Host and Environmental Factors Influencing Individual Human Cytokine Responses.

Differences in susceptibility to immune-mediated diseases are determined by variability in immune responses. In three studies within the Human Functional Genomics Project, we assessed the effect of environmental and non-genetic host factors of the genetic make-up of the host and of the intestinal microbiome on the cytokine responses in humans. We analyzed the association of these factors with circulating mediators and with six cytokines after stimulation with 19 bacterial, fungal, viral, and non-microbial metabolic stimuli in 534 healthy subjects. In this first study, we show a strong impact of non-genetic host factors (e.g., age and gender) on cytokine production and circulating mediators. Additionally, annual seasonality is found to be an important environmental factor influencing cytokine production. Alpha-1-antitrypsin concentrations partially mediate the seasonality of cytokine responses, whereas the effect of vitamin D levels is limited. The complete dataset has been made publicly available as a comprehensive resource for future studies. PAPERCLIP.

Primary Exposure to SARS-CoV-2 via Infection or Vaccination Determines Mucosal Antibody-Dependent ACE2 Binding Inhibition.

BACKGROUND: Mucosal antibodies play a critical role in preventing SARS-CoV-2 infections or reinfections by blocking the interaction of the receptor-binding domain (RBD) with the angiotensin-converting enzyme 2 (ACE2) receptor on the cell surface. In this study, we investigated the difference between the mucosal antibody response after primary infection and vaccination. METHODS: We assessed longitudinal changes in the quantity and capacity of nasal antibodies to neutralize the interaction of RBD with the ACE2 receptor using the spike protein and RBD from ancestral SARS-CoV-2 (Wuhan-Hu-1), as well as the RBD from the Delta and Omicron variants. RESULTS: Significantly higher mucosal IgA concentrations were detected postinfection vs postvaccination, while vaccination induced higher IgG concentrations. However, ACE2-inhibiting activity did not differ between the cohorts. Regarding whether IgA or IgG drove ACE2 inhibition, infection-induced binding inhibition was driven by both isotypes, while postvaccination binding inhibition was mainly driven by IgG. CONCLUSIONS: Our study provides new insights into the relationship between antibody isotypes and neutralization by using a sensitive and high-throughput ACE2 binding inhibition assay. Key differences are highlighted between vaccination and infection at the mucosal level, showing that despite differences in the response quantity, postinfection and postvaccination ACE2 binding inhibition capacity did not differ.

NLRC4 inflammasomes in dendritic cells regulate noncognate effector function by memory CD8⁺ T cells.

Memory T cells exert antigen-independent effector functions, but how these responses are regulated is unclear. We discovered an in vivo link between flagellin-induced NLRC4 inflammasome activation in splenic dendritic cells (DCs) and host protective interferon-γ (IFN-γ) secretion by noncognate memory CD8(+) T cells, which could be activated by Salmonella enterica serovar Typhimurium, Yersinia pseudotuberculosis and Pseudomonas aeruginosa. We show that CD8α(+) DCs were particularly efficient at sensing bacterial flagellin through NLRC4 inflammasomes. Although this activation released interleukin 18 (IL-18) and IL-1ß, only IL-18 was required for IFN-γ production by memory CD8(+) T cells. Conversely, only the release of IL-1ß, but not IL-18, depended on priming signals mediated by Toll-like receptors. These findings provide a comprehensive mechanistic framework for the regulation of noncognate memory T cell responses during bacterial immunity.

Antibody and T-Cell Responses 6 Months After Coronavirus Disease 2019 Messenger RNA-1273 Vaccination in Patients With Chronic Kidney Disease, on Dialysis, or Living With a Kidney Transplant.

