Immune profiling of COVID-19 vaccine responses in people with multiple sclerosis on B cell-depleting therapy (preprint)

Background and ObjectivePeople with multiple sclerosis (pwMS) receiving B cell-depleting therapies have impaired antibody responses to vaccination. In a proportion of individuals, repeat vaccination against COVID-19 leads to seroconversion. We sought to describe the immune phenotype of pwMS on ocrelizumab, and identify clinical and immunological determinants of an effective vaccine response. MethodsThis was a single-centre, prospective cohort study. Peripheral blood samples were collected from pwMS receiving ocrelizumab (n = 38) pre and post administration of a third dose of mRNA COVID-19 vaccine. Immunogenicity was measured by T cell IFN{gamma} ELISpot, antibody titres, and live virus neutralisation. Humoral immunity was benchmarked against pwMS receiving natalizumab (n = 15), and against a correlate of real-world protection (50% reduction in incidence of infection) from SARS-CoV-2 ancestral and omicron BA.5 variants. The peripheral immune phenotype was comprehensively assessed by flow cytometry, and potential clinical and phenotypic determinants of response to vaccination identified. ResultsImmune cell populations relevant to disease and vaccine response were altered in pwMS receiving ocrelizumab versus natalizumab treatment, including depleted CD20-expressing B cell, T cell and NK cell populations, and elevated CD27+CD38+ T cell and NK8 cell frequencies. Following a third vaccine dose, 51% of pwMS on ocrelizumab were seropositive for SARS-CoV-2 receptor-binding-domain IgG, and 25% and 14% met the threshold for effective neutralisation of live SARS-CoV-2 ancestral and omicron BA.5 virus, respectively. B cell frequency at the time of vaccination, but not time since ocrelizumab infusion, was positively correlated with antibody response, while a strong negative correlation was observed between CD56bright NK cell frequency and antibody response in the ocrelizumab group. In this exploratory cohort, CD3-CD20+ B cells (% of lymphocytes; OR=3.92) and CD56bright NK cells (% of NK cells; OR=0.94) were predictive of an effective neutralising antibody response in second dose non-responders (AUC: 0.98). DiscussionOcrelizumab treatment was associated with an altered immune phenotype, including recently described T cell and NK populations with potential roles in disease pathogenesis. However, seroconversion was severely impaired by ocrelizumab, and less than half of those who seroconverted following a third vaccine dose demonstrated effective immunity against SARS-CoV-2 ancestral or omicron BA.5. B cell frequency was associated with an effective antibody response, while immunomodulatory CD56bright NK cells were identified as a potential negative determinant of response in those with inadequate B cell numbers. Immune phenotype rather than time since ocrelizumab infusion may help to stratify individuals for prophylaxis.

Impact of the COVID-19 Pandemic on Patient Satisfaction After Total Joint Arthroplasty.

The coronavirus disease 2019 (COVID-19) pandemic impacted the inpatient experience before and after total joint arthroplasty (TJA). This study aimed to examine how these changes affected patient satisfaction following TJA as recorded by Hospital Consumer Assessment of Healthcare Providers and Systems (HCAHPS) postdischarge surveys and comments at 2 large academic institutions. A retrospective review identified patients who completed HCAHPS surveys following primary and revision TJA at 2 academic institutions: 1 in a predominately rural southern state (Institution A) and 1 in a northeastern metropolitan city (Institution B). Patients were grouped by discharge date: pre-COVID-19 (April 1, 2019, to October 31, 2019) or COVID-19 affected (April 1, 2020, to October 31, 2020). Differences in demographics, survey responses, and comment sentiments and themes were collected and evaluated. The number of HCAHPS surveys completed increased between periods at Institution A but decreased at Institution B (Institution A, 61 vs 103; Institution B, 524 vs 296). Rates of top-box survey responses remained the same across the 2 periods. The number of comments decreased at Institution B (1977 vs 1012) but increased at Institution A (55 vs 88). During the COVID-19-affected period, there was a significant increase in the negative comment rate from Institution B (11.6% vs 14.8%, P=.013) and a significant decrease in the positive comment rate from Institution A (70.9% vs 44.3%, P<.001). There was an increase in negative patient sentiments following TJA during the COVID-19 pandemic as seen in qualitative comments but not quantitative responses. This suggests that certain aspects of the TJA patient experience were impacted by COVID-19. [Orthopedics. 2023;46(2):e105-e110.].

