The global impact of the COVID-19 pandemic is now compounded by a new challenge, Post-COVID Syndrome (PCS), affecting over 65 million individuals. This study aimed to: (i) comprehensively characterize acute effects of MHV-A59 betacoronavirus inoculation in mice; (ii) investigate possible PCS manifestations: (iii) assess gender-specific differences, and (iv) to explore the impact of acute antiviral (Remdesivir) or a pro-resolving (the melanocortin agonist, AP1189) interventions on the establishment and severity of PCS. Male and female C57Bl/6 mice were inoculated with 3×104 PFU of MHV-A59. Mice exhibited clinical (body weight loss) and haematological (altered neutrophil/lymphocyte ratio) from the 2nd to 5th days post-infection (dpi). Marked lung lesions were characterized by hyperplasia of the alveolar walls, infiltration of polymorphonuclear leukocytes (PMN) and mononuclear leukocytes, hemorrhage, increased concentrations of CCL2, CCL3, CCL5, and CXCL1 chemokines, as well as high viral titers until the 5th dpi. While these lung inflammatory signs resolved, other manifestations were observed up to the 60th dpi, including mild brain lesions with gliosis and hyperemic blood vessels, reduced BDNF levels and augmented CD4+ T cells producing IFN-γ in the brain, along with neuromuscular dysfunctions, anhedonic-like behavior, deficits in spatial working memory, and short-term aversive memory. These musculoskeletal and neuropsychiatric complications were exclusive to female mice and were prevented after ovariectomy. Similar results were observed in SARS-CoV-2 infected mice. Finally, early antiviral or pro-resolving interventions (from day 2 to 5 pi) completely prevented neuropsychiatric sequelae induced by MHV-A59 infection .This study unveils a novel sex-dependent PCS model with a focus on neuropsychiatric and musculoskeletal disorders, offering insights into acute therapeutic interventions' impact on betacoronavirus-induced long-term sequelae.

C5a, an end-product of complement activation, is one of the most potent inflammatory peptides, playing a crucial role in the pathogenesis of numerous inflammatory disorders. Vilobelimab, a first-in-class anti-C5a monoclonal antibody, recently received emergency use authorization (EUA) from FDA for treating critically ill adult COVID-19 patients within 48 hours of receiving invasive mechanical ventilation or extracorporeal membrane oxygenation. FDA granted the EUA based on Phase III clinical trial results (PANAMO trial, N=369). The trial demonstrated the life-saving potential of vilobelimab with a significant relative reduction in 28-day all-cause mortality by 23.9% compared to the placebo (P<0.05; non-stratified Cox regression). Furthermore, a prior preclinical study revealed that vilobelimab substantially improved systemic inflammation and acute lung injury in a monkey model infected with the influenza H7N9 virus. This improvement was associated with decreases in lung infiltrates of neutrophils and macrophages. In preclinical settings, blocking the C5a/C5aR1 axis was beneficial in controlling inflammation in rodent models of bacterial and malaria sepsis. The robust anti-inflammatory effect resulting from inhibiting the C5a/C5aR1 axis is primarily attributed to attenuation of the “cytokine storm” and neutrophil activation, thereby preventing tissue damage caused by the release of toxic components such as enzymes, oxidants, and neutrophil extracellular traps (NETs). Importantly, blocking the C5a/C5aR1 pathway requires a target-specific approach because upstream blockade of C5 has proven inefficient in controlling C5a generation in patients suffering from strong inflammatory conditions such as COVID-19. This inefficiency is attributed to the fact that C5a can be generated by direct enzymatic cleavage of C5 independent of the conventional complement pathways (classical, lectin, and alternative) and not inhibited by known upstream complement inhibitors such as eculizumab. Target-specific inhibition of the C5a/C5aR1 axis emerges as a powerful means to control inflammation, warranting further exploration in various other inflammatory diseases.