BACKGROUND: The immune response to COVID-19 vaccination is inferior in kidney transplant recipients (KTRs) and to a lesser extent in patients on dialysis or with chronic kidney disease (CKD). We assessed the immune response 6 months after mRNA-1273 vaccination in kidney patients and compared this to controls. METHODS: A total of 152 participants with CKD stages G4/5 (eGFR <30 mL/min/1.73 m2), 145 participants on dialysis, 267 KTRs, and 181 controls were included. SARS-CoV-2 Spike S1 specific IgG antibodies were measured using fluorescent bead-based multiplex-immunoassay, neutralizing antibodies to ancestral, Delta, and Omicron (BA.1) variants by plaque reduction, and T-cell responses by interferon-γ release assay. RESULTS: At 6 months after vaccination, S1-specific antibodies were detected in 100% of controls, 98.7% of CKD G4/5 patients, 95.1% of dialysis patients, and 56.6% of KTRs. These figures were comparable to the response rates at 28 days, but antibody levels waned significantly. Neutralization of the ancestral and Delta variants was detected in most participants, whereas neutralization of Omicron was mostly absent. S-specific T-cell responses were detected at 6 months in 75.0% of controls, 69.4% of CKD G4/5 patients, 52.6% of dialysis patients, and 12.9% of KTRs. T-cell responses at 6 months were significantly lower than responses at 28 days. CONCLUSIONS: Although seropositivity rates at 6 months were comparable to rates at 28 days after vaccination, significantly decreased antibody levels and T-cell responses were observed. The combination of low antibody levels, reduced T-cell responses, and absent neutralization of the newly emerging variants indicates the need for additional boosts or alternative vaccination strategies in KTRs. CLINICAL TRIALS REGISTRATION: NCT04741386.

The role of interleukin-21 in COVID-19 vaccine-induced B cell-mediated immune responses in patients with kidney disease and kidney transplant recipients.

T-cell-mediated help to B cells is required for the development of humoral responses, in which the cytokine interleukin (IL)-21 is key. Here, we studied the mRNA-1273 vaccine-induced SARS-CoV-2-specific memory T-cell IL-21 response, memory B cell response, and immunoglobulin (Ig)G antibody levels in peripheral blood at 28 days after the second vaccination by ELISpot and the fluorescent bead-based multiplex immunoassay, respectively. We included 40 patients with chronic kidney disease (CKD), 34 patients on dialysis, 63 kidney transplant recipients (KTR), and 47 controls. We found that KTR, but not patients with CKD and those receiving dialysis, showed a significantly lower number of SARS-CoV-2-specific IL-21 producing T cells than controls (P < .001). KTR and patients with CKD showed lower numbers of SARS-CoV-2-specific IgG-producing memory B cells when compared with controls (P < .001 and P = .01, respectively). The T-cell IL-21 response was positively associated with the SARS-CoV-2-specific B cell response and the SARS-CoV-2 spike S1-specific IgG antibody levels (both Pearson r = 0.5; P < .001). In addition, SARS-CoV-2-specific B cell responses were shown to be IL-21 dependent. Taken together, we show that IL-21 signaling is important in eliciting robust B cell-mediated immune responses in patients with kidney disease and KTR.

Mucosal immunity to severe acute respiratory syndrome coronavirus 2 infection.

PURPOSE OF REVIEW: Despite its crucial role in protection against viral infections, mucosal immunity has been largely understudied in the context of coronavirus disease 2019 (COVID-19). This review outlines the current evidence about the role of mucosal immune responses in the clearance of severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) infection, as well as potential mucosal mechanisms of protection against (re-)infection. RECENT FINDINGS: The angiotensin-converting enzyme 2 cellular entry receptor for SARS-CoV-2 is most highly expressed in the upper respiratory tract and most SARS-CoV-2 shedding occurs from the upper respiratory tract. Viral shedding peaks early during infection around the onset of symptoms, before dropping rapidly in most individuals within 7 days of symptom onset, suggesting mucosal inhibition of viral infection. Serum and mucosal immunoglobulin G and immunoglobulin M responses were found to be strongly correlated in infected patients, whereas correlations were much weaker for immunoglobulin A (IgA). Mucosal IgA responses have been detected in infected cases in the absence of serum antibody responses, with mucosal antibody levels correlating strongly with virus neutralization. Bulk and single-cell RNA sequencing analysis of nasopharyngeal swabs and bronchoalveolar lavage samples of COVID-19 patients revealed the induction of mucosal chemokine and cytokine genes, complement pathways, Janus Kinase/Signal Transducer and Activator of Transcription signaling and cytotoxic T cells. SUMMARY: Although most clinical studies focus on antibodies and cellular immunity in peripheral blood, mucosal immune responses in the respiratory tract play a key role in the early restriction of viral replication and the clearance of SARS-CoV-2. Identification of mucosal biomarkers associated with viral clearance will allow monitoring of infection-induced immunity. Further studies are needed to understand how the systemic immunological endpoints measured in vaccination studies translate to mucosal protection against SARS-CoV-2 infection.