Retrospective record review on timing of COVID-19 vaccination and cardiac surgery.

BACKGROUND: Novel clinical challenges are faced by cardiac surgeons under the coronavirus disease 2019 (COVID-19) pandemic. Amidst the uncertainties faced due to the socioeconomic and public health impact, there is little evidence surrounding COVID-19 vaccination in patients undergoing cardiac surgery. Timing of vaccination and postvaccination adverse effects are required parameters to discuss with cardiac surgical patients. METHODS: This is a single-center, retrospective observational study. All patients who underwent adult cardiac surgery at the Prince of Wales Hospital, Hong Kong from January 2021 to December 2021 were included. Postoperative clinical outcomes, COVID-19 vaccination status, and vaccination-related adverse effects were collected. RESULTS: A total of 426 patients; 117 (27%) underwent isolated coronary artery bypass grafting, 111 (26%) underwent valvular surgery, and 97 (23%) underwent aortic surgery. Patients received either Sinovac CoronaVac or Pfizer BNT162b2 vaccine. Overall vaccination rate with at least 1 dose was 52% (n = 212), 15% (n = 63) received the first dose before surgery, 36% (n = 149) received the first dose vaccination after surgery. Rate of completion with second and third doses of vaccination were 22% (n = 89) and 4.9% (n = 20), respectively. The mean timing of first dose of vaccine after surgery was 216 ± 84 days from operation. Three (1.4%) patients recorded vaccination-related complications. CONCLUSIONS: COVID-19 vaccination is safe in patients who received major cardiac surgery, with low adverse effects recorded and no vaccine-related mortality observed. A time frame of 3-6 months after cardiac surgery receiving COVID-19 vaccination is reasonable and could serve as a guidance for future COVID-19 vaccination booster programs.

mTOR inhibition improves the formation of functional T cell memory following COVID-19 vaccination of kidney transplant recipients (preprint)

Inadequate immune response to vaccination is a long-standing problem faced by immunosuppressed kidney transplant recipients (KTRs), requiring novel strategies to improve vaccine efficacy. In this study, the potential of mechanistic target of rapamycin inhibitors (mTORi) to improve T cell responses to COVID-19 vaccination was investigated. Following primary vaccination with adenoviral (ChAdOx1) or mRNA (BNT162b2) COVID-19 vaccines, KTRs receiving rapamycin demonstrated T cell responses greater than those of healthy individuals, characterized by increased frequencies of vaccine-specific central memory, effector memory and TEMRA T cells, in both the CD4+ and CD8+ compartments. Relative to standard-of-care triple therapy, mTORi-based therapy was associated with a 12-fold greater functional T cell response to primary vaccination of KTRs. The use of rapamycin to augment T cell responses to COVID-19 booster (third dose) vaccination was next investigated in a randomized, controlled trial. Immunosuppression modification with rapamycin was feasible and well-tolerated, but did not improve vaccine-specific T cell responses in this cohort. To understand the parameters for effective use of rapamycin as a vaccine adjuvant, mice were treated with rapamycin before primary or booster vaccination with ancestral and/or Omicron COVID-19 vaccines. Supporting the findings from KTRs, significant enhancement of functional and stem-like memory T cell responses was observed when rapamycin was administered from the time of primary, rather than booster, vaccination. Collectively, a positive effect of mTOR inhibitors on vaccine-induced T cell immunity against COVID-19 in humans was demonstrated.

