Prolonged adaptive immune activation in COVID-19: implications for maintenance of long-term immunity?

Concurrent glomerular PCDH7 deposits in PLA2R-associated membranous nephropathy

The understanding of membranous nephropathy (MN) has undergone impressive advancements in the last 5 years, particularly due to identification of novel antigenic targets. M-type phospholipase A2 receptor (PLA2R) and thrombospondin type 1 domain-containing 7A (THSD7A) account for approximately 70% and 1-5% of the target antigens in primary MN, respectively. Recently, more novel/putative antigens have been identified in the remaining cases of MN that include exostosin 1/exostosin 2 (EXT1/EXT2), neural epidermal growth factor-like 1 protein (NELL-1), semaphorin 3B (SEMA3B) and protocadherin 7 (PCDH7). However, comparatively little is known about the PCDH7 among these novel antigens. As such, we herein described a unique case of positive glomerular PCDH7 deposits in PLA2R-associated MN, which may offer a deeper insight into the role of PCDH7 in MN and improve our understanding of glomerular diseases in the post-COVID era, particularly with the emerging variants.

Gut Microbiota and Mitochondria: Health and Pathophysiological Aspects of Long COVID

The current understanding of long COVID (LC) is still limited. This review highlights key findings regarding the role of gut microbiota, mitochondria, and the main pathophysiological aspects of LC revealed by clinical studies, related to the complex interplay between infection, intestinal dysbiosis, dysfunctional mitochondria, and systemic inflammation generated in a vicious circle, reflecting the molecular and cellular processes from the "leaky gut" to the "leaky electron transport chain (ETC)" into a quantum leap. The heterogeneity of LC has hindered progress in deciphering all the pathophysiological mechanisms, and therefore, the approach must be multidisciplinary, with a special focus not only on symptomatic management but also on addressing the underlying health problems of the patients. It is imperative to further assess and validate the effects of COVID-19 and LC on the gut microbiome and their relationship to infections with other viral agents or pathogens. Further studies are needed to better understand LC and expand the interdisciplinary points of view that are required to accurately diagnose and effectively treat this heterogeneous condition. Given the ability of SARS-CoV-2 to induce autoimmunity in susceptible patients, they should be monitored for symptoms of autoimmune disease after contracting the viral infection. One question remains open, namely, whether the various vaccines developed to end the pandemic will also induce autoimmunity. Recent data highlighted in this review have revealed that the persistence of SARS-CoV-2 and dysfunctional mitochondria in organs such as the heart and, to a lesser extent, the kidneys, liver, and lymph nodes, long after the organism has been able to clear the virus from the lungs, could be an explanation for LC.

COVID-19 associated development of antibody mediated rejection in orthotopic heart transplantation patients

Solid organ transplant candidates encountered increased wait times and mortality rates during the coronavirus 2019 (COVID-19) pandemic. Despite improvement in medical management and vaccination efficacy, this patient population remains at increased risk for complications post COVID-19 including organ rejection. We describe the development of antibody mediated rejection with or without cellular rejection in heart transplant (HT) recipients and previous COVID-19 infection or vaccination. Although centers have changed their management of outpatient follow-up for orthotopic heart transplant patients, little is known on surveillance of rejection and management of HT recipients after COVID-19 infection. We recommend frequent surveillance for rejection or allograft dysfunction after COVID-19 infection. We have adopted a transplant surveillance protocol for HT recipients with COVID-19 infection, given our recent experience with transplanted patients affected of COVID-19.

The role of immune activation and antigen persistence in acute and long COVID

In late 2019, severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) triggered the global coronavirus disease 2019 (COVID-19) pandemic. Although most infections cause a self-limited syndrome comparable to other upper respiratory viral pathogens, a portion of individuals develop severe illness leading to substantial morbidity and mortality. Furthermore, an estimated 10%-20% of SARS-CoV-2 infections are followed by post-acute sequelae of COVID-19 (PASC), or long COVID. Long COVID is associated with a wide variety of clinical manifestations including cardiopulmonary complications, persistent fatigue, and neurocognitive dysfunction. Severe acute COVID-19 is associated with hyperactivation and increased inflammation, which may be an underlying cause of long COVID in a subset of individuals. However, the immunologic mechanisms driving long COVID development are still under investigation. Early in the pandemic, our group and others observed immune dysregulation persisted into convalescence after acute COVID-19. We subsequently observed persistent immune dysregulation in a cohort of individuals experiencing long COVID. We demonstrated increased SARS-CoV-2-specific CD4⁺ and CD8⁺ T-cell responses and antibody affinity in patients experiencing long COVID symptoms. These data suggest a portion of long COVID symptoms may be due to chronic immune activation and the presence of persistent SARS-CoV-2 antigen. This review summarizes the COVID-19 literature to date detailing acute COVID-19 and convalescence and how these observations relate to the development of long COVID. In addition, we discuss recent findings in support of persistent antigen and the evidence that this phenomenon contributes to local and systemic inflammation and the heterogeneous nature of clinical manifestations seen in long COVID.

