Bacterial coinfection restrains antiviral CD8 T-cell response via LPS-induced inhibitory NK cells

Parasitic worms affect virus coinfection: a mechanistic overview

Helminths are parasitic worms that coevolve with their host, usually resulting in long-term persistence through modulating host immunity. The multifarious mechanisms altering the immune system induced by helminths have significant implications on the control of coinfecting pathogens such as viruses. Here, we explore the recent literature to highlight the main immune alterations and mechanisms that affect the control of viral coinfection. Insights from these mechanisms are valuable in the understanding of clinical observations in helminth-prevalent areas and in the design of new therapeutic and vaccination strategies to control viral diseases.

Helminth Infection-Induced Increase in Virtual Memory CD8 T Cells Is Transient, Driven by IL-15, and Absent in Aged Mice

CD8 virtual memory T (TVM) cells are Ag-naive CD8 T cells that have undergone partial differentiation in response to common γ-chain cytokines, particularly IL-15 and IL-4. TVM cells from young individuals are highly proliferative in response to TCR and cytokine stimulation but, with age, they lose TCR-mediated proliferative capacity and exhibit hallmarks of senescence. Helminth infection can drive an increase in TVM cells, which is associated with improved pathogen clearance during subsequent infectious challenge in young mice. Given the cytokine-dependent profile of TVM cells and their age-associated dysfunction, we traced proliferative and functional changes in TVM cells, compared with true naive CD8 T cells, after helminth infection of young and aged C57BL/6 mice. We show that IL-15 is essential for the helminth-induced increase in TVM cells, which is driven only by proliferation of existing TVM cells, with negligible contribution from true naive cell differentiation. Additionally, TVM cells showed the greatest proliferation in response to helminth infection and IL-15 compared with other CD8 T cells. Furthermore, TVM cells from aged mice did not undergo expansion after helminth infection due to both TVM cell-intrinsic and -extrinsic changes associated with aging.

Erlotinib protests against LPS-induced parthanatos through inhibiting macrophage surface TLR4 expression

Sepsis is a life-threatening cascading systemic inflammatory response syndrome on account of serve infection. In inflamed tissues, activated macrophages generate large amounts of inflammatory cytokines reactive species, and are exposed to the damaging effects of reactive species. However, comparing with necroptosis and pyroptosis, so far, there are few studies focusing on the overproduction-related cell death, such as parthanatos in macrophage during sepsis. In LPS-treated macrophage, we observed PARP-1 activation, PAR formation and AIF translocation. All these phenomena could be inhibited by both erlotinib and 3-AB, indicating the presence of parthanatos in endotoxemia. We further found that LPS induced the increase of cell surface TLR4 expression responsible for the production of ROS and subsequent parthanatos in endotoxemia. All these results shed a new light on how TLR4 regulating the activation of PARP-1 by LPS in macrophage.

Interaction between Lipopolysaccharide and Gut Microbiota in Inflammatory Bowel Diseases

Lipopolysaccharides (LPSs) are bacterial surface glycolipids, produced by Gram-negative bacteria. LPS is known to determine acute inflammatory reactions, particularly in the context of sepsis. However, LPS can also trigger chronic inflammation. In this case, the source of LPS is not an external infection, but rather an increase in endogenous production, which is usually sustained by gut microbiota (GM), and LPS contained in food. The first site in which LPS can exert its inflammatory action is the gut: both GM and gut-associated lymphoid tissue (GALT) are influenced by LPS and shift towards an inflammatory pattern. The changes in GM and GALT induced by LPS are quite similar to the ones seen in IBD: GM loses diversity, while GALT T regulatory (Tregs) lymphocytes are reduced in number, with an increase in Th17 and Th1 lymphocytes. Additionally, the innate immune system is triggered, through the activation of toll-like receptor (TLR)-4, while the epithelium is directly damaged, further triggering inflammation. In this review, we will discuss the importance of the crosstalk between LPS, GM, and GALT, and discuss the possible implications.

