Roles of Type 1, 2, and 3 Innate Lymphoid Cells in Herpes Simplex Virus 1 Infection In Vitro and In Vivo

The miR-183/96/182 cluster is a checkpoint for resident immune cells and shapes the cellular landscape of the cornea

PURPOSE

The conserved miR-183/96/182 cluster (miR-183C) regulates both corneal sensory innervation and corneal resident immune cells (CRICs). This study is to uncover its role in CRICs and in shaping the corneal cellular landscape at a single-cell (sc) level.

METHODS

Corneas of naïve, young adult [2 and 6 months old (mo)], female miR-183C knockout (KO) mice and wild-type (WT) littermates were harvested and dissociated into single cells. Dead cells were removed using a Dead Cell Removal kit. CD45+ CRICs were enriched by Magnetic Activated Cell Sorting (MACS). scRNA libraries were constructed and sequenced followed by comprehensive bioinformatic analyses.

RESULTS

The composition of major cell types of the cornea stays relatively stable in WT mice from 2 to 6 mo, however the compositions of subtypes of corneal cells shift with age. Inactivation of miR-183C disrupts the stability of the major cell-type composition and age-related transcriptomic shifts of subtypes of corneal cells. The diversity of CRICs is enhanced with age. Naïve mouse cornea contains previously-unrecognized resident fibrocytes and neutrophils. Resident macrophages (ResMφ) adopt cornea-specific function by expressing abundant extracellular matrix (ECM) and ECM organization-related genes. Naïve cornea is endowed with partially-differentiated proliferative ResMφ and contains microglia-like Mφ. Resident lymphocytes, including innate lymphoid cells (ILCs), NKT and γδT cells, are the major source of innate IL-17a. miR-183C limits the diversity and polarity of ResMφ.

CONCLUSION

miR-183C serves as a checkpoint for CRICs and imposes a global regulation of the cellular landscape of the cornea.

Posterior corneoscleral limbus: Architecture, stem cells, and clinical implications

The limbus is a transition from the cornea to conjunctiva and sclera. In human eyes, this thin strip has a rich variation of tissue structures and composition, typifying a change from scleral irregularity and opacity to corneal regularity and transparency; a variation from richly vascularized conjunctiva and sclera to avascular cornea; the neural passage and drainage of aqueous humor. The limbal stroma is enriched with circular fibres running parallel to the corneal circumference, giving its unique role in absorbing small pressure changes to maintain corneal curvature and refractivity. It contains specific niches housing different types of stem cells for the corneal epithelium, stromal keratocytes, corneal endothelium, and trabecular meshwork. This truly reflects the important roles of the limbus in ocular physiology, and the limbal functionality is crucial for corneal health and the entire visual system. Since the anterior limbus containing epithelial structures and limbal epithelial stem cells has been extensively reviewed, this article is focused on the posterior limbus. We have discussed the structural organization and cellular components of the region beneath the limbal epithelium, the characteristics of stem cell types: namely corneal stromal stem cells, endothelial progenitors and trabecular meshwork stem cells, and recent advances leading to the emergence of potential cell therapy options to replenish their respective mature cell types and to correct defects causing corneal abnormalities. We have reviewed different clinical disorders associated with defects of the posterior limbus and summarized the available preclinical and clinical evidence about the developing topic of cell-based therapy for corneal disorders.

Characterization of the Immunologic Phenotype of Dendritic Cells Infected With Herpes Simplex Virus 1

Due to viral envelope glycoprotein D binding to cellular membrane HVEM receptor, HSV-1 can infect certain dendritic cells, which becomes an event in the viral strategy to interfere with the host’s immune system. We previously generated the HSV-1 mutant strain M6, which produced an attenuated phenotype in mice and rhesus monkeys. The attenuated M6 strain was used to investigate how HSV-1 infection of dendritic cells interferes with both innate and adaptive immunity. Our study showed that dendritic cells membrane HVEM receptors could mediate infection of the wild-type strain and attenuated M6 strain and that dendritic cells infected by both viruses in local tissues of animals exhibited changes in transcriptional profiles associated with innate immune and inflammatory responses. The infection of pDCs and cDCs by the two strains promoted cell differentiation to the CD103+ phenotype, but varied transcriptional profiles were observed, implying a strategy that the HSV-1 wild-type strain interferes with antiviral immunity, probably due to viral modification of the immunological phenotype of dendritic cells during processing and presentation of antigen to T cells, leading to a series of deviations in immune responses, ultimately generating the deficient immune phenotype observed in infected individuals in the clinical.

