Immunoglobulin A antibody composition is sculpted to bind the self gut microbiome

Despite being the most abundantly secreted immunoglobulin isotype, the pattern of reactivity of immunoglobulin A (IgA) antibodies toward each individual's own gut commensal bacteria still remains elusive. By colonizing germ-free mice with defined commensal bacteria, we found that the binding specificity of bulk fecal and serum IgA toward resident gut bacteria resolves well at the species level and has modest strain-level specificity. IgA hybridomas generated from lamina propria B cells of gnotobiotic mice showed that most IgA clones recognized a single bacterial species, whereas a small portion displayed cross-reactivity. Orally administered hybridoma-produced IgAs still retained bacterial antigen binding capability, implying the potential for a new class of therapeutic antibodies. Species-specific IgAs had a range of strain specificities. Given the distinctive bacterial species and strain composition found in each individual's gut, our findings suggest the IgA antibody repertoire is shaped uniquely to bind "self" gut bacteria.

Development of broadly neutralizing antibodies targeting the cytomegalovirus subdominant antigen gH

Human cytomegalovirus (HCMV) is a β-herpesvirus that increases morbidity and mortality in immunocompromised individuals including transplant recipients and newborns. New anti-HCMV therapies are an urgent medical need for diverse patient populations. HCMV infection of a broad range of host tissues is dependent on the gH/gL/gO trimer and gH/gL/UL28/UL130/UL131A pentamer complexes on the viral envelope. We sought to develop safe and effective therapeutics against HCMV by generating broadly-neutralizing, human monoclonal antibodies (mAbs) from VelocImmune® mice immunized with gH/gL cDNA. Following high-throughput binding and neutralization screening assays, 11 neutralizing antibodies were identified with unique CDR3 regions and a high-affinity (KD 1.4-65 nM) to the pentamer complex. The antibodies bound to distinct regions within Domains 1 and 2 of gH and effectively neutralized diverse clinical strains in physiologically relevant cell types including epithelial cells, trophoblasts, and monocytes. Importantly, combined adminstration of mAbs with ganciclovir, an FDA approved antiviral, greatly limited virus dissemination. Our work identifies several anti-gH/gL mAbs and sheds light on gH neutralizing epitopes that can guide future vaccine strategies.

Quantifying Absolute Neutralization Titers against SARS-CoV-2 by a Standardized Virus Neutralization Assay Allows for Cross-Cohort Comparisons of COVID-19 Sera

The global coronavirus disease 2019 (COVID-19) pandemic has mobilized efforts to develop vaccines and antibody-based therapeutics, including convalescent-phase plasma therapy, that inhibit viral entry by inducing or transferring neutralizing antibodies (nAbs) against the severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) spike glycoprotein (CoV2-S). However, rigorous efficacy testing requires extensive screening with live virus under onerous biosafety level 3 (BSL3) conditions, which limits high-throughput screening of patient and vaccine sera. Myriad BSL2-compatible surrogate virus neutralization assays (VNAs) have been developed to overcome this barrier. Yet, there is marked variability between VNAs and how their results are presented, making intergroup comparisons difficult. To address these limitations, we developed a standardized VNA using CoV2-S pseudotyped particles (CoV2pp) based on vesicular stomatitis virus bearing the Renilla luciferase gene in place of its G glycoprotein (VSVΔG); this assay can be robustly produced at scale and generate accurate neutralizing titers within 18 h postinfection. Our standardized CoV2pp VNA showed a strong positive correlation with CoV2-S enzyme-linked immunosorbent assay (ELISA) results and live-virus neutralizations in confirmed convalescent-patient sera. Three independent groups subsequently validated our standardized CoV2pp VNA (n > 120). Our data (i) show that absolute 50% inhibitory concentration (absIC50), absIC80, and absIC90 values can be legitimately compared across diverse cohorts, (ii) highlight the substantial but consistent variability in neutralization potency across these cohorts, and (iii) support the use of the absIC80 as a more meaningful metric for assessing the neutralization potency of a vaccine or convalescent-phase sera. Lastly, we used our CoV2pp in a screen to identify ultrapermissive 293T clones that stably express ACE2 or ACE2 plus TMPRSS2. When these are used in combination with our CoV2pp, we can produce CoV2pp sufficient for 150,000 standardized VNAs/week.IMPORTANCE Vaccines and antibody-based therapeutics like convalescent-phase plasma therapy are premised upon inducing or transferring neutralizing antibodies that inhibit SARS-CoV-2 entry into cells. Virus neutralization assays (VNAs) for measuring neutralizing antibody titers (NATs) are an essential part of determining vaccine or therapeutic efficacy. However, such efficacy testing is limited by the inherent dangers of working with the live virus, which requires specialized high-level biocontainment facilities. We therefore developed a standardized replication-defective pseudotyped particle system that mimics the entry of live SARS-CoV-2. This tool allows for the safe and efficient measurement of NATs, determination of other forms of entry inhibition, and thorough investigation of virus entry mechanisms. Four independent labs across the globe validated our standardized VNA using diverse cohorts. We argue that a standardized and scalable assay is necessary for meaningful comparisons of the myriad of vaccines and antibody-based therapeutics becoming available. Our data provide generalizable metrics for assessing their efficacy.

Quantifying absolute neutralization titers against SARS-CoV-2 by a standardized virus neutralization assay allows for cross-cohort comparisons of COVID-19 sera

The global COVID-19 pandemic has mobilized efforts to develop vaccines and antibody-based therapeutics, including convalescent plasma therapy, that inhibit viral entry by inducing or transferring neutralizing antibodies (nAbs) against the SARS-CoV-2 spike glycoprotein (CoV2-S). However, rigorous efficacy testing requires extensive screening with live virus under onerous BSL3 conditions which limits high throughput screening of patient and vaccine sera. Myriad BSL-2 compatible surrogate virus neutralization assays (VNAs) have been developed to overcome this barrier. Yet, there is marked variability between VNAs and how their results are presented, making inter-group comparisons difficult. To address these limitations, we developed a standardized VNA using VSVΔG-based CoV-2-S pseudotyped particles (CoV2pp) that can be robustly produced at scale and generate accurate neutralizing titers within 18 hours post-infection. Our standardized CoV2pp VNA showed a strong positive correlation with CoV2-S ELISA and live virus neutralizations in confirmed convalescent patient sera. Three independent groups subsequently validated our standardized CoV2pp VNA (n>120). Our data show that absolute (abs) IC50, IC80, and IC90 values can be legitimately compared across diverse cohorts, highlight the substantial but consistent variability in neutralization potency across these cohorts, and support the use of absIC80 as a more meaningful metric for assessing the neutralization potency of vaccine or convalescent sera. Lastly, we used our CoV2pp in a screen to identify ultra-permissive 293T clones that stably express ACE2 or ACE2+TMPRSS2. When used in combination with our CoV2pp, we can now produce CoV2pp sufficient for 150,000 standardized VNA/week.

Interleukin 22 disrupts pancreatic function in newborn mice expressing IL-23

Neonatal inflammatory diseases are associated with severe morbidity, but the inflammatory factors underlying them and their potential effector mechanisms are poorly defined. Here we show that necrotizing enterocolitis in neonate mice is accompanied by elevation of IL-23 and IL-22 and decreased production of pancreatic enzymes. These phenotypes are mirrored in neonate mice overexpressing IL-23 in CX3CR1+ myeloid cells or in keratinocytes. The mice fail to grow and die prematurely, displaying systemic inflammation, nutrient malabsorption and decreased expression of intestinal and pancreatic genes mediating digestion and absorption of carbohydrates, proteins, and lipids. Germ-free environment improves, and genetic ablation of IL-22 restores normal growth in mice overexpressing IL-23. Mechanistically, IL-22 acts directly at the level of pancreatic acinar cells to decrease expression of the pancreas associated transcription factor 1a (PTF1a). These results show that augmented production of IL-23 and IL-22 in early life has a negative impact on pancreatic enzyme secretion and food absorption.