Enteric helminth coinfection enhances host susceptibility to neurotropic flaviviruses via a tuft cell-IL-4 receptor signaling axis

Although enteric helminth infections modulate immunity to mucosal pathogens, their effects on systemic microbes remain less established. Here, we observe increased mortality in mice coinfected with the enteric helminth Heligmosomoides polygyrus bakeri (Hpb) and West Nile virus (WNV). This enhanced susceptibility is associated with altered gut morphology and transit, translocation of commensal bacteria, impaired WNV-specific T cell responses, and increased virus infection in the gastrointestinal tract and central nervous system. These outcomes were due to type 2 immune skewing, because coinfection in Stat6-/- mice rescues mortality, treatment of helminth-free WNV-infected mice with interleukin (IL)-4 mirrors coinfection, and IL-4 receptor signaling in intestinal epithelial cells mediates the susceptibility phenotypes. Moreover, tuft cell-deficient mice show improved outcomes with coinfection, whereas treatment of helminth-free mice with tuft cell-derived cytokine IL-25 or ligand succinate worsens WNV disease. Thus, helminth activation of tuft cell-IL-4-receptor circuits in the gut exacerbates infection and disease of a neurotropic flavivirus.

Systemic Inflammation Suppresses Lymphoid Tissue Remodeling and B Cell Immunity during Concomitant Local Infection

Concurrent infection with multiple pathogens occurs frequently in individuals and can result in exacerbated infections and altered immunity. However, the impact of such coinfections on immune responses remains poorly understood. Here, we reveal that systemic infection results in an inflammation-induced suppression of local immunity. During localized infection or vaccination in barrier tissues including the skin or respiratory tract, concurrent systemic infection induces a type I interferon-dependent lymphopenia that impairs lymphocyte recruitment to the draining lymph node (dLN) and induces sequestration of lymphocytes in non-draining LN. This contributes to suppressed fibroblastic reticular cell and endothelial cell expansion and dLN remodeling and impairs induction of B cell responses and antibody production. Our data suggest that contemporaneous systemic inflammation constrains the induction of regional immunity.

Targeting of Perforin Inhibitor into the Brain Parenchyma Via a Prodrug Approach Can Decrease Oxidative Stress and Neuroinflammation and Improve Cell Survival

The cytolytic protein perforin has a crucial role in infections and tumor surveillance. Recently, it has also been associated with many brain diseases, such as neurodegenerative diseases and stroke. Therefore, inhibitors of perforin have attracted interest as novel drug candidates. We have previously reported that converting a perforin inhibitor into an L-type amino acid transporter 1 (LAT1)-utilizing prodrug can improve the compound's brain drug delivery not only across the blood-brain barrier (BBB) but also into the brain parenchymal cells: neurons, astrocytes, and microglia. The present study evaluated whether the increased uptake into mouse primary cortical astrocytes and subsequently improvements in the cellular bioavailability of this brain-targeted perforin inhibitor prodrug could enhance its pharmacological effects, such as inhibition of production of caspase-3/-7, lipid peroxidation products and prostaglandin E2 (PGE2) in the lipopolysaccharide (LPS)-induced neuroinflammation mouse model. It was demonstrated that increased brain and cellular drug delivery could improve the ability of perforin inhibitors to elicit their pharmacological effects in the brain at nano- to picomolar levels. Furthermore, the prodrug displayed multifunctional properties since it also inhibited the activity of several key enzymes related to Alzheimer's disease (AD), such as the β-site amyloid precursor protein (APP) cleaving enzyme 1 (BACE1), acetylcholinesterase (AChE), and most probably also cyclooxygenases (COX) at micromolar concentrations. Therefore, this prodrug is a potential drug candidate for preventing Aβ-accumulation and ACh-depletion in addition to combatting neuroinflammation, oxidative stress, and neural apoptosis within the brain. Graphical abstract.

NK1.1+ innate lymphoid cells in salivary glands inhibit establishment of tissue-resident memory CD8+ T cells in mice

NK1.1⁺ cells found in salivary glands (SG) represent a unique cell population of innate lymphoid cells (ILC) with characteristics of both conventional NK cells and ILC1. Here, we demonstrate that these NK1.1⁺  cells limit the accumulation and differentiation of virus-specific tissue-resident memory CD8⁺ T cells (T_RM  cells) in SG of mice infected with lymphocytic choriomeningitis virus (LCMV). The negative regulation of LCMV-specific CD8⁺ T_RM  cells by NK1.1⁺  cells in SG is independent of NKG2D, NKp46, TRAIL, and perforin. Moreover, analysis of NKp46^iCre+ Eomes^fl/fl mice revealed that Eomes-dependent conventional NK cells are dispensable for negative regulation. Since the SG are prone to autoimmune reactions, regulation of T_RM  cells by tissue-resident ILC may be particularly important to prevent immunopathology in this organ.

