Type 1 Treg cells promote the generation of CD8+ tissue-resident memory T cells.

Tissue-resident memory T (TRM) cells, functionally distinct from circulating memory T cells, have a critical role in protective immunity in tissues, are more efficacious when elicited after vaccination and yield more effective antitumor immunity, yet the signals that direct development of TRM cells are incompletely understood. Here we show that type 1 regulatory T (Treg) cells, which express the transcription factor T-bet, promote the generation of CD8+ TRM cells. The absence of T-bet-expressing type 1 Treg cells reduces the presence of TRM cells in multiple tissues and increases pathogen burden upon infectious challenge. Using infection models, we show that type 1 Treg cells are specifically recruited to local inflammatory sites via the chemokine receptor CXCR3. Close proximity with effector CD8+ T cells and Treg cell expression of integrin-ß8 endows the bioavailability of transforming growth factor-ß in the microenvironment, thereby promoting the generation of CD8+ TRM cells.

Interleukin 17 is a chief orchestrator of immunity.

Increased understanding of the biology of interleukin 17 (IL-17) has revealed that this cytokine is a central player in immunity at the sites most exposed to microorganisms. Although it has been strongly associated with immunopathology, IL-17 also has an important role in host defense. The regulation of IL-17 secretion seems to be shared among various cell types, each of which can concomitantly secrete additional products. IL-17 has only modest activity on its own; its impact in immunity arises from its synergistic action with other factors, its self-sustaining feedback loop and, in some cases, its role as a counterpart of interferon-γ (IFN-γ). Together these attributes provide a robust response against microorganisms, but they can equally contribute to immune pathology. Here we focus on a discussion of the role of IL-17 during infection.

Feeding immunity: skepticism, delicacies and delights.

Immunologists studying the relationship between nutrition and immunological function face many challenges. We discuss here some of the historical skepticism with which nutritional research has often been faced and the complexities that need to be overcome in order to provide meaningful mechanistic insights.

Inflammation-induced formation of fat-associated lymphoid clusters.

Fat-associated lymphoid clusters (FALCs) are a type of lymphoid tissue associated with visceral fat. Here we found that the distribution of FALCs was heterogeneous, with the pericardium containing large numbers of these clusters. FALCs contributed to the retention of B-1 cells in the peritoneal cavity through high expression of the chemokine CXCL13, and they supported B cell proliferation and germinal center differentiation during peritoneal immunological challenges. FALC formation was induced by inflammation, which triggered the recruitment of myeloid cells that expressed tumor-necrosis factor (TNF) necessary for signaling via the TNF receptors in stromal cells. Natural killer T cells (NKT cells) restricted by the antigen-presenting molecule CD1d were likewise required for the inducible formation of FALCs. Thus, FALCs supported and coordinated the activation of innate B cells and T cells during serosal immune responses.

Host and microbes date exclusively.

The significant impact of commensal microorganisms on metabolism, susceptibility to disease, and general well-being of their host has become increasingly clear in recent years. Chung et al. now show that the maturation and performance of the immune system depend on organism-specific bacterial species.

Th17 Cells Require You to Chew before You Swallow.

How immunity is regulated at distinct epithelial tissues that vary in microbial occupancy and environmental and tissue specific cues isn't clear. Dutzan et al. (2017) report that mechanical-derived signals, not those from micro-organisms, are key to maintaining interleukin-17-expressing T helper (Th17) cells at the oral epithelia.

Exogenous stimuli maintain intraepithelial lymphocytes via aryl hydrocarbon receptor activation.

The body's surfaces form the interface with the external environment, protecting the host. These epithelial barriers are also colonized by a controlled diversity of microorganisms, disturbances of which can give rise to disease. Specialized intraepithelial lymphocytes (IELs), which reside at these sites, are important as a first line of defense as well as in epithelial barrier organization and wound repair. We show here that the aryl hydrocarbon receptor (AhR) is a crucial regulator in maintaining IEL numbers in both the skin and the intestine. In the intestine, AhR deficiency or the lack of AhR ligands compromises the maintenance of IELs and the control of the microbial load and composition, resulting in heightened immune activation and increased vulnerability to epithelial damage. AhR activity can be regulated by dietary components, such as those present in cruciferous vegetables, providing a mechanistic link between dietary compounds, the intestinal immune system, and the microbiota.