Abstract 2124: Concurrent in vitro and in silico approach for the identification of surface proteome targets on HPV-associated cancer cells

Human papillomavirus (HPV)-associated Head and neck cancer (HNSCC) are among the fastest growing cancer types. In contrast to non-viral HNSCC caused by traditional risk factors, tobacco and alcohol, HPV-HNSCC displayed distinct molecular alterations and prognosis from HPV-negative HNSCC. Currently, there is no clinically-approved therapeutic vaccine, and no targeted therapy approach for HPV-driven cancer which exploits the unique biology of HPV infection. In order to identify novel targets suitable for therapeutic and diagnostic development, we developed two parallel approaches to identification of proteins/antigens expressed on the surface of the host cells, whose expression is altered by HPV infection. One is an “antigen-agnostic” approach by using immortalized HNSCC cell membrane fractions to generate monoclonal antibodies, which does not require advance knowledge of the identities of target antigens. The second approach is bioinformatics analyses of the TCGA database using the epigenomic deconvolution tool (EDec) to identify surface proteins that are differentially overexpressed in HPV- HNSCC. Five thousand hybridoma colonies were generated by the “antigen-agnostic” approach, and were then screened by flow cytometry to test the specificity of binding to HPV-positive cancer cell lines (2 HNSCC and 2 Cervical Cancer) and HPV-negative cancer cell lines (4 HNSCC and 1 CC). After primary screening, we narrowed down to forty-four clones with preliminarily favorable binding characteristics; among these hybridoma clones, we have identified seven which preferentially bind to HPV-positive cancer cells. We then identified the binding targets of three clones via immunoprecipitation and mass spectrometry. These targets are integrin alpha6 beta4 (ITGA6, ITGB4), tissue factor (F3) and keratin 8 (KRT8) respectively. The bioinformatics-based approach identified several surface proteins that are differentially overexpressed in HPV-positive HNSCC and at levels significantly higher than found in normal control tissue. Evaluation of gene and protein expression in cancer cell lines and/or patient tissue validated several genes identified by the deconvolution approach, including: ROR2, a non-canonical WNT member not previously associated with head and neck cancer; and LY6K, a cancer-testis antigen that overexpressed in both HPV-positive and negative HNSCC. We propose targeting membrane-expressed antigens on HPV-related cancer cells as a platform for further development of novel tumor imaging and therapeutic approaches for HNSCC and other HPV-associated cancers.

Citation Format: Hsuan-Chen Liu, Ivenise Carrero, Falguni Parikh, Thomas Kraus, Thomas M. Moran, Mathew J. Ellis, Elizabeth Y. Chiao, Aleksandar Milosavljevic, Andrew G. Sikora. Concurrent in vitro and in silico approach for the identification of surface proteome targets on HPV-associated cancer cells [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2019; 2019 Mar 29-Apr 3; Atlanta, GA. Philadelphia (PA): AACR; Cancer Res 2019;79(13 Suppl):Abstract nr 2124.

Perfluoroalkyl substance serum concentrations and immune response to FluMist vaccination among healthy adults

Perfluoroalkyl substances (PFAS) were shown to be immunotoxic in laboratory animals. There is some epidemiological evidence that PFAS exposure is inversely associated with vaccine-induced antibody concentration. We examined immune response to vaccination with FluMist intranasal live attenuated influenza vaccine in relation to four PFAS (perfluorooctanoate, perfluorononanoate, perfluorooctane sulfonate, perfluorohexane sulfonate) serum concentrations among 78 healthy adults vaccinated during the 2010-2011 influenza season. We measured anti-A H1N1 antibody response and cytokine and chemokine concentrations in serum pre-vaccination, 3 days post-vaccination, and 30 days post-vaccination. We measured cytokine, chemokine, and mucosal IgA concentration in nasal secretions 3 days post-vaccination and 30 days post-vaccination. Adults with higher PFAS concentrations were more likely to seroconvert after FluMist vaccination as compared to adults with lower PFAS concentrations. The associations, however, were imprecise and few participants seroconverted as measured either by hemagglutination inhibition (9%) or immunohistochemical staining (25%). We observed no readily discernable or consistent pattern between PFAS concentration and baseline cytokine, chemokine, or mucosal IgA concentration, or between PFAS concentration and change in these immune markers between baseline and FluMist-response states. The results of this study do not support a reduced immune response to FluMist vaccination among healthy adults in relation to serum PFAS concentration. Given the study's many limitations, however, it does not rule out impaired vaccine response to other vaccines or vaccine components in either children or adults.

CYLD Proteolysis Protects Macrophages from TNF-Mediated Auto-necroptosis Induced by LPS and Licensed by Type I IFN

Tumor necrosis factor (TNF) induces necroptosis, a RIPK3/MLKL-dependent form of inflammatory cell death. In response to infection by Gram-negative bacteria, multiple receptors on macrophages, including TLR4, TNF, and type I IFN receptors, are concurrently activated, but it is unclear how they crosstalk to regulate necroptosis. We report that TLR4 activates CASPASE-8 to cleave and remove the deubiquitinase cylindromatosis (CYLD) in a TRIF- and RIPK1-dependent manner to disable necroptosis in macrophages. Inhibiting CASPASE-8 leads to CYLD-dependent necroptosis caused by the TNF produced in response to TLR4 ligation. While lipopolysaccharides (LPS)-induced necroptosis was abrogated in Tnf(-/-) macrophages, a soluble TNF antagonist was not able to do so in Tnf(+/+) macrophages, indicating that necroptosis occurs in a cell-autonomous manner. Surprisingly, TNF-mediated auto-necroptosis of macrophages requires type I IFN, which primes the expression of key necroptosis-signaling molecules, including TNFR2 and MLKL. Thus, the TNF necroptosis pathway is regulated by both negative and positive crosstalk.

Polymorphisms in inflammatory genes are associated with term small for gestational age and preeclampsia

PROBLEM

Inflammatory biomarkers are associated with preeclampsia (PE) and poor fetal growth; however, genetic epidemiologic studies have been limited by reduced gene coverage and the exclusion of African American mothers.

METHOD OF STUDY

Cases and controls (N = 1646) from a pregnancy cohort were genotyped for 503 tagSNPs in 40 genes related to inflammation. Gene-set analyses were stratified by race and were followed by a single SNP analysis within significant gene sets.

RESULTS

Gene-level associations were found for IL6 and KLRD1 for term small for gestational age (SGA) among African Americans. LTA/TNF and TBX21 were associated with PE among European Americans. The strongest association was for PE among European Americans for an upstream regulator of TNF with RR = 1.8 (95% CI 1.1-2.7).

CONCLUSION

Although previous studies have suggested null associations, increased tagging and stratification by genetic ancestry suggests important associations between IL6 and term SGA for African Americans, and a TNF regulator and PE among European Americans (N = 149).

Combinatorial cytokine code generates anti-viral state in dendritic cells

The physiological function of the immune system and the response to therapeutic immunomodulators may be sensitive to combinatorial cytokine micro-environments that shape the responses of specific immune cells. Previous work shows that paracrine cytokines released by virus-infected human dendritic cells (DC) can dictate the maturation state of naïve DCs. To understand the effects of paracrine signaling, we systematically studied the effects of combinations cytokines in this complex mixture in generating an anti-viral state. After naïve DCs were exposed to either IFNβ or to paracrine signaling released by DCs infected by Newcastle disease virus (NDV), microarray analysis revealed a large number of genes that were differently regulated by the DC-secreted paracrine signaling. In order to identify the cytokine mechanisms involved, we identified 20 cytokines secreted by NDV infected DCs for which the corresponding receptor gene is expressed in naïve DCs. By exposing cells to all combinations of 19 cytokines (leave-one-out studies), we identified five cytokines (IFNβ, TNFα, IL-1β, TNFSF15, and IL28) as candidates for regulating DC maturation markers. Subsequent experiments identified IFNβ, TNFα, and IL1β as the major contributors to this anti-viral state. This finding was supported by infection studies in vitro, by T-cell activation studies and by in vivo infection studies in mouse. Combination of cytokines can cause response states in DCs that differ from those achieved by the individual cytokines alone. These results suggest that the cytokine microenvironment may act via a combinatorial code to direct the response state of specific immune cells. Further elucidation of this code may provide insight into responses to infection and neoplasia as well as guide the development of combinatorial cytokine immunomodulation for infectious, autoimmune, and immunosurveillance-related diseases.