Non-atopic Neonatal Thymic Innate Lymphoid Cell Subsets (ILC1, ILC2, and ILC3) Identification and the Modulatory Effect of IgG From Dermatophagoides Pteronyssinus (Derp)-Atopic Individuals

Innate lymphoid cells (ILCs) are classified into distinct subsets termed ILC1, ILC2, and ILC3 cells. The existing literature lacks evidence identifying ILCs and their subsets in the human thymus but already demonstrates that they can exert several functions in regulating immune responses. Furthermore, it was already described that IgG's repertoires could modulate lymphocytes' maturation in the human thymus. Here we aimed to identify ILCs subsets in the human thymus and provide insight into the possible modulatory effect of purified IgG on these cells. Thymic tissues were obtained from 12 infants without an allergic background (non-atopic), and a literature-based peripheral ILCs staining protocol was used. Purified IgG was obtained from non-atopic individuals (n-At), atopic individuals reactive to allergens non-related to dust mites (nr-At), and atopic individuals reactive to the mite Dermatophagoides pteronyssinus (Derp-At). As with all tissues in which they have already been detected, thymic ILCs are rare, but we could detect viable ILCs in all tested tissues, which did not occur with the ILC1 subset. ILC2 and ILC3 NKp44+ subsets could be detected in all evaluated thymus, but ILC3 NKp44- subset could not. Next, we observed that Derp-At IgG could induce the expression of ILC2 phenotype, higher levels of IL-13, and lower levels of IL-4 when compared to IgG purified from non-atopic or non-related atopic (atopic to allergens excluding dust mites) individuals. These results contribute to the elucidation of human thymic ILCs and corroborate emerging evidence about IgG's premature effect on allergy development-related human lymphocytes' modulation.

Innate Lymphoid Cells and Natural Killer Cells in Bacterial Infections: Function, Dysregulation, and Therapeutic Targets

Infectious diseases represent one of the largest medical challenges worldwide. Bacterial infections, in particular, remain a pertinent health challenge and burden. Moreover, such infections increase over time due to the continuous use of various antibiotics without medical need, thus leading to several side effects and bacterial resistance. Our innate immune system represents our first line of defense against any foreign pathogens. This system comprises the innate lymphoid cells (ILCs), including natural killer (NK) cells that are critical players in establishing homeostasis and immunity against infections. ILCs are a group of functionally heterogenous but potent innate immune effector cells that constitute tissue-resident sentinels against intracellular and extracellular bacterial infections. Being a nascent subset of innate lymphocytes, their role in bacterial infections is not clearly understood. Furthermore, these pathogens have developed methods to evade the host immune system, and hence permit infection spread and tissue damage. In this review, we highlight the role of the different ILC populations in various bacterial infections and the possible ways of immune evasion. Additionally, potential immunotherapies to manipulate ILC responses will be briefly discussed.

Essential role of M1 macrophages in blocking cytokine storm and pathology associated with murine HSV-1 infection

Ocular HSV-1 infection is a major cause of eye disease and innate and adaptive immunity both play a role in protection and pathology associated with ocular infection. Previously we have shown that M1-type macrophages are the major and earliest infiltrates into the cornea of infected mice. We also showed that HSV-1 infectivity in the presence and absence of M2-macrophages was similar to wild-type (WT) control mice. However, it is not clear whether the absence of M1 macrophages plays a role in protection and disease in HSV-1 infected mice. To explore the role of M1 macrophages in HSV-1 infection, we used mice lacking M1 activation (M1^-/- mice). Our results showed that macrophages from M1^-/- mice were more susceptible to HSV-1 infection in vitro than were macrophages from WT mice. M1^-/- mice were highly susceptible to ocular infection with virulent HSV-1 strain McKrae, while WT mice were refractory to infection. In addition, M1^-/- mice had higher virus titers in the eyes than did WT mice. Adoptive transfer of M1 macrophages from WT mice to M1^-/- mice reduced death and rescued virus replication in the eyes of infected mice. Infection of M1^-/- mice with avirulent HSV-1 strain KOS also increased ocular virus replication and eye disease but did not affect latency-reactivation seen in WT control mice. Severity of virus replication and eye disease correlated with significantly higher inflammatory responses leading to a cytokine storm in the eyes of M1^-/- infected mice that was not seen in WT mice. Thus, for the first time, our study illustrates the importance of M1 macrophages specifically in primary HSV-1 infection, eye disease, and survival but not in latency-reactivation.