Intestinal tissue-resident T cell activation depends on metabolite availability.

The metabolic capacity of many cells is tightly regulated and can adapt to changes in metabolic resources according to environmental changes. Tissue-resident memory (TRM) CD8+ T cells are one of the most abundant T cell populations and offer rapid protection against invading pathogens, especially at the epithelia. TRM cells metabolically adapt to their tissue niche, such as the intestinal epithelial barrier. In the small intestine, the types of TRM cells are intraepithelial lymphocytes (IELs), which contain high levels of cytotoxic molecules and express activation markers, suggesting a heightened state of activation. We hypothesize that the tissue environment may determine IEL activity. We show that IEL activation, in line with its semiactive status, is metabolically faster than circulating CD8+ T cells. IEL glycolysis and oxidative phosphorylation (OXPHOS) are interdependently regulated and are dependent on rapid access to metabolites from the environment. IELs are restrained by local availability of metabolites, but, especially, glucose levels determine their activity. Importantly, this enables functional control of intestinal TRM cells by metabolic means within the fragile environment of the intestinal epithelial barrier.

De Novo Human Angiotensin-Converting Enzyme 2 Decoy NL-CVX1 Protects Mice From Severe Disease After Severe Acute Respiratory Syndrome Coronavirus 2 Infection.

The emergence of novel variants of severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) underscores the need to investigate alternative approaches to prevent infection and treat patients with coronavirus disease 2019. Here, we report the preclinical efficacy of NL-CVX1, a de novo decoy that blocks virus entry into cells by binding with nanomolar affinity and high specificity to the receptor-binding domain of the SARS-CoV-2 spike protein. Using a transgenic mouse model of SARS-CoV-2 infection, we showed that a single prophylactic intranasal dose of NL-CVX1 conferred complete protection from severe disease following SARS-CoV-2 infection. Multiple therapeutic administrations of NL-CVX1 also protected mice from succumbing to infection. Finally, we showed that infected mice treated with NL-CVX1 developed both anti-SARS-CoV-2 antibodies and memory T cells and were protected against reinfection a month after treatment. Overall, these observations suggest NL-CVX1 is a promising therapeutic candidate for preventing and treating severe SARS-CoV-2 infections.

Longitudinal SARS-CoV-2 seroprevalence in Portugal and antibody maintenance 12 months after infection.

During the COVID-19 pandemic, Portugal has experienced three distinct SARS-CoV-2 infection waves. We previously documented the prevalence of SARS-CoV-2 immunity, measured by specific antibodies, in September 2020, 6 months after the initial moderate wave. Here, we show the seroprevalence changes 6 months later, up to the second week of March 2021, shortly following the third wave, which was one of the most severe in the world, and 2 months following the start of the vaccination campaign. A longitudinal epidemiological study was conducted, with a stratified quota sample of the Portuguese population. Serological testing was performed, including ELISA determination of antibody class and titers. The proportion of seropositives, which was 2.2% in September 2020, rose sharply to 17.3% (95% CI: 15.8-18.8%) in March 2021. Importantly, circulating IgG and IgA antibody levels were very stable 6 months after the initial determination and up to a year after initial infection, indicating long-lasting infection immunity against SARS-CoV-2. Moreover, vaccinated people had higher IgG levels from 3 weeks post-vaccination when compared with previously infected people at the same time post-infection.

SARS-CoV-2 clearance after breakthrough infection correlates with fit and happy T cells.

Koutsakos et al. have recently published an article showing that SARS-CoV-2 breakthrough infection results in robust naïve and memory T cell activation, and the activity of CD8 T cells strongly correlates with viral clearance.

