Protective reactive thymus hyperplasia in COVID-19 acute respiratory distress syndrome

Genetically determined thymic function affects strength and duration of immune response in COVID patients with pneumonia

Thymic activation improves the outcome of COVID-19 patients with severe pneumonia. The rs2204985 genetic polymorphism within the TCRA-TCRD locus, which affects thymic output in healthy individuals, was found here to modify SARS-CoV-2-specific immunity and disease severity in COVID-19 patients with severe pneumonia. Forty patients with severe COVID-19 pneumonia were investigated. The GG genotype at the rs2204985 locus was associated, independently of age and sex, with stronger and long-lasting anti-SARS-CoV-2 helper and cytotoxic T cell responses 6 months after recovery. The GG genotype was also associated with less severe lung involvement, higher thymic production, and higher counts of blood naïve T lymphocytes, including recent thymic emigrants, and a larger population of activated stem cell memory CD4+ T cells. Overall, GG patients developed a more robust and sustained immunity to SARS-CoV-2. Polymorphism at rs2204985 locus should be considered as an additional predictive marker of anti-SARS-CoV-2 immune response.

Rare Variants in Primary Immunodeficiency Genes and Their Functional Partners in Severe COVID-19

The development of severe COVID-19, which is a complex multisystem disease, is thought to be associated with many genes whose action is modulated by numerous environmental and genetic factors. In this study, we focused on the ideas of the omnigenic model of heritability of complex traits, which assumes that a small number of core genes and a large pool of peripheral genes expressed in disease-relevant tissues contribute to the genetics of complex traits through interconnected networks. We hypothesized that primary immunodeficiency disease (PID) genes may be considered as core genes in severe COVID-19, and their functional partners (FPs) from protein-protein interaction networks may be considered as peripheral near-core genes. We used whole-exome sequencing data from patients aged ≤ 45 years with severe (n = 9) and non-severe COVID-19 (n = 11), and assessed the cumulative contribution of rare high-impact variants to disease severity. In patients with severe COVID-19, an excess of rare high-impact variants was observed at the whole-exome level, but maximal association signals were detected for PID + FP gene subsets among the genes intolerant to LoF variants, haploinsufficient and essential. Our exploratory study may serve as a model for new directions in the research of host genetics in severe COVID-19.

Differentiation between rebound thymic hyperplasia and thymic relapse after chemotherapy in pediatric Hodgkin lymphoma

BACKGROUND

Rebound thymic hyperplasia (RTH) is a common phenomenon caused by stress factors such as chemotherapy (CTX) or radiotherapy, with an incidence between 44% and 67.7% in pediatric lymphoma. Misinterpretation of RTH and thymic lymphoma relapse (LR) may lead to unnecessary diagnostic procedures including invasive biopsies or treatment intensification. The aim of this study was to identify parameters that differentiate between RTH and thymic LR in the anterior mediastinum.

METHODS

After completion of CTX, we analyzed computed tomographies (CTs) and magnetic resonance images (MRIs) of 291 patients with classical Hodgkin lymphoma (CHL) and adequate imaging available from the European Network for Pediatric Hodgkin lymphoma C1 trial. In all patients with biopsy-proven LR, an additional fluorodeoxyglucose (FDG)-positron emission tomography (PET)-CT was assessed. Structure and morphologic configuration in addition to calcifications and presence of multiple masses in the thymic region and signs of extrathymic LR were evaluated.

RESULTS

After CTX, a significant volume increase of new or growing masses in the thymic space occurred in 133 of 291 patients. Without biopsy, only 98 patients could be identified as RTH or LR. No single finding related to thymic regrowth allowed differentiation between RTH and LR. However, the vast majority of cases with thymic LR presented with additional increasing tumor masses (33/34). All RTH patients (64/64) presented with isolated thymic growth.

CONCLUSION

Isolated thymic LR is very uncommon. CHL relapse should be suspected when increasing tumor masses are present in distant sites outside of the thymic area. Conversely, if regrowth of lymphoma in other sites can be excluded, isolated thymic mass after CTX likely represents RTH.