Sphingosine-1-phosphate (S1P) receptor ligands reduce lung damage and endothelial activation in models of virus-induced pneumonia. We documented the feasibility of administering an S1P receptor ligand to hospitalized COVID-19 patients (NCT04405102; Chest, Oct 28th 2023). Clinical, biochemical, immunological data were obtained longitudinally and exploratory analyses relating to the effects of an S1P receptor ligand on COVID-19 pathognomonic features will be presented. Twenty-three patients were randomized to standard of care (SOC), and 20 were randomized to receive standard of care plus ozanimod (OZA; oral, once daily for a maximum of 14 days). The OZA group showed nonsignificant reductions of median time to clinical improvement (4 [range, 3-7] vs 7 [range, 3-11] days; p =0.12) for SOC. Ozanimod appeared to prevent the increase of circulating neutrophils and monocytes, the latter likely involving a decreased proportion of classical monocytes. Interestingly C-reactive protein circulating levels were lower for the OZA group on study day 7 (p=0.06) and similar trends were observed for IL-8 and CCL2 on study day 3. We also found that ozanimod dampened the circulating levels of SARS-CoV-2 S1 protein-specific IgGs (p=0.06) on study day 90, which was overcome by the administration of a vaccine shot. This is the very first study investigating putative leads on the mechanisms of action of S1P receptor ligands for patients with acute pneumonia. We found that ozanimod likely interferes with the kinetics of neutrophil and classical monocyte circulation, may affect specific cytokines linked with S1P signalling and ARDS, and that it may interfere with the primary humoral response to infection, while this can be mitigated by vaccination. Our findings recapitulate some of the beneficial mechanisms of S1P receptor ligands previously seen in animal models of virus-induced ARDS. Our work may pave the way for the safe off label use of S1P receptor ligands in patients with severe pneumonia.

Cytokines, such as IL-17A and IL-17F, are pivotal in immune responses, with Th17 cells and innate immune cells producing these proteins. Their involvement extends beyond anti-infectious and anti-fungal responses and is linked to inflammatory conditions like psoriasis. The IL-17 receptors family is composed of IL-17RA, IL-17RB, IL-17RC, IL-17RD, and IL-17RE, They trigger a cascade of events leading to the activation of immune cells. Regulatory mechanisms exist to prevent excessive immune responses. Notably, IL17RD displays anti-inflammatory activities in part believed to be mediated through its negative impact on signaling cascades including the mitogen-activated protein kinases (MAPKs) and toll-like receptor-dependent pathways. Recognizing IL-17RD as a potential antiviral repressor, our study aims to elucidate its function. Specifically, we hypothesize that IL-17RD is a repressor of antiviral innate immune responses following RNA virus infection, influencing the type I/III interferon (IFN) responses. Using IL17RD-deficient A549 pneumocytes as a cellular model, we demonstrate that the melanoma differentiation-associated protein 5 (MDA5) signaling pathway is hyperactivated, resulting in an upregulation of key inflammatory genes, including IFNβ, IFNL3, CCl5, and IL6 as observed through qPCR. Additionally, western blot analysis revealed a more robust activation of the MDA5 pathway, indicated by increased in the activation of interferon-regulatory factor 3 (IRF3), in the absence of IL-17RD. Conversely, overexpression of IL17RD led to decreased IRF3 activity in response to MDA5 engagement. Moreover, silencing IL17RD in the SARS-Cov2 cellular model, A549-ACE2 resulted in the exacerbation of numerous inflammatory genes. IL-17RD expression profiles will be next examined in severe COVID-19 patients, offering insights into its relevance in real-world viral infections. Understanding IL-17RD's role as an antiviral repressor holds significant promise. It could pave the way for targeted treatments, potentially reducing its expression in immunocompromised patients and strengthening their immune defenses against viral infections. This research advances our understanding of antiviral immunity and opens new possibilities for effective antiviral treatments, with potential implications for mitigating the severity of viral infections across diverse populations, including addressing challenges posed by viruses such as COVID-19.