From trained immunity in allergy to trained immunity-based allergen vaccines

Innate immune cells experience long lasting metabolic and epigenetic changes after an encounter with specific stimuli. This facilitates enhanced immune responses upon secondary exposition to both the same and unrelated pathogens, a process termed trained immunity. Trained immunity-based vaccines (TIbV) are vaccines able to induce innate immune memory, thus conferring heterologous protection against a broad range of pathogens. While trained immunity has been well documented in the context of infections and multiple immune-mediated diseases, the role of innate immune memory and its contribution to the initiation and maintenance of chronic allergic diseases remains poorly understood. Over the last years, different studies attempting to uncover the role of trained immunity in allergy have emerged. Exposition to environmental factors impacting allergy development such as allergens or viruses induces the reprogramming of innate immune cells to acquire a more pro-inflammatory phenotype in the context of asthma or food allergy. Several studies have convincingly demonstrated that prevention of viral infections using TIbV contributes to reduce wheezing attacks in children, which represent a high-risk factor for asthma development later in life. Innate immune cells trained with specific stimuli might also acquire anti-inflammatory features and promote tolerance, which may have important implications for chronic inflammatory diseases such as allergies. Recent findings showed that allergoid-mannan conjugates, which are next generation vaccines for allergen-specific immunotherapy (AIT), are able to reprogram monocytes into tolerogenic dendritic cells by mechanisms depending on metabolic and epigenetic rewiring. A better understanding of the underlying mechanisms of trained immunity in allergy will pave the way for the design of novel trained immunity-based allergen vaccines as potential alternative strategies for the prevention and treatment of allergic diseases.     

The role of Toll-like receptor 10 in modulation of trained immunity

Toll-like receptor 10 (TLR10) is the only member of the human Toll-like receptor family with an inhibitory function on the induction of innate immune responses and inflammation. However, its role in the modulation of trained immunity (innate immune memory) is unknown. In the present study, we assessed whether TLR10 modulates the induction of trained immunity induced by β-glucan or bacillus Calmette–Guérin (BCG). Interleukin 10 receptor antagonist production was increased upon activation of TLR10 ex vivo after BCG vaccination, and TLR10 protein expression on monocytes was increased after BCG vaccination, whereas anti-TLR10 antibodies did not significantly modulate β-glucan or BCG-induced trained immunity in vitro. A known immunomodulatory TLR10 missense single-nucleotide polymorphism (rs11096957) influenced trained immunity responses by β-glucan or BCG in vitro. However, the in vivo induction of trained immunity by BCG vaccination was not influenced by TLR10 polymorphisms. In conclusion, TLR10 has a limited, non-essential impact on the induction of trained immunity in humans.     

The role of the interleukin-1 family in trained immunity

Immunological memory was long considered a trait exclusive to cells of the adaptive immune system. However, recent studies have shown that after activation of the innate immune system, innate immune cells may undergo long-term functional reprogramming characterized by the ability to mount either a stronger or attenuated inflammatory response upon reactivation. This phenomenon, which has been termed trained immunity and is a de facto innate immune memory, is regulated by a network of integrated metabolic and epigenetic rewiring. The endogenous mediators that modulate trained immunity in the host are only partially understood, but increasing evidence supports the concept that the interleukin (IL)-1 family of cytokines plays an important role. In this review, we will highlight key findings from studies that provide insight into the multifaceted roles of members of the IL-1 family for trained immunity. Finally, we will discuss how the recent advances of our understanding on the role of IL-1 cytokines in this field may lead to new therapeutic strategies for treatment of common conditions, such as IL-1-driven autoinflammatory diseases.     

Early-life EV-A71 infection augments allergen-induced airway inflammation in asthma through trained macrophage immunity

Virus-induced asthma is prevalent among children, but its underlying mechanisms are unclear. Accumulated evidence indicates that early-life respiratory virus infection increases susceptibility to allergic asthma. Nonetheless, the relationship between systemic virus infections, such as enterovirus infection, and the ensuing effects on allergic asthma development is unknown. Early-life enterovirus infection was correlated with higher risks of allergic diseases in children. Adult mice exhibited exacerbated mite allergen-induced airway inflammation following recovery from EV-A71 infection in the neonatal period. Bone marrow-derived macrophages (BMDMs) from recovered EV-A71-infected mice showed sustained innate immune memory (trained immunity) that could drive naïve T helper cells toward Th2 and Th17 cell differentiation when in contact with mites. Adoptive transfer of EV-A71-trained BMDMs induced augmented allergic inflammation in naïve recipient mice, which was inhibited by 2-deoxy-D-glucose (2-DG) pretreatment, suggesting that trained macrophages following enterovirus infection are crucial in the progression of allergic asthma later in life.     

