The role of the thymus in COVID-19 disease severity: implications for antibody treatment and immunization.
TL;DR: The thymus is a largely neglected organ but plays a significant role in the regulation of adaptive immune responses and may be incorporated in COVID-19 management.
Abstract: The thymus is a largely neglected organ but plays a significant role in the regulation of adaptive immune responses. The effect of aging on the thymus and immune senescence is well established, and the resulting inflammaging is found to be implicated in the development of many chronic diseases including atherosclerosis, hypertension and type 2 diabetes. Both aging and diseases of inflammaging are associated with severe COVID-19 disease, and a dysfunctional thymus may be a predisposing factor. In addition, insults on the thymus during childhood may lead to abnormal thymic function and may explain severe COVID-19 disease among younger individuals; therefore, measurement of thymic function may assist COVID-19 care. Those with poor thymic function may be treated prophylactically with convalescent serum or recombinant antibodies, and they may respond better to high-dose or adjuvanted COVID-19 vaccines. Treatments inducing thymic regeneration may improve patients' overall health and may be incorporated in COVID-19 management.
Citations
More filters
01 Jan 2009
TL;DR: In this article, a review outlines the current understanding of miRNA target recognition in animals and discusses the widespread impact of miRNAs on both the expression and evolution of protein-coding genes.
Abstract: MicroRNAs (miRNAs) are endogenous ∼23 nt RNAs that play important gene-regulatory roles in animals and plants by pairing to the mRNAs of protein-coding genes to direct their posttranscriptional repression. This review outlines the current understanding of miRNA target recognition in animals and discusses the widespread impact of miRNAs on both the expression and evolution of protein-coding genes.
646 citations
TL;DR: In this article, the authors performed an in-depth genetic analysis of chromosome 21 exploiting the genome-wide association study data, including 6,406 individuals hospitalized for COVID-19 and 902,088 controls with European genetic ancestry from the COVID19 Host Genetics Initiative.
46 citations
TL;DR: In this paper, the role of the thymus and T cells in COVID-19 immunity during aging (a synergistic effect of diminished responses to pathogens and enhanced responses to self) impacting age-related clinical severity of CoV-19 was investigated.
Abstract: Severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) caused the global pandemic of coronavirus disease 2019 (COVID-19) and particularly exhibits severe symptoms and mortality in elderly individuals. Mounting evidence shows that the characteristics of the age-related clinical severity of COVID-19 are attributed to insufficient antiviral immune function and excessive self-damaging immune reaction, involving T cell immunity and associated with pre-existing basal inflammation in the elderly. Age-related changes to T cell immunosenescence is characterized by not only restricted T cell receptor (TCR) repertoire diversity, accumulation of exhausted and/or senescent memory T cells, but also by increased self-reactive T cell- and innate immune cell-induced chronic inflammation, and accumulated and functionally enhanced polyclonal regulatory T (Treg) cells. Many of these changes can be traced back to age-related thymic involution/degeneration. How these changes contribute to differences in COVID-19 disease severity between young and aged patients is an urgent area of investigation. Therefore, we attempt to connect various clues in this field by reviewing and discussing recent research on the role of the thymus and T cells in COVID-19 immunity during aging (a synergistic effect of diminished responses to pathogens and enhanced responses to self) impacting age-related clinical severity of COVID-19. We also address potential combinational strategies to rejuvenate multiple aging-impacted immune system checkpoints by revival of aged thymic function, boosting peripheral T cell responses, and alleviating chronic, basal inflammation to improve the efficiency of anti-SARS-CoV-2 immunity and vaccination in the elderly.
31 citations
TL;DR: For example, this article found that COVID-19 hospitalization rates follow an exponential relationship with age, doubling for every 16 years of age or equivalently increasing by 4.5% per year of life (R2 = 0.98).
