Persistent immune and clotting dysfunction detected in saliva and blood plasma after COVID-19

The peptidoglycan of Borrelia burgdorferi can persist in discrete tissues and cause systemic responses consistent with chronic illness

Persistent symptoms after an acute infection is an emerging public health concern, but the pathobiology of such conditions is not well understood. One possible scenario involves the persistence of lingering antigen. We have previously reported that patients with postinfectious Lyme arthritis often harbor the peptidoglycan (PG) cell wall of Borrelia burgdorferi, the Lyme disease agent, in the synovial fluid of their inflamed joints after treatment. However, it is not yet known how B. burgdorferi PG persists, in what form, or if it may play a role in other postinfectious complications after Lyme disease. Using a murine model, we developed a real-time in vivo system to track B. burgdorferi PG as a function of cell wall chemistry and validated our findings using both molecular and cellular approaches. Unlike typical bacterial PG, the unique chemical properties of polymeric B. burgdorferi PG drive murine liver accumulation, where the cell wall material persists for weeks. Kupffer cells and hepatocytes phagocytose and retain B. burgdorferi PG and, although liver occupancy coincides with minimal pathology, both organ-specific and secreted protein profiles produced under these conditions bear some similarities to reported proteins enriched in patients with chronic illness after acute infection. Moreover, transcriptomic profiling indicated that B. burgdorferi PG affects energy metabolism in peripheral blood mononuclear cells. Our findings provide mechanistic insights into how a pathogenic molecule can persist after agent clearance, potentially contributing to illness after infection.

Natural and induced immune responses in oral cavity and saliva

This review comprehensively explores the intricate immune responses within the oral cavity, emphasizing the pivotal role of saliva in maintaining both oral and systemic health. Saliva, a complex biofluid, functions as a dynamic barrier against pathogens, housing diverse cellular components including epithelial cells, neutrophils, monocytes, dendritic cells, and lymphocytes, which collectively contribute to robust innate and adaptive immune responses. It acts as a physical and immunological barrier, providing the first line of defense against pathogens. The multifaceted protective mechanisms of salivary proteins, cytokines, and immunoglobulins, particularly secretory IgA (SIgA), are elucidated. We explore the natural and induced immune responses in saliva, focusing on its cellular and molecular composition. In addition to saliva, we highlight the significance of a serum-like fluid, the gingival crevicular fluid (GCF), in periodontal health and disease, and its potential as a diagnostic tool. Additionally, the review delves into the impact of diseases such as periodontitis, oral cancer, type 2 diabetes, and lupus on salivary immune responses, highlighting the potential of saliva as a non-invasive diagnostic tool for both oral and systemic conditions. We describe how oral tissue and the biofluid responds to diseases, including considerations to periodontal tissue health and in disease periodontitis. By examining the interplay between oral and systemic health through the oral-systemic axis, this review underscores the significance of salivary immune mechanisms in overall well-being and disease pathogenesis, emphasizing the importance of salivary mechanisms across the body.

4D-DIA Proteomics Uncovers New Insights into Host Salivary Response Following SARS-CoV-2 Omicron Infection

Since late 2021, Omicron variants have dominated the epidemiological scenario as the most successful severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) sublineages, driving new and breakthrough infections globally over the past two years. In this study, we investigated for the first time the host salivary response of COVID-19 patients infected with Omicron variants (BA.1, BA.2, and BA.4/5) by using an untargeted four-dimensional data-independent acquisition (4D-DIA)-based proteomics approach. We identified 137 proteins whose abundance levels differed between the COVID-19 positive and negative groups. Salivary signatures were mainly enriched in ribosomal proteins, linked to mRNAviral translation, protein synthesis and processing, immune innate, and antiapoptotic signaling. The higher abundance of 14-3-3 proteins (YWHAG, YWHAQ, YWHAE, and SFN) in saliva, first reported here, may be associated with increased infectivity and improved viral replicative fitness. We also identified seven proteins (ACTN1, H2AC2, GSN, NDKA, CD109, GGH, and PCYOX) that yielded comprehension into Omicron infection and performed outstandingly in screening patients with COVID-19 in a hospital setting. This panel also presented an enhanced anti-COVID-19 and anti-inflammatory signature, providing insights into disease severity, supported by comparisons with other proteome data sets. The salivary signature provided valuable insights into the host's response to SARS-CoV-2 Omicron infection, shedding light on the pathophysiology of COVID-19, particularly in cases associated with mild disease. It also underscores the potential clinical applications of saliva for disease screening in hospital settings. Data are available via ProteomeXchange with the identifier PXD054133.