Bimodal Targeting of Human Leukocytes by Fc- and CpG-Decorated Polymersomes to Tune Immune Induction.

The use of well-defined nanovesicles composed of amphiphilic block copolymers (polymersomes) for delivery of adjuvants and antigens is a promising strategy for vaccine development. However, the potency of nanoparticle vaccines depends on efficient interaction with and activation of cells involved in antigen presentation, which can be achieved by targeting cellular receptors. Here, we showed that the Fc fragment display on the polymersome surface resulted in markedly improved interactions with granulocytes, monocytes, and NK cells, while for "naked" polymersomes, virtually no binding to leukocytes was observed. Moreover, CpG-decorated polymersomes were found to also interact with T and/or B cells. Interestingly, whole blood stimulations with Fc fragment and CpG-decorated polymersomes induced interleukin (IL)-6, IL-8, and TNF-α production, while naked polymersomes did not induce any cytokine production. In conclusion, specific immune induction by polymersomes can be controlled using bimodal targeting of different immune receptors, which is an essential feature for targeted vaccine delivery.

Interacting, Nonspecific, Immunological Effects of Bacille Calmette-Guérin and Tetanus-diphtheria-pertussis Inactivated Polio Vaccinations: An Explorative, Randomized Trial.

BACKGROUND: Certain vaccines, such as Bacille Calmette-Guérin (BCG), have nonspecific effects, which modulate innate immune responses and lead to protection against mortality from unrelated infections (trained immunity). In contrast, in spite of the disease-specific effects, an enhanced overall mortality has been described after diphtheria-tetanus-pertussis (DTP) vaccination in females. This randomized trial aimed to investigate the nonspecific immunological effects of BCG and DTP-containing vaccines on the immune response to unrelated pathogens. METHODS: We randomized 75 healthy, female, adult volunteers to receive either BCG, followed by a booster dose of tetanus-diphtheria-pertussis inactivated polio vaccine (Tdap) 3 months later; BCG and Tdap combined; or Tdap followed by BCG 3 months later. Blood was collected before vaccination, as well as at 1 day, 4 days, 2 weeks, and 3 months after the first vaccination(s), plus 2 weeks after the second vaccination. Ex vivo leukocyte responses to unrelated stimuli and pathogens were assessed. RESULTS: Tdap vaccination led to short-term potentiation and long-term repression of monocyte-derived cytokine responses, and short-term as well as long-term repression of T-cell reactivity to unrelated pathogens. BCG led to short-term and long-term potentiation of monocyte-derived cytokine responses. When given together with Tdap or after Tdap, BCG abrogated the immunosuppressive effects of Tdap vaccination. CONCLUSIONS: Tdap induces immunotolerance to unrelated antigens, which is partially restored by concurrent or subsequent BCG vaccination. These data indicate that the modulation of heterologous immune responses is induced by vaccination with Tdap and BCG, and more studies are warranted to investigate whether this is involved in the nonspecific effects of vaccines on mortality. CLINICAL TRIALS REGISTRATION: NCT02771782.

Controlled Human Infection With Bordetella pertussis Induces Asymptomatic, Immunizing Colonization.

