Dysbiosis-induced IL-33 contributes to impaired antiviral immunity in the genital mucosa

Microbes and Viruses Are Bugging the Gut in Celiac Disease. Are They Friends or Foes?

The links between microorganisms/viruses and autoimmunity are complex and multidirectional. A huge number of studies demonstrated the triggering impact of microbes and viruses as the major environmental factors on the autoimmune and inflammatory diseases. However, growing evidences suggest that infectious agents can also play a protective role or even abrogate these processes. This protective crosstalk between microbes/viruses and us might represent a mutual beneficial equilibrium relationship between two cohabiting ecosystems. The protective pathways might involve post-translational modification of proteins, decreased intestinal permeability, Th1 to Th2 immune shift, induction of apoptosis, auto-aggressive cells relocation from the target organ, immunosuppressive extracellular vesicles and down regulation of auto-reactive cells by the microbial derived proteins. Our analysis demonstrates that the interaction of the microorganisms/viruses and celiac disease (CD) is always a set of multidirectional processes. A deeper inquiry into the CD interplay with Herpes viruses and Helicobacter pylori demonstrates that the role of these infections, suggested to be potential CD protectors, is not as controversial as for the other infectious agents. The outcome of these interactions might be due to a balance between these multidirectional processes.

Transient Depletion of CD169+ Cells Contributes to Impaired Early Protection and Effector CD8+ T Cell Recruitment against Mucosal Respiratory Syncytial Virus Infection

Respiratory syncytial virus (RSV) is a major cause of respiratory viral infections in infants and children. Alveolar macrophages (AMs) play a crucial role in combatting airborne pathogens, strongly express CD169, and are localized in the lung alveoli. Therefore, we used CD169-diphtheria toxin receptor (DTR) transgenic mice to explore the roles of CD169⁺ cells in immune responses to mucosal RSV infection. The administration of diphtheria toxin to CD169-DTR mice induced specific AM depletion and reduced the recruitment of Ly6C^hi monocytes. Notably, CD169⁺ cell depletion reduced levels of innate cytokines, such as interferon-β, IL-6, and TNF-α, in bronchoalveolar lavage fluid during RSV infection without affecting the production of proinflammatory chemokines. Moreover, the depletion of CD169⁺ cells increased the recruitment of inflammatory cells to the lung during the early stage of RSV infection, although not during the later stages of RSV infection. Furthermore, the depletion of CD169⁺ cells reduced the recruitment of effector CD8⁺ T cells to the lungs after RSV mucosal infection. Our findings suggest that modulating the number of CD169⁺ cells to enhance immune responses to RSV infection may be useful as a new therapeutic strategy.

IL-33 and the intestine: The good, the bad, and the inflammatory

Interleukin-33 (IL-33) is a member of the IL-1 cytokine family that has been widely studied since its discovery in 2005 for its dichotomous functions in homeostasis and inflammation. IL-33, along with its receptor suppression of tumorigenicity 2 (ST2), has been shown to modulate both the innate and adaptive immune system. Originally, the IL-33/ST2 signaling axis was studied in the context of inducing type 2 immune responses with the expression of ST2 by T helper 2 (T_H2) cells. However, the role of IL-33 is not limited to T_H2 responses. Rather, IL-33 is a potent activator of T_H1 cells, group 2 innate lymphoid cells (ILC2s), regulatory T (Treg) cells, and CD8⁺ T cells. The intestine is uniquely important in this discussion, as the intestinal epithelium is distinctively positioned to interact with both pathogens and the immune cells housed in the mucosa. In the intestine, IL-33 is expressed by the pericryptal fibroblasts and its expression is increased particularly in disease states. Moreover, IL-33/ST2 signaling aberrancy is implicated in the pathogenesis of inflammatory bowel disease (IBD). Accordingly, for this review, we will focus on the role of IL-33 in the regulation of intestinal immunity, involvement in intestinal disease, and implication in potential therapeutics.

Vaginal Microbiome and Its Relationship to Behavior, Sexual Health, and Sexually Transmitted Diseases

The vaginal microbiota has great significance in maintaining vaginal health and protecting the host from disease. Recent advances in molecular techniques and informatics allow researchers to explore microbial composition in detail and to compare the structure of vaginal microbial communities with behavior and health outcomes, particularly acquisition and transmission of sexually transmitted diseases (STDs) and poor birth outcomes. Vaginal flora have been found to cluster into a limited number of communities, although community structure is dynamic. Certain community types are more associated with poor reproductive outcomes and STDs; communities dominated by Lactobacillus species, particularly Lactobacillus crispatus, are most associated with vaginal health. Modifiable and nonmodifiable factors are strongly associated with community composition, including behavior, race or ethnicity, and hygiene. In this review, we describe the state of the science on the vaginal microbiome and its relationship to behavior, sexual health, and STDs, including determinants of the microbiome that go beyond an individual level.

Challenges in conducting research on sexual violence and HIV and approaches to overcome them

Studies have implicated sexual violence as a strong correlate of HIV acquisition in women. Characterizing how such violence affects the female immune system may provide insight into the biological mechanisms of HIV transmission and ultimately improve global HIV prevention strategies. Little research has been carried out in this domain, and the obstacles to investigation can be daunting. Here, we describe methodological challenges encountered and solutions explored while implementing a study of dysregulation of immune biomarkers potentially indicative of increased HIV susceptibility in women following sexual assault. Challenges included accessing sexual assault survivors and defining sexual assault, promoting study participant well-being during research engagement, reducing selection and information bias, collecting and processing biological samples, and adjusting for confounders such as reproductive tract infections and emotional and physical abuse. We found that many survivors of sexual assault welcomed the attention from study staff and felt empowered by the opportunity to help other women at risk for violence. Well-trained research staff and well-articulated community and medical partnerships were key methods to overcoming challenges while promoting the safety and welfare of vulnerable study participants.