Translating insights into therapies for Long Covid

Long Covid is defined by a wide range of symptoms that persist after the acute phase of severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) infection. Commonly reported symptoms include fatigue, weakness, postexertional malaise, and cognitive dysfunction, with many other symptoms reported. Symptom range, duration, and severity are highly variable and partially overlap with symptoms of myalgic encephalomyelitis/chronic fatigue syndrome and other post-acute infectious syndromes, highlighting opportunities to define shared mechanisms of pathogenesis. Potential mechanisms of Long Covid are diverse, including persistence of viral reservoirs, dysregulated immune responses, direct viral damage of tissues targeted by SARS-CoV-2, inflammation driven by reactivation of latent viral infections, vascular endothelium activation or dysfunction, and subsequent thromboinflammation, autoimmunity, metabolic derangements, microglial activation, and microbiota dysbiosis. The heterogeneity of symptoms and baseline characteristics of people with Long Covid, as well as the varying states of immunity and therapies given at the time of acute infection, have made etiologies of Long Covid difficult to determine. Here, we examine progress on preclinical models for Long Covid and review progress being made in clinical trials, highlighting the need for large human studies and further development of models to better understand Long Covid. Such studies will inform clinical trials that will define treatments to benefit those living with this condition.

Proteomics of serum-derived extracellular vesicles are associated with the severity and different clinical profiles of patients with COVID-19: An exploratory secondary analysis

BACKGROUND AIMS

Coronavirus disease 2019 (COVID-19) is characterized by a broad spectrum of clinical manifestations with the potential to progress to multiple organ dysfunction in severe cases. Extracellular vesicles (EVs) carry a range of biological cargoes, which may be used as biomarkers of disease state.

METHODS

An exploratory secondary analysis of the SARITA-2 and SARITA-1 datasets (randomized clinical trials on patients with mild and moderate/severe COVID-19) was performed. Serum-derived EVs were used for proteomic analysis to identify enriched biological processes and key proteins, thus providing insights into differences in disease severity. Serum-derived EVs were separated from patients with COVID-19 by size exclusion chromatography and nanoparticle tracking analysis was used to determine particle concentration and diameter. Liquid chromatography coupled with tandem mass spectrometry (LC-MS/MS) was performed to identify and quantify protein signatures. Bioinformatics and multivariate statistical analysis were applied to distinguish candidate proteins associated with disease severity (mild versus moderate/severe COVID-19).

RESULTS

No differences were observed in terms of the concentration and diameter of enriched EVs between mild (n = 14) and moderate/severe (n = 30) COVID-19. A total of 414 proteins were found to be present in EVs, of which 360 were shared while 48 were uniquely present in severe/moderate compared to mild COVID-19. The main biological signatures in moderate/severe COVID-19 were associated with platelet degranulation, exocytosis, complement activation, immune effector activation, and humoral immune response. Von Willebrand factor, serum amyloid A-2 protein, histone H4 and H2A type 2-C, and fibrinogen β-chain were the most differentially expressed proteins between severity groups.

CONCLUSION

Exploratory proteomic analysis of serum-derived EVs from patients with COVID-19 detected key proteins related to immune response and activation of coagulation and complement pathways, which are associated with disease severity. Our data suggest that EV proteins may be relevant biomarkers of disease state and prognosis.

Host-microbiome associations in saliva predict COVID-19 severity

Established evidence indicates that oral microbiota plays a crucial role in modulating host immune responses to viral infection. Following severe acute respiratory syndrome coronavirus 2, there are coordinated microbiome and inflammatory responses within the mucosal and systemic compartments that are unknown. The specific roles the oral microbiota and inflammatory cytokines play in the pathogenesis of coronavirus disease 2019 (COVID-19) are yet to be explored. Here, we evaluated the relationships between the salivary microbiome and host parameters in different groups of COVID-19 severity based on their oxygen requirement. Saliva and blood samples (n = 80) were collected from COVID-19 and from noninfected individuals. We characterized the oral microbiomes using 16S ribosomal RNA gene sequencing and evaluated saliva and serum cytokines and chemokines using multiplex analysis. Alpha diversity of the salivary microbial community was negatively associated with COVID-19 severity, while diversity increased with health. Integrated cytokine evaluations of saliva and serum showed that the oral host response was distinct from the systemic response. The hierarchical classification of COVID-19 status and respiratory severity using multiple modalities separately (i.e. microbiome, salivary cytokines, and systemic cytokines) and simultaneously (i.e. multimodal perturbation analyses) revealed that the microbiome perturbation analysis was the most informative for predicting COVID-19 status and severity, followed by the multimodal. Our findings suggest that oral microbiome and salivary cytokines may be predictive of COVID-19 status and severity, whereas atypical local mucosal immune suppression and systemic hyperinflammation provide new cues to understand the pathogenesis in immunologically compromised populations.