Yin and yang of cytokine regulation in solid organ graft rejection and tolerance

Hussein S, Abdalhabib EK, Nabi SU. The critical impacts of cytokine storms in respiratory disorders

Cytokine storm (CS) refers to the spontaneous dysregulated and hyper-activated inflammatory reaction occurring in various clinical conditions, ranging from microbial infection to end-stage organ failure. Recently the novel coronavirus involved in COVID-19 (Coronavirus disease-19) caused by SARS-CoV-2 (Severe Acute Respiratory Syndrome Coronavirus 2) has been associated with the pathological phenomenon of CS in critically ill patients. Furthermore, critically ill patients suffering from CS are likely to have a grave prognosis and a higher case fatality rate. Pathologically CS is manifested as hyper-immune activation and is clinically manifested as multiple organ failure. An in-depth understanding of the etiology of CS will enable the discovery of not just disease risk factors of CS but also therapeutic approaches to modulate the immune response and improve outcomes in patients with respiratory diseases having CS in the pathogenic pathway. Owing to the grave consequences of CS in various diseases, this phenomenon has attracted the attention of researchers and clinicians throughout the globe. So in the present manuscript, we have attempted to discuss CS and its ramifications in COVID-19 and other respiratory diseases, as well as prospective treatment approaches and biomarkers of the cytokine storm. Furthermore, we have attempted to provide in-depth insight into CS from both a prophylactic and therapeutic point of view. In addition, we have included recent findings of CS in respiratory diseases reported from different parts of the world, which are based on expert opinion, clinical case-control research, experimental research, and a case-controlled cohort approach.

Immunomodulating Phytochemicals: An Insight Into Their Potential Use in Cytokine Storm Situations

Phytochemicals are compounds found in plants that possess a variety of bioactive properties, including antioxidant and immunomodulatory properties. Recent studies have highlighted the potential of phytochemicals in targeting specific signalling pathways involved in cytokine storm, a life-threatening clinical condition resulting from excessive immune cell activation and oversupply of proinflammatory cytokines. Several studies have documented the immunomodulatory effects of phytochemicals on immune function, including their ability to regulate essential cellular and molecular interactions of immune system cells. This makes them a promising alternative for cytokine storm management, especially when combined with existing chemotherapies. Furthermore, phytochemicals have been found to target multiple signalling pathways, including the TNF-α/NF-κB, IL-1/NF-κB, IFN-γ/JAK/STAT, and IL-6/JAK-STAT. These pathways play critical roles in the development and progression of cytokine storm, and targeting them with phytochemicals represents a promising strategy for controlling cytokine release and the subsequent inflammation. Studies have also investigated certain families of plant-related constituents and their potential immunomodulatory actions. In vivo and in vitro studies have reported the immunomodulatory effects of phytochemicals, which provide viable alternatives in the management of cytokine storm syndrome. The collective data from previous studies suggest that phytochemicals represent a potentially functional source of cytokine storm treatment and promote further exploration of these compounds as immunomodulatory agents for suppressing specific signalling cascade responses. Overall, the previous research findings support the use of phytochemicals as a complementary approach in managing cytokine storm and improving patient outcomes.

Surviving the Storm: Cytokine Biosignature in SARS-CoV-2 Severity Prediction

Simple Summary

The world has been stricken mentally, physically, and economically by the COVID-19 virus. However, while SARS-CoV-2 viral infection results in mild flu-like symptoms in most patients, a number of those infected develop severe illness. These patients require hospitalization and intensive care. The severe disease can spiral downwards with eventual severe damage to the lungs and failure of multiple organs, leading to the individual’s demise. It is necessary to identify those who are developing a severe form of illness to provide early management. Therefore, it is crucial to learn about the mechanisms and chemical mediators that lead to critical conditions in SARS-CoV-2 infection. This paper reviews studies regarding the individual chemical mediators, pathways, and means that contribute to worsening health conditions in SARS-CoV-2 infection.