Macrophages circulating in the blood or present in different tissues constitute an important barrier against infection. We previously showed that the absence of M2 macrophages does not impact HSV-1 infectivity in vivo. However, in this study we demonstrated an essential role of M1 macrophages in protection from primary HSV-1 replication, death, and eye disease but not in latency-reactivation.

Innate Lymphoid Cells Activation and Transcriptomic Changes in Response to Human Dengue Infection

Background

Dengue virus (DENV) infection has a global impact on public health. The clinical outcomes (of DENV) can vary from a flu-like illness called dengue fever (DF), to a more severe form, known as dengue hemorrhagic fever (DHF). The underlying innate immune mechanisms leading to protective or detrimental outcomes have not been fully elucidated. Helper innate lymphoid cells (hILCs), an innate lymphocyte recently discovered, functionally resemble T-helper cells and are important in inflammation and homeostasis. However, the role of hILCs in DENV infection had been unexplored.

Methods

We performed flow cytometry to investigate the frequency and phenotype of hILCs in peripheral blood mononuclear cells from DENV-infected patients of different disease severities (DF and DHF), and at different phases (febrile and convalescence) of infection. Intracellular cytokine staining of hILCs from DF and DHF were also evaluated by flow cytometry after ex vivo stimulation. Further, the hILCs were sorted and subjected to transcriptome analysis using RNA sequencing. Differential gene expression analysis was performed to compare the febrile and convalescent phase samples in DF and DHF. Selected differentially expressed genes were then validated by quantitative PCR.

Results

Phenotypic analysis showed marked activation of all three hILC subsets during the febrile phase as shown by higher CD69 expression when compared to paired convalescent samples, although the frequency of hILCs remained unchanged. Upon ex vivo stimulation, hILCs from febrile phase DHF produced significantly higher IFN-γ and IL-4 when compared to those of DF. Transcriptomic analysis showed unique hILCs gene expression in DF and DHF, suggesting that divergent functions of hILCs may be associated with different disease severities. Differential gene expression analysis indicated that hILCs function both in cytokine secretion and cytotoxicity during the febrile phase of DENV infection.

Conclusions

Helper ILCs are activated in the febrile phase of DENV infection and display unique transcriptomic changes as well as cytokine production that correlate with severity. Targeting hILCs during early innate response to DENV might help shape subsequent immune responses and potentially lessen the disease severity in the future.

Biology and therapeutic potential of human innate lymphoid cells

In the last decade, innate lymphoid cells (ILCs) have become established as important players in different areas such as tissue homeostasis, integrity of mucosal barriers and regulation of inflammation. While most of the early work on ILCs was based on murine studies, our knowledge on human ILCs is rapidly accumulating, opening novel perspectives towards the translation of ILC biology into the clinic. In this State-of-the-Art Review, we focus on the current knowledge of these most recently discovered members of the lymphocyte family and highlight their role in three major burdens of humanity: infectious diseases, cancer, and allergy and/or autoimmunity. IL-22-producing type 3 innate lymphoid cells (ILC3s) have become established as important players at the interface between gut epithelia and intestinal microbiome and are implicated in protection from inflammatory bowel disease, the control of graft-versus-host disease and intestinal graft rejection. In contrast, type 2 innate lymphoid cells (ILC2s) exert pro-inflammatory functions and contribute to the pathology of asthma and allergy, which has already been started to be pharmacologically targeted. The contribution of ILCs to the control of viral infection constitutes another emerging topic. Finally, ILCs seem to play a dual role in cancer with beneficial and detrimental contributions depending on the clinical setting. The exploitation of the therapeutic potential of ILCs will constitute an exciting task in the foreseeable future.

