Congenital iRHOM2 deficiency causes ADAM17 dysfunction and environmentally directed immunodysregulatory disease.

We report a pleiotropic disease due to loss-of-function mutations in RHBDF2, the gene encoding iRHOM2, in two kindreds with recurrent infections in different organs. One patient had recurrent pneumonia but no colon involvement, another had recurrent infectious hemorrhagic colitis but no lung involvement and the other two experienced recurrent respiratory infections. Loss of iRHOM2, a rhomboid superfamily member that regulates the ADAM17 metalloproteinase, caused defective ADAM17-dependent cleavage and release of cytokines, including tumor-necrosis factor and amphiregulin. To understand the diverse clinical phenotypes, we challenged Rhbdf2-/- mice with Pseudomonas aeruginosa by nasal gavage and observed more severe pneumonia, whereas infection with Citrobacter rodentium caused worse inflammatory colitis than in wild-type mice. The fecal microbiota in the colitis patient had characteristic oral species that can predispose to colitis. Thus, a human immunodeficiency arising from iRHOM2 deficiency causes divergent disease phenotypes that can involve the local microbial environment.

Respiratory Syncytial Virus Uses CX3CR1 as a Receptor on Primary Human Airway Epithelial Cultures.

Respiratory syncytial virus (RSV) is the most frequent cause of lower respiratory disease in infants, but no vaccine or effective therapy is available. The initiation of RSV infection of immortalized cells is largely dependent on cell surface heparan sulfate (HS), a receptor for the RSV attachment (G) glycoprotein in immortalized cells. However, RSV infects the ciliated cells in primary well differentiated human airway epithelial (HAE) cultures via the apical surface, but HS is not detectable on this surface. Here we show that soluble HS inhibits infection of immortalized cells, but not HAE cultures, confirming that HS is not the receptor on HAE cultures. Conversely, a "non-neutralizing" monoclonal antibody against the G protein that does not block RSV infection of immortalized cells, does inhibit infection of HAE cultures. This antibody was previously shown to block the interaction between the G protein and the chemokine receptor CX3CR1 and we have mapped the binding site for this antibody to the CX3C motif and its surrounding region in the G protein. We show that CX3CR1 is present on the apical surface of ciliated cells in HAE cultures and especially on the cilia. RSV infection of HAE cultures is reduced by an antibody against CX3CR1 and by mutations in the G protein CX3C motif. Additionally, mice lacking CX3CR1 are less susceptible to RSV infection. These findings demonstrate that RSV uses CX3CR1 as a cellular receptor on HAE cultures and highlight the importance of using a physiologically relevant model to study virus entry and antibody neutralization.

Differences in antibody responses between trivalent inactivated influenza vaccine and live attenuated influenza vaccine correlate with the kinetics and magnitude of interferon signaling in children.

BACKGROUND: Live attenuated influenza vaccine (LAIV) and trivalent inactivated influenza vaccine (TIV) are effective for prevention of influenza virus infection in children, but the mechanisms associated with protection are not well defined. METHODS: We analyzed the differences in B-cell responses and transcriptional profiles in children aged 6 months to 14 years immunized with these 2 vaccines. RESULTS: LAIV elicited a significant increase in naive, memory, and transitional B cells on day 30 after vaccination, whereas TIV elicited an increased number of plasmablasts on day 7. Antibody titers against the 3 vaccine strains (H1N1, H3N2, and B) were significantly higher in the TIV group and correlated with number of antibody-secreting cells. Both vaccines induced overexpression of interferon (IFN)-signaling genes but with different kinetics. TIV induced expression of IFN genes on day 1 after vaccination in all age groups, and LAIV induced expression of IFN genes on day 7 after vaccination but only in children <5 years old. IFN-related genes overexpressed in both vaccinated groups correlated with H3N2 antibody titers. CONCLUSIONS: These results suggest that LAIV and TIV induced significantly different B-cell responses in vaccinated children. Early induction of IFN appears to be important for development of antibody responses.