Abstract

A significant part of the world population has been affected by the devastating SARS-CoV-2 infection. It has deleterious effects on mental and physical health and global economic conditions. Evidence suggests that the pathogenesis of SARS-CoV-2 infection may result in immunopathology such as neutrophilia, lymphopenia, decreased response of type I interferon, monocyte, and macrophage dysregulation. Even though most individuals infected with the SARS-CoV-2 virus suffer mild symptoms similar to flu, severe illness develops in some cases, including dysfunction of multiple organs. Excessive production of different inflammatory cytokines leads to a cytokine storm in COVID-19 infection. The large quantities of inflammatory cytokines trigger several inflammation pathways through tissue cell and immune cell receptors. Such mechanisms eventually lead to complications such as acute respiratory distress syndrome, intravascular coagulation, capillary leak syndrome, failure of multiple organs, and, in severe cases, death. Thus, to devise an effective management plan for SARS-CoV-2 infection, it is necessary to comprehend the start and pathways of signaling for the SARS-CoV-2 infection-induced cytokine storm. This article discusses the current findings of SARS-CoV-2 related to immunopathology, the different paths of signaling and other cytokines that result in a cytokine storm, and biomarkers that can act as early signs of warning for severe illness. A detailed understanding of the cytokine storm may aid in the development of effective means for controlling the disease’s immunopathology. In addition, noting the biomarkers and pathophysiology of severe SARS-CoV-2 infection as early warning signs can help prevent severe complications.

Cytokine Storms in the Course of COVID-19 and Haemophagocytic Lymphohistiocytosis in Pregnant and Postpartum Women

The term 'cytokine storm' (CS) applies to a pathological autoimmune reaction when the interactions that lead to cytokine production are destabilised and may even lead to death. CS may be induced by severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) infection. In this study, we present our analysis of certain pathological processes that induce a CS in pregnant and postpartum women. We draw our attention to the similarities between the severe course of Coronavirus Disease 2019 (COVID-19) and haemophagocytic lymphohistiocytosis (HLH). It is noteworthy that many of the criteria used to diagnose HLH are described as COVID-19 mortality predictors. Cytokine storms are considered to be an important cause of death in patients with the severe course of SARS-CoV-2 infection. Due to the fact that pregnant women are in an immunosuppressive state, viral pulmonary infections are more perilous for them-possible risks include miscarriage, intrauterine growth restriction or birth before the term; sometimes ventilation support is needed. HLH should be considered in pregnant and puerperal women suffering from moderately severe to severe COVID-19 and presenting with: fever unresponsive to antibiotic therapy, cytopenia, hepatitis and hyperferritinaemia. The HLH disorder is rare and difficult to diagnose; however, its early detection could reduce patient mortality.

The signal pathways and treatment of cytokine storm in COVID-19

The Coronavirus Disease 2019 (COVID-19) pandemic has become a global crisis and is more devastating than any other previous infectious disease. It has affected a significant proportion of the global population both physically and mentally, and destroyed businesses and societies. Current evidence suggested that immunopathology may be responsible for COVID-19 pathogenesis, including lymphopenia, neutrophilia, dysregulation of monocytes and macrophages, reduced or delayed type I interferon (IFN-I) response, antibody-dependent enhancement, and especially, cytokine storm (CS). The CS is characterized by hyperproduction of an array of pro-inflammatory cytokines and is closely associated with poor prognosis. These excessively secreted pro-inflammatory cytokines initiate different inflammatory signaling pathways via their receptors on immune and tissue cells, resulting in complicated medical symptoms including fever, capillary leak syndrome, disseminated intravascular coagulation, acute respiratory distress syndrome, and multiorgan failure, ultimately leading to death in the most severe cases. Therefore, it is clinically important to understand the initiation and signaling pathways of CS to develop more effective treatment strategies for COVID-19. Herein, we discuss the latest developments in the immunopathological characteristics of COVID-19 and focus on CS including the current research status of the different cytokines involved. We also discuss the induction, function, downstream signaling, and existing and potential interventions for targeting these cytokines or related signal pathways. We believe that a comprehensive understanding of CS in COVID-19 will help to develop better strategies to effectively control immunopathology in this disease and other infectious and inflammatory diseases.