Impact of a Demyelination-Inducing Central Nervous System Virus on Expression of Demyelination Genes in Type 2 Lymphoid Cells

We recently reported the role of type 2 innate lymphoid cells (ILC2s) in central nervous system (CNS) demyelination using a model of CNS demyelination involving recombinant herpes simplex virus 1 (HSV-1) that constitutively expresses mouse interleukin 2 (HSV-IL-2). In this investigation, we studied how ILC2s respond to HSV-IL-2 at the cellular level using cytokine and gene expression profiling. ILC2s infected with HSV-IL-2 expressed higher levels of granulocyte-macrophage colony-stimulating factor (GM-CSF), IL-5, IL-6, IL-13, IP-10, MIP-2, and RANTES, which include proinflammatory cytokines, than did those infected with parental control virus. In contrast, T_H2 cytokines IL-4 and IL-9, which are typically expressed by ILC2s, were not induced upon HSV-IL-2 infection. Transcriptome sequencing (RNA-seq) analysis of HSV-IL-2 infected ILC2s showed significant upregulation of over 350 genes and downregulation of 157 genes compared with parental virus-infected ILC2s. Gene Ontology (GO) term analysis indicated that genes related to "mitosis" and "inflammatory response" were among the upregulated genes, suggesting that HSV-IL-2 infection drives the excessive proliferation and atypical inflammatory response of ILC2s. This change in ILC2 activation state could underlie the pathology of demyelinating diseases.IMPORTANCE Innate lymphocytes have plasticity and can change functionality; type 2 innate lymphoid cells (ILC2s) can convert to ILC1 or ILC3 cells or change their activation state to produce IL-17 or IL-10 depending on environmental cues. In this study, we investigated the gene and cytokine profiles of ILC2s, which play a major role in HSV-IL-2-induced CNS demyelination. ILC2s infected with HSV-IL-2 displayed a massive remodeling of cellular state. Additionally, ILC2s infected with HSV-IL-2 differed from those infected with parental HSV in cellular and viral gene expression profiles and in cytokine/chemokine induction, and they displayed enhanced activation and proinflammatory responses. These changes in ILC2 activation state could underlie the pathology of demyelinating diseases. These results also highlight the possible importance of pathogens as environmental cues to modify innate lymphocyte functionalities.

Skin Viral Infections: Host Antiviral Innate Immunity and Viral Immune Evasion

The skin is an active immune organ that functions as the first and largest site of defense to the outside environment. Serving as the primary interface between host and pathogen, the skin’s early immune responses to viral invaders often determine the course and severity of infection. We review the current literature pertaining to the mechanisms of cutaneous viral invasion for classical skin-tropic, oncogenic, and vector-borne skin viruses. We discuss the skin’s evolved mechanisms for innate immune viral defense against these invading pathogens, as well as unique strategies utilized by the viruses to escape immune detection. We additionally explore the roles that demographic and environmental factors, such as age, biological sex, and the cutaneous microbiome, play in altering the host immune response to viral threats.

Type 2 Innate Lymphoid Cells Induce CNS Demyelination in an HSV-IL-2 Mouse Model of Multiple Sclerosis

We previously reported that infection of different mouse strains with a recombinant HSV-1 expressing IL-2 (HSV-IL-2) caused CNS demyelination. Histologic examination of infected IL-2rα^-/-, IL-2rβ^-/-, and IL-2rγ^-/- mice showed demyelination in the CNS of IL-2rα^-/- and IL-2rβ^-/- mice but not in the CNS of IL-2rγ^-/--infected mice. No demyelination was detected in mice infected with control virus. IL-2rγ^-/- mice that lack type 2 innate lymphoid cells (ILC2s) and ILCs, play important roles in host defense and inflammation. We next infected ILC1^-/-, ILC2^-/-, and ILC3^-/- mice with HSV-IL-2 or wild-type (WT) HSV-1. In contrast to ILC1^-/- and ILC3^-/- mice, no demyelination was detected in the CNS of ILC2^-/--sinfected mice. However, transfer of ILC2s from WT mice to ILC2^-/- mice restored demyelination in infected recipient mice. CNS demyelination correlated with downregulation of CCL5 and CXCL10. This study demonstrates that ILC2s contribute to HSV-IL-2-induced CNS demyelination in a mouse model of multiple sclerosis.

Role of TH17 Responses in Increasing Herpetic Keratitis in the Eyes of Mice Infected with HSV-1

Purpose

T_H17 cells play an important role in host defense and autoimmunity yet very little is known about the role of IL17 in herpes simplex virus (HSV)-1 infectivity. To better understand the relationship between IL17 and HSV-1 infection, we assessed the relative impact of IL17A-deficiency and deficiency of its receptors on HSV-1 responses in vivo.