Local blockade of epithelial PDL-1 in the airways enhances T cell function and viral clearance during influenza virus infection.

In order to maintain the gas exchange function of the lung following influenza virus infection, a delicate orchestration of positive and negative regulatory pathways must be maintained to attain viral eradication while minimizing local inflammation. The programmed death receptor 1 ligand/programmed death receptor 1 (PDL-1/PD-1) pathway plays an important immunoregulatory role, particularly in the context of T cell function. Here, we have shown that influenza virus infection of primary airway epithelial cells strongly enhances PDL-1 expression and does so in an alpha interferon receptor (IFNAR) signaling-dependent manner. PD-1 is expressed primarily on effector T cells in the lung, compared to effector memory and central memory cells, and shortly after influenza virus infection, an increased number of PD-1(+) T cells are recruited to the airways. Using in vitro cocultures of airway epithelial cells and T cells and in vivo models of influenza virus infection, we have demonstrated that blockade of airway epithelial PDL-1 improves CD8 T cell function, defined by increased production of gamma interferon (IFN-γ) and granzyme B and expression of CD107ab. Furthermore, PDL-1 blockade in the airways served to accelerate influenza virus clearance and enhance infection recovery. Our findings suggest that local manipulation of the PDL-1/PD-1 axis in the airways may represent a therapeutic alternative during acute influenza virus infection.

Toll-like receptor expression and induction of type I and type III interferons in primary airway epithelial cells.

Interferons (IFNs) are a critical component of the first line of antiviral defense. The activation of Toll-like receptors (TLRs) expressed by dendritic cells triggers different signaling cascades that result in the production of large amounts of IFNs. However, the functional consequences of TLR activation and differential IFN production in specific cell populations other than antigen-presenting cells have not yet been fully elucidated. In this study, we investigated TLR expression and polarization in airway epithelial cells (AECs) and the consequences of TLR agonist stimulation for the production of type I (IFN-α/ß) and type III (IFN-λ) IFNs. Our results show that the pattern of expression and polarization of all TLRs in primary AEC cultures mirrors that of the human airways ex vivo and is receptor specific. The antiviral TLRs (TLR3, TLR7, and TLR9) are mostly expressed on the apical cell surfaces of epithelial cells in the human trachea and in primary polarized AECs. Type III IFN is the predominant IFN produced by the airway epithelium, and TLR3 is the only TLR that mediates IFN production by AECs, while all TLR agonists tested are capable of inducing AEC activation and interleukin-8 production. In response to influenza virus infection, AECs can produce IFN-λ in an IFNAR- and STAT1-independent manner. Our results emphasize the importance of using primary well-differentiated AECs to study TLR and antiviral responses and provide further insight into the regulation of IFN production during the antiviral response of the lung epithelium.

Contribution of pulmonary KLRG1(high) and KLRG1(low) CD8 T cells to effector and memory responses during influenza virus infection.

In response to pathogen insult, CD8 T cells undergo expansion and a dynamic differentiation process into functionally different subpopulations. In this study, we show that during the effector response to influenza virus infection lung CD8 T cell subsets expressing killer cell lectin-like receptor G1 (KLRG1)(high) or KLRG1(low) had similar effector functions and immediate recall efficacy. The KLRG1 expression profile of lung CD8 T cells was not permanent after adoptive transfer and recall. Airway CD8 T cells exhibited a unique phenotype expressing low levels of KLRG1 together with high levels of markers of cellular activation. We investigated the functional characteristics of these cells by analyzing their capacity to survive and to respond to a secondary challenge outside of the airway environment. KLRG1(high) CD8 T cells isolated from the lung during the peak of the effector T cell response could survive for more than a month in the absence of cognate viral Ags after systemic adoptive transfer, and these "rested" CD8 T cells proliferated and participated in a recall response to influenza virus infection. These data highlight the unique phenotype and plasticity of effector CD8 T cell responses in the lung.

Killer cell lectin-like receptor G1 deficiency significantly enhances survival after Mycobacterium tuberculosis infection.