Plasma level of interferon γ induced protein 10 is a marker of sarcoidosis disease activity

RATIONALE

Sarcoidosis is an idiopathic granulomatous disorder with heterogeneous clinical manifestations and variable prognosis. Monitoring disease activity is important to identify patients requiring treatment. Several cytokines have previously been shown to be elevated in the serum of patients with sarcoidosis and may be useful biomarkers of disease activity.

OBJECTIVES

To identify novel biomarkers of sarcoidosis disease activity. To identify the relationship between plasma cytokines, disease severity and prognosis.

METHODS

The study was approved by the institutional review board. Plasma concentration of 19 cytokines was measured in 112 subjects with chronic sarcoidosis and 52 matched controls, using the bead-based Milliplex xMAP multiplex technology. Plasma levels of individual cytokines were compared between the two groups, and between the groups with clinically active vs. inactive disease. Sensitivity, specificity and receiver operating characteristics curves were used to evaluate biomarker performance. Linear regression analyses were performed to identify associations between cytokine levels, pulmonary function tests and changes in pulmonary function.

MEASUREMENTS AND MAIN RESULTS

Subjects with sarcoidosis had higher plasma levels of interferon gamma induced protein 10 (IP-10) and tumor necrosis factor α (TNFα). IP-10 had the highest sensitivity and specificity in identifying active disease. Higher levels of IP-10 and TNFα were associated with greater disease severity and better prognosis.

CONCLUSIONS

IP-10 is a potentially useful biomarker of sarcoidosis and its severity.

The influence of pregnancy on systemic immunity

Adaptations in maternal systemic immunity are presumed to be responsible for observed alterations in disease susceptibility and severity as pregnancy progresses. Epidemiological evidence as well as animal studies have shown that influenza infections are more severe during the second and third trimesters of pregnancy, resulting in greater morbidity and mortality, although the reason for this is still unclear. Our laboratory has taken advantage of 20 years of experience studying the murine immune response to respiratory viruses to address questions of altered immunity during pregnancy. With clinical studies and unique animal model systems, we are working to define the mechanisms responsible for altered immune responses to influenza infection during pregnancy and what roles hormones such as estrogen or progesterone play in these alterations.

Mouse dendritic cell (DC) influenza virus infectivity is much lower than that for human DCs and is hemagglutinin subtype dependent

We show that influenza A H1N1 virus infection leads to very low infectivity in mouse dendritic cells (DCs) in vitro compared with that in human DCs. This holds when H3 or H5 replaces H1 in recombinant viruses. Viruslike particles confirm the difference between mouse and human, suggesting that reduced virus entry contributes to lower mouse DC infectivity. Low infectivity of mouse DCs should be considered when they are used to study responses of DCs that are actually infected.

Localized mucosal response to intranasal live attenuated influenza vaccine in adults

BACKGROUND

Influenza virus infection is a major public health burden worldwide. Available vaccines include the inactivated intramuscular trivalent vaccine and, more recently, an intranasal live attenuated influenza vaccine (LAIV). The measure of successful vaccination with the inactivated vaccine is a systemic rise in immunoglobulin G (IgG) level, but for the LAIV no such correlate has been established.

METHODS

Seventy-nine subjects were given the LAIV FluMist. Blood was collected prior to vaccination and 3 days and 30 days after vaccination. Nasal wash was collected 3 days and 30 days after vaccination. Responses were measured systemically and in mucosal secretions for cytokines, cell activation profiles, and antibody responses.

RESULTS

Only 9% of subjects who received LAIV seroconverted, while 33% of patients developed at least a 2-fold increase in influenza virus-specific immunoglobulin A (IgA) antibodies in nasal wash. LAIV induced a localized inflammation, as suggested by increased expression of interferon-response genes in mucosal RNA and increased granulocyte colony-stimulating factor (G-CSF) and IP-10 in nasal wash. Interestingly, patients who seroconverted had significantly lower serum levels of G-CSF before vaccination.

CONCLUSIONS

Protection by LAIV is likely provided through mucosal IgA and not by increases in systemic IgG. LAIV induces local inflammation. Seroconversion is achieved in a small fraction of subjects with a lower serum G-CSF level.

Estrogen mediates innate and adaptive immune alterations to influenza infection in pregnant mice

Pregnancy is a leading risk factor for severe complications during an influenza virus infection. Women infected during their second and third trimesters are at increased risk for severe cardiopulmonary complications, premature delivery, and death. Here, we establish a murine model of aerosolized influenza infection during pregnancy. We find significantly altered innate antiviral responses in pregnant mice, including decreased levels of IFN-β, IL-1α, and IFN-γ at early time points of infection. We also find reduced cytotoxic T cell activity and delayed viral clearance. We further demonstrate that pregnancy levels of the estrogen 17-β-estradiol are able to induce key anti-inflammatory phenotypes in immune responses to the virus independently of other hormones or pregnancy-related stressors. We conclude that elevated estrogen levels result in an attenuated anti-viral immune response, and that pregnancy-associated morbidities occur in the context of this anti-inflammatory phenotype.

Granulocyte colony-stimulating factor protects mice during respiratory virus infections

A burst in the production of pro-inflammatory molecules characterizes the beginning of the host response to infection. Cytokines, chemokines, and growth factors work in concert to control pathogen replication and activate innate and adaptive immune responses. Granulocyte colony-stimulating factor (G-CSF) mobilizes and activates hematopoietic cells from the bone marrow, and it has been shown to mediate the generation of effective immunity against bacterial and fungal infections. G-CSF is produced at high levels in the lungs during infection with influenza and parainfluenza viruses, but its role during these infections is unknown. Here we show that during infection of mice with a non-lethal dose of influenza or Sendai virus, G-CSF promotes the accumulation of activated Ly6G⁺ granulocytes that control the extent of the lung pro-inflammatory response. Remarkably, these G-CSF-mediated effects facilitate viral clearance and sustain mouse survival.

High-throughput detection method for influenza virus

Influenza virus is a respiratory pathogen that causes a high degree of morbidity and mortality every year in multiple parts of the world. Therefore, precise diagnosis of the infecting strain and rapid high-throughput screening of vast numbers of clinical samples is paramount to control the spread of pandemic infections. Current clinical diagnoses of influenza infections are based on serologic testing, polymerase chain reaction, direct specimen immunofluorescence and cell culture (1,2). Here, we report the development of a novel diagnostic technique used to detect live influenza viruses. We used the mouse-adapted human A/PR/8/34 (PR8, H1N1) virus (3) to test the efficacy of this technique using MDCK cells (4). MDCK cells (10(4) or 5 x 10(3) per well) were cultured in 96- or 384-well plates, infected with PR8 and viral proteins were detected using anti-M2 followed by an IR dye-conjugated secondary antibody. M2 (5) and hemagglutinin (1) are two major marker proteins used in many different diagnostic assays. Employing IR-dye-conjugated secondary antibodies minimized the autofluorescence associated with other fluorescent dyes. The use of anti-M2 antibody allowed us to use the antigen-specific fluorescence intensity as a direct metric of viral quantity. To enumerate the fluorescence intensity, we used the LI-COR Odyssey-based IR scanner. This system uses two channel laser-based IR detections to identify fluorophores and differentiate them from background noise. The first channel excites at 680 nm and emits at 700 nm to help quantify the background. The second channel detects fluorophores that excite at 780 nm and emit at 800 nm. Scanning of PR8-infected MDCK cells in the IR scanner indicated a viral titer-dependent bright fluorescence. A positive correlation of fluorescence intensity to virus titer starting from 10(2)-10(5) PFU could be consistently observed. Minimal but detectable positivity consistently seen with 10(2)-10(3) PFU PR8 viral titers demonstrated the high sensitivity of the near-IR dyes. The signal-to-noise ratio was determined by comparing the mock-infected or isotype antibody-treated MDCK cells. Using the fluorescence intensities from 96- or 384-well plate formats, we constructed standard titration curves. In these calculations, the first variable is the viral titer while the second variable is the fluorescence intensity. Therefore, we used the exponential distribution to generate a curve-fit to determine the polynomial relationship between the viral titers and fluorescence intensities. Collectively, we conclude that IR dye-based protein detection system can help diagnose infecting viral strains and precisely enumerate the titer of the infecting pathogens.

