Memory regulatory T cells home to the lung and control influenza A virus infection

Memory regulatory T cells in pregnancy

Pregnancy requires the process of maternal immune tolerance to semi-allogeneic embryos. In contrast, an overreactive maternal immune system to embryo-specific antigens is likely to result in the rejection of embryos while damaging the invading placenta, such that the likelihood of adverse pregnancy outcomes can be increased. Regulatory T cells (Tregs) are capable of suppressing excessive immune responses and regulating immune homeostasis. When stimulating Tregs, specific antigens will differentiate into memory Tregs with long-term survival and rapid and powerful immune regulatory ability. Immunomodulatory effects mediated by memory Tregs at the maternal-fetal interface take on critical significance in a successful pregnancy. The impaired function of memory Tregs shows a correlation with various pregnancy complications (e.g., preeclampsia, gestational diabetes mellitus, and recurrent pregnancy losses). However, the differentiation process and characteristics of memory Tregs, especially their role in pregnancy, remain unclear. In this study, a review is presented in terms of memory Tregs differentiation and activation, the characteristics of memory Tregs and their role in pregnancy, and the correlation between memory Tregs and pregnancy complications. Furthermore, several potential therapeutic methods are investigated to restore the function of memory Tregs in accordance with immunopathologies arising from memory Tregs abnormalities and provide novel targets for diagnosing and treating pregnancy-associated diseases.

Determination of Tr1 cell populations correlating with distinct activation states in acute IAV infection

Type I regulatory (Tr1) cells are defined as FOXP3-IL-10-secreting clusters of differentiation (CD4+) T cells that contribute to immune suppression and typically express the markers LAG-3 and CD49b and other co-inhibitory receptors. These cells have not been studied in detail in the context of the resolution of acute infection in the lung. Here, we identify FOXP3- interleukin (IL)-10+ CD4+ T cells transiently accumulating in the lung parenchyma during resolution of the response to sublethal influenza A virus (IAV) infection in mice. These cells were dependent on IL-27Rα, which was required for timely recovery from IAV-induced weight loss. LAG-3 and CD49b were not generally co-expressed by FOXP3- IL-10+ CD4+ T cells in this model and four populations of these cells based on LAG-3 and CD49b co-expression were apparent [LAG-3-CD49b- (double negative), LAG-3+CD49b+ (double positive), LAG-3+CD49b- (LAG-3+), LAG-3-CD49b+ (CD49b+)]. However, each population exhibited suppressive potential consistent with the definition of Tr1 cells. Notably, differences between these populations of Tr1 cells were apparent including differential dependence on IL-10 to mediate suppression and expression of markers indicative of different activation states and terminal differentiation. Sort-transfer experiments indicated that LAG-3+ Tr1 cells exhibited the capacity to convert to double negative and double positive Tr1 cells, indicative of plasticity between these populations. Together, these data determine the features and suppressive potential of Tr1 cells in the resolution of IAV infection and identify four populations delineated by LAG-3 and CD49b, which likely correspond to different Tr1 cell activation states.

The functional adaptation of effector Foxp3+ regulatory T cells to pulmonary inflammation

During infections, the timings of effector differentiation of pulmonary immune responses are of paramount importance, as pathogen persistence and unsuppressed inflammation can rapidly lead to a loss of function, increased frailty, and death. Thus, both an efficient clearance of the danger and a rapid resolution of inflammation are critical to host survival. We now know that tissue-localized FoxP3+ regulatory T cells, a subset of CD4+ T cells, are highly attuned to the type of immune response, acquiring unique phenotypic characteristics that allow them to adapt their suppressive functions with the nature of inflammatory cells. To achieve this, activated effector TREG cells acquire specialized TH 1, TH 2, and TH 17-like characteristics that allow them to migrate, survive, and time their function(s) through refined mechanisms. Herein, we describe how this process requires a unique developmental path that includes the acquisition of master transcription factors and the expression of receptors adapted to sense local danger signals that are found during pulmonary inflammation. In turn, we offer an overview of how these characteristics promote the capacity of local effector TREG cells to proliferate, survive, and display suppressive strategies to resolve lung injury.