Defective antifungal immunity in patients with COVID-19

The COVID-19 pandemic has placed a huge strain on global healthcare and been a significant cause of increased morbidity and mortality, particularly in at-risk populations. This disease attacks the respiratory systems and causes significant immune dysregulation in affected patients creating a perfect opportunity for the development of invasive fungal disease (IFD). COVID-19 infection can instill a significant, poorly regulated pro-inflammatory response. Clinically induced immunosuppression or pro-inflammatory damage to mucosa facilitate the development of IFD and Aspergillus, Mucorales, and Candida infections have been regularly reported throughout the COVID-19 pandemic. Corticosteroids and immune modulators are used in the treatment of COVID-19. Corticosteroid use is also a risk factor for IFD, but not the only reason for IFD in COVID -19 patients. Specific dysregulation of the immune system through functional exhaustion of Natural killer (NK) cells and T cells has been observed in COVID-19 through the expression of the exhaustion markers NK-G2A and PD-1. Reduced fungicidal activity of neutrophils from COVID-19 patients indicates that immune dysfunction/imbalance are important risk factors for IFD. The COVID-19 pandemic has significantly increased the at-risk population for IFD. Even if the incidence of IFD is relatively low, the size of this new at-risk population will result in a substantial increase in the overall, annual number of IFD cases. It is important to understand how and why certain patients with COVID-19 developed increased susceptibility to IFD, as this will improve our understanding of risk of IFD in the face of future pandemics but also in a clinical era of increased clinical immuno-suppression/modulation.

COVID-19 disease and immune dysregulation

The SARS-CoV-2 virus has complex and divergent immune alterations in differing hosts and over disease evolution. Much of the nuanced COVID-19 disease immune dysregulation was originally dominated by innate cytokine changes, which has since been replaced with a more complex picture of innate and adaptive changes characterized by simultaneous hyperinflammatory and immunosuppressive phenomena in effector cells. These intricacies are summarized in this review as well as potential relevance from acute infection to a multisystem inflammatory syndrome commonly seen in children. Additional consideration is made for the influence of variant to variant host cellular changes and the impact of potential vaccination upon these phenotypes. Finally, therapeutic benefit for immune alterations are discussed.

Immunosenescence and Altered Vaccine Efficiency in Older Subjects: A Myth Difficult to Change

Organismal ageing is associated with many physiological changes, including differences in the immune system of most animals. These differences are often considered to be a key cause of age-associated diseases as well as decreased vaccine responses in humans. The most often cited vaccine failure is seasonal influenza, but, while it is usually the case that the efficiency of this vaccine is lower in older than younger adults, this is not always true, and the reasons for the differential responses are manifold. Undoubtedly, changes in the innate and adaptive immune response with ageing are associated with failure to respond to the influenza vaccine, but the cause is unclear. Moreover, recent advances in vaccine formulations and adjuvants, as well as in our understanding of immune changes with ageing, have contributed to the development of vaccines, such as those against herpes zoster and SARS-CoV-2, that can protect against serious disease in older adults just as well as in younger people. In the present article, we discuss the reasons why it is a myth that vaccines inevitably protect less well in older individuals, and that vaccines represent one of the most powerful means to protect the health and ensure the quality of life of older adults.

Stem cell therapy for COVID-19 pneumonia

Severe Acute Respiratory Syndrome Coronavirus 2 (SARS-CoV-2) virus is a highly contagious microorganism, and despite substantial investigation, no progress has been achieved in treating post-COVID complications. However, the virus has made various mutations and has spread around the world. Researchers have tried different treatments to reduce the side effects of the COVID-19 symptoms. One of the most common and effective treatments now used is steroid therapy to reduce the complications of this disease. Long-term steroid therapy for chronic inflammation following COVID-19 is harmful and increases the risk of secondary infection, and effective treatment remains challenging owing to fibrosis and severe inflammation and infection. Sometimes our immune system can severely damage ourselves in disease. In the past, many researchers have conducted various studies on the immunomodulatory properties of stem cells. This property of stem cells led them to modulate the immune system of autoimmune diseases like diabetes, multiple sclerosis, and Parkinson's. Because of their immunomodulatory properties, stem cell-based therapy employing mesenchymal or hematopoietic stem cells may be a viable alternative treatment option in some patients. By priming the immune system and providing cytokines, chemokines, and growth factors, stem cells can be employed to build a long-term regenerative and protective response. This review addresses the latest trends and rapid progress in stem cell treatment for Acute Respiratory Distress Syndrome (ARDS) following COVID-19.