p53 serves as a host antiviral factor that enhances innate and adaptive immune responses to influenza A virus

Several direct target genes of the p53 tumor suppressor have been identified within pathways involved in viral sensing, cytokine production, and inflammation, suggesting a potential role of p53 in antiviral immunity. The increasing need to identify immune factors to devise host-targeted therapies against pandemic influenza A virus (IAV) led us to investigate the role of endogenous wild-type p53 on the immune response to IAV. We observed that the absence of p53 resulted in delayed cytokine and antiviral gene responses in lung and bone marrow, decreased dendritic cell activation, and reduced IAV-specific CD8(+) T cell immunity. Consequently, p53(-/-) mice showed a more severe IAV-induced disease compared with their wild-type counterparts. These findings establish that p53 influences the antiviral response to IAV, affecting both innate and adaptive immunity. Thus, in addition to its established functions as a tumor suppressor gene, p53 serves as an IAV host antiviral factor that might be modulated to improve anti-IAV therapy and vaccines.

Unique type I interferon responses determine the functional fate of migratory lung dendritic cells during influenza virus infection

Migratory lung dendritic cells (DCs) transport viral antigen from the lungs to the draining mediastinal lymph nodes (MLNs) during influenza virus infection to initiate the adaptive immune response. Two major migratory DC subsets, CD103⁺ DCs and CD11b^high DCs participate in this function and it is not clear if these antigen presenting cell (APC) populations become directly infected and if so whether their activity is influenced by the infection. In these experiments we show that both subpopulations can become infected and migrate to the draining MLN but a difference in their response to type I interferon (I-IFN) signaling dictates the capacity of the virus to replicate. CD103⁺ DCs allow the virus to replicate to significantly higher levels than do the CD11b^high DCs, and they release infectious virus in the MLNs and when cultured ex-vivo. Virus replication in CD11b^high DCs is inhibited by I-IFNs, since ablation of the I-IFN receptor (IFNAR) signaling permits virus to replicate vigorously and productively in this subset. Interestingly, CD103⁺ DCs are less sensitive to I-IFNs upregulating interferon-induced genes to a lesser extent than CD11b^high DCs. The attenuated IFNAR signaling by CD103⁺ DCs correlates with their described superior antigen presentation capacity for naïve CD8⁺ T cells when compared to CD11b^high DCs. Indeed ablation of IFNAR signaling equalizes the competency of the antigen presenting function for the two subpopulations. Thus, antigen presentation by lung DCs is proportional to virus replication and this is tightly constrained by I-IFN. The “interferon-resistant” CD103⁺ DCs may have evolved to ensure the presentation of viral antigens to T cells in I-IFN rich environments. Conversely, this trait may be exploitable by viral pathogens as a mechanism for systemic dissemination.

Migratory lung dendritic cells (DCs) control the initiation of the adaptive immune responses to influenza virus by expanding virus-specific T cells in draining lymph nodes (MLNs) that will subsequently clear the pathogen from the respiratory tract. Here we demonstrate that both subsets of lung DCs, CD103⁺ DCs and CD11b^high DCs become infected by influenza virus in vivo and migrate to the MLNs, but only CD103⁺ DCs support productive virus replication. Enhanced virus replication in CD103⁺ DCs compared to CD11b^high DCs was responsible for their superior antigen presentation efficacy for naïve CD8⁺ T cells and originated from a difference in sensitivity of the two DC populations to type I interferon (I-IFN). These data show that in contrast to most other immune cell types, DCs can become productively infected with influenza virus and I-IFN operates as a master regulator controlling which DC subset will present antigen during a viral infection. A deeper understanding of basic innate and adaptive immune response mechanisms regulated by I-FN may lead to the development of cutting edge therapies and improve vaccine efficacy against influenza and other viruses.

Alpha-defensins 1-3 release by dendritic cells is reduced by estrogen

BACKGROUND

During pregnancy the immune system of the mother must protect any activation that may negatively affect the fetus. Changes in susceptibility to infection as well as resolution of some autoimmune disorders represent empirical evidence for pregnancy related alterations in immunity. Sex hormones reach extremely high levels during pregnancy and have been shown to have direct effects on many immune functions including the antiviral response of dendritic cells. Among the immunologically active proteins secreted by monocyte derived DCs (MDDC) are the alpha-defensins 1-3. This family of cationic antimicrobial peptides has a broad spectrum of microbicidal activity and has also been shown to link innate to adaptive immunity by attracting T cells and immature DCs, which are essential for initiating and polarizing the immune response.

METHODS

We compare culture-generated monocyte derived DCs (MDDCs) with directly isolated myeloid dendritic cells (mDCs) and plasmacytoid dendritic cells (pDCs) and measure their alpha-defensins 1-3 secretion by ELISA both, in basal situations and after hormone (E2 or PG) treatments. Moreover, using a cohort of pregnant women we isolated mDCs from blood and also measure the levels of these anti-microbial peptides along pregnancy.

RESULTS

We show that mDCs and pDCs constitutively produce alpha-defensins 1-3 and at much higher levels than MDDCs. Alpha-defensins 1-3 production from mDCs and MDDCs but not pDCs is inhibited by E2. PG does not affect alpha-defensins 1-3 in any of the populations. Moreover, alpha-defensins 1-3 production by mDCs was reduced in the later stages of pregnancy in 40% of the patients.

CONCLUSIONS

Here, we demonstrate that mDCs and pDCs secrete alpha-defensins 1-3 and present a novel effect of E2 on the secretion of alpha-defensins 1-3 by dendritic cells.

Buying time-the immune system determinants of the incubation period to respiratory viruses

Respiratory viruses cause disease in humans characterized by an abrupt onset of symptoms. Studies in humans and animal models have shown that symptoms are not immediate and appear days or even weeks after infection. Since the initial symptoms are a manifestation of virus recognition by elements of the innate immune response, early virus replication must go largely undetected. The interval between infection and the emergence of symptoms is called the incubation period and is widely used as a clinical score. While incubation periods have been described for many virus infections the underlying mechanism for this asymptomatic phase has not been comprehensively documented. Here we review studies of the interaction between human pathogenic respiratory RNA viruses and the host with a particular emphasis on the mechanisms used by viruses to inhibit immunity. We discuss the concept of the "stealth phase", defined as the time between infection and the earliest detectable inflammatory response. We propose that the "stealth phase" phenomenon is primarily responsible for the suppression of symptoms during the incubation period and results from viral antagonism that inhibits major pathways of the innate immune system allowing an extended time of unhindered virus replication.

Peripheral blood cytokine profiling during pregnancy and post-partum periods

PROBLEM

Pregnancy requires that the maternal immune system adapt to prevent rejection of the fetal semi-allograft. This immunologic adaptation may contribute to pregnancy-related alterations in disease susceptibility and severity of infections from viral pathogens such as influenza virus.

METHOD OF STUDY

As part of a larger study investigating the maternal systemic immune response during pregnancy, peripheral blood was collected three times during pregnancy and twice post-partum to measure serum levels of 23 cytokines, chemokines, and growth factors. This longitudinal study design allowed each woman's post-partum blood draw to serve as her own comparison, thus controlling for interpersonal variability in expression levels.

RESULTS

When compared to the post-partum samples, significant pregnancy-related changes in IFNγ, TNFα, VEGF, GCSF, Eotaxin, and MCP-1 expression were observed. These changes have significant immunologic effects in vivo and in culture.

CONCLUSION

Pregnancy-associated changes to steady state serum cytokines may have important immunologic consequence.