What came first, the virus or the egg: Innate immunity during viral coinfections

Infections with any pathogen can be severe and present with numerous complications caused by the pathogen or the host immune response to the invading microbe. However, coinfections, also called polymicrobial infections or secondary infections, can further exacerbate disease. Coinfections are more common than is often appreciated. In this review, we focus specifically on coinfections between viruses and other viruses, bacteria, parasites, or fungi. Importantly, innate immune signaling and innate immune cells that facilitate clearance of the initial viral infection can affect host susceptibility to coinfections. Understanding these immune imbalances may facilitate better diagnosis, prevention, and treatment of such coinfections.

Innate lymphoid cells control signaling circuits to regulate tissue-specific immunity

The multifaceted organization of the immune system involves not only patrolling lymphocytes that constantly monitor antigen-presenting cells in secondary lymphoid organs but also immune cells that establish permanent tissue-residency. The integration in the respective tissue and the adaption to the organ milieu enable tissue-resident cells to establish signaling circuits with parenchymal cells to coordinate immune responses and maintain tissue homeostasis. Innate lymphoid cells (ILCs) are tissue-resident innate immune cells that have a similar functional diversity to T cells including lineage-specifying transcription factors that drive certain effector programs. Since their formal discovery 10 years ago, it has become clear that ILCs are present in almost every tissue but strongly enriched at barrier surfaces, where they regulate immunity to infection, chronic inflammation, and tissue maintenance. In this context, recent research has identified ILCs as key in orchestrating tissue homeostasis through their ability to sustain bidirectional interactions with epithelial cells, neurons, stromal cells, adipocytes, and many other tissue-resident cells. In this review, we provide a comprehensive discussion of recent studies that define the development and heterogeneity of ILC populations and their impact on innate and adaptive immunity. Further, we discuss emerging research on the influence of the nervous system, circadian rhythm, and developmental plasticity on ILC function. Uncovering the signaling circuits that control development and function of ILCs will provide an integrated view on how immune responses in tissues are synchronized with functional relevance far beyond the classical view of the role of the immune system in discrimination between self/non-self and host defense.

[Pulmonary sonography-a valuable supplement to basic diagnostics for timely outpatient clarification of cough and dyspnea]

Cough and dyspnea are among the most common symptoms in primary medical care and potentially threatening diseases must be excluded in a timely manner, especially acute heart failure and its causes, pneumonia, pleural effusion, pulmonary embolism and pneumothorax. Anamnesis, inspection, physical examination and technical basic diagnostics are usually sufficient for an initial risk stratification. A reliable suspected diagnosis can often be made in this way; however, it is not uncommon for the findings to be ambiguous. Chest X‑ray diagnostics and laboratory diagnostics are established as the standard approach for these situations; however, a major limitation of these diagnostic techniques is the lack of immediate availability in the general practitioner's office and laboratory results are not available until the next day or the day after. Furthermore, the sensitivity and specificity of these diagnostic procedures are limited but often overestimated, especially in the case of mild to moderately pronounced alterations and in early stages of a disease. Thoracic sonography can be used in these situations as a direct extension of the physical examination. Its diagnostic value is undisputed. The most important pathological findings, such as pleural effusion and subpleural consolidations can be immediately visualized with sufficient certainty using miniaturized handheld ultrasound devices. The concept of the ultrasound stethoscope, which has been under discussion for more than 15 years, can also be implemented as point-of-care ultrasound (POCUS). The POCUS will become established as routine diagnostics in the future, for example in emergency outpatient diagnostics. It is time for pulmonary ultrasound to be added to the repertoire of primary care diagnostics.

Hemorrhagic Fever-Causing Arenaviruses: Lethal Pathogens and Potent Immune Suppressors

Hemorrhagic fevers (HF) resulting from pathogenic arenaviral infections have traditionally been neglected as tropical diseases primarily affecting African and South American regions. There are currently no FDA-approved vaccines for arenaviruses, and treatments have been limited to supportive therapy and use of non-specific nucleoside analogs, such as Ribavirin. Outbreaks of arenaviral infections have been limited to certain geographic areas that are endemic but known cases of exportation of arenaviruses from endemic regions and socioeconomic challenges for local control of rodent reservoirs raise serious concerns about the potential for larger outbreaks in the future. This review synthesizes current knowledge about arenaviral evolution, ecology, transmission patterns, life cycle, modulation of host immunity, disease pathogenesis, as well as discusses recent development of preventative and therapeutic pursuits against this group of deadly viral pathogens.