Meeting report: 6th Global Forum on Tuberculosis Vaccines, 22–25 February 2022, Toulouse, France

Safe, effective, and accessible vaccines are urgently needed to end tuberculosis (TB) by 2030. The 6th Global Forum on TB Vaccines, convened virtually 22–25 February 2022, was hosted by Toulouse, France, under the high patronage of President Emmanuel Macron, and the patronages of Minister for Solidarity and Health, Olivier Véran, and Minister for Higher Education, Research and Innovation, Frédérique Vidal. The theme for the meeting, "New horizons for TB vaccines”, reflected the changing landscape in which TB vaccine research and development (R&D) is being conducted: TB vaccines advancing into late-stage clinical trials and toward licensure, innovative research toward diversifying the TB vaccine pipeline and developing the next generation of candidates, increasing political, civil society, and community support for TB vaccines, and the ongoing COVID-19 pandemic. In this report, we summarize key themes and findings from the meeting, highlighting progress and gaps in the TB vaccine field.

Severity of Covid-19 Lockdown Orders Corresponds to Orthopaedic Trauma Volume.

During the Coronavirus Disease 2019 (COVID-19) pandemic, states implemented social distancing guidelines. This study examines the effect of the severity of lockdown orders on orthopaedic trauma volume. Two institutions, one in a state with strict stay home (SH) orders and one in a state with lax social distancing (SD) orders, were examined. Surgical case counts, total orthopaedic case counts, orthopaedic trauma case counts, institution trauma activations, and mechanism of injury data were collected and compared to control periods. For SH versus SD, total surgical cases decreased 48.6% vs. 62%; orthopaedic cases decreased 51.8% vs. 62%, and orthopaedic trauma cases decreased 34% v. 0%. Orthopaedic trauma cases comprised more of both institutions' total cases. Total surgical cases decreased at both SH and SD, but orthopaedic trauma cases did not decrease at SD. More strict social distancing orders correlate with greater reduction in orthopaedic trauma cases. (Journal of Surgical Orthopaedic Advances 31(4):222-225, 2022).

Pan-neutralizing, germline-encoded antibodies against SARS-CoV-2: Addressing the long-term problem of escape variants.

Despite the initially reported high efficacy of vaccines directed against ancestral SARS-CoV-2, repeated infections in both unvaccinated and vaccinated populations remain a major global health challenge. Because of mutation-mediated immune escape by variants-of-concern (VOC), approved neutralizing antibodies (neutAbs) effective against the original strains have been rendered non-protective. Identification and characterization of mutation-independent pan-neutralizing antibody responses are therefore essential for controlling the pandemic. Here, we characterize and discuss the origins of SARS-CoV-2 neutAbs, arising from either natural infection or following vaccination. In our study, neutAbs in COVID-19 patients were detected using the combination of two lateral flow immunoassay (LFIA) tests, corroborated by plaque reduction neutralization testing (PRNT). A point-of-care neutAb LFIA, NeutraXpress™, was validated using serum samples from historical pre-COVID-19 negative controls, patients infected with other respiratory pathogens, and PCR-confirmed COVID-19 patients. Surprisingly, potent neutAb activity was mainly noted in patients generating both IgM and IgG against the Spike receptor-binding domain (RBD), in contrast to samples possessing anti-RBD IgG alone. We propose that low-affinity, high-avidity, germline-encoded natural IgM and subsequent generation of class-switched IgG may have an underappreciated role in cross-protection, potentially offsetting immune escape by SARS-CoV-2 variants. We suggest Reverse Vaccinology 3.0 to further exploit this innate-like defense mechanism. Our proposition has potential implications for immunogen design, and provides strategies to elicit pan-neutAbs from natural B1-like cells. Refinements in future immunization protocols might further boost long-term cross-protection, even at the mucosal level, against clinical manifestations of COVID-19.

