenta signal displays a second harmonic generation (SHG) of collagen structures (see also <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0035194#pone.0035194.s002" target="_blank">Movie S1</a>). Scale bars (left corner) represent 100 µm. Representative pictures are shown from movies that were made in three healthy control subjects and three subjects with CIA. B)–D): Quantification of cell velocity (b), displacement over time (c) and the motility index (total displacement/cumulative path length) (d) are shown for GMC cells in healthy subjects, in CIA subjects (CIA) and in CIA subjects treated with prednisolone (CIA+Pred). For (b) and (c), data points represent individual cells (healthy: n = 142; CIA: n = 4055; CIA+Pred: n = 3787) compiled from three independent imaging sessions involving individual joints of three animals. Mean values±s.e.m. are shown. Graph bars show mean±s.e.m. (d). Asterisks (*) indicate significant p values (<0.05). E) Cell immigration describes the number of cells immigrating into the ROI at each time point. Few cells immigrate in healthy subjects. CIA diseased subjects start with high numbers of GMC cells and increasing numbers of cells immigrate into the scanned area. Prednisolone stabilizes cell immigration to comparable numbers of cells immigrating at each time point. Data are mean values from experiment that were performed in three healthy controls, three CIA subjects and three CIA+Prednisolone subjects. Asterisks (*) indicate significant p values (<0.05).</p

Immigration of GMC over time.

<p>Mean values±s.e.m. were calculated using a linear mixed-effects model including the random factor animal and the interaction between group and time.</p

The lipid-sensor TREM2 aggravates disease in a model of LCMV-induced hepatitis

textabstractLipid metabolism is increasingly being appreciated to affect immunoregulation, inflammation and pathology. In this study we found that mice infected with lymphocytic choriomeningitis virus (LCMV) exhibit global perturbations of circulating serum lipids. Mice lacking the lipid-sensing surface receptor triggering receptor expressed on myeloid cells 2 (Trem2 -/-) were protected from LCMV-induced hepatitis and showed improved virus control despite comparable virus-specific T cell responses. Non-hematopoietic expression of TREM2 was found to be responsible for aggravated hepatitis, indicating a novel role for TREM2 in the non-myeloid compartment. These results suggest a link between virus-perturbed lipids and TREM2 that modulates liver pathogenesis upon viral infection. Targeted interventions of this immunoregulatory axis may ameliorate tissue pathology in hepatitis