"Cytokine storm", not only in COVID-19 patients. Mini-review

Cytokine storm is a form of uncontrolled systemic inflammatory reaction activated by a variety of factors and leading to a harmful homeostatic process, even to patient's death. Triggers that start the reaction are infection, systemic diseases and rarely anaphylaxis. Cytokine storm is frequently mentioned in connection to medical interventions such as transplantation or administration of drugs. Presented mini-review would like to show current possibilities how to fight or even stop such a life-threatening, immune-mediated process in order to save lives, not only in COVID-19 patients. Early identification of rising state and multilevel course of treatment is imperative. The most widely used molecule for systemic treatment remains tocilizumab. Except for anti IL-6 treatment, contemporary research opens the possibilities for combination of pharmaceutical, non-pharmaceutical and adjunctive treatment in a successful fight with consequences of cytokine storm. Further work is needed to discover the exact signaling pathways that lead to cytokine storm and to determine how these effector molecules and/or combination of processes can help to resolve this frequently fatal episode of inflammation. It is a huge need for all scientists and clinicians to establish a physiological rational for new therapeutic targets that might lead to more personalized medicine approaches.

A Critical Role for TGF-β/Fc and Nonlytic IL-2/Fc Fusion Proteins in Promoting Chimerism and Donor-Specific Tolerance

BACKGROUND

Immunoglobulin-cytokine fusion molecules have been shown to be the new generation of immunomodulating agents in transplantation tolerance induction. In the present study, we tested whether immunoregulatory cytokine fusion proteins of IL-10/Fc, TGF-β/Fc, or IL-2/Fc would enhance allogeneic bone marrow cell (BMC) engraftment and promote tolerance induction.

METHODS

B6 (H2) mice were conditioned with anti-CD154 (MR1) and rapamycin (Rapa) plus 100 cGy total body irradiation (MR1/Rapa/100 cGy) and transplanted with allogeneic B10.D2 (H2) BMC. Recipients were treated with lytic IL-2/Fc, nonlytic IL-2/Fc, TGF-β/Fc, or IL-10/Fc fusion proteins to promote chimerism to induce tolerance.

RESULTS

Donor chimerism was achieved in 20% of recipients conditioned with MR1/Rapa/100 cGy. The addition of TGF-β/Fc (5- or 10-day treatment) or nonlytic IL-2/Fc (10-day treatment) fusion proteins to the conditioning resulted in engraftment in nearly 100% of recipients. In contrast, lytic IL-2/Fc or IL-10/Fc had no effect. The combination of nonlytic IL-2/Fc and TGF-β/Fc had a synergistic effect to promote engraftment and resulted in significantly higher donor chimerism compared with recipients conditioned with TGF-β/MR1/Rapa/100 cGy. Engraftment was durable in the majority of chimeras and increased over time. The chimeras accepted donor skin grafts and promptly rejected third-party skin grafts. Moreover, specific T cell receptor-Vβ5.½ and TCR-Vβ11 clonal deletion was detected in host T cells in chimeras, suggesting central tolerance to donor alloantigens.

CONCLUSIONS

Allogeneic BMC engraftment is enhanced with TGF-β/Fc fusion protein treatment. TGF-β/Fc and nonlytic IL-2/Fc exert a synergistic effect in promotion of alloengraftment and donor-specific transplant tolerance, significantly decreasing the minimum total body irradiation dose required.

Eosinophil count, allergies, and rejection in pediatric heart transplant recipients

BACKGROUND

Allograft rejection and long-term immunosuppression remain significant challenges in pediatric heart transplantation. Pediatric recipients are known to have fewer rejection episodes and to develop more allergic conditions than adults. A T-helper 2 cell dominant phenotype, manifested clinically by allergies and an elevated eosinophil count, may be associated with immunologic quiescence in transplant recipients. This study assessed whether the longitudinal eosinophil count and an allergic phenotype were associated with freedom from rejection.

METHODS

This single-center, longitudinal, observational study included 86 heart transplant patients monitored from 1994 to 2011. Post-transplant biannual complete blood counts, allergic conditions, and clinical characteristics related to rejection risk were examined.