Association between dietary antioxidant quality score and severity of coronavirus infection: a case-control study

The purpose of this study was to examine the association between the dietary antioxidant quality score (DAQS) and the severity of Coronavirus disease 2019 (COVID-19). The present case-control study was carried out on 295 patients diagnosed with COVID-19 (≥18 years old), including 104 critical patients (Intensive care unit [ICU] admission) and 191 COVID-19 patients without severe complications (Non-intensive care unit [Non-ICU] patients) as cases. Dietary intake was assessed by a 147-item, semi-quantitative food frequency questionnaire (FFQ). Logistic regression was performed to calculate the odds ratio (OR) and 95% confidence interval (CI) for the considered risk factors. Our outcomes (after multivariate adjustment) suggested that higher adherence to DAQS was significantly associated with a decreased risk of COVID-19 infection severity (OR = 0.12; 95% CI: 0.04-0.29, p < 0.001). Similar results were seen when analyzed by sex [men (OR = 0.02; 95% CI: 0.002-0.15, p < 0.001) and women (OR = 0.21; 95% CI: 0.06-0.68, p = 0.012)]. A significant association between vitamin D3 intake and decreased risk of COVID-19 severity (OR = 0.91; 95% CI: 0.89-0.94, p < 0.001) was also observed. Moreover, multivariate results revealed that there were no significant associations between vitamin C (OR = 1.00; 95% CI: 0.99-1.00, p = 0.067), vitamin E (OR = 0.98; 95% CI: 0.86-1.11, p = 0.798), zinc (OR = 1.02; 95% CI: 0.86-1.20, p = 0.805), and selenium (OR = 0.99; 95% CI: 0.99-1.00, p = 0.077) intakes with the risk of COVID-19 severity. However, subgroup analyses by sex suggested a significant association between vitamin C intake and the risk of COVID-19 infection severity in women (OR = 1.00; 95% CI: 1.00-1.00, p = 0.028). Our findings showed a negative association between DAQS adherence and the risk of COVID-19 infection severity. Our results may be used to develop potential dietary therapies to decrease COVID-19 severity.

The Role of Cluster of Differentiation 39 (CD39) and Purinergic Signaling Pathway in Viral Infections

CD39 is a marker of immune cells such as lymphocytes and monocytes. The CD39/CD73 pathway hydrolyzes ATP into adenosine, which has a potent immunosuppressive effect. CD39 regulates the function of a variety of immunologic cells through the purinergic signaling pathways. CD39+ T cells have been implicated in viral infections, including Human Immunodeficiency Virus (HIV), Cytomegalovirus (CMV), viral hepatitis, and Corona Virus Disease 2019 (COVID-19) infections. The expression of CD39 is an indicator of lymphocyte exhaustion, which develops during chronicity. During RNA viral infections, the CD39 marker can profile the populations of CD4+ T lymphocytes into two populations, T-effector lymphocytes, and T-regulatory lymphocytes, where CD39 is predominantly expressed on the T-regulatory cells. The level of CD39 in T lymphocytes can predict the disease progression, antiviral immune responses, and the response to antiviral drugs. Besides, the percentage of CD39 and CD73 in B lymphocytes and monocytes can affect the status of viral infections. In this review, we investigate the impact of CD39 and CD39-expressing cells on viral infections and how the frequency and percentage of CD39+ immunologic cells determine disease prognosis.

Erratum: Type 1 regulatory T cell-mediated tolerance in health and disease

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Type 1 regulatory T cell-mediated tolerance in health and disease

Type 1 regulatory T (Tr1) cells, in addition to other regulatory cells, contribute to immunological tolerance to prevent autoimmunity and excessive inflammation. Tr1 cells arise in the periphery upon antigen stimulation in the presence of tolerogenic antigen presenting cells and secrete large amounts of the immunosuppressive cytokine IL-10. The protective role of Tr1 cells in autoimmune diseases and inflammatory bowel disease has been well established, and this led to the exploration of this population as a potential cell therapy. On the other hand, the role of Tr1 cells in infectious disease is not well characterized, thus raising concern that these tolerogenic cells may cause general immune suppression which would prevent pathogen clearance. In this review, we summarize current literature surrounding Tr1-mediated tolerance and its role in health and disease settings including autoimmunity, inflammatory bowel disease, and infectious diseases.