BACKGROUND: Bordetella pertussis is among the leading causes of vaccine-preventable deaths and morbidity globally. Human asymptomatic carriage as a reservoir for community transmission of infections might be a target of future vaccine strategies, but has not been demonstrated. Our objective was to demonstrate that asymptomatic nasopharyngeal carriage of Bordetella pertussis is inducible in humans and to define the microbiological and immunological features of presymptomatic infection. METHODS: Healthy subjects aged 18-45 years with an antipertussis toxin immunoglobin G (IgG) concentration of <20 international units/ml were inoculated intranasally with nonattenuated, wild-type Bordetella pertussis strain B1917. Safety, colonization, and shedding were monitored over 17 days in an inpatient facility. Colonization was assessed by culture and quantitative polymerase chain reaction. Azithromycin was administered from Day 14. The inoculum dose was escalated, aiming to colonize at least 70% of participants. Immunological responses were measured. RESULTS: There were 34 participants challenged, in groups of 4 or 5. The dose was gradually escalated from 103 colony-forming units (0% colonized) to 105 colony-forming units (80% colonized). Minor symptoms were reported in a minority of participants. Azithromycin eradicated colonization in 48 hours in 88% of colonized individuals. Antipertussis toxin IgG seroconversion occurred in 9 out of 19 colonized participants and in none of the participants who were not colonized. Nasal wash was a more sensitive method to detect colonization than pernasal swabs. No shedding of Bordetella pertussis was detected in systematically collected environmental samples. CONCLUSIONS: Bordetella pertussis colonization can be deliberately induced and leads to a systemic immune response without causing pertussis symptoms. CLINICAL TRIALS REGISTRATION: NCT03751514.

Functional Programming of Innate Immune Cells in Response to Bordetella pertussis Infection and Vaccination.

Despite widespread vaccination, B. pertussis remains one of the least controlled vaccine-preventable diseases. Although it is well known that acellular and whole cell pertussis vaccines induce distinct immune functionalities in memory cells, much less is known about the role of innate immunity in this process. In this review, we provide an overview of the known differences and similarities in innate receptors, innate immune cells and inflammatory signalling pathways induced by the pertussis vaccines either licensed or in development and compare this to primary infection with B. pertussis. Despite the crucial role of innate immunity in driving memory responses to B. pertussis, it is clear that a significant knowledge gap remains in our understanding of the early innate immune response to vaccination and infection. Such knowledge is essential to develop the next generation of pertussis vaccines with improved host defense against B. pertussis.

Adaptation of Bordetella pertussis to the Respiratory Tract.

There is a lack of insight into the basic mechanisms by which Bordetella pertussis adapts to the local host environment during infection. We analyzed B. pertussis gene expression in the upper and lower airways of mice and compared this to SO4-induced in vitro Bvg-regulated gene transcription. Approximately 30% of all genes were differentially expressed between in vitro and in vivo conditions. This included several novel potential vaccine antigens that were exclusively expressed in vivo. Significant differences in expression profile and metabolic pathways were identified between the upper versus the lower airways, suggesting distinct antigenic profiles. We found high-level expression of several Bvg-repressed genes during infection, and mouse vaccination experiments using purified protein fractions from both Bvg- and Bvg+ cultures demonstrated protection against intranasal B. pertussis challenge. This study provides novel insights into the in vivo adaptation of B. pertussis and may facilitate the improvement of pertussis vaccines.

The Complement System Contributes to Functional Antibody-Mediated Responses Induced by Immunization with Plasmodium falciparum Malaria Sporozoites.

Long-lasting and sterile homologous protection against malaria can be achieved by the exposure of malaria-naive volunteers under chemoprophylaxis to Plasmodium falciparum-infected mosquitoes (chemoprophylaxis and sporozoite [CPS] immunization). While CPS-induced antibodies neutralize sporozoite infectivity in vitro and in vivo, antibody-mediated effector mechanisms are still poorly understood. Here, we investigated whether complement contributes to CPS-induced preerythrocytic immunity. Sera collected before and after CPS immunization in the presence of active or inactive complement were assessed for the recognition of homologous NF54 and heterologous NF135.C10 sporozoites, complement fixation, sporozoite lysis, and possible subsequent effects on in vitro sporozoite infectivity in human hepatocytes. CPS immunization induced sporozoite-specific IgM (P < 0.0001) and IgG (P = 0.001) antibodies with complement-fixing capacities (P < 0.0001). Sporozoite lysis (P = 0.017), traversal (P < 0.0001), and hepatocyte invasion inhibition (P < 0.0001) by CPS-induced antibodies were strongly enhanced in the presence of active complement. Complement-mediated invasion inhibition in the presence of CPS-induced antibodies negatively correlated with cumulative parasitemia during CPS immunizations (P = 0.013). While IgG antibodies similarly recognized homologous and heterologous sporozoites, IgM binding to heterologous sporozoites was reduced (P = 0.023). Although CPS-induced antibodies did not differ in their abilities to fix complement, lyse sporozoites, or inhibit the traversal of homologous and heterologous sporozoites, heterologous sporozoite invasion was more strongly inhibited in the presence of active complement (P = 0.008). These findings demonstrate that CPS-induced antibodies have complement-fixing activity, thereby significantly further enhancing the functional inhibition of homologous and heterologous sporozoite infectivity in vitro The combined data highlight the importance of complement as an additional immune effector mechanism in preerythrocytic immunity after whole-parasite immunization against Plasmodium falciparum malaria.