Sustaining aviation workforce after the pandemic: Evidence from Hong Kong aviation students toward skills, specialised training, and career prospects through a mixed-method approach.

The aviation industry is in a recession with the rapid and immense outbreak of COVID-19 under globalisation. The future young aviation professionals might suffer from a 'career shock'. This study analysed the post-pandemic career prospects for Hong Kong aviation students using mixed-method research considering specialised and licensed training. We conducted a survey (N = 101) and focus group interviews (N = 6) to investigate students' perceived impediments and potential support from the institutions. Matt-Whitney U test is used to compare the perceptual difference in the impediments, career prospects, skills required, and institutional supports between (non-)specialised training students, (non-)engineering-related students, and (non-)final-year students. The results demonstrated no significant difference between students with and without specialised training. While final-year students perceive themselves as lacking more in terms of non-technical skills than non-final-year students, students are interested in broadening their career options to include airline operations, aircraft engineering and maintenance via acquiring a variety of emerging knowledge and technical skills. Given most studies focus on the recovery pattern of the aviation industry, this study is original in considering Hong Kong aviation students' career impediments and prospects using a mixed-method approach to provide policy insights.

Sustaining aviation workforce after the pandemic: Evidence from Hong Kong aviation students toward skills, specialised training, and career prospects through a mixed-method approach

The aviation industry is in a recession with the rapid and immense outbreak of COVID-19 under globalisation. The future young aviation professionals might suffer from a ‘career shock’. This study analysed the post-pandemic career prospects for Hong Kong aviation students using mixed-method research considering specialised and licensed training. We conducted a survey (N = 101) and focus group interviews (N = 6) to investigate students' perceived impediments and potential support from the institutions. Matt-Whitney U test is used to compare the perceptual difference in the impediments, career prospects, skills required, and institutional supports between (non-)specialised training students, (non-)engineering-related students, and (non-)final-year students. The results demonstrated no significant difference between students with and without specialised training. While final-year students perceive themselves as lacking more in terms of non-technical skills than non-final-year students, students are interested in broadening their career options to include airline operations, aircraft engineering and maintenance via acquiring a variety of emerging knowledge and technical skills. Given most studies focus on the recovery pattern of the aviation industry, this study is original in considering Hong Kong aviation students' career impediments and prospects using a mixed-method approach to provide policy insights.

IL27 gene expression distinguishes multisystem inflammatory syndrome in children from febrile illness in a South African cohort

Introduction Multisystem inflammatory syndrome in children (MIS-C) is a severe acute inflammatory reaction to SARS-CoV-2 infection in children. There is a lack of data describing differential expression of immune genes in MIS-C compared to healthy children or those with other inflammatory conditions and how expression changes over time. In this study, we investigated expression of immune-related genes in South African MIS-C patients and controls. Methods The cohort included 30 pre-treatment MIS-C cases and 54 healthy non-inflammatory paediatric controls. Other controls included 34 patients with juvenile systemic lupus erythematosus, Kawasaki disease or other inflammatory conditions. Longitudinal post-treatment MIS-C specimens were available at various timepoints. Expression of 80 immune-related genes was determined by real-time quantitative PCR. Results A total of 29 differentially expressed genes were identified in pre-treatment MIS-C compared to healthy controls. Up-regulated genes were found to be overrepresented in innate immune pathways including interleukin-1 processing and pyroptosis. Post-treatment follow-up data were available for up to 1,200 hours after first treatment. All down-regulated genes and 17/18 up-regulated genes resolved to normal levels in the timeframe, and all patients clinically recovered. When comparing MIS-C to other febrile conditions, only IL27 expression could differentiate these two groups with high sensitivity and specificity. Conclusions These data indicate a unique 29-gene signature of MIS-C in South African children. The up-regulation of interleukin-1 and pyroptosis pathway genes highlights the role of the innate immune system in MIS-C. IL-27 is a potent anti-inflammatory and antiviral cytokine that may distinguish MIS-C from other conditions in our setting.