Dynamics of Mycobacterium tuberculosis-Specific and Nonspecific Immune Responses in Women with Tuberculosis Infection during Pregnancy

The immune control of tuberculosis (TB) infection could be influenced by pregnancy. To elucidate this, we longitudinally characterized Mycobacterium tuberculosis (Mtb)-specific and nonspecific immune responses in women during pregnancy and postpartum. HIV-uninfected women without past or current active TB, and with blood samples available from the 1st/2nd trimester, 3rd trimester, and 9 months postpartum, were identified at Ethiopian antenatal care clinics. Twenty-two TB+ women and 10 TB- women, defined according to Mtb-stimulated interferon-γ levels (≥0.35 and <0.20 IU/mL, respectively, in the Quantiferon-TB Gold-Plus assay), were included in the study. Longitudinal dynamics of six cytokines (IL-1ra, IL-2, IP-10, MCP-2, MCP-3, and TGF-β1) were analyzed in supernatants from Mtb-stimulated and unstimulated whole blood. In TB+ women, Mtb-specific expression of IL-2 and IP-10 was higher at 3rd compared to 1st/2nd trimester (median 139 pg/mL versus 62 pg/mL, P = 0.006; 4,999 pg/mL versus 2,310 pg/mL, P = 0.031, respectively), whereas level of Mtb-triggered TGF-β1 was lower at 3rd compared to 1st/2nd trimester (-6.8 ng/mL versus 2.3 ng/mL, P = 0.020). Unstimulated IL-2, IP-10, and MCP-2 levels were increased postpartum, compared with those noted during pregnancy, in TB+ women. Additionally, postpartum levels of proinflammatory cytokines in unstimulated blood were higher in TB+ women, than in TB- women. None of the women developed active TB during follow-up. Taken together, dynamic changes of Mtb-specific cytokine expression revealed during the 3rd trimester in TB+ women indicate increased Mtb-antigen stimulation at later stages of pregnancy. This could reflect elevated bacterial activity, albeit without transition to active TB, during pregnancy. IMPORTANCE Tuberculosis (TB) is globally one of the most common causes of death, and a quarter of the world's population is estimated to have TB infection. The risk of active TB is increased in connection to pregnancy, a phenomenon that could be due to physiological immune changes. Here, we studied the effect of pregnancy on immune responses triggered in HIV-uninfected women with TB infection, by analyzing blood samples obtained longitudinally during pregnancy and after childbirth. We found that the dynamics of Mtb-specific and nonspecific immune responses changed during pregnancy, especially in later stages of pregnancy, although none of the women followed in this study developed active TB. This suggests that incipient TB, with elevated bacterial activity, occurs during pregnancy, but progression of infection appears to be counteracted by Mtb-specific immune responses. Thus, this study sheds light on immune control of TB during pregnancy, which could be of importance for future intervention strategies.

The Regulatory-T-Cell Memory Phenotype: What We Know

In immunology, the discovery of regulatory T (Treg) cells was a major breakthrough. Treg cells play a key role in pregnancy maintenance, in the prevention of autoimmune responses, and in the control of all immune responses, including responses to self cells, cancer, infection, and a transplant. It is currently unclear whether Treg cells are capable of long-term memory of an encounter with an antigen. Although the term “immunological memory” usually means an enhanced ability to protect the body from reinfection, the memory of the suppressive activity of Treg cells helps to avoid the state of generalized immunosuppression that may result from the second activation of the immune system. In this review, we would like to discuss the concept of regulatory memory and in which tissues memory Treg cells can perform their functions.

Moving to the Outskirts: Interplay Between Regulatory T Cells and Peripheral Tissues

Regulatory T cells (Tregs) restrain excessive immune responses and dampen inflammation. In addition to this classical immune suppressive role, Tregs in non-lymphoid tissues also promote tissue homeostasis, regeneration and repair. In this review, we outline our current understanding of how Tregs migrate to peripheral tissues and the factors required for their maintenance at these sites. We discuss the tissue-specific adaptations of Tregs at barrier and immuno-privileged sites and the mechanisms that regulate their function within these organs. Furthermore, we outline what is known about the interactions of Tregs with non-immune cells in the different peripheral tissues at steady state and upon challenge or tissue damage. A thorough understanding of the tissue-specific adaptations and functions of Tregs will potentially pave the way for therapeutic approaches targeting their regenerative role.

Virus-Specific Regulatory T Cells Persist as Memory in a Neurotropic Coronavirus Infection

Regulatory T cells (Tregs) are critical for regulating immunopathogenic responses in a variety of infections, including infection of mice with JHM strain of mouse hepatitis virus (JHMV), a neurotropic coronavirus that causes immune-mediated demyelinating disease. Although virus-specific Tregs are known to mitigate disease in this infection by suppressing pathogenic effector T cell responses of the same specificity, it is unclear whether these virus-specific Tregs form memory populations and persist similar to their conventional T cell counterparts of the same epitope specificity. Using congenically labeled JHMV-specific Tregs, we found that virus-specific Tregs persist long-term after murine infection, through at least 180 d postinfection and stably maintain Foxp3 expression. We additionally demonstrate that these cells are better able to proliferate and inhibit virus-specific T cell responses postinfection than naive Tregs of the same specificity, further suggesting that these cells differentiate into memory Tregs upon encountering cognate Ag. Taken together, these data suggest that virus-specific Tregs are able to persist long-term in the absence of viral Ag as memory Tregs.

