Long COVID: Clinical characteristics, proposed pathogenesis and potential therapeutic targets.

The emergence of persistent ill-health in the aftermath of SARS-CoV-2 infection has presented significant challenges to patients, healthcare workers and researchers. Termed long COVID, or post-acute sequelae of COVID-19 (PASC), the symptoms of this condition are highly variable and span multiple body systems. The underlying pathophysiology remains poorly understood, with no therapeutic agents proven to be effective. This narrative review describes predominant clinical features and phenotypes of long COVID alongside the data supporting potential pathogenesis of these phenotypes including ongoing immune dysregulation, viral persistence, endotheliopathy, gastrointestinal microbiome disturbance, autoimmunity, and dysautonomia. Finally, we describe current potential therapies under investigation, as well as future potential therapeutic options based on the proposed pathogenesis research.

Immune Dysregulation in Acute SARS-CoV-2 Infection.

Introduction: Neutralizing antibodies have been shown to develop rapidly following SARS-CoV-2 infection, specifically against spike (S) protein, where cytokine release and production is understood to drive the humoral immune response during acute infection. Thus, we evaluated the quantity and function of antibodies across disease severities and analyzed the associated inflammatory and coagulation pathways to identify acute markers that correlate with antibody response following infection. Methods: Blood samples were collected from patients at time of diagnostic SARS-CoV-2 PCR testing between March 2020-November 2020. Plasma samples were analyzed using the MesoScale Discovery (MSD) Platform using the COVID-19 Serology Kit and U-Plex 8 analyte multiplex plate to measure anti-alpha and beta coronavirus antibody concentration and ACE2 blocking function, as well as plasma cytokines. Results: A total of 230 (181 unique patients) samples were analyzed across the 5 COVID-19 disease severities. We found that antibody quantity directly correlated with functional ability to block virus binding to membrane-bound ACE2, where a lower SARS-CoV-2 anti-spike/anti-RBD response corresponded with a lower antibody blocking potential compared to higher antibody response (anti-S1 r = 0.884, P < 0.001; anti-RBD r = 0.75, P < 0.001). Across all the soluble proinflammatory markers we examined, ICAM, IL-1ß, IL-4, IL-6, TNFα, and Syndecan showed a statistically significant positive correlation between cytokine or epithelial marker and antibody quantity regardless of COVID-19 disease severity. Analysis of autoantibodies against type 1 interferon was not shown to be statistically significant between disease severity groups. Conclusion: Previous studies have shown that proinflammatory markers, including IL-6, IL-8, IL-1ß, and TNFα, are significant predictors of COVID-19 disease severity, regardless of demographics or comorbidities. Our study demonstrated that not only are these proinflammatory markers, as well as IL-4, ICAM, and Syndecan, correlative of disease severity, they are also correlative of antibody quantity and quality following SARS-CoV-2 exposure.

Performance and validation of an adaptable multiplex assay for detection of serologic response to SARS-CoV-2 infection or vaccination.

Measurement of quantitative antibody responses are increasingly important in evaluating the immune response to infection and vaccination. In this study we describe the validation of a quantitative, multiplex serologic assay utilising an electrochemiluminescence platform, which measures IgG against the receptor binding domain (RBD), spike S1 and S2 subunits and nucleocapsid antigens of SARS-CoV-2. The assay displayed a sensitivity ranging from 73 to 91% and specificity from 90 to 96% in detecting previous infection with SARS-CoV-2 depending on antigenic target and time since infection, and this assay highly correlated with commercially available assays. The within-plate coefficient of variation ranged from 3.8-3.9% and the inter-plate coefficient of variation from 11 to 13% for each antigen.

Individuals with obesity who survive SARS-CoV-2 infection have preserved antigen-specific T cell frequencies.

OBJECTIVE: Obesity is a major risk factor for severe disease in COVID-19, with increased hospitalization, intensive care unit admission, and mortality. This increased impact of COVID-19 in people with obesity (PWO) is likely driven, in part, by the well-described obesity-induced immune dysregulation. Obesity has also been associated with impaired immune memory in many settings, including weakened responses to hepatitis B, tetanus, rabies, and influenza vaccination. Recently, it was reported that PWO who have COVID-19 have reduced IgG antibody titers with defective neutralizing capabilities. However, it remains unknown whether PWO generate durable T cell immunity to SARS-CoV-2. METHODS: This study investigated SARS-CoV-2-specific T cell responses in a cohort of 40 patients (n = 20 PWO and n = 20 matched control individuals) who had recovered from COVID-19. T cell (CD4+ , CD8+ ) cytokine responses (IFNγ, TNFα) to SARS-CoV-2 peptide pools (spike, membrane) were determined using multicolor flow cytometry. RESULTS: Circulating T cells specific for SARS-CoV-2 were readily detected in the total cohort. PWO displayed comparable levels of SARS-CoV-2 spike- and membrane-specific T cells, with both T cell subsets responding. CONCLUSIONS: These data indicate that PWO who survive COVID-19 generate robust and durable SARS-CoV-2-specific T cell immunity that is equivalent to that seen in those without obesity.

Markers of fungal translocation are elevated during post-acute sequelae of SARS-CoV-2 and induce NF-κB signaling.