Thymic Parenchymal Hyperplasia

Thymic hyperplasia is a rare condition generally caused by lymphoid follicular hyperplasia associated with autoimmune disorders. True thymic parenchymal hyperplasia unassociated with lymphoid follicular hyperplasia is extremely rare and may give rise to difficulties in diagnosis. We have studied 44 patients with true thymic hyperplasia (38 females and 6 males) aged 7 months to 64 years (mean, 36 years). Eighteen patients presented with symptoms of chest discomfort or shortness of breath; in 20 patients, the lesions were discovered incidentally. Imaging studies demonstrated enlargement of the mediastinum by a mass lesion suspicious for malignancy. All patients were treated with complete surgical excision. The tumors measured from 3.5 to 24 cm (median, 10 cm; mean, 10.46 cm). Histologic examination showed lobules of thymic tissue displaying well-developed corticomedullary architecture, with scattered Hassall corpuscles separated by mature adipose tissue and bounded by a thin fibrous capsule. No cases showed evidence of lymphoid follicular hyperplasia, cytologic atypia, or confluence of the lobules. Immunohistochemical studies showed a normal pattern of distribution for keratin-positive thymic epithelial cells against a background rich in CD3/TdT/CD1a+ lymphocytes. Twenty-nine cases had an initial clinical or pathological diagnosis of thymoma or thymoma vs thymic hyperplasia. Clinical follow-up in 26 cases showed that all patients were alive and well between 5 and 15 years after diagnosis (mean, 9 years). Thymic parenchymal hyperplasia causing significant enlargement of the normal thymus that is sufficient to cause symptoms or worrisome imaging findings should be considered in the differential diagnosis of anterior mediastinal masses. The criteria for distinguishing such lesions from lymphocyte-rich thymoma are presented.

Multilocular thymic cyst detected during COVID‑19 treatment in an HIV‑positive adult man: A case report and literature review

A multilocular thymic cyst (MTC) is a rare mediastinal tumor with multiloculated cyst-like structures in the anterior mediastinum. This tumfor is associated with inflammatory diseases, including human immunodeficiency virus (HIV) infection. The present study reports a case of MTC detected during coronavirus disease 2019 (COVID-19) treatment in an adult who was tested HIV positive. An anterior mediastinal tumor was incidentally detected on computed tomography in a 52-year-old man with a 20-year history of HIV infection on the 9th day of COVID-19. The patient was asymptomatic with no notable physical findings. Magnetic resonance imaging revealed a 28-mm bilocular cyst. Robot-assisted thoracoscopic tumor resection was performed. Pathological examination showed that the cyst was lined with squamous or cuboidal epithelium, and the cystic lesion wall was mainly composed of thymic tissue with follicular hyperplasia. Based on these findings, the patient was diagnosed with MTC. To date, only 15 MTC cases have been reported in patients with HIV, and the majority of cases showed HIV infection-related symptoms such as lymphoid interstitial pneumonia and parotid gland enlargement. The present case was atypical for an HIV-related MTC because it did not involve HIV infection-related symptoms, suggesting the possibility for an alternative etiology such as COVID-19. Further reports on MTC development in patients with COVID-19 are required to elucidate the relationship between MTC and COVID-19.

SARS-CoV-2 infection of thymus induces loss of function that correlates with disease severity

BACKGROUND

Lymphopenia, particularly when restricted to the T-cell compartment, has been described as one of the major clinical hallmarks in patients with coronavirus disease 2019 (COVID-19) and proposed as an indicator of disease severity. Although several mechanisms fostering COVID-19-related lymphopenia have been described, including cell apoptosis and tissue homing, the underlying causes of the decline in T-cell count and function are still not completely understood.

OBJECTIVE

Given that viral infections can directly target thymic microenvironment and impair the process of T-cell generation, we sought to investigate the impact of severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) on thymic function.

METHODS

We performed molecular quantification of T-cell receptor excision circles and κ-deleting recombination excision circles to assess, respectively, T- and B-cell neogenesis in SARS-CoV-2-infected patients. We developed a system for in vitro culture of primary human thymic epithelial cells (TECs) to mechanistically investigate the impact of SARS-CoV-2 on TEC function.