Antiviral instruction of bone marrow leukocytes during respiratory viral infections

Respiratory viral infections trigger a robust inflammatory response in the lung, producing cytokines, chemokines, and growth factors that promote infiltration of effector leukocytes. Whereas the role of chemokines and infiltrating leukocytes in antiviral immunity is well studied, the effect that lung cytokines have on leukocytes in distal hematopoietic and lymphoid tissues and their role in antiviral immunity is unknown. We show that, during infection with influenza or Sendai virus, the lung communicates with the sterile bone marrow, the primary site of hematopoiesis, through type I interferons. While in the bone marrow, leukocytes exposed to type I interferons activate an antiviral transcriptional program and become resistant to infection with different viruses. The protected bone marrow leukocytes are capable of migrating to the infected lung and contribute to virus clearance. These findings show that appropriate instruction of cells during their development in the bone marrow is needed for effective control of infection.

Immune response modeling of interferon beta-pretreated influenza virus-infected human dendritic cells

The pretreatment of human dendritic cells with interferon-beta enhances their immune response to influenza virus infection. We measured the expression levels of several key players in that response over a period of 13 h both during pretreatment and after viral infection. Their activation profiles reflect the presence of both negative and positive feedback loops in interferon induction and interferon signaling pathway. Based on these measurements, we have developed a comprehensive computational model of cellular immune response that elucidates its mechanism and its dynamics in interferon-pretreated dendritic cells, and provides insights into the effects of duration and strength of pretreatment.

Broadly protective monoclonal antibodies against H3 influenza viruses following sequential immunization with different hemagglutinins

As targets of adaptive immunity, influenza viruses are characterized by the fluidity with which they respond to the selective pressure applied by neutralizing antibodies. This mutability of structural determinants of protective immunity is the obstacle in developing universal influenza vaccines. Towards the development of such vaccines and other immune therapies, our studies are designed to identify regions of influenza viruses that are conserved and that mediate virus neutralization. We have specifically focused on viruses of the H3N2 subtype, which have persisted as a principal source of influenza-related morbidity and mortality in humans since the pandemic of 1968. Three monoclonal antibodies have been identified that are broadly-neutralizing against H3 influenza viruses spanning 40 years. The antibodies react with the hemagglutinin glycoprotein and appear to bind in regions that are refractory to the structural variation required for viral escape from neutralization. The antibodies demonstrate therapeutic efficacy in mice against H3N2 virus infection and have potential for use in the treatment of human influenza disease. By mapping the binding region of one antibody, 12D1, we have identified a continuous region of the hemagglutinin that may act as an immunogen to elicit broadly protective immunity to H3 viruses. The anti-H3 monoclonal antibodies were identified after immunization of mice with the hemagglutinin of four different viruses (A/Hong Kong/1/1968, A/Alabama/1/1981, A/Beijing/47/1992, A/Wyoming/3/2003). This immunization schedule was designed to boost B cells specific for conserved regions of the hemagglutinin from distinct antigenic clusters. Importantly, our antibodies are of naturally occurring specificity rather than selected from cloned libraries, demonstrating that broad-spectrum humoral immunity to influenza viruses can be elicited in vivo.

Influenza viruses remain a formidable public health threat. Because of a dramatic increase in drug resistant strains of influenza viruses and due to the semi-regular emergence of pandemic virus strains, the development of novel antibody-based therapies and influenza vaccine constructs is of great interest. Recently, monoclonal antibodies with broad neutralizing activity against an array of Group 1 influenza viruses (including H5 and H1 subtypes) were identified; studies using these antibodies have expanded our understanding of structural aspects of the viral hemagglutinin, the molecule mediating protective immunity to influenza viruses. We have identified the first broadly neutralizing antibodies against viruses in Group 2—specifically, they are active against H3 influenza viruses spanning 40 years. The antibodies react with the hemagglutinin and appear to bind in regions that are refractory to the structural variation required for viral escape from neutralization. The antibodies demonstrate therapeutic efficacy in mice against H3N2 virus infection and have potential for use in the treatment of human influenza disease. By mapping the binding region of one antibody, 12D1, we have identified a continuous region of the hemagglutinin that may act as an immunogen to elicit an immune response conferring broad protection against H3 viruses.

The virion host shut-off (vhs) protein blocks a TLR-independent pathway of herpes simplex virus type 1 recognition in human and mouse dendritic cells

Molecular pathways underlying the activation of dendritic cells (DCs) in response to Herpes Simplex Virus type 1 (HSV-1) are poorly understood. Removal of the HSV virion host shut-off (vhs) protein relieves a block to DC activation observed during wild-type infection. In this study, we utilized a potent DC stimulatory HSV-1 recombinant virus lacking vhs as a tool to investigate the mechanisms involved in the activation of DCs by HSV-1. We report that the release of pro-inflammatory cytokines by conventional DC (cDC) during HSV-1 infection is triggered by both virus replication-dependent and replication-independent pathways. Interestingly, while vhs is capable of inhibiting the release of cytokines during infection of human and mouse cDCs, the secretion of cytokines by plasmacytoid DC (pDC) is not affected by vhs. These data prompted us to postulate that infection of cDCs by HSV triggers a TLR independent pathway for cDC activation that is susceptible to blockage by the vhs protein. Using cDCs isolated from mice deficient in both the TLR adaptor protein MyD88 and TLR3, we show that HSV-1 and the vhs-deleted virus can activate cDCs independently of TLR signaling. In addition, virion-associated vhs fails to block cDC activation in response to treatment with TLR agonists, but it efficiently blocked cDC activation triggered by the paramyxoviruses Sendai Virus (SeV) and Newcastle Disease Virus (NDV). This block to SeV- and NDV-induced activation of cDC resulted in elevated SeV and NDV viral gene expression indicating that infection with HSV-1 enhances the cell's susceptibility to other pathogens through the action of vhs. Our results demonstrate for the first time that a viral protein contained in the tegument of HSV-1 can block the induction of DC activation by TLR-independent pathways of viral recognition.

IL-11 regulates autoimmune demyelination

Current therapies for the autoimmune demyelinating disease multiple sclerosis (MS) target inflammation, but do not directly address neuroprotection or lesion repair. Cytokines of the gp130 family regulate survival and differentiation of both neural and immune cells, and we recently identified expression of the family member IL-11 in active MS plaques. In this study, we show that IL-11 regulates the clinical course and neuropathology of experimental autoimmune encephalomyelitis, a demyelinating model that mimics many of the clinical and pathologic features of MS. Importantly, the effects of IL-11 are achieved via a combination of immunoregulation and direct neuroprotection. IL-11R-alpha-null (IL-11Ralpha(-/-)) mice displayed a significant increase in clinical severity and neuropathology of experimental autoimmune encephalomyelitis compared with wild-type littermates. Inflammation, demyelination, and oligodendrocyte and neuronal loss were all exacerbated in IL-11Ra(-/-) animals. Conversely, wild-type mice treated with IL-11 displayed milder clinical signs and neuropathology than vehicle-treated controls. In cocultures of murine myelin oligodendrocyte glycoprotein(35-55)-specific CD4+ T lymphocytes and CD11c+ APCs, IL-11 treatment resulted in a significant decrease in T cell-derived effector cytokine production. This effect was generated via modulation of CD11c+ APC-mediated lymphocyte activation, and was associated with a decrease in the size of the CD11c+ cell population. Conversely, IL-11 strongly reduced apoptosis and potentiated mitosis in primary cultures of mouse oligodendrocyte progenitors. Collectively, these data reveal that IL-11 regulates inflammatory demyelination via a unique combination of immunoregulation and neuroprotection. IL-11 signaling may represent a therapeutic avenue to restrict CNS inflammation and potentiate oligodendrocyte survival in autoimmune demyelinating disease.

The functional impairment of natural killer cells during influenza virus infection

Natural killer (NK) cells have a critical role in clearing influenza virus, which primarily infects the lung epithelial cells. However, the ability of influenza virus to infect and manipulate NK cells has not been studied. In this context, we hypothesized that influenza virus can target NK cells leading to a functional impairment in their ability to mediate cytotoxicity and cytokine/chemokine generations. Here, we show influenza virus, PR8, can enter and infect NK cells. This infection did not alter the expression levels of activating, inhibitory or developmental receptors of NK cells. However, infection of NK cells by PR8 reduced the cytotoxicity to tumor cells that represent 'induced-self' and 'missing-self'. PR8-infection also significantly downregulated the NCR1, NKG2D, Nkpr1c, Ly49D and CD244 receptors-mediated generation of pro-inflammatory cytokines and chemokines. Mutations in the non-structural protein 1 (NS1) of influenza virus further augmented the functional impairment of NK cells. Our observations show the presence of a new, but yet to be explored, mechanism by which the influenza virus can evade immune detection.