SARS-CoV-2 Omicron variant escapes neutralizing antibodies and T cell responses more efficiently than other variants in mild COVID-19 convalescents.

Coronavirus disease 2019 (COVID-19) convalescents living in regions with low vaccination rates rely on post-infection immunity for protection against re-infection with severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2). We evaluate humoral and T cell immunity against five variants of concern (VOCs) in mild-COVID-19 convalescents at 12 months after infection with ancestral virus. In this cohort, ancestral, receptor-binding domain (RBD)-specific antibody and circulating memory B cell levels are conserved in most individuals, and yet serum neutralization against live B.1.1.529 (Omicron) is completely abrogated and significantly reduced for other VOCs. Likewise, ancestral SARS-CoV-2-specific memory T cell frequencies are maintained in >50% of convalescents, but the cytokine response in these cells to mutated spike epitopes corresponding to B.1.1.529 and B.1.351 (Beta) VOCs were impaired. These results indicate that increased antigen variability in VOCs impairs humoral and spike-specific T cell immunity post-infection, strongly suggesting that COVID-19 convalescents are vulnerable and at risk of re-infection with VOCs, thus stressing the importance of vaccination programs.

Management of epistaxis in hereditary haemorrhagic telangiectasia (HHT) patients using pulsed dye laser and the effect of withholding treatment during the COVID pandemic.

Using a patient survey, pulsed dye laser (PDL) treatment of epistaxis for hereditary haemorrhagic telangiectasia (HHT) patients was evaluated after initial referral. Subsequently, due to the COVID pandemic, a natural experimental set-up allowed assessment of an enforced withdrawal of treatment. A total of 34 subjects were identified as undergoing PDL for HHT-related epistaxis. They were surveyed to look at the effectiveness of PDL treatment after initial referral and at the effect of delay to treatment during COVID on epistaxis and the associated quality of life. The survey also examined the comparison to other available treatments. Retrospective pre-COVID Epistaxis Severity Scores (ESS) were compared to post-COVID data to assess the effect of treatment withdrawal. The patients were then followed up after resumption of their treatment to assess the ensuing change in ESS. After initial referral, frequency and severity of epistaxis decreased. Fifty-six percent of patients experienced several bleeds per day before treatment, compared to 12% after. 88% of patients had episodes of epistaxis longer than 5 min, which was halved to 44% after treatment. Average ESS pre-COVID was 4.42 compared to 5.43 post-COVID delay, with a significant statistical difference (p = 0.02). On resumption of treatment, average ESS reduced to below pre-COVID levels at 4.39 after only 2 sessions. Seventy-six percent of patients found that withdrawal of PDL during COVID diminished their quality of life. PDL treatment of nasal mucosal telangiectasia reduces the frequency and duration of epistaxis. The ESS is reduced following treatment with PDL and quality of life subjectively improved.

Severe Acute Respiratory Syndrome Coronavirus 2 Viremia Is Associated With Coronavirus Disease 2019 Severity and Predicts Clinical Outcomes.

BACKGROUND: Severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) viral RNA (vRNA) is detected in the bloodstream of some patients with coronavirus disease 2019 (COVID-19), but it is not clear whether this RNAemia reflects viremia (ie, virus particles) and how it relates to host immune responses and outcomes. METHODS: SARS-CoV-2 vRNA was quantified in plasma samples from observational cohorts of 51 COVID-19 patients including 9 outpatients, 19 hospitalized (non-intensive care unit [ICU]), and 23 ICU patients. vRNA levels were compared with cross-sectional indices of COVID-19 severity and prospective clinical outcomes. We used multiple imaging methods to visualize virions in plasma. RESULTS: SARS-CoV-2 vRNA was detected in plasma of 100%, 52.6%, and 11.1% of ICU, non-ICU, and outpatients, respectively. Virions were detected in plasma pellets using electron tomography and immunostaining. Plasma vRNA levels were significantly higher in ICU > non-ICU > outpatients (P < .0001); for inpatients, plasma vRNA levels were strongly associated with higher World Health Organization (WHO) score at admission (P = .01), maximum WHO score (P = .002), and discharge disposition (P = .004). A plasma vRNA level >6000 copies/mL was strongly associated with mortality (hazard ratio, 10.7). Levels of vRNA were significantly associated with several inflammatory biomarkers (P < .01) but not with plasma neutralizing antibody titers (P = .8). CONCLUSIONS: Visualization of virus particles in plasma indicates that SARS-CoV-2 RNAemia is due, at least in part, to viremia. The levels of SARS-CoV-2 RNAemia correlate strongly with disease severity, patient outcome, and specific inflammatory biomarkers but not with neutralizing antibody titers.