BCG-induced trained immunity in macrophage: reprograming of glucose metabolism

Abstract

Memory is no longer a privilege of adaptive immunity. Innate immune cells can exhibit a long-term immune activation after infection or vaccination, which is called “trained immunity.” In addition to defense against mycobacterial infection, BCG-induced trained immunity can also exert nonspecific protection, which is regulated by metabolic rewiring and epigenetic reprograming. Enhanced glycolysis and glutamine-driven tricarboxylic acid cycle have been proven to be important metabolic pathways for trained immunity induced by BCG, which is dependent on Akt/mTOR pathway.     

The role of neutrophils in trained immunity

The principle of trained immunity represents innate immune memory due to sustained, mainly epigenetic, changes triggered by endogenous or exogenous stimuli in bone marrow (BM) progenitors (central trained immunity) and their innate immune cell progeny, thereby triggering elevated responsiveness against secondary stimuli. BM progenitors can respond to microbial and sterile signals, thereby possibly acquiring trained immunity-mediated long-lasting alterations that may shape the fate and function of their progeny, for example, neutrophils. Neutrophils, the most abundant innate immune cell population, are produced in the BM from committed progenitor cells in a process designated granulopoiesis. Neutrophils are the first responders against infectious or inflammatory challenges and have versatile functions in immunity. Together with other innate immune cells, neutrophils are effectors of peripheral trained immunity. However, given the short lifetime of neutrophils, their ability to acquire immunological memory may lie in the central training of their BM progenitors resulting in generation of reprogrammed, that is, “trained”, neutrophils. Although trained immunity may have beneficial effects in infection or cancer, it may also mediate detrimental outcomes in chronic inflammation. Here, we review the emerging research area of trained immunity with a particular emphasis on the role of neutrophils and granulopoiesis.     

The perplexing question of trained immunity vs adaptive memory in COVID-19

The wide spectrum of symptoms observed in coronavirus disease 2019 appears to defy explanation. Apart from geographic limitation to people with prior exposure to other coronaviruses and air pollutants, inflammatory comorbidities and older ages are also among the main factors of susceptibility to severe illness. The unusual epidemiological data pointed out in children and African territories have revealed new insights in host-pathogen interplay with more focus on epigenetic regulation of cognitive compartments belonging to innate immunity. Should trained immunity be proven to be involved in timely immune responsiveness against severe acute respiratory syndrome coronavirus 2 and that adaptive memory could be detrimental, both treatment regimens and vaccine design will tremendously change accordingly with more focus on upper respiratory tissue innate immunity to subdue this threat underway.     

MYD88‐dependent and ‐independent activation of TREM‐1 via specific TLR ligands

Triggering receptor expressed on myeloid cells (TREM)‐1 plays an important role in myeloid cell‐activated inflammatory responses. Although TLR ligands such as LPS and lipoteichoic acid have been shown to upregulate TREM‐1 expression in macrophage and neutrophils, the role of specific TLR in inducing the expression of TREM‐1 remains unclear. In this study, we investigated whether the presence of TLR is necessary for the expression of TREM‐1. We show that BM‐derived macrophages from TLR4 and TLR2 KO mice failed to induce expression of TREM‐1 message and protein in response to their specific ligands. Interestingly, the expression of TREM‐1 in response to LPS is not altered in myeloid differentiation factor 88 (MyD88) KO macrophages, suggesting that downstream of TLR a MyD88‐independent pathway induces the expression of TREM‐1. Inhibiting toll/IL‐1R domain‐containing adaptor‐inducing IFN‐β (TRIF) expression by siRNA decreased TREM‐1 expression in response to LPS, suggesting that the expression of TREM‐1 in response to LPS was mediated by the TRIF signaling pathway. On the other hand, the expression of TREM‐1 in response to lipoteichoic acid is dependent on MyD88 expression. These data indicate that the expression of TREM‐1 in response to TLR ligands occurs secondary to downstream signaling events and that the presence of TLR is necessary for the expression of TREM‐1 in response to their specific ligands. However, the downstream signaling required for the expression of TREM‐1 is dependent on the stimulus and the surface receptor through which the signaling is initiated.     