Fate mapping of IL-17-producing T cells in inflammatory responses.

Here we describe a reporter mouse strain designed to map the fate of cells that have activated interleukin 17A (IL-17A). We found that IL-17-producing helper T cells (T(H)17 cells) had distinct plasticity in different inflammatory settings. Chronic inflammatory conditions in experimental autoimmune encephalomyelitis (EAE) caused a switch to alternative cytokines in T(H)17 cells, whereas acute cutaneous infection with Candida albicans did not result in the deviation of T(H)17 cells to the production of alternative cytokines, although IL-17A production was shut off in the course of the infection. During the development of EAE, interferon-γ (IFN-γ) and other proinflammatory cytokines in the spinal cord were produced almost exclusively by cells that had produced IL-17 before their conversion by IL-23 ('ex-T(H)17 cells'). Thus, this model allows the actual functional fate of effector T cells to be related to T(H)17 developmental origin regardless of IL-17 expression.

Humoral and T cell responses to SARS-CoV-2 reveal insights into immunity during the early pandemic period in Pakistan.

BACKGROUND: Protection against SARS-CoV-2 is mediated by humoral and T cell responses. Pakistan faced relatively low morbidity and mortality from COVID-19 through the pandemic. To examine the role of prior immunity in the population, we studied IgG antibody response levels, virus neutralizing activity and T cell reactivity to Spike protein in a healthy control group (HG) as compared with COVID-19 cases and individuals from the pre-pandemic period (PP). METHODS: HG and COVID-19 participants were recruited between October 2020 and May 2021. Pre-pandemic sera was collected before 2018. IgG antibodies against Spike and its Receptor Binding Domain (RBD) were determined by ELISA. Virus neutralization activity was determined using a PCR-based micro-neutralization assay. T cell - IFN-γ activation was assessed by ELISpot. RESULTS: Overall, the magnitude of anti-Spike IgG antibody levels as well as seropositivity was greatest in COVID-19 cases (90%) as compared with HG (39.8%) and PP (12.2%). During the study period, Pakistan experienced three COVID-19 waves. We observed that IgG seropositivity to Spike in HG increased from 10.3 to 83.5% during the study, whilst seropositivity to RBD increased from 7.5 to 33.3%. IgG antibodies to Spike and RBD were correlated positively in all three study groups. Virus neutralizing activity was identified in sera of COVID-19, HG and PP. Spike reactive T cells were present in COVID-19, HG and PP groups. Individuals with reactive T cells included those with and without IgG antibodies to Spike. CONCLUSIONS: Antibody and T cell responses to Spike protein in individuals from the pre-pandemic period suggest prior immunity against SARS-CoV-2, most likely from cross-reactive responses. The rising seroprevalence observed in healthy individuals through the pandemic without known COVID-19 may be due to the activation of adaptive immunity from cross-reactive memory B and T cells. This may explain the more favourable COVID-19 outcomes observed in this population.

Loss of Phosphatidylinositol 3-Kinase Activity in Regulatory T Cells Leads to Neuronal Inflammation.

Class I PI3K enzymes are critical for the maintenance of effective immunity. In T cells, PI3Kα and PI3Kδ are activated by the TCR and costimulatory receptors, whereas PI3Kγ is activated by G protein-coupled chemokine receptors. PI3Kδ is a key regulator of regulatory T (Treg) cell function. PI3K isoform-selective inhibitors are in development for the treatment of diseases associated with immune dysregulation, including chronic inflammatory conditions, cancer, and autoimmune diseases. Idelalisib (PI3Kδ), alpelisib (PI3Kα), duvelisib (PI3Kδ/γ), and copanlisib (pan-PI3K) have recently been approved for use in cancer treatment. Although effective, these therapies often have severe side effects associated with immune dysregulation and, in particular, loss of Treg cells. Therefore, it is important to gain a better understanding of the relative contribution of different PI3K isoforms under homeostatic and inflammatory conditions. Experimental autoimmune encephalitis is a mouse model of T cell-driven CNS inflammation, in which Treg cells play a key protective role. In this study, we show that PI3Kδ is required to maintain normal Treg cell development and phenotype under homeostatic conditions but that loss of PI3Kδ alone in Treg cells does not lead to autoimmunity. However, combined loss of PI3Kα and PI3Kδ signaling resulted in increased experimental autoimmune encephalitis disease severity. Moreover, mice lacking PI3Kα and PI3Kδ in Treg cells developed spontaneous peripheral nerve inflammation. These results show a key role for PI3K signaling in Treg cell-mediated protection against CNS inflammation.