Methods

We generated IL17RA^−/− and IL17RA^−/−RC^−/− mice in-house and infected them along with IL17A^−/− and IL17RC^−/− mice in the eyes with 2 × 10⁵ PFU/eye of wild type (WT) HSV-1 strain McKrae. WT C57BL/6 mice were used as control. Virus replication in the eye, survival, corneal scarring (CS), angiogenesis, levels of latency-reactivation, and levels of CD8 and exhaustion markers (PD1, TIM3, LAG3, CTLA4, CD244, and CD39) in the trigeminal ganglia (TG) of infected mice were determined on day 28 postinfection.

Results

No significant differences in virus replication in the eye, survival, latency, reactivation, and exhaustion markers were detected among IL17A^−/−, IL17RA^−/−, IL17RC^−/−, IL17RA^−/−RC^−/−, and WT mice. However, mice lacking IL17 had significantly less CS and angiogenesis than WT mice. In addition, angiogenesis levels in the absence of IL17RC and irrespective of the absence of IL17RA were significantly less than in IL17A- or IL17RA-deficient mice.

Conclusions

Our results suggest that the absence of IL17 protects against HSV-1-induced eye disease, but has no role in protecting against virus replication, latency, or reactivation. In addition, our data provide rationale for blocking IL17RC function rather than IL17A or IL17RA function as a key driver of HSV-1-induced eye disease.

High Frequency of Gamma Interferon-Producing PLZFloRORγtlo Invariant Natural Killer 1 Cells Infiltrating Herpes Simplex Virus 1-Infected Corneas Is Associated with Asymptomatic Ocular Herpesvirus Infection

Invariant natural killer (iNKT) cells are among the first innate immune cells to elicit early protective immunity that controls invading viral pathogens. The role of the iNKT cell subsets iNKT1, iNKT2, and iNKT17 in herpesvirus immunity remains to be fully elucidated. In this study, we examined the protective role of cornea-resident iNKT cell subsets using the mouse model of ocular herpesvirus infection and disease. Wild-type (WT) C57BL/6 (B6) mice and CD1d knockout (KO) mice were infected ocularly with herpes simplex virus 1 (HSV-1) (strain McKrae). Cornea, spleen, and liver were harvested at 0, 2, 5, 8, and 14 days postinfection (p.i.), and the frequency and function of the three major iNKT cell subsets were analyzed and correlated with symptomatic and asymptomatic corneal herpesvirus infections. The profiles of 16 major pro- and anti-inflammatory cytokines were analyzed in corneal lysates using Western blot and Luminex assays. Early during ocular herpesvirus infection (i.e., day 2), the gamma interferon (IFN-γ)-producing PLZFloRORγtlo (promyelocytic leukemia zinc finger, retinoic acid-related orphan receptor gT) iNKT1 cell subset was the predominant iNKT cell subset in infected asymptomatic corneas. Moreover, compared to the asymptomatic corneas of HSV-1-infected WT mice, the symptomatic corneas CD1d KO mice, with iNKT cell deficiency, had increased levels of the inflammatory cytokine interleukin-6 (IL-6) and decreased levels of IL-12, IFN-γ, and the JAK1, STAT1, NF-κB, and extracellular signal-regulated kinase 1/2 (ERK1/2) pathways. Our findings suggest that IFN-γ-producing PLZFloRORγtlo iNKT1 cells play a role in the protective innate immune response against symptomatic ocular herpes.IMPORTANCE We investigated the protective role of iNKT cell subsets in asymptomatic ocular herpesvirus infection. We found that early during ocular herpesvirus infection (i.e., on day 2 postinfection), IFN-γ-producing PLZFloRORγtlo iNKT1 cells were the predominant iNKT cell subset in infected corneas of asymptomatic B6 mice (with little to no corneal herpetic disease), compared to corneas of symptomatic mice (with severe corneal herpetic disease). Moreover, compared to asymptomatic corneas of wild-type (WT) B6 mice, the symptomatic corneas of CD1d KO mice, which lack iNKT cells, showed (i) decreases in the levels of IFN-γ and IL-12, (ii) an increase in the level of the inflammatory cytokine IL-6; and (iii) downregulation of the JAK1, STAT1, NF-κB, and ERK1/2 pathways. The findings suggest that early during ocular herpesvirus infection, cornea-resident IFN-γ-producing PLZFloRORγtlo iNKT1 cells provide protection from symptomatic ocular herpes.