Infiltration of inflammatory macrophages and neutrophils and widespread pyroptosis in lung drive influenza lethality in nonhuman primates.

Severe influenza kills tens of thousands of individuals each year, yet the mechanisms driving lethality in humans are poorly understood. Here we used a unique translational model of lethal H5N1 influenza in cynomolgus macaques that utilizes inhalation of small-particle virus aerosols to define mechanisms driving lethal disease. RNA sequencing of lung tissue revealed an intense interferon response within two days of infection that resulted in widespread expression of interferon-stimulated genes, including inflammatory cytokines and chemokines. Macaques with lethal disease had rapid and profound loss of alveolar macrophages (AMs) and infiltration of activated CCR2+ CX3CR1+ interstitial macrophages (IMs) and neutrophils into lungs. Parallel changes of AMs and neutrophils in bronchoalveolar lavage (BAL) correlated with virus load when compared to macaques with mild influenza. Both AMs and IMs in lethal influenza were M1-type inflammatory macrophages which expressed neutrophil chemotactic factors, while neutrophils expressed genes associated with activation and generation of neutrophil extracellular traps (NETs). NETs were prominent in lung and were found in alveolar spaces as well as lung parenchyma. Genes associated with pyroptosis but not apoptosis were increased in lung, and activated inflammatory caspases, IL-1ß and cleaved gasdermin D (GSDMD) were present in bronchoalveolar lavage fluid and lung homogenates. Cleaved GSDMD was expressed by lung macrophages and alveolar epithelial cells which were present in large numbers in alveolar spaces, consistent with loss of epithelial integrity. Cleaved GSDMD colocalized with viral NP-expressing cells in alveoli, reflecting pyroptosis of infected cells. These novel findings reveal that a potent interferon and inflammatory cascade in lung associated with infiltration of inflammatory macrophages and neutrophils, elaboration of NETs and cell death by pyroptosis mediates lethal H5N1 influenza in nonhuman primates, and by extension humans. These innate pathways represent promising therapeutic targets to prevent severe influenza and potentially other primary viral pneumonias in humans.

The very low risk of myocarditis and pericarditis after mRNA COVID-19 vaccination should not discourage vaccination.

The benefits of vaccination - regarding COVID-19 infection and transmission, as well as COVID-associated complications - clearly outweigh the potential risk of vaccine-associated inflammation of the heart and other adverse events. Given the current state of knowledge, the outcome of myocarditis and pericarditis following vaccination is generally good. This review aims to guide physicians in the early diagnosis and management of suspected myocarditis following mRNA COVID vaccination. The initial work-up should include detailed history, a 12-lead electrocardiogram and serological biomarkers (high-sensitivity cardiac troponin T/I, natriuretic peptides and markers of inflammation) in accordance with the assessments recommended in current clinical practice guidelines for patients presenting with acute chest pain. In patients with suspected myocarditis, further assessment with transthoracic echocardiography and cardiovascular magnetic resonance imaging should be undertaken to confirm peri-/myocarditis and to distinguish the findings from other diseases with similar presentation. Patients with mRNA vaccine-associated myocarditis should be followed-up at least once to exclude chronic myocardial inflammation and deterioration of left ventricular ejection fraction. Consultation with an expert such as an immunologist with experience in vaccination regarding further mRNA vaccinations is advised in all patients with mRNA vaccine-associated perimyocarditis. Reporting of mRNA vaccine-associated myocarditis to Swissmedic is mandatory. Cohort studies prospectively follow-up on young adult and paediatric populations following immunisation with an mRNA COVID vaccine to monitor cardiac and immune parameters would generate valuable knowledge to better understand pathogenesis and risk factors for vaccine-associated perimyocarditis.