The expression of T cell differentiation markers is known to increase during Mycobacterium tuberculosis infection, and yet the biological role of such markers remains unclear. We examined the requirement of the T cell differentiation marker killer cell lectin-like receptor G1 (KLRG1) during M. tuberculosis infection using mice deficient in KLRG1. KLRG1(-/-) mice had a significant survival extension after M. tuberculosis infection compared to wild-type controls, and maintained a significantly lower level of pulmonary M. tuberculosis throughout chronic infection. Improved control of M. tuberculosis infection was associated with an increased number of activated pulmonary CD4(+) T cells capable of secreting gamma interferon (IFN-γ). Our report is the first to show an in vivo impact of KLRG1 on disease control.

Plasticity and virus specificity of the airway epithelial cell immune response during respiratory virus infection.

Airway epithelial cells (AECs) provide the first line of defense in the respiratory tract and are the main target of respiratory viruses. Here, using oligonucleotide and protein arrays, we analyze the infection of primary polarized human AEC cultures with influenza virus and respiratory syncytial virus (RSV), and we show that the immune response of AECs is quantitatively and qualitatively virus specific. Differentially expressed genes (DEGs) specifically induced by influenza virus and not by RSV included those encoding interferon B1 (IFN-B1), type III interferons (interleukin 28A [IL-28A], IL-28B, and IL-29), interleukins (IL-6, IL-1A, IL-1B, IL-23A, IL-17C, and IL-32), and chemokines (CCL2, CCL8, and CXCL5). Lack of type I interferon or STAT1 signaling decreased the expression and secretion of cytokines and chemokines by the airway epithelium. We also observed strong basolateral polarization of the secretion of cytokines and chemokines by human and murine AECs during infection. Importantly, the antiviral response of human AECs to influenza virus or to RSV correlated with the infection signature obtained from peripheral blood mononuclear cells (PBMCs) isolated from patients with acute influenza or RSV bronchiolitis, respectively. IFI27 (also known as ISG12) was identified as a biomarker of respiratory virus infection in both AECs and PBMCs. In addition, the extent of the transcriptional perturbation in PBMCs correlated with the clinical disease severity. Our results demonstrate that the human airway epithelium mounts virus-specific immune responses that are likely to determine the subsequent systemic immune responses and suggest that the absence of epithelial immune mediators after RSV infection may contribute to explaining the inadequacy of systemic immunity to the virus.

KLRG1+NKG2A+ CD8 T cells mediate protection and participate in memory responses during γ-herpesvirus infection.

Functional CD8 T cell effector and memory responses are generated and maintained during murine γ-herpesvirus 68 (γHV68) persistent infection despite continuous presentation of viral lytic Ags. However, the identity of the CD8 T cell subpopulations that mediate effective recall responses and that can participate in the generation of protective memory to a γ-herpesvirus infection remains unknown. During γHV68 persistence, ∼75% of γHV68-specific CD8 T cells coexpress the NK receptors killer cell lectin-like receptor G1 (KLRG1) and NKG2A. In this study, we take advantage of this unique phenotype to analyze the capacity of CD8 T cells expressing or not expressing KLRG1 and NKG2A to mediate effector and memory responses. Our results show that γHV68-specific KLRG1(+)NKG2A(+) CD8 T cells have an effector memory phenotype as well as characteristics of polyfunctional effector cells such us IFN-γ and TNF-α production, killing capacity, and are more efficient at protecting against a γHV68 challenge than their NKG2A(-)KLRG1(-) counterparts. Nevertheless, γHV68-specific NKG2A(+)KLRG1(+) CD8 T cells express IL-7 and IL-15 receptors, can survive long-term without cognate Ag, and subsequently mount a protective response during antigenic recall. These results highlight the plasticity of the immune system to generate protective effector and proliferative memory responses during virus persistence from a pool of KLRG1(+)NKG2A(+) effector memory CD8 T cells.