RESULTS

We showed that patients with COVID-19 had reduced thymic function that was inversely associated with the severity of the disease. We found that angiotensin-converting enzyme 2, through which SARS-CoV-2 enters the host cells, was expressed by thymic epithelium, and in particular by medullary TECs. We also demonstrated that SARS-CoV-2 can target TECs and downregulate critical genes and pathways associated with epithelial cell adhesion and survival.

CONCLUSIONS

Our data demonstrate that the human thymus is a target of SARS-CoV-2 and thymic function is altered following infection. These findings expand our current knowledge of the effects of SARS-CoV-2 infection on T-cell homeostasis and suggest that monitoring thymic activity may be a useful marker to predict disease severity and progression.

Predicting model of mild and severe types of COVID-19 patients using Thymus CT radiomics model: A preliminary study

OBJECTIVE

To predict COVID-19 severity by building a prediction model based on the clinical manifestations and radiomic features of the thymus in COVID-19 patients.

METHOD

We retrospectively analyzed the clinical and radiological data from 217 confirmed cases of COVID-19 admitted to Xiangyang NO.1 People's Hospital and Jiangsu Hospital of Chinese Medicine from December 2019 to April 2022 (including 118 mild cases and 99 severe cases). The data were split into the training and test sets at a 7:3 ratio. The cases in the training set were compared in terms of clinical data and radiomic parameters of the lasso regression model. Several models for severity prediction were established based on the clinical and radiomic features of the COVID-19 patients. The DeLong test and decision curve analysis (DCA) were used to compare the performances of several models. Finally, the prediction results were verified on the test set.

RESULT

For the training set, the univariate analysis showed that BMI, diarrhea, thymic steatosis, anorexia, headache, findings on the chest CT scan, platelets, LDH, AST and radiomic features of the thymus were significantly different between the two groups of patients (P < 0.05). The combination model based on the clinical and radiomic features of COVID-19 patients had the highest predictive value for COVID-19 severity [AUC: 0.967 (OR 0.0115, 95%CI: 0.925-0.989)] vs. the clinical feature-based model [AUC: 0.772 (OR 0.0387, 95%CI: 0.697-0.836), P < 0.05], laboratory-based model [AUC: 0.687 (OR 0.0423, 95%CI: 0.608-0.760), P < 0.05] and model based on CT radiomics [AUC: 0.895 (OR 0.0261, 95%CI: 0.835-0.938), P < 0.05]. DCA also confirmed the high clinical net benefits of the combination model. The nomogram drawn based on the combination model could help differentiate between the mild and severe cases of COVID-19 at an early stage. The predictions from different models were verified on the test set.

CONCLUSION

Severe cases of COVID-19 had a higher level of thymic involution. The thymic differentiation in radiomic features was related to disease progression. The combination model based on the radiomic features of the thymus could better promote early clinical intervention of COVID-19 and increase the cure rate.

New-onset Myasthenia Gravis after SARS-CoV-2 infection: case report and literature review

We report the case of a 19-year-old female patient who developed Myasthenia Gravis 13 days after SARS-CoV-2 infection with positive RT-PCR testing. Her symptoms initially involved the oculo-bulbar district, but they gradually worsened in 3 months converting into a generalized form of Myasthenia Gravis complicated with a myasthenic crisis. A high level of anti-acetylcholine receptor antibodies was found in the serum, while anti-MuSK antibodies were negative; Repetitive Nerve Stimulation and Single-fiber Electromyography were suggestive of Myasthenia Gravis. Intravenous immunoglobulin courses and specific therapy were able to improve her symptoms, but thymic resection was needed to control the disease. This is a report of new-onset Myasthenia Gravis correlated to COVID-19 in which thymic resection was described and the histologic analysis of the thymus was performed showing thymic hyperplasia despite negative thoracic Magnetic Resonance Imaging. SARS-CoV-2 infection releases inflammatory cytokines that could dysregulate the immune system and lead to Myasthenia Gravis in susceptible subjects.