Prevalence of SARS-CoV-2 Antibodies after First 6 Months of COVID-19 Pandemic, Portugal.

In September 2020, we tested 13,398 persons in Portugal for antibodies against severe acute respiratory syndrome coronavirus 2 by using a quota sample stratified by age and population density. We found a seroprevalence of 2.2%, 3-4 times larger than the official number of cases at the end of the first wave of the pandemic.

Humoral Immune Response of SARS-CoV-2-Infected Patients with Cancer: Influencing Factors and Mechanisms.

BACKGROUND: Severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2)-infected patients with cancer show worse outcomes compared with patients without cancer. The humoral immune response (HIR) of patients with cancer against SARS-CoV-2 is not well characterized. To better understand it, we conducted a serological study of hospitalized patients with cancer infected with SARS-CoV-2. MATERIALS AND METHODS: This was a unicentric, retrospective study enrolling adult patients with SARS-CoV-2 admitted to a central hospital from March 15 to June 17, 2020, whose serum samples were quantified for anti-SARS-CoV-2 receptor-binding domain or spike protein IgM, IgG, and IgA antibodies. The aims of the study were to assess the HIR to SARS-CoV-2; correlate it with different cancer types, stages, and treatments; clarify the interplay between the HIR and clinical outcomes of patients with cancer; and compare the HIR of SARS-CoV-2-infected patients with and without cancer. RESULTS: We included 72 SARS-CoV-2-positive subjects (19 with cancer, 53 controls). About 90% of controls revealed a robust serological response. Among patients with cancer, a strong response was verified in 57.9%, with 42.1% showing a persistently weak response. Treatment with chemotherapy within 14 days before positivity was the only factor statistically shown to be associated with persistently weak serological responses among patients with cancer. No significant differences in outcomes were observed between patients with strong and weak responses. All IgG, IgM, IgA, and total Ig antibody titers were significantly lower in patients with cancer compared with those without. CONCLUSION: A significant portion of patients with cancer develop a proper HIR. Recent chemotherapy treatment may be associated with weak serological responses among patients with cancer. Patients with cancer have a weaker SARS-CoV-2 antibody response compared with those without cancer. IMPLICATIONS FOR PRACTICE: These results place the spotlight on patients with cancer, particularly those actively treated with chemotherapy. These patients may potentially be more vulnerable to severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) infection, so it is important to provide oncologists further theoretical support (with concrete examples and respective mechanistic correlations) for the decision of starting, maintaining, or stopping antineoplastic treatments (particularly chemotherapy) not only on noninfected but also on infected patients with cancer in accordance with cancer type, stage and prognosis, treatment agents, treatment setting, and SARS-CoV-2 infection risks.

Seroprevalence of anti-SARS-CoV-2 antibodies in COVID-19 patients and healthy volunteers up to 6 months post disease onset.