Cutting edge: activation of virus-specific CD4 T cells throughout γ-herpesvirus latency.

CD4 T cells are essential for immune control of γ-herpesvirus latency. We previously identified a murine MHC class II-restricted epitope in γ-herpesvirus-68 gp150 (gp150(67-83)I-A(b)) that elicits CD4 T cells that are maintained throughout long-term infection. However, it is unknown whether naive cells can be recruited into the antiviral CD4 T cell pool during latency. In this study, we generate a mouse transgenic for a gp150-specific TCR and show epitope-specific activation of transgenic CD4 T cells during acute and latent infections. Furthermore, although only dendritic cells can stimulate virus-specific CD8 T cells during latency, we show that both dendritic cells and B cells stimulate transgenic CD4 T cells. These studies demonstrate that naive CD4 T cells specific for a viral glycoprotein can be stimulated throughout infection, even during quiescent latency, suggesting that CD4 T cell memory is maintained in part by the continual recruitment of naive cells.

Postinfection A77-1726 treatment improves cardiopulmonary function in H1N1 influenza-infected mice.

Acute respiratory disease is associated with significant morbidity and mortality in influenza. Because antiviral drugs are only effective early in infection, new agents are needed to treat nonvaccinated patients presenting with late-stage disease, particularly those who develop acute respiratory distress syndrome. We found previously that the de novo pyrimidine synthesis inhibitor A77-1726 reversed the influenza-induced impairment of alveolar fluid clearance. Patients with acute respiratory distress syndrome and intact alveolar fluid clearance demonstrate lower mortality than those with compromised fluid clearance. We therefore investigated the effects of treatment with nebulized A77-1726 (67.5 mg/kg) on indices of cardiopulmonary function relevant to the diagnosis of acute respiratory distress syndrome. BALB/cAnNCr mice (8-12 wk old) were inoculated intranasally with 10,000 plaque-forming units/mouse influenza A/WSN/33 (H1N1). Pulse oximetry was performed daily. Alveolar fluid clearance, lung water, and lung mechanics were measured at 2 and 6 days after inoculation in live, ventilated mice by BSA instillation, magnetic resonance imaging, and forced-oscillation techniques, respectively. A77-1726 treatment at 1 day after inoculation delayed mortality. Treatment on Days 1 or 5 reduced viral replication on Day 6, and improved alveolar fluid clearance, peripheral oxygenation, and cardiac function. Nebulized A77-1726 also reversed influenza-induced increases in lung water content and volume, improved pulmonary mechanics, reduced bronchoalveolar lavage fluid ATP and neutrophil content, and increased IL-6 concentrations. The ability of A77-1726 to improve cardiopulmonary function in influenza-infected mice and to reduce the severity of ongoing acute respiratory distress syndrome late in infection suggests that pyrimidine synthesis inhibitors are promising therapeutic candidates for the management of severe influenza.

Persistent gamma-herpesvirus infection induces a CD4 T cell response containing functionally distinct effector populations.

The direct effector mechanisms of CD4 T cells during gamma-herpesvirus 68 (gammaHV68)-persistent infection are less well understood than those of their CD8 T cell counterparts, although there is substantial evidence that CD4 T cells are critical for the control of persistent gamma-herpesvirus infection. Our results show that in gammaHV68-persistently infected mice, CD4 T cells are not cytokine polyfunctional, but there is a division of labor in the CD4 T cell compartment in which CD4 T cells polarize toward two distinct populations with different effector functions: IFN-gamma producers and CD107(+) cytolytic effectors. These two CD4 T cell effector populations degranulate and produce IFN-gamma during steady state without need for exogenous antigenic restimulation, which is fundamentally different from that observed with gammaHV68-specific CD8 T cells. By using anti-IFN-gamma Ab depletions and IFN-gamma-deficient mice, we show that CD4 T cell-mediated cytotoxicity in vivo is not dependent on IFN-gamma activity. In addition, our data show that purified CD4 T cells isolated from gammaHV68-latently infected mice have the capacity to inhibit gammaHV68 reactivation from latency. Our results support the concept that CD4 T cells are critical effectors for the control of gamma-herpesvirus latent infection, and they mediate this effect by two independent mechanisms: IFN-gamma production and cytotoxicity.