Exploiting Signal Joint T Cell Receptor Excision Circle to Investigate the Impact of COVID-19 and Autoimmune Diseases on Age Prediction and Immunosenescence

Signal joint T cell receptor excision circles (sjTRECs) are a promising marker for age estimation and immunosenescence in different ethnic groups. Several limitations are expected to overshadow their use as accurate markers for age prediction. The current study was conducted to determine the influence of immunologic disorders, such as autoimmune diseases and COVID-19, on the accuracy of sjTRECs as molecular markers for age estimation and immunosenescence among living Egyptians. Peripheral blood sjTRECs level was measured by qPCR in 90 autoimmune patients, 58 COVID-19 patients, and 85 healthy controls. The mean dCt values were significantly (p = 0.0002) different between the three groups, with the highest values in healthy subjects, followed by autoimmune and COVID-19 patients. A significant negative correlation was identified between the sjTRECs levels and ages in all studied cases. There were significant positive correlations between chronological age and predicted age for healthy individuals, autoimmune, and COVID-19 patients with mean absolute deviations (MAD) of 9.40, 11.04, and 9.71, respectively. The two patients' groups exhibited early immunosenescence, which was more noticeable among the young adults with COVID-19 and autoimmune patients of age range (18-49 years). Autoimmunity may represent a critical factor impacting the accuracy of sjTRECs quantitation for age prediction.

Thymus CT-grading and rebound hyperplasia during COVID-19 infection: a CT volumetric study with multivariate linear regression analysis

Background

The importance of thymic CT-grading and presence of thymic rebound hyperplasia during COVID-19 infection were only investigated in a few studies. This multivariate study aims to evaluate the relation between thymus CT-grading and rebound during COVID-19 infection and the following: (1) the patients' age, (2) the patients' blood lymphocytic count, (3) the CT-volumetry of the diseased lung parenchyma, (4) the patient's clinical course and prognosis, and finally (5) the final radiological diagnosis.

Results

Multicenter retrospective analyses were conducted between March and June 2021 on 325 adult COVID-19 patients with positive PCR results and negative history of malignant or autoimmune diseases. They included 186 males and 139 females (57.2%:42.8%). Their mean age was 40.42 years ± 14.531 SD. Three consulting radiologists performed CT-grading of the thymus gland (grade 0–3) and CT-severity scoring (CT-SS) of the pathological lung changes in consensus. Two consulting pulmonologists correlated the clinical severity and blood lymphocytic count. Pearson correlation coefficient (r) and linear regression analyses were statistically utilized. Sub-involuted thymus (with CT-grade 0:2) was detected in 42/325 patients (12.9%); all of them had a mild clinical course and low CT-SS (0–1). Thymic rebound hyperplasia was the only positive CT-finding in 15/325 patients (4.6%) without pathological lung changes. A weak positive significant correlation was proved between thymic grade and patient's age, clinical course, and CT-SS (r = 0.217, 0.163, and 0.352 with p ≤ 0.0001, < 0.0001, and 0.002, respectively). A weak negative significant correlation was found between thymic grade and lymphocytic count (r = − 0.343 and p ≤ 0.0001). A strong positive significant correlation was encountered between clinical severity against patients' age and CT-SS (r = 0.616 and 0.803 with p ≤ 0.0001).

Conclusions

The presence of sub-involuted thymus or thymic rebound should not be radiologically overlooked in COVID-19 patients. During COVID-19 infection, the presence of sub-involuted thymus with low CT-grading (0–2) was correlated with young age groups, low CT-severity scoring, mild clinical course, and better prognosis (good prognostic factor). It was seldom seen in old hospitalized patients. Atypically, it was also correlated with normal lymphocytic count or even lymphocytosis. The thymic rebound could be the only positive CT-finding even during the absence of lung involvement.