Abstract: Here, we report that COVID-19 hospitalization rates follow an exponential relationship with age, doubling for every 16 years of age or equivalently increasing by 4.5% per year of life (R2 = 0.98). This mirrors the well-studied exponential decline of both thymus volume and T-cell production, which halve every 16 years. COVID-19 can therefore be added to the list of other diseases with this property, including those caused by methicillin-resistant Staphylococcus aureus, MERS-CoV, West Nile virus, Streptococcus pneumoniae and certain cancers, such as chronic myeloid leukaemia and brain cancers. In addition, the incidence of severe disease and mortality due to COVID-19 are both higher in men, consistent with the degree to which thymic involution (and the decrease in T-cell production with age) is more severe in men compared to women. Since these properties are shared with some non-contagious diseases, we hypothesized that the age dependence does not come from social-mixing patterns, i.e. that the probability of hospitalization given infection rises exponentially, doubling every 16 years. A Bayesian analysis of daily hospitalizations, incorporating contact matrices, found that this relationship holds for every age group except for the under 20s. While older adults have fewer contacts than young adults, our analysis suggests that there is an approximate cancellation between the effects of fewer contacts for the elderly and higher infectiousness due to a higher probability of developing severe disease. Our model fitting suggests under 20s have 49-75% additional immune protection beyond that predicted by strong thymus function alone, consistent with increased juvenile cross-immunity from other viruses. We found no evidence for differences between age groups in susceptibility to infection or infectiousness to others (given disease state), i.e. the only important factor in the age dependence of hospitalization rates is the probability of hospitalization given infection. These findings suggest the existence of a T-cell exhaustion threshold, proportional to thymic output and that clonal expansion of peripheral T-cells does not affect disease risk. The strikingly simple inverse relationship between risk and thymic T-cell output adds to the evidence that thymic involution is an important factor in the decline of the immune system with age and may also be an important clue in understanding disease progression, not just for COVID-19 but other diseases as well.
18 citations
TL;DR: The elderly is the main risk group in the COVID-19 pandemic, and aging is recognized as a major risk factor for the severity of infection and mortality of COVID 19 as mentioned in this paper.
Abstract: The elderly is the main risk group in the COVID- 19 pandemic, and aging is recognized as a major risk factor for the severity of infection and mortality of COVID- 19. The severity of the infection in children is milder than in adults. Although the pathophysiology of COVID- 19 infection is not fully understood, several possible factors and mechanisms have been suggested for lower severity of infection in children.
16 citations
References
More filters
TL;DR: The current understanding of miRNA target recognition in animals is outlined and the widespread impact of miRNAs on both the expression and evolution of protein-coding genes is discussed.
18,036 citations
"The role of the thymus in COVID-19 ..." refers background in this paper
...Males and females are affected equally regardless of their race and ethnicity.(17,18) However, the penetrance and disease severity varies among those affected, which is explained by novel genetic and epigenetic differences as well as differ-...
[...]
Book•
01 Jan 1843
TL;DR: The Liddell & Scott's Greek-English Lexicon (9/e 1940) is the most comprehensive and up-to-date ancient Greek dictionary in the world.
Abstract: Liddell & Scott's Greek-English Lexicon (9/e 1940) is the most comprehensive and up-to-date ancient Greek dictionary in the world. It is used by every student of ancient Greek in the English-speaking world, and is an essential library and scholarly purchase there and in W. Europe and Japan. The main dictionary covers every surviving ancient Greek author and text discovered up to 1940, from the Pre-Classical Greek of the 11C - 8C BC (for example Homer and Hesiod), through Classical Greek (7C - 5C BC) to the Hellenistic Period, including the Greek Old and New Testaments. Entries list irregular inflections, and together with the definition, each sense includes citations from Greek authors illustrating usage. The Lexicon is Greek into English only, as are other ancient Greek dictionaries. This is the market expectation among both students and scholars. In 1968 the Lexicon was updated with a Supplement, which was available as a separate volume (until 1992) or bound together with the dictionary. Representing the culmination of 13 years' work, the new Revised Supplement is a complete replacement for the 1968 Supplement. Nearly twice the size of the 1968 edition, with over 20,000 entries, it adds to the dictionary words and forms from papyri and inscriptions discovered between 1940 and the 1990s as well as a host of other revisions, updatings, and corrections to the main dictionary. Linear B forms are shown within entries for the first time, and the Revised Supplement gives the dictionary a date-range from 1200 BC to 600 AD. It is fully cross-referenced to the main text but additions have been designed to be easily used without constant reference to the main text.
2,083 citations
TL;DR: Age and comorbidities were found to be strong predictors of hospital admission and to a lesser extent of critical illness and mortality in people with coronavirus disease 2019 in the United States; however, impairment of oxygen on admission and markers of inflammation were most strongly associated with critical illnesses and mortality.