Alpha-C-galactosylceramide as an adjuvant for a live attenuated influenza virus vaccine

There is a substantial need to develop better influenza virus vaccines that can protect populations that are not adequately protected by the currently licensed vaccines. While live attenuated influenza virus vaccines induce superior immune responses compared to inactivated vaccines, the manufacturing process of both types of influenza virus vaccines is time consuming and may not be adequate during a pandemic. Adjuvants would be particularly useful if they could enhance the immune response to live attenuated influenza virus vaccines so that the amount of vaccine needed for a protective dose could be reduced. The glycolipid, alpha-galactosylceramide (alpha-GalCer), has recently been shown to have adjuvant activity for both inactivated and replicating recombinant vaccines. The goal of these experiments was to determine whether a derivative of alpha-GalCer, alpha-C-galactosylceramide (alpha-C-GalCer) can enhance the immune response elicited by a live attenuated influenza virus vaccine containing an NS1 protein truncation and reduce the amount of vaccine required to provide protection after challenge. Our results indicated that the adjuvant reduced both morbidity and mortality in BALB/c mice after challenge with wild type influenza virus. The adjuvant also increased the amount of influenza virus specific total IgG, IgG1, and IgG2a antibodies as well as IFN-gamma secreting CD8(+) T cells. By using knockout mice that are not able to generate NKT cells, we were able to demonstrate that the mechanism of adjuvant activity is dependent on NKT cells. Thus, our data indicate that stimulators of NKT cells represent a new avenue of adjuvants to pursue for live attenuated virus vaccines.

Modeling the Maturation Process of Dendritic Cells (134.40)

Dendritic cells are antigen-presenting cells responsible for the initiation of immunity. Immature DCs act as sentinels that, upon recognizing a pathogen, alter their gene expression pattern; the mature DCs then secrete signals to stimulate the appropriate immune response. One of these signals is the cytokine IL-12, composed of IL-12p35 and IL-12p40; the interaction of both subunits is required for the production of bioactive IL-12. A related cytokine, IL-23, is formed by the interaction of IL-12p40 with IL-23p19. The relative proportions of IL-23 and IL-12 depend on the pathogen recognized by the DC. Consequently, a model is being built in order to attain a more accurate understanding of IL-12 synthesis. The first part of the model encompasses the transcriptional activation of IL-12 genes. Previous research has identified some of the transcription factors involved and it has been found that the transcriptional regulation of IL-12 and IL-23 involves both common and distinct signaling pathways. However, further experiments are required to obtain a more complete signaling network from virus infection to the activation of these transcription factors. The second part of the IL-12 model involves the synthesis of bioactive IL-12 and mass-action kinetic equations have been developed to approximate the transcription and translation of the two subunits, their dimerization and secretion. Experimental data are currently being obtained for kinetic parameter estimation, as well as for testing the model; this proposed methodology can then be extended to other DC maturation signals in order to acquire a more complete understanding of the initiation of immunity.

Multiplex paracrine signaling leads to antiviral activated DC State (133.40)

Infection of immature dendritic cells (DCs) by virus stimulates their maturation into antigen presenting cells (APC). Infected DCs secrete TNFα, IFNα, IFNβ, MIP1α, RANTES, IL-6 and IL-8 which expose uninfected DCs to this complex cytokines/chemokines milieu. Recently, we showed that this paracrine signaling from infected DCs induced an antiviral-primed DC state referred to as antiviral activated DCs (AVDCs, J Immunology 2008 PMID: 18981106). AVDCs are relatively resistant to virus infection in comparison with naïve DCs and achieve accelerated and augmented levels of co-stimulatory molecule expression with virus infection. Here we investigate the factors reponsible for AVDC formation. No single factor induces a similar surface marker pattern in DCs as observed in AVDCs. The effects of all possible double combinations on naive DCs have been evaluated by RNA expression pattern, surface marker expression, as well as imaging flow analysis of rate of phagocytosis and DC-T cell interaction. The results illuminate how DCs integrate multiple paracrine signals to modulate their antiviral state.

Impact of alpha-defensins1-3 on the maturation and differentiation of human monocyte-derived DCs. Concentration-dependent opposite dual effects

alpha-defensins1-3 are potent antimicrobial molecules that also link innate and adaptive immunity, depending on the concentration range. However, their effects on the biology of human DCs remain largely unknown. We analyzed the impact of different concentrations of alpha-defensins1-3 on the maturation and differentiation of monocyte-derived DCs (MDDCs). Low doses of alpha-defensins1-3 up-regulated CD83, CD86 and HLA-DR expression, increased TNF-alpha, IL-1beta, IL-12p40, IL-10 and IL-8 secretion, and slightly augmented allostimulatory capacity. By contrast, high doses down-regulated CD86 and HLA-DR expression, TNF-alpha, IL-1beta, IL-12p40 and IL-10 secretion and allostimulatory capacity, whereas strongly up-regulated IL-8. Furthermore, during the MDDC differentiation process, high doses of alpha-defensins1-3 affected CD14, CD11c and CD86 expression and strongly up-regulated IL-8. Results suggest that alpha-defensins1-3 might modulate the maturation and differentiation of MDDCs in vivo and therefore could be of special interest in the field of vaccine development.

Antiviral-activated dendritic cells: a paracrine-induced response state

Infection of immature dendritic cells (DCs) by virus stimulates their maturation into APC. Infected DCs can also expose uninfected DCs to a panoply of cytokines/chemokines via paracrine signaling. Mathematical modeling suggests that a high rate of paracrine signaling is likely to occur among DCs located in three-dimensional space. Relatively little is known about how secreted factors modify the early response to virus infection. We used a transwell experimental system that allows passage of secreted factors, but not direct contact, between virus-infected DCs and uninfected DCs to investigate paracrine signaling responses. Paracrine signaling from infected DCs induced an antiviral-primed DC state distinct from that of mature virus-infected DCs that we refer to as antiviral-activated DCs (AVDCs). AVDCs had increased surface MHC class II and CD86 levels, but in contrast to virus-infected DCs, their MHC class I levels were unchanged. Imaging flow cytometry showed that AVDCs had an increased rate of phagocytosis compared with naive DCs. Experiments with IFN-beta cytokine indicated that it may be responsible for CD86, but not MHC class II regulation in AVDCs. Both IFN-inducible and IFN-independent genes are up-regulated in AVDCs. Notably, AVDCs are relatively resistant to virus infection in comparison to naive DCs and achieve accelerated and augmented levels of costimulatory molecule expression with virus infection. AVDCs show a distinct antiviral-primed state of DC maturation mediated by DC paracrine signaling. Although further in vivo study is needed, the characteristics of the AVDC suggest that it is well suited to play a role in the early innate-adaptive transition of the immune system.

Estrogen inhibits dendritic cell maturation to RNA viruses

Dendritic cells (DCs) play a central role in initiating and polarizing the immune response. Therefore, DC maturation represents a key control point in the shift from innate to adaptive immunity. It is suspected that during pregnancy, hormones are critical factors that modulate changes reported to occur in maternal immunity. Here we examined the effect of 17-beta-estradiol (E2) on the maturational response triggered by virus in human DCs and its influence on their ability to activate naive T cells. We developed an in vitro system to measure the response of DCs to virus infection with Newcastle disease virus (NDV) after a 24-hour E2 treatment. Using this system, we demonstrated that E2 pretreatment down-regulated the antiviral response to RNA viruses in DCs by profoundly suppressing type I interferon (IFN) synthesis and other important inflammatory products. In addition, the DCs capacity to stimulate naive CD4 T cells was also reduced. These results suggest an important role for E2 in suppressing the antiviral response and provide a mechanism for the reduced immunity to virus infection observed during pregnancy.