Abdominal and Thoracic Imaging Features in Children with MIS-C

(1) Background: Currently, multisystem inflammatory syndrome in children (MIS-C) is diagnosed based on clinical symptoms and laboratory findings of inflammation in the body. Once MIS-C is diagnosed, children will need to be followed over time. The imaging modalities most commonly used in the evaluation of patients with MIS-C include radiographs, ultrasound (US), and computed tomography (CT). Our study aims to summarise the literature data for the main gastrointestinal and pulmonary imaging features in children diagnosed with MIS-C and to share a single-centre experience. (2) Methods: We present the imaging findings in a cohort of 51 children diagnosed with MIS-C, admitted between December 2020 and February 2022. Imaging studies include chest and abdominal radiographs, thoracic, abdominal, and neck US and echocardiography (ECHO), and CT of the chest, abdomen, and pelvis. (3) Results: In accordance with the results in other studies, our observations show predominantly gastrointestinal involvement (GI) with ascites (33/51, 65%) and lymphadenopathy (19/51, 37%), ileitis or colitis (18/51, 35%), some cases of splenomegaly (9/51, 18%), hepatomegaly (8/51, 16%), and a few cases of renal enlargement (3/51, 6%) and gallbladder fossa oedema/wall thickening (2/51, 4%). Most common among the thoracic findings are posterior–basal consolidations (16/51, 31%), pleural effusion (14/51, 27%), and ground-glass opacities (12/51, 24%). We also register the significant involvement of the cardiovascular system with pericarditis (30/51, 58%), pericardial effusion (16/51, 31%), and myocarditis (6/51, 12%). (4) Conclusions: Radiologists should be aware of those imaging findings in order to take an important and active role not only in applying an accurate diagnosis, but also in the subsequent management of children with MIS-C. Radiological findings are not the primary diagnostic tool, but can assist in the evaluation of the affected systems and guide treatment.

Pneumonia and Related Conditions in Critically Ill Patients—Insights from Basic and Experimental Studies

Pneumonia is an acute infectious disease with high morbidity and mortality rates. Pneumonia’s development, severity and outcome depend on age, comorbidities and the host immune response. In this study, we combined theoretical and experimental investigations to characterize pneumonia and its comorbidities as well as to assess the host immune response measured by TREC/KREC levels in patients with pneumonia. The theoretical study was carried out using the Columbia Open Health Data (COHD) resource, which provides access to clinical concept prevalence and co-occurrence from electronic health records. The experimental study included TREC/KREC assays in young adults (18–40 years) with community-acquired (CAP) (n = 164) or nosocomial (NP) (n = 99) pneumonia and healthy controls (n = 170). Co-occurring rates between pneumonia, sepsis, acute respiratory distress syndrome (ARDS) and some other related conditions common in intensive care units were the top among 4170, 3382 and 963 comorbidities in pneumonia, sepsis and ARDS, respectively. CAP patients had higher TREC levels, while NP patients had lower TREC/KREC levels compared to controls. Low TREC and KREC levels were predictive for the development of NP, ARDS, sepsis and lethal outcome (AUC_TREC in the range 0.71–0.82, AUC_KREC in the range 0.67–0.74). TREC/KREC analysis can be considered as a potential prognostic test in patients with pneumonia.

A cautionary note on altered pace of aging in the COVID-19 era

Coronavirus disease 2019 (COVID-19) is highly age-dependent due to hi-jacking the molecular control of the immune cells by the severe acute respiratory syndrome-corona virus 2 (SARS-CoV-2) leading to aberrant DNA methylation (DNAm) pattern of blood in comparison to normal individuals. These epigenetic modifications have been linked to perturbations to the epigenetic clock, development of long COVID-19 syndrome, and all-cause mortality risk. I reviewed the effects of COVID-19 on different molecular age markers such as the DNAm, telomere length (TL), and signal joint T-cell receptor excision circle (sjTREC). Integrating the accumulated clinical research data, COVID-19 and novel medical management may alter the pace of aging in adult individuals (<60 years). As such, COVID-19 might be a confounder in epigenetic age estimation similar to life style diversities, pathogens and pathologies which may influence the interpretation of DNAm data. Similarly, the SARS-CoV-2 affects T-lymphocyte function with possible influence on sjTREC levels. In contrast, TL measurements performed years before the SARS-CoV-2 pandemic proved that short TL predisposes to severe COVID- 19 independently from chronological age. However, the persistence of COVID-19 epigenetic scars and the durability of the immune response after vaccination and their effect on the ongoing pace of aging are still unknown. In the light of these data, the heterogeneous nature of the samples in these studies mandates a systematic evaluation of the currrent methods. SARS-CoV-2 may modify the reliability of the age estimation models in real casework because blood is the most common biological sample encountered in forensic contexts.