Dendritic cells loaded with tumor B cells elicit broad immunity against murine gammaherpesvirus 68 but fail to prevent long-term latency.

It is still unknown whether a noninfectious gammaherpesvirus vaccine is able to prevent or reduce virus persistence. This led us to use dendritic cells loaded with tumor B cells as a vaccine approach for the murine gammaherpesvirus 68 (gammaHV68) model of infection. Dendritic cells loaded with UV-irradiated latently infected tumor B cells induce broad, strong, and long-lasting immunity against gammaHV68. Dendritic cell vaccination prevents the enlargement of lymph nodes and severely limits acute infection and early latency but does not prevent gammaHV68 from establishing long-term latency. Our findings support the concept that attenuated viruses may be the best vaccine option for preventing gammaherpesvirus persistence.

Lambda interferon is the predominant interferon induced by influenza A virus infection in vivo.

The type I alpha/beta interferons (IFN-α/ß) are known to play an important role in host defense against influenza A virus infection, but we have now discovered that the recently identified type III IFNs (IFN-λ) constitute the major response to intranasal infection with this virus. Type III IFNs were present at much higher levels than type I IFNs in the lungs of infected mice, and the enhanced susceptibility of STAT2-/- animals demonstrated that only signaling through the IFN-α/ß or IFN-λ pathways was sufficient to mediate protection. This finding offers a possible explanation for the similar levels of antiviral protection found in wild-type (WT) mice and in animals lacking a functional type I IFN receptor (IFNAR-/-) but also argues that our current understanding of type III IFN induction is incomplete. While murine IFN-λ production is thought to depend on signaling through the type I IFN receptor, we demonstrate that intranasal influenza A virus infection leads to the robust type III IFN induction in the lungs of both WT and IFNAR-/- mice. This is consistent with previous studies showing that IFNAR-mediated protection is redundant for mucosal influenza virus infection and with data showing that the type III IFN receptor is expressed primarily by epithelial cells. However, the overlapping effects of these two cytokine families are limited by their differential receptor expression, with a requirement for IFN-α/ß signaling in combating systemic disease.

Protective antigen-independent CD8 T cell memory is maintained during {gamma}-herpesvirus persistence.

Ag persistence during high-titer chronic viral infections induces CD8 T cell dysfunction and lack of Ag-independent CD8 T cell memory formation. However, we have a poor understanding of the generation and maintenance of CD8 T cell memory during asymptomatic persistent viral infections, particularly gamma-herpesvirus infections. In this study, we demonstrate that the continuous presence of cognate Ag in the host is not required for the maintenance of CD8 T cell memory during a persistent gamma-herpesvirus infection. Importantly, the Ag-independent CD8 T cell memory that is maintained during gamma-herpesvirus persistence has the capacity to survive long-term under homeostatic conditions and to mount a protective recall response to a secondary encounter with the pathogen. These data highlight the ability of the immune system to maintain a population of protective memory CD8 T cells with capacity for long-term Ag-independent survival in the presence of systemic virus persistence.

Gamma-herpesvirus latency is preferentially maintained in splenic germinal center and memory B cells.

The gamma-herpesviruses are oncogenic B cell lymphotrophic viruses that establish life-long latency in the host. Murine gamma-herpesvirus 68 (MHV-68) infection of mice represents a unique system for analyzing gamma-herpesvirus latency in splenic B cells at different stages of infection. After intranasal infection with MHV-68 we analyzed the establishment of latency 14 days after infection, and the maintenance of latency 3 months after infection in different purified subpopulations of B cells in the spleen. The data show that MHV-68 latency is mainly established in germinal center B cells and that long-term latency is preferentially maintained in two different subsets of isotype-switched B cells, germinal center and memory B cells. Cell cycle analysis indicates that MHV-68 is located in both cycling and resting isotype-switched B cells. Analysis of viral gene expression showed that both lytic and latent viral transcripts were differentially expressed in germinal center and memory B cells during long-term latency. Together, these observations suggested that gamma-herpesviruses exploit the B cell life cycle in the spleen.