B‐1‐cell subpopulations contribute differently to gut immunity

In mice, B‐1 (B1a/B1b) cells are mainly located in the peritoneal cavity. B‐1 cells are well known for their role in the early stages of Ab‐mediated immune responses against pathogenic invasion as well as for the production of natural IgM antibodies. Although such B cells have been claimed to give rise to intestinal plasma cells producing IgA, a clear role of B‐1 cells in IgA production in the gut‐associated tissues is still not defined. Here, we employed the transgenic L2 mouse model characterized by the lack of B‐2 cells and presence of B‐1 cells as major B‐cell subpopulation. The oligoclonality of the Ab repertoire in this mouse allowed us to take typical B1a cell VH sequences as indicators of the presence of IgM‐producing B‐1a cells in Peyer's patches as well as in lamina propria. However, amongst the IgAVH sequences recovered from the same tissues, none of the sequences showed B1a‐cell specificity. Interestingly, all IgAVH sequences derived from the lamina propria of L2 mice displayed extensive numbers of nucleotide exchanges, indicating somatic hypermutation, and affinity maturation. This suggests that the contribution of natural unmutated IgA by B‐1a cells to intestinal immunity is negligible.     

Immunometabolic circuits in trained immunity

The classical view that only adaptive immunity can build immunological memory has recently been challenged. Both in organisms lacking adaptive immunity as well as in mammals, the innate immune system can adapt to mount an increased resistance to reinfection, a de facto innate immune memory termed trained immunity. Recent studies have revealed that rewiring of cellular metabolism induced by different immunological signals is a crucial step for determining the epigenetic changes underlying trained immunity. Processes such as a shift of glucose metabolism from oxidative phosphorylation to aerobic glycolysis, increased glutamine metabolism and cholesterol synthesis, play a crucial role in these processes. The discovery of trained immunity opens the door for the design of novel generations of vaccines, for new therapeutic strategies for the treatment of immune deficiency states, and for modulation of exaggerated inflammation in autoinflammatory diseases.     

Cellular immunity in recurrent vulvovaginal candidiasis

Impaired T cell function has been reported to predispose women to recurrent vulvovaginal candidiasis, but conflicting results have been noted in the literature. Most clinical episodes occur in the late luteal phase, suggesting hormonal influence on host resistance. The present study assesses the cellular immune responses of 28 women with recurrent vaginal candidiasis (patients) and 25 control women (controls), noting results in relation to whether the women were in the follicular or luteal phase of the menstrual cycle at the time of sampling. Candida-stimulated peripheral blood lymphocyte proliferation was significantly reduced in patients compared with controls. Interferon-gamma (IFN-γ) production in response to both Candida and purified protein derivative (PPD) stimulation was significantly lower in patients compared with controls. Skin test responses were comparable in both groups. A significant reduction in Candida-stimulated IFN-γ production was seen in patients but not controls in the follicular phase compared with those in the luteal phase. There was also a trend towards lower proliferation in response to Candida in patients but not controls in the follicular phase compared with patients in the luteal phase. These results suggest that there is a partial T cell dysregulation in recurrent vaginal candidiasis which may be exacerbated by the hormonal balance present during the follicular phase, correlating with the risk of clinical infection.     

Lapatinib and doxorubicin enhance the Stat1‐dependent antitumor immune response

The dual erbB1/2 tyrosine kinase inhibitor lapatinib as well as the anthracycline doxorubicin are both used in the therapy of HER2‐positive breast cancer. Using MMTV‐neu mice as an animal model for HER2‐positive breast cancer, we observed enhanced tumor infiltration by IFN‐γ‐secreting T cells after treatment with doxorubicin and/or lapatinib. Antibody depletion experiments revealed a contribution of CD8⁺ but not CD4⁺ T cells to the antitumor effect of these drugs. Doxorubicin treatment additionally decreased the content of immunosuppressive tumor‐associated macrophages (TAMs) in the tumor bed. In contrast, Stat1‐deficient mice were resistant to tumor growth inhibition by lapatinib and/or doxorubicin and exhibited impaired T‐cell activation and reduced T‐cell infiltration of the tumor in response to drug treatment. Furthermore, Stat1‐deficiency resulted in reduced expression of the T‐cell chemotactic factors CXCL9, CXCL10, and CXCL11 in the tumor epithelium. The inhibition of TAM infiltration of the tumor by doxorubicin and the immunosuppressive function of TAMs were found to be Stat1 independent. Taken together, the results point to an important contribution toward enhancing T‐cell and IFN‐γ‐based immunity by lapatinib as well as doxorubicin and emphasize the role of Stat1 in building an effective antitumor immune response.     