Long COVID, a type of post-acute sequelae of SARS-CoV-2 (PASC), has been associated with sustained elevated levels of immune activation and inflammation. However, the mechanisms that drive this inflammation remain unknown. Inflammation during acute coronavirus disease 2019 could be exacerbated by microbial translocation (from the gut and/or lung) to blood. Whether microbial translocation contributes to inflammation during PASC is unknown. We did not observe a significant elevation in plasma markers of bacterial translocation during PASC. However, we observed higher levels of fungal translocation - measured as ß-glucan, a fungal cell wall polysaccharide - in the plasma of individuals experiencing PASC compared with those without PASC or SARS-CoV-2-negative controls. The higher ß-glucan correlated with higher inflammation and elevated levels of host metabolites involved in activating N-methyl-d-aspartate receptors (such as metabolites within the tryptophan catabolism pathway) with established neurotoxic properties. Mechanistically, ß-glucan can directly induce inflammation by binding to myeloid cells (via Dectin-1) and activating Syk/NF-κB signaling. Using a Dectin-1/NF-κB reporter model, we found that plasma from individuals experiencing PASC induced higher NF-κB signaling compared with plasma from negative controls. This higher NF-κB signaling was abrogated by piceatannol (Syk inhibitor). These data suggest a potential targetable mechanism linking fungal translocation and inflammation during PASC.

Identification of Distinct Long COVID Clinical Phenotypes Through Cluster Analysis of Self-Reported Symptoms.

Background: We aimed to describe the clinical presentation of individuals presenting with prolonged recovery from coronavirus disease 2019 (COVID-19), known as long COVID. Methods: This was an analysis within a multicenter, prospective cohort study of individuals with a confirmed diagnosis of COVID-19 and persistent symptoms >4 weeks from onset of acute symptoms. We performed a multiple correspondence analysis (MCA) on the most common self-reported symptoms and hierarchical clustering on the results of the MCA to identify symptom clusters. Results: Two hundred thirty-three individuals were included in the analysis; the median age of the cohort was 43 (interquartile range [IQR], 36-54) years, 74% were women, and 77.3% reported a mild initial illness. MCA and hierarchical clustering revealed 3 clusters. Cluster 1 had predominantly pain symptoms with a higher proportion of joint pain, myalgia, and headache; cluster 2 had a preponderance of cardiovascular symptoms with prominent chest pain, shortness of breath, and palpitations; and cluster 3 had significantly fewer symptoms than the other clusters (2 [IQR, 2-3] symptoms per individual in cluster 3 vs 6 [IQR, 5-7] and 4 [IQR, 3-5] in clusters 1 and 2, respectively; P < .001). Clusters 1 and 2 had greater functional impairment, demonstrated by significantly longer work absence, higher dyspnea scores, and lower scores in SF-36 domains of general health, physical functioning, and role limitation due to physical functioning and social functioning. Conclusions: Clusters of symptoms are evident in long COVID patients that are associated with functional impairments and may point to distinct underlying pathophysiologic mechanisms of disease.

Dynamic Change and Clinical Relevance of Postinfectious SARS-CoV-2 Antibody Responses.

BACKGROUND: Although reports suggest that most individuals with coronavirus disease 2019 (COVID-19) develop detectable antibodies postinfection, the kinetics, durability, and relative differences between immunoglobulin M (IgM) and immunoglobulin G (IgG) responses beyond the first few weeks after symptom onset remain poorly understood. METHODS: Within a large, well-phenotyped, diverse, prospective cohort of subjects with and without severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) polymerase chain reaction (PCR)-confirmed infection and historical controls derived from cohorts with high prevalence of viral coinfections and samples taken during prior flu seasons, we measured SARS-CoV-2 serological responses (both IgG and IgM) using commercially available assays. We calculated sensitivity, specificity, and relationship with disease severity and mapped the kinetics of antibody responses over time using generalized additive models. RESULTS: We analyzed 1001 samples from 752 subjects, 327 with confirmed SARS-CoV-2 (29.7% with severe disease) spanning a period of 90 days from symptom onset. Sensitivity was lower (44.1%-47.1%) early (<10 days) after symptom onset but increased to >80% after 10 days. IgM positivity increased earlier than IgG-targeted assays, but positivity peaked between days 32 and 38 post-onset of symptoms and declined thereafter, a dynamic that was confirmed when antibody levels were analyzed, with a more rapid decline observed with IgM. Early (<10 days) IgM but not IgG levels were significantly higher in those who subsequently developed severe disease (signal/cutoff 4.20 [0.75-17.93] vs 1.07 [0.21-5.46]; P = .048). CONCLUSIONS: This study suggests that postinfectious antibody responses in those with confirmed COVID-19 begin to decline relatively early postinfection and suggests a potential role for higher IgM levels early in infection in the prediction of subsequent disease severity.

Tocilizumab for the treatment of non-critical COVID-19 pneumonia: an overview of the rationale and clinical evidence to date.

Introduction: Tocilizumab is one of the main repurposed therapies investigated for COVID-19 pneumonia since the start of the pandemic, but there has been conflicting evidence for its use.Areas covered: This review covers the physiology of interleukin-6 and its role in the pathophysiology of COVID-19. We discuss the use of tocilizumab in other diseases and the rationale for its use in COVID-19. We summarize the design, contrasting results, and implications of the clinical trials of tocilizumab in COVID-19 to date and discuss the current guidance for its use.Expert opinion: The evidence to date suggests benefit with the use of tocilizumab in some but not all patients with COVID-19. Benefit seems to be greatest when given early after clinical deterioration with the presence of systemic inflammation. However, questions remain around the optimal timing, patient selection, and concomitant treatments.

COVID19- clinical presentation and therapeutic considerations.

The emergence of severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) as a pandemic infection in 2020 has presented many therapeutic challenges. Not least among these is the importance of abnormal host response to infection that is one of the main drivers of more severe disease. Despite significant research endeavours, very few effective therapies have been identified, in part related to the different pathogenic mechanisms underlying different stages of clinical COVID-19. This mini review summarises data related to current and potential future therapies for COVID-19 and highlights the many challenges inherent in developing effective therapeutic options for new pandemic infection.