Adolescents' longitudinal trajectories of mental health and loneliness: The impact of COVID-19 school closures.

INTRODUCTION: Longitudinal research examining the impact of coronavirus disease 2019 (COVID-19) school closures on the mental health of adolescents is scarce. Prolonged periods of physical and social isolation because of such restrictions may have impacted heavily on adolescents' mental health and loneliness. METHODS: The current study addresses a major gap by examining the impact of school closures on the mental health and loneliness of 785, 10- to 17-year-old Western Australian adolescents (mean age = 14.1, SD = 1.31), who were surveyed across four time points: twice before COVID-19, once as schools closed, and once post reopening of schools. Pre- and post-COVID-19 changes in mental health and loneliness were compared using linear mixed models. Random intercept cross-lagged panel models (RI-CLPMs) assessed temporal associations between loneliness, depression symptoms, and positive mental wellbeing. RESULTS: Compared with pre-COVID-19 symptom levels, there were significant increases in depression symptoms, internalizing and externalizing symptoms, and a significant decrease in positive mental wellbeing at different points over time. Symptom change over time differed according to gender and pre-COVID-19 symptom severity. Significant increases in positive attitudes towards being alone and feelings of isolation occurred at different points over time. Gender differences were evident. RI-CLPMs highlighted the predictive significance of friendship quality and having a negative attitude towards being alone over time in relation to depression symptoms. A positive or negative attitude towards being alone was predictive of positive mental wellbeing over time. CONCLUSION: Findings provide evidence that COVID-19-related school closures adversely affected adolescents' mental health and feelings of loneliness.

Cerebral microvascular endothelial glycocalyx damage, its implications on the blood-brain barrier and a possible contributor to cognitive impairment.

The socio-economic impact of diseases associated with cognitive impairment is increasing. According to the Alzheimer's Society there are over 850,000 people with dementia in the UK, costing the UK £26 billion in 2013. Therefore, research into treatment of those conditions is vital. Research into the cerebral endothelial glycocalyx (CeGC) could offer effective treatments. The CeGC, consisting of proteoglycans, glycoproteins and glycolipids, is a dynamic structure covering the luminal side oftheendothelial cells of capillaries throughout the body. The CeGC is thicker in cerebral micro vessels, suggesting specialisation for its function as part of the blood-brain barrier (BBB). Recent research evidences that the CeGC is vital in protecting fragile parenchymal tissue and effective functioning of the BBB, as one particularly important CeGC function is to act as a protective barrier and permeability regulator. CeGC degradation is one of the factors which can lead to an increase in BBB permeability. It occurs naturally in aging, nevertheless, premature degradationhas beenevidencedin multipleconditions linked to cognitive impairment, such as inflammation,brain edema, cerebral malaria, Alzheimer's and recently Covid-19. Increasing knowledge of the mechanisms of CeGC damage has led to research into preventative techniques showing that CeGC is a possible diagnostic marker and a therapeutic target. However, the evidence is relatively new, inconsistent and demonstrated mainly in experimental models. This review evaluates the current knowledge of the CeGC, its structure, functions, damage and repair mechanisms and the impact of its degeneration on cognitive impairment in multiple conditions, highlighting the CeGC as a possible diagnostic marker and a potential target for therapeutic treatment.