Interferon-beta pretreatment of conventional and plasmacytoid human dendritic cells enhances their activation by influenza virus

Influenza virus produces a protein, NS1, that inhibits infected cells from releasing type I interferon (IFN) and blocks maturation of conventional dendritic cells (DCs). As a result, influenza virus is a poor activator of both mouse and human DCs in vitro. However, in vivo a strong immune response to virus infection is generated in both species, suggesting that other factors may contribute to the maturation of DCs in vivo. It is likely that the environment in which a DC encounters a virus would contain multiple pro-inflammatory molecules, including type I IFN. Type I IFN is a critical component of the viral immune response that initiates an antiviral state in cells, primarily by triggering a broad transcriptional program that interferes with the ability of virus to establish infection in the cell. In this study, we have examined the activation profiles of both conventional and plasmacytoid dendritic cells (cDCs and pDCs) in response to an influenza virus infection in the context of a type I IFN-containing environment. We found that both cDCs and pDCs demonstrate a greater activation response to influenza virus when pre-exposed to IFN-β (IFN priming); although, the priming kinetics are different in these two cell types. This strongly suggests that type I IFN functions not only to reduce viral replication in these immune cells, but also to promote greater DC activation during influenza virus infections.

Influenza infection leads to a serious respiratory infection of the lung epithelium. Lying directly below the epithelial cells are immune system sentinels known as dendritic cells. These cells interact with the virus and carry parts of the virus to draining lymph nodes to activate killer T cells. In order to effectively carry out this function, DCs must perceive the presence of a virus using receptors specially adapted for this function. However, when DCs are mixed with influenza virus in the laboratory, no activation occurs because the virus produces a protein called NS1 that blocks the receptors. Yet, patients infected with influenza virus develop a strong adaptive response that leads to recovery from infection. This observation suggests that additional factors must be present that contribute to the activation of the DCs. The most likely contributor is type I interferon, a ubiquitous protein released from many cells upon exposure to virus. In this study, we mixed influenza virus with DCs in the presence of type I interferon and found that this greatly enhanced their activation. Treatment with interferon allowed the DC to bypass the block in activation mediated by the influenza NS1 protein. Our data suggest that the production of type I interferon within an infected patient may endow the DCs with the ability to fully respond to influenza virus.

The tumour suppressor CYLD is a negative regulator of RIG-I-mediated antiviral response

On detecting viral RNAs, the RNA helicase retinoic acid-inducible gene I (RIG-I) activates the interferon regulatory factor 3 (IRF3) signalling pathway to induce type I interferon (IFN) gene transcription. How this antiviral signalling pathway might be negatively regulated is poorly understood. Microarray and bioinformatic analysis indicated that the expression of RIG-I and that of the tumour suppressor CYLD (cylindromatosis), a deubiquitinating enzyme that removes Lys 63-linked polyubiquitin chains, are closely correlated, suggesting a functional association between the two molecules. Ectopic expression of CYLD inhibits the IRF3 signalling pathway and IFN production triggered by RIG-I; conversely, CYLD knockdown enhances the response. CYLD removes polyubiquitin chains from RIG-I as well as from TANK binding kinase 1 (TBK1), the kinase that phosphorylates IRF3, coincident with an inhibition of the IRF3 signalling pathway. Furthermore, CYLD protein level is reduced in the presence of tumour necrosis factor and viral infection, concomitant with enhanced IFN production. These findings show that CYLD is a negative regulator of RIG-I-mediated innate antiviral response.

A comprehensive evaluation of human plasmacytoid dendritic cells using small volumes of human blood

Elucidation of the role played by cells of the innate immune system, particularly the dendritic cell (DC) populations, has led to a precipitous growth in our understanding of immunity to pathogens and foreign antigens. Much of this information has been derived from studies using mouse model systems. However, mice and human DCs differ drastically in the relative distribution of the toll-like receptors (TLRs) critical for immune activation. This is particularly true for the plasmacytoid DCs (pDCs), which are activated almost exclusively through TLR signaling. Variation in this DC subpopulation has been implicated in a number of pathological syndromes; therefore, a thorough understanding of their steady state and activation profiles in human patients is essential. A number of factors, including the relatively low numbers of these cells in blood, have precluded careful analysis in clinical trials. To overcome these limitations, we have developed a technique for studying the steady state and activation profile of pDCs collected from small amounts of human blood. This technique can be performed with 10,000 cells to obtain the immune transcriptome of the pDCs analyzed by quantitative PCR using amplified RNA. In addition, we have used multiplex enzyme-linked immunosorbent assays to measure secreted proteins. We demonstrate the validity of this technique and document its potential for use with blood from human study populations.

MDA5 participates in the detection of paramyxovirus infection and is essential for the early activation of dendritic cells in response to Sendai Virus defective interfering particles

Defective interfering (DI) particles are byproducts of virus replication that potently enhance dendritic cell (DC) maturation by virus infection. DI particles have been reported for many different viruses and are strong inducers of type I IFNs. The cellular mechanisms involved in the response to DI particles are not known. In this study, we show that 1) DI particles are recognized by more than one viral sensor independently of TLRs and type I IFN signaling; 2) The helicase MDA5 participates in the detection of DI genomes as MDA5-deficient DCs respond inefficiently to Sendai virus stocks containing DI particles; 3) DI particles stimulate the expression of IRF3-responsive genes by a uniquely potent mechanism when compared with other prototypic viral stimulus; and 4) the efficient detection of DI particles overcomes virus immune antagonism. These data highlight the outstanding adjuvant capacity of DI particles in stimulating mouse and human DCs. They also offer biological relevance to the previously reported inhibition of MDA5 by different paramyxovirus V proteins. The unique mechanism by which DI particles trigger the maturation of DCs represents a novel strategy that could be further exploited for the development of potent adjuvant molecules.

A prospective, comparative study of the immune response to inactivated influenza vaccine in pediatric liver transplant recipients and their healthy siblings

BACKGROUND

Annual influenza vaccination is routinely recommended for pediatric solid organ transplant recipients. However, there are limited data defining the immune response to the inactivated vaccine in this population.

METHODS

This prospective study compared the humoral and cell-mediated immune responses to the trivalent subvirion influenza vaccine in pediatric liver transplant recipients with those in their healthy siblings. All subjects received inactivated influenza vaccine. Hemagglutination inhibition and interferon-gamma (IFN-gamma) enzyme-linked immunosorbent spot assays for New Caledonia and Shanghai strains were performed at baseline, after each vaccine dose, and 3 months after the series. Seroconversion was defined as a 4-fold increase in antibody titers; seroprotection was defined as an antibody titer > or =1:40. An increase in the number of T cells secreting IFN-gamma was considered to be a positive enzyme-linked immunosorbent spot response.

RESULTS

After 1 dose of vaccine, transplant recipients achieved rates of antibody seroprotection and seroconversion that were similar to those achieved by their healthy siblings. However, for both influenza strains, IFN-gamma responses by enzyme-linked immunosorbent spot were significantly attenuated in transplant recipients after 2 doses of vaccine. No cases of influenza or vaccine-related serious adverse events were documented in the study.

CONCLUSIONS

The diminished cell-mediated immune response to influenza vaccination that was observed in pediatric liver transplant recipients suggests that the current vaccine strategy may not provide optimal protection. Because of concerns regarding potential emergence of more virulent influenza strains, further studies are warranted to determine if IFN-gamma responses are predictive of efficacy and to identify the optimal vaccination strategy to protect populations with a high risk of infection.

Chromosome-specific and noisy IFNB1 transcription in individual virus-infected human primary dendritic cells

The induction of interferon beta (IFNB1) is a key event in the antiviral immune response. We studied the role of transcriptional noise in the regulation of the IFNB1 locus in primary cultures of human dendritic cells (DCs), which are important ‘first responders’ to viral infection. In single cell assays, IFNB1 mRNA expression in virus-infected DCs showed much greater cell-to-cell variation than that of a housekeeping gene, another induced transcript and viral RNA. We determined the contribution of intrinsic noise by measuring the allelic origin of transcripts in each cell and found that intrinsic noise is a very significant part of total noise. We developed a stochastic model to investigate the underlying mechanisms. We propose that the surprisingly high levels of IFNB1 transcript noise originate from the complexity of IFNB1 enhanceosome formation, which leads to a range up to many minutes in the differences within each cell in the time of activation of each allele.