A mechanism for the induction of type 2 immune responses by a protease allergen in the genital tract

The genital mucosa is a barrier that is constantly exposed to a variety of pathogens, allergens, and external stimuli. Although both allergen exposure and parasite infections frequently occur in the genital area, the mechanism by which immune responses-particularly type 2 immunity-are induced has rarely been studied in the genital mucosa. Here, we demonstrate the induction of T helper type 2 (Th2) immunity in the genital mucosa in response to a model allergen, the protease papain. Intravaginal papain immunization induced type 2 immunity in a manner that was dependent on protease activity and the estrous phase of the mice. In addition, IL-33 was released from the vaginal epithelia after intravaginal papain immunization, leading to the activation of type 2 innate lymphoid cells (ILC2s). Moreover, the IL-33-MyD88 (myeloid differentiation primary response gene 88) signaling pathway was critical for the induction of type 2 immunity. We also found that Th2 differentiation in response to intravaginal papain treatment requires a specific dendritic cell (DC) subset that is controlled by interferon regulatory factor 4 (IRF4). These findings suggest that type 2 immunity is induced by a unique mechanism in the genital tract, which is an important, but often overlooked, barrier surface.

Dampened antiviral immunity to intravaginal exposure to RNA viral pathogens allows enhanced viral replication

Khan et al. demonstrate that the lower female reproductive tract is exceptionally vulnerable to infection by LCMV and Zika virus, as intravaginal exposure to these RNA viral pathogens elicits a dampened antiviral immune response.

Understanding the host immune response to vaginal exposure to RNA viruses is required to combat sexual transmission of this class of pathogens. In this study, using lymphocytic choriomeningitis virus (LCMV) and Zika virus (ZIKV) in wild-type mice, we show that these viruses replicate in the vaginal mucosa with minimal induction of antiviral interferon and inflammatory response, causing dampened innate-mediated control of viral replication and a failure to mature local antigen-presenting cells (APCs). Enhancement of innate-mediated inflammation in the vaginal mucosa rescues this phenotype and completely inhibits ZIKV replication. To gain a better understanding of how this dampened innate immune activation in the lower female reproductive tract may also affect adaptive immunity, we modeled CD8 T cell responses using vaginal LCMV infection. We show that the lack of APC maturation in the vaginal mucosa leads to a delay in CD8 T cell activation in the draining lymph node and hinders the timely appearance of effector CD8 T cells in vaginal mucosa, thus further delaying viral control in this tissue. Our study demonstrates that vaginal tissue is exceptionally vulnerable to infection by RNA viruses and provides a conceptual framework for the male to female sexual transmission observed during ZIKV infection.

Cervicovaginal Microbiomes-Threats and Possibilities

The microbiome of the vagina has universal traits that override race, diet, lifestyle, and socioeconomic status. While five community state types have been proposed, the actual number is likely closer to ten. Nevertheless, while lactobacilli dominate in health for most women, a highly diverse community or single pathogens are associated with morbidity. The fact that four or five Lactobacillus species are dominant in healthy women worldwide, raises questions of why they evolved in this niche, what they are doing, and how their apparent protective properties can be harnessed? This opinion article explores this universality, elements of lactobacilli that may imprint women's health and that of their offspring, and proposes key areas for future study.

The Dynamic Role of the IL-33/ST2 Axis in Chronic Viral-infections: Alarming and Adjuvanting the Immune Response

Interleukin 33 (IL-33), a member of the IL-1 family, is constitutively expressed in epithelial and in endothelial cells at barrier sites, acting as a danger signal and adjuvanting the immune response following tissue damage and infection. Originally implicated in allergy, IL-33 is also known to be involved in innate and adaptive immune responses by enhancing natural killer, Th1, and CD4 and CD8 T-cell functions. The nature of the antiviral immune response orchestrated by IL-33 depends on the site of infection, the duration of the disease and the cytokine milieu. In this review, we focus on the distinctive contribution of IL-33 as an anti-infective and proinflammatory cytokine in response to cell death and viral infections. The dynamic role of IL-33 in the acute and chronic phases of infection with HIV, hepatitis B and C viruses, and with CMV is highlighted. This review will also discuss the potential immunotherapeutic and adjuvant roles of IL-33.

Search Strategy and Selection Criteria

English language, indexed publications in PubMed were searched using combinations of following key words: “interleukin-33”, “IL-33”, “suppression of tumorigenicity 2”, ST2”, “sST2”, “HIV”, “HBV”, “HCV”, “CMV”, “HPV”, “immunotherapy” and “vaccine”. Except for seminal studies, only articles published between 2010 and 2016 were included.

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IL-33, a guardian of barriers, acts as an alarmin and as an enhancer of immune responses following injury or infection.

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sST2, the IL-33 decoy receptor, is considered as a biomarker for allergies, cardiac conditions and infections.

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IL-33 has immunotherapeutic and/or adjuvant potential.

Interleukin-33, friend and foe in type-2 immune responses

IL-33 is the most recent addition to the IL-1 cytokine family, identified in 2005 as the ligand of T1/ST2 and inducer of type-2 immune responses. IL-33 has been implicated in a wide range of disease settings, in anti-inflammatory responses and homeostasis, and thus signalling must be strictly regulated. Altered gene expression, post-translational modification, decoy receptor, and receptor signalling are all modulatory mechanisms used to control the IL-33 pathway. Understanding both the genetic and post-translational factors influencing IL-33 activity will be critical for provision of safe effective treatment of type-2 disorders.