Mitochondrial Dysfunction Associates With Acute T Lymphocytopenia and Impaired Functionality in COVID-19 Patients

Severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) infection results in rapid T lymphocytopenia and functional impairment of T cells. The underlying mechanism, however, remains incompletely understood. In this study, we focused on characterizing the phenotype and kinetics of T-cell subsets with mitochondrial dysfunction (MD) by multicolor flow cytometry and investigating the association between MD and T-cell functionality. While 73.9% of study subjects displayed clinical lymphocytopenia upon hospital admission, a significant reduction of CD4 or CD8 T-cell frequency was found in all asymptomatic, symptomatic, and convalescent cases. CD4 and CD8 T cells with increased MD were found in both asymptomatic and symptomatic patients within the first week of symptom onset. Lower proportion of memory CD8 T cell with MD was found in severe patients than in mild ones at the stage of disease progression. Critically, the frequency of T cells with MD in symptomatic patients was preferentially associated with CD4 T-cell loss and CD8 T-cell hyperactivation, respectively. Patients bearing effector memory CD4 and CD8 T cells with the phenotype of high MD exhibited poorer T-cell responses upon either phorbol 12-myristate-13-acetate (PMA)/ionomycin or SARS-CoV-2 peptide stimulation than those with low MD. Our findings demonstrated an MD-associated mechanism underlying SARS-CoV-2-induced T lymphocytopenia and functional impairment during the acute phase of infection.

Primary immune responses are negatively impacted by persistent herpesvirus infections in older people: results from an observational study on healthy subjects and a vaccination trial on subjects aged more than 70 years old

Background

Advanced age is accompanied by a decline of immune functions, which may play a role in increased vulnerability to emerging pathogens and low efficacy of primary vaccinations in elderly people. The capacity to mount immune responses against new antigens is particularly affected in this population. However, its precise determinants are not fully understood. We aimed here at establishing the influence of persistent viral infections on the naive T-cell compartment and primary immune responsiveness in older adults.

Methods

We assessed immunological parameters, related to CD8⁺ and CD4⁺ T-cell responsiveness, according to the serological status for common latent herpesviruses in two independent cohorts: 1) healthy individuals aged 19y to 95y (n = 150) and 2) individuals above 70y old enrolled in a primo-vaccination clinical trial (n = 137).

Findings

We demonstrate a prevalent effect of age and CMV infection on CD8⁺ and CD4⁺ naive T cells, respectively. CMV seropositivity was associated with blunted CD4⁺ T-cell and antibody responses to primary vaccination.

Interpretation

These data provide insights on the changes in adaptive immunity over time and the associated decline in vaccine efficacy with ageing. This knowledge is important for the management of emerging infectious diseases in elderly populations.

Peculiarities of the T Cell Immune Response in COVID-19

Understanding the T cell response to SARS-CoV-2 is critical to vaccine development, epidemiological surveillance, and control strategies for this disease. This review provides data from studies of the immune response in coronavirus infections. It describes general mechanisms of immunity, its T cell components, and presents a detailed scheme of the T cell response in SARS-CoV-2 infection, including from the standpoint of determining the most promising targets for assessing its level. In addition, we reviewed studies investigating post-vaccination immunity in the development of vaccines against COVID-19. This review also includes the peculiarities of immunity in different age and gender groups, and in the presence of a number of factors, for example, comorbidity or disease severity. This study summarizes the most informative methods for assessing the immune response to SARS-CoV-2 infection.

Study of thymus volume and density in COVID-19 patients: Is there a correlation in terms of pulmonary CT severity score?

Background

Thymus has a pivotal role in combating infectious diseases. Although some reviews have been published about its critical role in COVID-19, there is not enough research. In this study, the size and density of thymus related to computed tomography pulmonary severity score (CT-SS) were researched.