Methylprednisolone Treatment Versus Standard Supportive Care for Adult COVID-19 Mechanically Ventilated, Acute Respiratory Distress Syndrome Patients

A myriad of symptoms presented by severely ill mechanically ventilated COVID-19 patients has added pressure on the caregivers to explore therapeutic options. Systemic steroids have been reported to therapeutically benefit patients, with elevated inflammatory markers, during the severe acute respiratory syndrome, and the Middle East respiratory syndrome outbreak. COVID-19 disease is characterized by inflammation of the respiratory system and acute respiratory distress syndrome. Given the lack of specific treatment for COVID-19, the current study aimed to evaluate the therapeutic benefit of methylprednisolone as an add-on treatment for mechanically ventilated hospitalized COVID-19 patients with severe COVID pneumonia. Data were collected retrospectively from the electronic patient medical records, and interrater reliability was determined to limit selection bias. Descriptive and inferential statistical methods were used to analyze the data. The variables were cross-tabulated with the clinical outcome, and the chi-square test was used to determine the association between the outcomes and other independent variables. Sixty-one percent (43/70) of the COVID-19 ARDS patients received standard supportive care, and the remainder were administered, methylprednisolone (minimum 40 mg daily to a maximum 40 mg q 6 h). A 28-day all-cause mortality rate, in the methylprednisolone group, was 18% (5/27, p < 0.01) significantly lower, compared to the group receiving standard supportive care (51%, 22/43). The median number of days, for the hospital length of stay (18 days), ICU length of stay (9.5 days), and the number of days intubated (6 days) for the methylprednisolone-treated group, was significantly lower (p < 0.01) when compared with the standard supportive care group. Methylprednisolone treatment also reduced the C-reactive protein levels, compared to the standard care group on day 7. Our results strengthen the evidence for the role of steroids in reducing mortality, ICU length of stay, and ventilator days in mechanically ventilated COVID-19 patients with respiratory distress syndrome.

Asymptomatic and Mild SARS-CoV-2 Infections Elicit Lower Immune Activation and Higher Specific Neutralizing Antibodies in Children Than in Adults

Background

The immune response plays a pivotal role in dictating the clinical outcome in severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2)-infected adults, but it is still poorly investigated in the pediatric population.

Methods

Of 209 enrolled subjects, 155 patients were confirmed by PCR and/or serology as having coronavirus disease 2019 (COVID-19). Blood samples were obtained at a median of 2.8 (interquartile, 2.1–3.7) and 6.1 (5.3–7.2) months after baseline (symptom onset and/or first positive virus detection). The immune profiles of activation, senescence, exhaustion, and regulatory cells were analyzed by flow cytometry. Neutralizing antibodies (nAbs) were detected by a plaque reduction neutralization test. In available nasopharyngeal swabs at baseline, SARS-CoV-2 levels were quantified by digital droplet PCR (ddPCR).

Results

Overall, COVID-19 patients had higher levels of immune activation, exhaustion, and regulatory cells compared to non-COVID-19 subjects. Within the COVID-19 group, activated and senescent cells were higher in adults than in children and inversely correlated with the nAbs levels. Conversely, Tregs and Bregs regulatory cells were higher in COVID-19 children compared to adults and positively correlated with nAbs. Higher immune activation still persisted in adults after 6 months of infection, while children maintained higher levels of regulatory cells. SARS-CoV-2 levels did not differ among age classes.

Conclusions

Adults displayed higher immune activation and lower production of anti-SARS-CoV-2 nAbs than children. The different immune response was not related to different viral load. The higher expression of regulatory cells in children may contribute to reduce the immune activation, thus leading to a greater specific response against the virus.

CXCL10 levels at hospital admission predict COVID-19 outcome: hierarchical assessment of 53 putative inflammatory biomarkers in an observational study

Background

Host inflammation contributes to determine whether SARS-CoV-2 infection causes mild or life-threatening disease. Tools are needed for early risk assessment.