RESULTS

At least 1 episode of acute cellular rejection (ACR) occurred in 38 patients (44%), antibody-mediated rejection (AMR) occurred in 11 (13%), and 49 patients (57%) were diagnosed with an allergic condition. Patients with ACR or AMR had a lower eosinophil count compared with non-rejectors (p = 0.011 and p = 0.022, respectively). In the multivariable regression analysis, the presence of panel reactive antibodies to human leukocyte antigen I (p = 0.014) and the median eosinophil count (p = 0.011) were the only independent covariates associated with AMR. Eosinophil count (p = 0.010) and female sex (p = 0.009) were independent risk factors for ACR. Allergic conditions or young age at transplant were not protective from rejection.

CONCLUSIONS

This study demonstrates a novel association between a high eosinophil count and freedom from rejection. Identifying a biomarker for low rejection risk may allow a reduction in immunosuppression. Further investigation into the role of the T-helper 2 cell phenotype and eosinophils in rejection quiescence is warranted.

Inflammatory signalling associated with brain dead organ donation: from brain injury to brain stem death and posttransplant ischaemia reperfusion injury

Brain death is associated with dramatic and serious pathophysiologic changes that adversely affect both the quantity and quality of organs available for transplant. To fully optimise the donor pool necessitates a more complete understanding of the underlying pathophysiology of organ dysfunction associated with transplantation. These injurious processes are initially triggered by catastrophic brain injury and are further enhanced during both brain death and graft transplantation. The activated inflammatory systems then contribute to graft dysfunction in the recipient. Inflammatory mediators drive this process in concert with the innate and adaptive immune systems. Activation of deleterious immunological pathways in organ grafts occurs, priming them for further inflammation after engraftment. Finally, posttransplantation ischaemia reperfusion injury leads to further generation of inflammatory mediators and consequent activation of the recipient's immune system. Ongoing research has identified key mediators that contribute to the inflammatory milieu inherent in brain dead organ donation. This has seen the development of novel therapies that directly target the inflammatory cascade.

A critical role for the TLR4/TRIF pathway in allogeneic hematopoietic cell rejection by innate immune cells

We show for the first time that signaling through the TLR4/TRIF pathway plays a critical role in allogeneic bone marrow cell (BMC) rejection. This appears to be unique to BMCs as organ allografts are rejected mainly via MyD88 signaling. Using T- or T-/B-cell-deficient mice, we found that BMC allorejection occurred early before T-cell activation and was T- and B-cell independent, suggesting an effector role for innate immune cells in BMC rejection. We further demonstrated the innate immune signaling in BMC allorejection by showing superior engraftment in mice deficient in TRIF or TLR4 but not in MyD88 or TLR3. The restored cytotoxicity in TRIF-deficient recipients transferred with wild-type F4/80(+) or NK1.1(+) cells suggests TRIF signaling dependence on macrophages or NK cells in early BMC rejection. Production of the proinflammatory cytokine IL-6 and TRIF relevant chemokine MCP-1 was significantly increased early after bone marrow transplantation. In vivo specific depletion of macrophages or NK innate immune cells in combination with anti-CD154/rapamycin resulted in additive-enhanced allogeneic engraftment. The requirement for irradiation was completely eliminated when both macrophages and NK cells were depleted in combination with anti-CD154/rapamycin to target T- and B-cells, supporting the hypothesis that two barriers involving innate and adaptive immunity exist in mediating the rejection of allogeneic BMCs. In summary, our results clearly demonstrate a previously unappreciated role for innate immunity in BMC allorejection via signaling through a unique MyD88-independent TLR4/TRIF mechanism. These findings may have direct clinical impact on strategies for conditioning recipients for stem cell transplantation.