Role of the influenza virus nonstructural 1 protein in evasion of immunity

The influenza virus nonstructural (NS)1 protein is a potent immune modulator that has multiple inhibitory functions in the infected cells. The NS1 protein blocks the production of interferon in infected cells by multiple actions, including the inhibition of transcription factors, such as nuclear factor-κB and interferon regulatory factor 3, and the cytoplasmic RNA sensor, retinoic acid-inducible gene-I. Additionally, our recent studies have demonstrated that the NS1 protein of influenza virus is able to inhibit both innate and adaptive immunity by targeting a very specific set of genes and proteins in dendritic cells (DCs). These genes are crucial for the activation of DCs and facilitate their interaction with T cells for the initiation of antiviral immune responses in the infected host. Thus, the NS1 protein is a dual-immune modulator that affects DC function profoundly.

Cytokine-independent upregulation of MDA5 in viral infection

The RNA helicases RIG-I and MDA5 detect virus infection of dendritic cells (DCs) leading to cytokine induction. Maximal sensitivity for virus detection by these helicases is obtained after their upregulation, which is thought to occur primarily through type I interferon (IFN) signaling. Here we demonstrate that in response to paramyxovirus infection, RIG-I upregulation requires type I IFN whereas MDA5 expression is increased by Sendai virus infection independently of signaling mediated by type I IFN, STAT1, tumor necrosis factor alpha, or NF-kappaB. This MDA5 upregulation is largely lost in IRF3 knockout DCs and is achieved in type I IFN-deficient cells expressing constitutively active IRF3.

A novel model of demyelinating encephalomyelitis induced by monocytes and dendritic cells

Local inflammation may be a precipitating event in autoimmune processes. In this study, we demonstrate that regulated influx of monocytes and dendritic cells (DC) into the CNS causes an acute neurological syndrome that results in a demyelinating encephalomyelitis. Expansion of monocytes and DC by conditional expression of Flt3 ligand in animals expressing CCL2 in the CNS promoted parenchymal cell infiltration and ascending paralysis in 100% of the mice within 9 days of Flt3 ligand induction. Depletion of circulating monocytes and DC reduced disease incidence and severity. Unlike the classical models of experimental autoimmune encephalomyelitis, depletion of CD4+ and CD8+ T cells did not affect disease induction. T cells and demyelinating lesions were observed in the CNS at a later stage as a result of organ-specific inflammation. We propose that alterations in the numbers or function of monocytes and DC coupled to dysregulated expression of chemokines in the neural tissues, favors development of CNS autoimmune disease.

A novel role for viral-defective interfering particles in enhancing dendritic cell maturation

Dendritic cell (DC) maturation is a crucial event in the development of adaptive immune responses that confer long-lasting protection against reinfection with the same virus. Sendai virus strain Cantell has a particularly strong ability to mature DCs independently of type I IFNs and TLR signaling, currently the best-described pathways for the induction of DC maturation. In this study, we demonstrate that defective-interfering (DI) particles present in Sendai virus-Cantell stocks are required for its robust DC maturation ability. DI particles contain incomplete genomes that are unable to replicate unless the viral polymerase is supplied by coinfection with complete virus. Accordingly, the improvement in the virus-induced maturation of DCs provided by DI particles requires standard virus coinfection and likely results from increased production of dsRNA replication intermediaries. This unique ability of DI particles to stimulate DC maturation cannot be mimicked by simply increasing the dose of standard virus. Furthermore, viruses with weak DC maturation abilities can be converted into potent DC stimulators with the addition of DI particles, supporting a potential application for DI particles as a novel natural adjuvant for viral immunizations.

Influenza virus evades innate and adaptive immunity via the NS1 protein

Both antibodies and T cells contribute to immunity against influenza virus infection. However, the generation of strong Th1 immunity is crucial for viral clearance. Interestingly, we found that human dendritic cells (DCs) infected with influenza A virus have lower allospecific Th1-cell stimulatory abilities than DCs activated by other stimuli, such as lipopolysaccharide and Newcastle disease virus infection. This weak stimulatory activity correlates with a suboptimal maturation of the DCs following infection with influenza A virus. We next investigated whether the influenza A virus NS1 protein could be responsible for the low levels of DC maturation after influenza virus infection. The NS1 protein is an important virulence factor associated with the suppression of innate immunity via the inhibition of type I interferon (IFN) production in infected cells. Using recombinant influenza and Newcastle disease viruses, with or without the NS1 gene from influenza virus, we found that the induction of a genetic program underlying DC maturation, migration, and T-cell stimulatory activity is specifically suppressed by the expression of the NS1 protein. Among the genes affected by NS1 are those coding for macrophage inflammatory protein 1beta, interleukin-12 p35 (IL-12 p35), IL-23 p19, RANTES, IL-8, IFN-alpha/beta, and CCR7. These results indicate that the influenza A virus NS1 protein is a bifunctional viral immunosuppressor which inhibits innate immunity by preventing type I IFN release and inhibits adaptive immunity by attenuating human DC maturation and the capacity of DCs to induce T-cell responses. Our observations also support the potential use of NS1 mutant influenza viruses as live attenuated influenza virus vaccines.

Sendai virus infection induces efficient adaptive immunity independently of type I interferons

Adaptive immunity in response to virus infection involves the generation of Th1 cells, cytotoxic T cells, and antibodies. This type of immune response is crucial for the clearance of virus infection and for long-term protection against reinfection. Type I interferons (IFNs), the primary innate cytokines that control virus growth and spreading, can influence various aspects of adaptive immunity. The development of antiviral immunity depends on many viral and cellular factors, and the extent to which type I IFNs contribute to the generation of adaptive immunity in response to a viral infection is controversial. Using two strains (Cantell and 52) of the murine respiratory Sendai virus (SeV) with differential abilities to induce type I IFN production from infected cells, together with type I IFN receptor-deficient mice, we examined the role of type I IFNs in the generation of adaptive immunity. Our results show that type I IFNs facilitate virus clearance and enhance the migration and maturation of dendritic cells after SeV infection in vivo; however, soon after infection, mice clear the virus from their lungs and efficiently generate cytotoxic T cells independently of type I IFN signaling. Furthermore, animals that are unresponsive to type I IFN develop long-term anti-SeV immunity, including CD8+ T cells and antibodies. Significantly, this memory response is able to protect mice against challenge with a lethal dose of virus. In conclusion, our results show that primary and secondary anti-SeV adaptive immunities are developed normally in the absence of type I IFN responsiveness.

Intensified and protective CD4+ T cell immunity in mice with anti-dendritic cell HIV gag fusion antibody vaccine

Current human immunodeficiency virus (HIV) vaccine approaches emphasize prime boost strategies comprising multiple doses of DNA vaccine and recombinant viral vectors. We are developing a protein-based approach that directly harnesses principles for generating T cell immunity. Vaccine is delivered to maturing dendritic cells in lymphoid tissue by engineering protein antigen into an antibody to DEC-205, a receptor for antigen presentation. Here we characterize the CD4⁺ T cell immune response to HIV gag and compare efficacy with other vaccine strategies in a single dose. DEC-205–targeted HIV gag p24 or p41 induces stronger CD4⁺ T cell immunity relative to high doses of gag protein, HIV gag plasmid DNA, or recombinant adenovirus-gag. High frequencies of interferon (IFN)-γ– and interleukin 2–producing CD4⁺ T cells are elicited, including double cytokine-producing cells. In addition, the response is broad because the primed mice respond to an array of peptides in different major histocompatibility complex haplotypes. Long-lived T cell memory is observed. After subcutaneous vaccination, CD4⁺ and IFN-γ–dependent protection develops to a challenge with recombinant vaccinia-gag virus at a mucosal surface, the airway. We suggest that a DEC-targeted vaccine, in part because of an unusually strong and protective CD4⁺ T cell response, will improve vaccine efficacy as a stand-alone approach or with other modalities.