Methods

We studied in 111 COVID-19 patients prospectively followed at a single reference Hospital fifty-three potential biomarkers including alarmins, cytokines, adipocytokines and growth factors, humoral innate immune and neuroendocrine molecules and regulators of iron metabolism. Biomarkers at hospital admission together with age, degree of hypoxia, neutrophil to lymphocyte ratio (NLR), lactate dehydrogenase (LDH), C-reactive protein (CRP) and creatinine were analysed within a data-driven approach to classify patients with respect to survival and ICU outcomes. Classification and regression tree (CART) models were used to identify prognostic biomarkers.

Results

Among the fifty-three potential biomarkers, the classification tree analysis selected CXCL10 at hospital admission, in combination with NLR and time from onset, as the best predictor of ICU transfer (AUC [95% CI] = 0.8374 [0.6233–0.8435]), while it was selected alone to predict death (AUC [95% CI] = 0.7334 [0.7547–0.9201]). CXCL10 concentration abated in COVID-19 survivors after healing and discharge from the hospital.

Conclusions

CXCL10 results from a data-driven analysis, that accounts for presence of confounding factors, as the most robust predictive biomarker of patient outcome in COVID-19.

Graphic abstract

Supplementary Information

The online version contains supplementary material available at 10.1186/s10020-021-00390-4.

Post-surgical pyoderma gangrenosum in otherwise healthy patient with history of COVID-19

There are increasing reports of autoimmune and dermatologic sequelae of COVID‐19. We describe an otherwise healthy patient with recent history of serious COVID‐19 infection who developed post‐surgical pyoderma gangrenosum following bilateral reduction mammoplasty and was successfully treated with infliximab, mycophenolic acid, and corticosteroids. We present this case to highlight the lingering systemic proinflammatory effects of COVID‐19 infection that may increase the risk of rare autoimmune complications of surgery. As a complete understanding of the long‐term effects of COVID‐19 is poorly understood, patients with a history of COVID‐19 infection should be appropriately counseled to these possible risks when discussing surgery.

Severe Acute Respiratory Syndrome-Associated Coronavirus 2 Infection and Organ Dysfunction in the ICU: Opportunities for Translational Research

OBJECTIVES

Since the beginning of the coronavirus disease 2019 pandemic, hundreds of thousands of patients have been treated in ICUs across the globe. The severe acute respiratory syndrome-associated coronavirus 2 virus enters cells via the angiotensin-converting enzyme 2 receptor and activates several distinct inflammatory pathways, resulting in hematologic abnormalities and dysfunction in respiratory, cardiac, gastrointestinal renal, endocrine, dermatologic, and neurologic systems. This review summarizes the current state of research in coronavirus disease 2019 pathophysiology within the context of potential organ-based disease mechanisms and opportunities for translational research.

DATA SOURCES

Investigators from the Research Section of the Society of Critical Care Medicine were selected based on expertise in specific organ systems and research focus. Data were obtained from searches conducted in Medline via the PubMed portal, Directory of Open Access Journals, Excerpta Medica database, Latin American and Caribbean Health Sciences Literature, and Web of Science from an initial search from December 2019 to October 15, 2020, with a revised search to February 3, 2021. The medRxiv, Research Square, and clinical trial registries preprint servers also were searched to limit publication bias.

STUDY SELECTION

Content experts selected studies that included mechanism-based relevance to the severe acute respiratory syndrome-associated coronavirus 2 virus or coronavirus disease 2019 disease.

DATA EXTRACTION

Not applicable.

DATA SYNTHESIS

Not applicable.

CONCLUSIONS

Efforts to improve the care of critically ill coronavirus disease 2019 patients should be centered on understanding how severe acute respiratory syndrome-associated coronavirus 2 infection affects organ function. This review articulates specific targets for further research.

Immunological Changes in Pregnancy and Its Relation to COVID-19 Infection

This chapter describes the immunological adaptation to pregnancy. A special focus is drawn on the susceptibility to viral infections, especially COVID-19. Older literature refers to the pregnancy as an immunosuppressive state, while recent studies show an immunomodulation to adapt to the growing semiallograftic fetus. Despite this, pregnant women are not susceptible to all viral infections. Regarding influenza, pregnant women are not more susceptible to the infection, but more severe maternal courses. To prevent this, influenza vaccination is recommended for pregnant women. Based on the available evidence, pregnant patients are also not more susceptible to infection with regard to COVID-19 infection. Yet, more severe courses are described throughout gestation with the onset of obstetrical complications.