Antigen-Independent Restriction of Pneumococcal Density by Mucosal Adjuvant Cholera Toxin Subunit B.

For many bacterial respiratory infections, development of (severe) disease is preceded by asymptomatic colonization of the upper airways. For Streptococcus pneumoniae, the transition to severe lower respiratory tract infection is associated with an increase in nasopharyngeal colonization density. Insight into how the mucosal immune system restricts colonization may provide new strategies to prevent clinical symptoms. Several studies have provided indirect evidence that the mucosal adjuvant cholera toxin subunit B (CTB) may confer nonspecific protection against respiratory infections. Here, we show that CTB reduces the pneumococcal load in the nasopharynx, which required activation of the caspase-1/11 inflammasome, mucosal T cells, and macrophages. Our findings suggest that CTB-dependent activation of the local innate response synergizes with noncognate T cells to restrict bacterial load. Our study not only provides insight into the immunological components required for containment and clearance of pneumococcal carriage, but also highlights an important yet often understudied aspect of adjuvants.

BCG Vaccination Enhances the Immunogenicity of Subsequent Influenza Vaccination in Healthy Volunteers: A Randomized, Placebo-Controlled Pilot Study.

BACKGROUND: Influenza-related morbidity and mortality remain high. Seasonal vaccination is the backbone of influenza management but does not always result in protective antibody titers. Nonspecific effects of BCG vaccination related to enhanced function of myeloid antigen-presenting cells have been reported. We hypothesized that BCG vaccination could also enhance immune responses to influenza vaccination. METHODS: Healthy volunteers received either live attenuated BCG vaccine (n = 20) or placebo (n = 20) in a randomized fashion, followed by intramuscular injection of trivalent influenza vaccine 14 days later. Hemagglutination-inhibiting (HI) antibodies and cellular immunity measured by ex vivo leukocyte responses were assessed. RESULTS: In BCG-vaccinated subjects, HI antibody responses against the 2009 pandemic influenza A(H1N1) vaccine strain were significantly enhanced, compared with the placebo group, and there was a trend toward more-rapid seroconversion. Additionally, apart from enhanced proinflammatory leukocyte responses following BCG vaccination, nonspecific effects of influenza vaccination were also observed, with modulation of cytokine responses against unrelated pathogens. CONCLUSIONS: BCG vaccination prior to influenza vaccination results in a more pronounced increase and accelerated induction of functional antibody responses against the 2009 pandemic influenza A(H1N1) vaccine strain. These results may have implications for the design of vaccination strategies and could lead to improvement of vaccination efficacy.

Antibodies mediate formation of neutrophil extracellular traps in the middle ear and facilitate secondary pneumococcal otitis media.

Otitis media (OM) (a middle ear infection) is a common childhood illness that can leave some children with permanent hearing loss. OM can arise following infection with a variety of different pathogens, including a coinfection with influenza A virus (IAV) and Streptococcus pneumoniae (the pneumococcus). We and others have demonstrated that coinfection with IAV facilitates the replication of pneumococci in the middle ear. Specifically, we used a mouse model of OM to show that IAV facilitates the outgrowth of S. pneumoniae in the middle ear by inducing middle ear inflammation. Here, we seek to understand how the host inflammatory response facilitates bacterial outgrowth in the middle ear. Using B cell-deficient infant mice, we show that antibodies play a crucial role in facilitating pneumococcal replication. We subsequently show that this is due to antibody-dependent neutrophil extracellular trap (NET) formation in the middle ear, which, instead of clearing the infection, allows the bacteria to replicate. We further demonstrate the importance of these NETs as a potential therapeutic target through the transtympanic administration of a DNase, which effectively reduces the bacterial load in the middle ear. Taken together, these data provide novel insight into how pneumococci are able to replicate in the middle ear cavity and induce disease.