Results

A total of 196 patients were analyzed with a mean age of 52.54 ± 18.78 years; 97 (49.5%) of them were RT-PCR (−) and 99 (50.5%) were RT-PCR (+). Within RT-PCR (+) group 62 (62.6%) of them had pneumonia with a mean CT-SS of 9.37 ± 8.83; within RT-PCR (−) group 20 (20.6%) of them had pneumonia with the mean CT-SS of 12.00 ± 10.18. CT-SS had moderate negative correlation with thymus volume and thymus maximum diameter in patients having nodular-type thymus (R  = −0.591, P  = 0.02; R  = −0.515, P  = 0.049, respectively). Homogenous fat infiltration was more commonly seen in RT-PCR (−) group while reticular and nodular types were commonly seen in RT-PCR (+) group (p  = 0.015). The mean volume and maximum diameter of thymus were statistically significantly higher in RT-PCR (+) group (p  = 0.027 and p  = 0.048, respectively).

Conclusion

This study showed the higher thymic volume and maximum diameter and more involution in COVID-19 patients. CT-SS had a moderate negative correlation with thymus volume and thymus maximum diameter. Pneumonia was more frequent in COVID patients, but mean CT-SS of the non-COVID cases was higher.

Thymus Gland: A Double Edge Sword for Coronaviruses

The thymus is the main lymphoid organ that regulates the immune and endocrine systems by controlling thymic cell proliferation and differentiation. The gland is a primary lymphoid organ responsible for generating mature T cells into CD4+ or CD8+ single-positive (SP) T cells, contributing to cellular immunity. Regarding humoral immunity, the thymic plasma cells almost exclusively secrete IgG1 and IgG3, the two main complement-fixing effector IgG subclasses. Deformity in the thymus can lead to inflammatory diseases. Hassall’s corpuscles’ epithelial lining produces thymic stromal lymphopoietin, which induces differentiation of CDs thymocytes into regulatory T cells within the thymus medulla. Thymic B lymphocytes produce immunoglobulins and immunoregulating hormones, including thymosin. Modulation in T cell and naive T cells decrement due to thymus deformity induce alteration in the secretion of various inflammatory factors, resulting in multiple diseases. Influenza virus activates thymic CD4+ CD8+ thymocytes and a large amount of IFNγ. IFNs limit virus spread, enhance macrophages’ phagocytosis, and promote the natural killer cell restriction activity against infected cells. Th2 lymphocytes-produced cytokine IL-4 can bind to antiviral INFγ, decreasing the cell susceptibility and downregulating viral receptors. COVID-19 epitopes (S, M, and N proteins) with ≥90% identity to the SARS-CoV sequence have been predicted. These epitopes trigger immunity for antibodies production. Boosting the immune system by improving thymus function can be a therapeutic strategy for preventing virus-related diseases. This review aims to summarize the endocrine-immunoregulatory functions of the thymus and the underlying mechanisms in the prevention of COVID-19.

Thymus Degeneration and Regeneration

The immune system’s ability to resist the invasion of foreign pathogens and the tolerance to self-antigens are primarily centered on the efficient functions of the various subsets of T lymphocytes. As the primary organ of thymopoiesis, the thymus performs a crucial role in generating a self-tolerant but diverse repertoire of T cell receptors and peripheral T cell pool, with the capacity to recognize a wide variety of antigens and for the surveillance of malignancies. However, cells in the thymus are fragile and sensitive to changes in the external environment and acute insults such as infections, chemo- and radiation-therapy, resulting in thymic injury and degeneration. Though the thymus has the capacity to self-regenerate, it is often insufficient to reconstitute an intact thymic function. Thymic dysfunction leads to an increased risk of opportunistic infections, tumor relapse, autoimmunity, and adverse clinical outcome. Thus, exploiting the mechanism of thymic regeneration would provide new therapeutic options for these settings. This review summarizes the thymus’s development, factors causing thymic injury, and the strategies for improving thymus regeneration.

Thymic hyperplasia after mRNA based Covid-19 vaccination

Reactive lymphadenopathy with increased 18F-Fluordeoxyglucose uptake in positron emission tomography/computed tomography scans is known after mRNA vaccination (BNT162B2, mRNA-1273) against severe acute respiratory syndrome coronavirus type 2. Besides this, increased 18F-Fluordeoxyglucose uptake in the thymus might occur after mRNA vaccination as shown in our case of a young patient with mantle cell lymphoma.

Especially in patients with lymphoma but also in other patients with cancer it is critical to distinguish between immune responses and involvement of the disease to avoid inadequate treatment decisions.