Selective CD28 blockade attenuates acute and chronic rejection of murine cardiac allografts in a CTLA-4-dependent manner

Selective blockade of CD28 is a promising therapy to inhibit pathogenic alloimmunity. However, evaluation of this approach in transplantation has been very limited. Using a novel nonactivating single-chain Fv-based reagent (α28scFv), we have investigated the role of CD28 and cytotoxic T lymphocyte antigen 4 (CTLA-4) in a murine cardiac transplant model. Blockade of CD28 for 2 weeks after engraftment promoted allograft survival, and significantly attenuated chronic rejection when combined with transient CD154-blockade or calcineurin inhibition. Graft acceptance was associated with decreased alloantibody production, increased proportion of early graft infiltration by regulatory T cells and increased expression of regulatory dendritic cell genes. Blockade of CTLA-4 during α28scFv-based treatments led to prompt rejection in all animals and inhibited expression of forkhead box P3 (Foxp3), programmed death (PD)-1 and 2,3-indoleamine dioxygenase (IDO) in the graft. These results show that CD28 signaling during the first weeks after transplant is a pivotal mediator of pathogenic alloimmunity, and that selective CD28 blockade prolongs graft acceptance by at least two immunomodulatory mechanisms. Selective CD28 inhibition while sparing CTLA-4 is thus a promising approach to inhibit pathogenic alloimmunity.

Emodin prolongs recipient survival time after orthotopic liver transplantation in rats by polarizing the Th1/Th2 paradigm to Th2

Advances in immunosuppressive drugs have improved the short-term survival of liver transplantation. However, drug toxicities have been a serious problem in patients after long-term administration. Therefore, it is necessary to develop a novel immunosuppressant with low-toxicity. We investigated the immunosuppressive effects of Emodin on acute graft rejection following liver transplantation in rats. The recipient rats of orthotopic liver transplantation were divided into groups as follows: isograft+NS group, allograft+NS group, and allograft+emodin group. The survival time of the recipients in each group was recorded. Histopathological changes in the liver, as well as serum concentrations of IL-2, TNF-α, and IL-10 and their expressions in liver tissue were determined. Our results showed that Emodin treatment prolonged liver allograft survival time and inhibited histopathologic changes of acute graft rejection. The rejection activity index in groups isograft+NS, allograft+NS, and allograft+emodin were 1.52 ± 0.37, 6.95 ± 0.75, and 4.23 ± 0.51, respectively (P < 0.01, isograft+NS group vs. allograft+emodin group and allograft+NS group vs. allograft+emodin group). The serum levels of IL-2 and TNF-α were down-regulated but that of IL-10 was up-regulated by Emodin. Serum levels of IL-2 and TNF-α were higher in allograft+NS group than the allograft+emodin group, but that of IL-10 showed opposite effects (P < 0.05 or 0.01). Changes in the expression of these cytokines in transplanted liver tissue were consistent with changes in serum concentrations. These results demonstrate that Emodin has therapeutic potentials for alleviating acute rejection following liver transplantation in rats and prolonging liver allograft survival. The mechanisms underlying this effect may be associated with polarizing the Th1/Th2 paradigm to Th2.

Th17 promotes acute rejection following liver transplantation in rats

T help cell 17 (Th17), recently identified as a new subset of CD4(+) T cells, has been implicated in autoimmune diseases, tumor immunity, and transplant rejection. To investigate the role of Th17 in acute hepatic rejection, a rat model of allogeneic liver transplantation (Dark Agouti (DA) to Brown Norway (BN)) was established and isogeneic liver transplantation (BN to BN) was used as controls in the study. The expression of Th17-related cytokines in the liver and peripheral blood was determined by immunohistochemistry, flow cytometry, enzyme-linked immunosorbent assay (ELISA), or real-time quantitative reverse transcription polymerase chain reaction (RT-qPCR). Strong expression of interleukin-17A (IL-17A), IL-6, transforming growth factor-β (TGF-β), IL-8, and myeloperoxidase (MPO) was observed in liver allografts. The ratios of Th17 to CD4(+) lymphocytes in the liver and peripheral blood were dramatically increased in the allograft group compared with the control (P<0.01). Secreted IL-17 and IL-6 in liver homogenate and serum were significantly elevated in the allograft group, while secreted TGF-β was increased in liver homogenate and decreased in serum compared with the control (P<0.01). The messenger RNA (mRNA) levels of IL-17, IL-21, and IL-23 were enhanced in the allografts compared with the control (P<0.01). Correlation analysis showed significant correlations between IL-17 and IL-6 and TGF-β and between IL-17 and IL-21 and IL-23. The present study demonstrates that Th17 plays a role in promoting rat liver allograft rejection.