Cimetidine does not influence cellular immunity in patients with chronic renal insufficiency

Numerical and functional markers of peripheral lymphocytes were adopted to study the influence of cimetidine on the immune response in immunocompromized patients.Twenty-three patients on regular dialysis treatment, who had been given cimetidine (400 mg daily) for peptic ulcer, were studied during a follow-up of 3 months. Thirty healthy people served as controls for the study of the immunological parameters, i.e. DNCB and PPD skin tests, E-rosetting assays, monoclonal antibodies to T-cells, membrane immunoglobulins for the B-cells, serum immunoglobulins and complement.Before therapy was started CMI was impaired in all patients, with a significant reduction in the E-rosette count (P < 0.01) and depressed DTH (DNCB, PPD). The number of active E-rosettes and OKT4 subsets increased slightly during the period of treatment, though this finding was not confirmed by functional in vivo tests. No change was observed in the B-lymphocyte count and in serum immunoglobulins or complement.The fact that treatment with cimetidine does not seem to influence the immune response in patients on RDT, may suggest that this therapy does not restore the principal immunopathological disorder of these patients, and further justifies its use in patients awaiting renal transplantation or in those who have been given transplant.     

Altered RIG‐I/DDX58‐mediated innate immunity in dermatomyositis

We investigated the molecular mechanisms involved in the pathogenesis of three inflammatory myopathies, dermatomyositis (DM), polymyositis (PM) and inclusion body myositis (IBM). We performed microarray experiments^? using microdissected pathological muscle fibres from 15 patients with these disorders and five controls. Differentially expressed candidate genes were validated by immunohistochemistry on muscle biopsies, and the altered pathways were analysed in human myotube cultures. Up‐regulation of genes involved in viral and nucleic acid recognition were found in the three myopathies but not in controls. In DM, retinoic acid‐inducible gene 1 (RIG‐I, DDX58) and the novel antiviral factor DDX60, which promotes RIG‐I‐mediated signalling, were significantly up‐regulated, followed by IFIH1 (MDA5) and TLR3. Immunohistochemistry confirmed over‐expression of RIG‐I in pathological muscle fibres in 5/5 DM, 0/5 PM and 0/5 IBM patients, and in 0/5 controls. Stimulation of human myotubes with a ligand of RIG‐I produced a significant secretion of interferon‐β (IFNβ; p < 0.05) and up‐regulation of class I MHC, RIG‐I and TLR3 (p < 0.05) by IFNβ‐dependent and TLR3‐independent mechanisms. RIG‐I‐mediated innate immunity, triggered by a viral or damage signal, plays a significant role in the pathogenesis of DM, but not in that of PM or IBM. Copyright © 2014 Pathological Society of Great Britain and Ireland. Published by John Wiley & Sons, Ltd     

Determination of rubella virus‐specific cell‐mediated immunity using IFNγ‐ELISpot

Immunity to rubella virus (RV) is conventionally determined by measuring specific immunoglobulin G (IgG). However, several individuals may be considered immune despite undetectable antibody levels. In the present study RV‐specific interferon‐gamma (IFNγ)‐ELISpot and rubella‐IgG‐ELISA were compared in 75 young adults aged between 20 and 30 years. In a subgroup, not only rubella‐like particles (RLP), but also HPV77 rubella vaccine derived antigen was used in IFNγ‐ELISpot. The results from both, ELISA and ELISpot were independent of previous encounter to RV (vaccination, exanthematous disease, or childhood infection). There was no difference between RLP and RV vaccine antigen in IFNγ‐ELISpot response, and there was no correlation between IFNγ‐ELISpot and RV‐specific IgG levels. IFNγ‐producing cells were found in 78.7% of all tested persons, and 83.8% of them were positive in ELISA. In almost all individuals seronegative for RV antibody, IFNγ‐producing cells were detected. Considering both humoral and cell‐mediated immune responses, a positive RV immune reaction was seen in 98.6%. The results indicate that the IFNγ‐ELISpot can provide valuable additional information in seronegative individuals. J. Med. Virol. 82:335–340, 2010. © 2009 Wiley‐Liss, Inc.     

Serum levels of malondialdehyde and 4-hydroxy-2,3-nonenal in patients affected by familial chronic nail candidiasis

Summary. Familial chronic nail candidiasis (FCNC.MIM 607644) is a rare disorder characterized by early onset infections caused by different species of Candida and restricted to the nails; this disorder is genetically associated with low serum concentration of intercellular adhesion molecule 1 (ICAM-1). Herein we report the evidence of high circulating levels of malondialdehyde (MDA) and 4-hydroxy-2,3-nonenal (HNE) in seven patients of a five-generation Italian family affected by FCNC.MIM 607644. The present data evidence, in these patients, an increase in circulating MDA and HNE levels. Only some merely speculative hypotheses may be suggested to explain the mechanisms subserving the oxidative stress condition observed in these genetically ICAM-1 deficient patients; however, one has to point out that a chronic oxidative stress condition could contribute to the development of concurrent pathological alterations in which an overproduction of free radicals may play a central role.Received 8 January 2004; accepted by N. Boughton-Smith 2 June 2004