Evidences suggesting a possible role of Vitamin D in COVID 19: The missing link

The severe acute respiratory syndrome coronavirus 2 is spreading like wildfire with no specific recommended treatment in sight. While some risk factors such as the presence of comorbidities, old age, and ethnicity have been recognized, not a lot is known about who the virus will strike first or impact more. In this hopeless scenario, exploration of time-tested facts about viral infections, in general, seems to be a sound basis to prop further research upon. The fact that immunity and its various determinants (e.g., micronutrients, sleep, and hygiene) have a crucial role to play in the defense against invading organisms, may be a good starting point for commencing research into these as yet undisclosed territories. Herein, the excellent immunomodulatory, antiviral, and anti-inflammatory roles of Vitamin D necessitate thorough investigation, particularly in COVID-19 perspective. This article reviews mechanisms and evidence suggesting the role Vitamin D plays in people infected by the newly identified COVID-19 virus. For this review, we searched the databases of Medline, PubMed, and Embase. We studied several meta-analyses and randomized controlled trials evaluating the role of Vitamin D in influenza and other contagious viral infections. We also reviewed the circumstantial and anecdotal evidence connecting Vitamin D with COVID-19 emerging recently. Consequently, it seems logical to conclude that the immune-enhancing, antiviral, anti-inflammatory, and lung-protective role of Vitamin D can be potentially lifesaving. Hence, Vitamin D deserves exhaustive exploration through rigorously designed and controlled scientific trials. Using Vitamin D as prophylaxis and/or chemotherapeutic treatment of COVID-19 infection is an approach worth considering. In this regard, mass assessment and subsequent supplementation can be tried, especially considering the mechanistic evidence in respiratory infections, low potential for toxicity, and widespread prevalence of the deficiency of Vitamin D affecting many people worldwide.

The role of influenza A virus-induced hypercytokinemia

Influenza viruses are one of the leading causes of respiratory tract infections in humans and their newly emerging and re-emerging virus strains are responsible for seasonal epidemics and occasional pandemics, leading to a serious threat to global public health systems. The poor clinical outcome and pathogenesis during influenza virus infection in humans and animal models are often associated with elevated proinflammatory cytokines and chemokines production, which is also known as hypercytokinemia or "cytokine storm", that precedes acute respiratory distress syndrome (ARDS) and often leads to death. Although we still do not fully understand the complex nature of cytokine storms, the use of immunomodulatory drugs is a promising approach for treating hypercytokinemia induced by an acute viral infection, including highly pathogenic avian influenza virus infection and Coronavirus Disease 2019 (COVID-19). This review aims to discuss the immune responses and cytokine storm pathology induced by influenza virus infection and also summarize alternative experimental strategies for treating hypercytokinemia caused by influenza virus.

Tbx21 and Foxp3 Are Epigenetically Stabilized in T-Bet+ Tregs That Transiently Accumulate in Influenza A Virus-Infected Lungs

During influenza A virus (IAV) infections, CD4⁺ T cell responses within infected lungs mainly involve T helper 1 (Th1) and regulatory T cells (Tregs). Th1-mediated responses favor the co-expression of T-box transcription factor 21 (T-bet) in Foxp3⁺ Tregs, enabling the efficient Treg control of Th1 responses in infected tissues. So far, the exact accumulation kinetics of T cell subsets in the lungs and lung-draining lymph nodes (dLN) of IAV-infected mice is incompletely understood, and the epigenetic signature of Tregs accumulating in infected lungs has not been investigated. Here, we report that the total T cell and the two-step Treg accumulation in IAV-infected lungs is transient, whereas the change in the ratio of CD4⁺ to CD8⁺ T cells is more durable. Within lungs, the frequency of Tregs co-expressing T-bet is steadily, yet transiently, increasing with a peak at Day 7 post-infection. Interestingly, T-bet⁺ Tregs accumulating in IAV-infected lungs displayed a strongly demethylated Tbx21 locus, similarly as in T-bet⁺ conventional T cells, and a fully demethylated Treg-specific demethylated region (TSDR) within the Foxp3 locus. In summary, our data suggest that T-bet⁺ but not T-bet^- Tregs are epigenetically stabilized during IAV-induced infection in the lung.