Abstract: Objective To describe outcomes of people admitted to hospital with coronavirus disease 2019 (covid-19) in the United States, and the clinical and laboratory characteristics associated with severity of illness. Design Prospective cohort study. Setting Single academic medical center in New York City and Long Island. Participants 5279 patients with laboratory confirmed severe acute respiratory syndrome coronavirus 2 (SARS-Cov-2) infection between 1 March 2020 and 8 April 2020. The final date of follow up was 5 May 2020. Main outcome measures Outcomes were admission to hospital, critical illness (intensive care, mechanical ventilation, discharge to hospice care, or death), and discharge to hospice care or death. Predictors included patient characteristics, medical history, vital signs, and laboratory results. Multivariable logistic regression was conducted to identify risk factors for adverse outcomes, and competing risk survival analysis for mortality. Results Of 11 544 people tested for SARS-Cov-2, 5566 (48.2%) were positive. After exclusions, 5279 were included. 2741 of these 5279 (51.9%) were admitted to hospital, of whom 1904 (69.5%) were discharged alive without hospice care and 665 (24.3%) were discharged to hospice care or died. Of 647 (23.6%) patients requiring mechanical ventilation, 391 (60.4%) died and 170 (26.2%) were extubated or discharged. The strongest risk for hospital admission was associated with age, with an odds ratio of >2 for all age groups older than 44 years and 37.9 (95% confidence interval 26.1 to 56.0) for ages 75 years and older. Other risks were heart failure (4.4, 2.6 to 8.0), male sex (2.8, 2.4 to 3.2), chronic kidney disease (2.6, 1.9 to 3.6), and any increase in body mass index (BMI) (eg, for BMI >40: 2.5, 1.8 to 3.4). The strongest risks for critical illness besides age were associated with heart failure (1.9, 1.4 to 2.5), BMI >40 (1.5, 1.0 to 2.2), and male sex (1.5, 1.3 to 1.8). Admission oxygen saturation of 1 (4.8, 2.1 to 10.9), C reactive protein level >200 (5.1, 2.8 to 9.2), and D-dimer level >2500 (3.9, 2.6 to 6.0) were, however, more strongly associated with critical illness than age or comorbidities. Risk of critical illness decreased significantly over the study period. Similar associations were found for mortality alone. Conclusions Age and comorbidities were found to be strong predictors of hospital admission and to a lesser extent of critical illness and mortality in people with covid-19; however, impairment of oxygen on admission and markers of inflammation were most strongly associated with critical illness and mortality. Outcomes seem to be improving over time, potentially suggesting improvements in care.
2,016 citations
"The role of the thymus in COVID-19 ..." refers background in this paper
...Although COVID-19 mostly affects those with comorbid conditions, even among those without comorbidities, age is a significant risk factor, and there is a direct relationship between age and COVID-19 severity and mortality.(6) This may be explained by the inappropriate COVID-19-induced immune responses in the elderly who are already experiencing...
[...]
...ovascular disease, hypertension, chronic obstructive lung disease and arthritis), and people who develop these comorbidities are known to be at higher risk for severe COVID-19 infection and death.(5,6)...
[...]
TL;DR: It is found that, although thymic function declines with age, substantial output is maintained into late adulthood and this results indicate that the adult thymus can contribute to immune reconstitution following HAART.
Abstract: The thymus represents the major site of the production and generation of T cells expressing alphabeta-type T-cell antigen receptors. Age-related involution may affect the ability of the thymus to reconstitute T cells expressing CD4 cell-surface antigens that are lost during HIV infection; this effect has been seen after chemotherapy and bone-marrow transplantation. Adult HIV-infected patients treated with highly active antiretroviral therapy (HAART) show a progressive increase in their number of naive CD4-positive T cells. These cells could arise through expansion of existing naive T cells in the periphery or through thymic production of new naive T cells. Here we quantify thymic output by measuring the excisional DNA products of TCR-gene rearrangement. We find that, although thymic function declines with age, substantial output is maintained into late adulthood. HIV infection leads to a decrease in thymic function that can be measured in the peripheral blood and lymphoid tissues. In adults treated with HAART, there is a rapid and sustained increase in thymic output in most subjects. These results indicate that the adult thymus can contribute to immune reconstitution following HAART.
1,849 citations
"The role of the thymus in COVID-19 ..." refers background or methods in this paper
...joint TCR excision circle (sjTREC), in naïve T cells by performing real-time polymerase chain reactions (PCR).(68,69) Higher TREC number is associated with better thymic function and repertoire diversity of the memory T-cell population....
[...]
...Higher TREC number is associated with better thymic function and repertoire diversity of the memory T-cell population.(69) Thymic output may also be monitored by conducting flow cytometry in the blood and measuring naïve CD45RA and CD62 ligand positive cells....
[...]
TL;DR: Emerging principles of miRNA regulation of stress signaling pathways are reviewed and applied to the authors' understanding of the roles of miRNAs in disease.
1,491 citations
"The role of the thymus in COVID-19 ..." refers background in this paper
...These molecules bind to diverse mRNA transcripts that play a role in cell function and target mRNA transcripts for degradation.(20,21) MiRNAs play an important role in thymic organogenesis, maturation and involution,(22) and conversely, aging influences miRNA levels....
[...]