SARS-CoV-2 has emerged as a human pathogen, causing clinical signs, from fever to pneumonia-COVID-19-but may remain mild or asymptomatic. To understand the continuing spread of the virus, to detect those who are and were infected, and to follow the immune response longitudinally, reliable and robust assays for SARS-CoV-2 detection and immunological monitoring are needed. We quantified IgM, IgG, and IgA antibodies recognizing the SARS-CoV-2 receptor-binding domain (RBD) or the Spike (S) protein over a period of 6 months following COVID-19 onset. We report the detailed setup to monitor the humoral immune response from over 300 COVID-19 hospital patients and healthcare workers, 2500 University staff, and 198 post-COVID-19 volunteers. Anti-SARS-CoV-2 antibody responses follow a classic pattern with a rapid increase within the first three weeks after symptoms. Although titres reduce subsequently, the ability to detect anti-SARS-CoV-2 IgG antibodies remained robust with confirmed neutralization activity for up to 6 months in a large proportion of previously virus-positive screened subjects. Our work provides detailed information for the assays used, facilitating further and longitudinal analysis of protective immunity to SARS-CoV-2. Importantly, it highlights a continued level of circulating neutralising antibodies in most people with confirmed SARS-CoV-2.

Regulation of Oxygen Homeostasis at the Intestinal Epithelial Barrier Site.

The unique biology of the intestinal epithelial barrier is linked to a low baseline oxygen pressure (pO2), characterised by a high rate of metabolites circulating through the intestinal blood and the presence of a steep oxygen gradient across the epithelial surface. These characteristics require tight regulation of oxygen homeostasis, achieved in part by hypoxia-inducible factor (HIF)-dependent signalling. Furthermore, intestinal epithelial cells (IEC) possess metabolic identities that are reflected in changes in mitochondrial function. In recent years, it has become widely accepted that oxygen metabolism is key to homeostasis at the mucosae. In addition, the gut has a vast and diverse microbial population, the microbiota. Microbiome-gut communication represents a dynamic exchange of mediators produced by bacterial and intestinal metabolism. The microbiome contributes to the maintenance of the hypoxic environment, which is critical for nutrient absorption, intestinal barrier function, and innate and/or adaptive immune responses in the gastrointestinal tract. In this review, we focus on oxygen homeostasis at the epithelial barrier site, how it is regulated by hypoxia and the microbiome, and how oxygen homeostasis at the epithelium is regulated in health and disease.

Transforming growth factor-beta 'reprograms' the differentiation of T helper 2 cells and promotes an interleukin 9-producing subset.

Since the discovery of T helper type 1 and type 2 effector T cell subsets 20 years ago, inducible regulatory T cells and interleukin 17 (IL-17)-producing T helper cells have been added to the 'portfolio' of helper T cells. It is unclear how many more effector T cell subsets there may be and to what degree their characteristics are fixed or flexible. Here we show that transforming growth factor-beta, a cytokine at the center of the differentiation of IL-17-producing T helper cells and inducible regulatory T cells, 'reprograms' T helper type 2 cells to lose their characteristic profile and switch to IL-9 secretion or, in combination with IL-4, drives the differentiation of 'T(H)-9' cells directly. Thus, transforming growth factor-beta constitutes a regulatory 'switch' that in combination with other cytokines can 'reprogram' effector T cell differentiation along different pathways.

Metabolic wiring of murine T cell and intraepithelial lymphocyte maintenance and activation.

Adaptive immunity critically depends on cell migration combined with clonal selection and rapid expansion of rare lymphocytes recognising their cognate antigen in secondary lymphoid organs. It has since become apparent that large populations of T cells are maintained in tissues, which do not migrate throughout the body and do not require clonal expansion. Murine intraepithelial lymphocytes (IELs), located in the skin and small intestines, are maintained in a state of semi-activation, in marked contrast to the quiescent condition naive and memory lymphocytes are kept in. The poised activation state of IELs, their location in the top layers of barrier organs and close bidirectional interactions with epithelial cells suggests IELs are part of a sophisticated strategy of immune-surveillance and compartmentalisation of immune responses. Recent murine studies have reemphasised the influence of metabolism in T-cell activation and differentiation, with different metabolic make up of naive, effector and memory T cells. Here we highlight and discuss some of the current insights on immunometabolism of IELs, with emphasis on novel data contrasting how IELs may be maintained in a semi-activated state and may become fully functional compared with conventional T cells.