CD4 T cells mediate killing during persistent gammaherpesvirus 68 infection.

CD4 T cells are critical for the control of gammaherpesvirus persistence, but their direct effector mechanisms of virus control in vivo are still poorly understood. In this study, we use murine gammaherpesvirus 68 (gammaHV68) in in vitro and in vivo cytotoxicity assays to show CD4-dependent killing of gammaHV68-loaded cells in mice persistently infected with gammaHV68. Our results underscore the cytotoxic capacity of CD4 T cells during gammaHV68 persistence.

A mouse model for infectious mononucleosis.

Epstein-Barr virus (EBV) is a ubiquitous human gamma-herpesvirus that establishes life-long latency and is associated with lymphoproliferative disorders and the development of several malignancies. EBV infection is frequently, but not always, associated with the development of a syndrome termed infectious mononucleosis. The recent isolation and characterization of a murine gamma-herpesvirus, MHV-68 (gammaHV-68) has provided the first small animal model for studying immunity and pathogenesis of a gamma-herpesvirus in its natural host. MHV-68 has important biological and genetic similarities with the human gamma-herpesviruses. Following intranasal infection of mice with MHV-68, an acute respiratory infection in the lung develops and is cleared, followed by the establishment of latency. Similar to EBV, MHV-68 latency is largely established in B cells, although other cell types can be latently infected. The establishment of latency correlates with a prominent splenomegaly, polyclonal B cell activation with associated autoantibody production, and CD8+ T cell-dominated peripheral blood lymphocytosis, in many aspects mirroring EBV-induced infectious mononucleosis. There are key differences in the MHV-68- and EBV-induced CD8+ T cell responses however. Whereas the expanded CD8+ T cells associated with EBV-induced mononucleosis are largely the outgrowth of T cells responding to lytic viral epitopes elicited during the acute phase of the response, the CD8+ T cell lymphocytosis associated with MHV-68-induced infectious mononucleosis is dominated by an oligoclonal population of T cells expressing Vbeta4+ T cell receptors that are not reactive to acute viral epitopes. The focus of this article will be to highlight the similarities and differences in the infectious mononucleosis syndrome associated with human and murine gamma-herpesviruses.

Induction of ICOS+CXCR3+CXCR5+ TH cells correlates with antibody responses to influenza vaccination.

Seasonal influenza vaccine protects 60 to 90% of healthy young adults from influenza infection. The immunological events that lead to the induction of protective antibody responses remain poorly understood in humans. We identified the type of CD4+ T cells associated with protective antibody responses after seasonal influenza vaccinations. The administration of trivalent split-virus influenza vaccines induced a temporary increase of CD4+ T cells expressing ICOS, which peaked at day 7, as did plasmablasts. The induction of ICOS was largely restricted to CD4+ T cells coexpressing the chemokine receptors CXCR3 and CXCR5, a subpopulation of circulating memory T follicular helper cells. Up to 60% of these ICOS+CXCR3+CXCR5+CD4+ T cells were specific for influenza antigens and expressed interleukin-2 (IL-2), IL-10, IL-21, and interferon-γ upon antigen stimulation. The increase of ICOS+CXCR3+CXCR5+CD4+ T cells in blood correlated with the increase of preexisting antibody titers, but not with the induction of primary antibody responses. Consistently, purified ICOS+CXCR3+CXCR5+CD4+ T cells efficiently induced memory B cells, but not naïve B cells, to differentiate into plasma cells that produce influenza-specific antibodies ex vivo. Thus, the emergence of blood ICOS+CXCR3+CXCR5+CD4+ T cells correlates with the development of protective antibody responses generated by memory B cells upon seasonal influenza vaccination.