Influenza virus infection selectively triggers the accumulation and persistence of more potent Helios-expressing Foxp3+ regulatory T cells in the lungs

Foxp3⁺ regulatory T cells (Tregs) represent a special lineage of CD4⁺ T cells. Analysis of Treg response during primary and secondary influenza virus infection clearly demonstrates a robust accumulation of Tregs into the infected lungs and the existence of a population of long-lived antigen-specific memory Tregs in the same tissues after resolution of the infection. However, it remains unknown whether these Tregs co-express Helios, a member of the Ikaros transcription factor family. In this study, Foxp3⁺ Helios⁺ and Foxp3⁺ Helios^- Tregs in the lungs, mLNs and spleens of influenza virus-infected and uninfected control mice were tracked. The data show that while there is a co-existence of Foxp3⁺ Helios⁺ and Foxp3⁺ Helios^- Tregs in the tissues, the accumulated Tregs in the lungs and lung-draining mediastinal lymph nodes (mLNs) of the infected mice are highly enriched for Foxp3⁺ Helios⁺ cells. It was further demonstrated that, after the clearance of primary infection, Foxp3⁺ Helios⁺ cells have the ability to persist in the tissues over their Helios^- counterparts. More importantly, Foxp3⁺ Helios⁺ Tregs accumulated in an accelerated kinetics during recall response to reinfection. In vitro analysis of Treg suppressive function revealed that Foxp3⁺ Helios⁺ Tregs are more capable of suppressing influenza virus-specific CD8⁺ T cell activation, cytokine production and proliferation. Together, the data provide new insights into Treg responses during primary and secondary influenza virus infection and suggest that Foxp3⁺ Helios⁺ Tregs predominantly drive the Treg responses.

Nutritional immunity: the impact of metals on lung immune cells and the airway microbiome during chronic respiratory disease

Nutritional immunity is the sequestration of bioavailable trace metals such as iron, zinc and copper by the host to limit pathogenicity by invading microorganisms. As one of the most conserved activities of the innate immune system, limiting the availability of free trace metals by cells of the immune system serves not only to conceal these vital nutrients from invading bacteria but also operates to tightly regulate host immune cell responses and function. In the setting of chronic lung disease, the regulation of trace metals by the host is often disrupted, leading to the altered availability of these nutrients to commensal and invading opportunistic pathogenic microbes. Similarly, alterations in the uptake, secretion, turnover and redox activity of these vitally important metals has significant repercussions for immune cell function including the response to and resolution of infection. This review will discuss the intricate role of nutritional immunity in host immune cells of the lung and how changes in this fundamental process as a result of chronic lung disease may alter the airway microbiome, disease progression and the response to infection.

Influenza sequelae: from immune modulation to persistent alveolitis

Acute influenza virus infections are a global public health concern accounting for millions of illnesses worldwide ranging from mild to severe with, at time, severe complications. Once an individual is infected, the immune system is triggered in response to the pathogen. This immune response can be beneficial ultimately leading to the clearance of the viral infection and establishment of immune memory mechanisms. However, it can be detrimental by increasing susceptibility to secondary bacterial infections and resulting in permanent changes to the lung architecture, in the form of fibrotic sequelae. Here, we review influenza associated bacterial super-infection, the formation of T-cell memory, and persistent lung injury resulting from influenza infection.

Does vitamin D deficiency increase the severity of COVID-19?

The severity of coronavirus 2019 infection (COVID-19) is determined by the presence of pneumonia, severe acute respiratory distress syndrome (SARS-CoV-2), myocarditis, microvascular thrombosis and/or cytokine storms, all of which involve underlying inflammation. A principal defence against uncontrolled inflammation, and against viral infection in general, is provided by T regulatory lymphocytes (Tregs). Treg levels have been reported to be low in many COVID-19 patients and can be increased by vitamin D supplementation. Low vitamin D levels have been associated with an increase in inflammatory cytokines and a significantly increased risk of pneumonia and viral upper respiratory tract infections. Vitamin D deficiency is associated with an increase in thrombotic episodes, which are frequently observed in COVID-19. Vitamin D deficiency has been found to occur more frequently in patients with obesity and diabetes. These conditions are reported to carry a higher mortality in COVID-19. If vitamin D does in fact reduce the severity of COVID-19 in regard to pneumonia/ARDS, inflammation, inflammatory cytokines and thrombosis, it is our opinion that supplements would offer a relatively easy option to decrease the impact of the pandemic.