Antiviral responses induced by Tdap-IPV vaccination are associated with persistent humoral immunity to Bordetella pertussis.

Many countries continue to experience pertussis epidemics despite widespread vaccination. Waning protection after booster vaccination has highlighted the need for a better understanding of the immunological factors that promote durable protection. Here we apply systems vaccinology to investigate antibody responses in adolescents in the Netherlands (N = 14; NL) and the United Kingdom (N = 12; UK) receiving a tetanus-diphtheria-acellular pertussis-inactivated poliovirus (Tdap-IPV) vaccine. We report that early antiviral and interferon gene expression signatures in blood correlate to persistence of pertussis-specific antibody responses. Single-cell analyses of the innate response identified monocytes and myeloid dendritic cells (MoDC) as principal responders that upregulate antiviral gene expression and type-I interferon cytokine production. With public data, we show that Tdap vaccination stimulates significantly lower antiviral/type-I interferon responses than Tdap-IPV, suggesting that IPV may promote antiviral gene expression. Subsequent in vitro stimulation experiments demonstrate TLR-dependent, IPV-specific activation of the pro-inflammatory p38 MAP kinase pathway in MoDCs. Together, our data provide insights into the molecular host response to pertussis booster vaccination and demonstrate that IPV enhances innate immune activity associated with persistent, pertussis-specific antibody responses.

Repeated COVID-19 Vaccination Drives Memory T- and B-cell Responses in Kidney Transplant Recipients: Results From a Multicenter Randomized Controlled Trial.

BACKGROUND: Insight into cellular immune responses to COVID-19 vaccinations is crucial for optimizing booster programs in kidney transplant recipients (KTRs). METHODS: In an immunologic substudy of a multicenter randomized controlled trial (NCT05030974) investigating different repeated vaccination strategies in KTR who showed poor serological responses after 2 or 3 doses of an messenger RNA (mRNA)-based vaccine, we compared SARS-CoV-2-specific interleukin-21 memory T-cell and B-cell responses by enzyme-linked immunosorbent spot (ELISpot) assays and serum IgG antibody levels. Patients were randomized to receive: a single dose of mRNA-1273 (100 µg, n = 25), a double dose of mRNA-1273 (2 × 100 µg, n = 25), or a single dose of adenovirus type 26 encoding the SARS-CoV-2 spike glycoprotein (Ad26.COV2.S) (n = 25). In parallel, we also examined responses in 50 KTR receiving 100 µg mRNA-1273, randomized to continue (n = 25) or discontinue (n = 25) mycophenolate mofetil/mycophenolic acid. As a reference, the data were compared with KTR who received 2 primary mRNA-1273 vaccinations. RESULTS: Repeated vaccination increased the seroconversion rate from 21% to 66% in all patients, which was strongly associated with enhanced levels of SARS-CoV-2-specific interleukin-21 memory T cells (odd ratio, 3.84 [1.89-7.78]; P < 0.001) and B cells (odd ratio, 35.93 [6.94-186.04]; P < 0.001). There were no significant differences observed in these responses among various vaccination strategies. In contrast to KTR vaccinated with 2 primary vaccinations, the number of antigen-specific memory B cells demonstrated potential for classifying seroconversion after repeated vaccination (area under the curve, 0.64; 95% confidence interval, 0.37-0.90; P = 0.26 and area under the curve, 0.95; confidence interval, 0.87-0.97; P < 0.0001, respectively). CONCLUSIONS: Our study emphasizes the importance of virus-specific memory T- and B-cell responses for comprehensive understanding of COVID-19 vaccine efficacy among KTR.

Influenza-induced inflammation drives pneumococcal otitis media.

Influenza A virus (IAV) predisposes individuals to secondary infections with the bacterium Streptococcus pneumoniae (the pneumococcus). Infections may manifest as pneumonia, sepsis, meningitis, or otitis media (OM). It remains controversial as to whether secondary pneumococcal disease is due to the induction of an aberrant immune response or IAV-induced immunosuppression. Moreover, as the majority of studies have been performed in the context of pneumococcal pneumonia, it remains unclear how far these findings can be extrapolated to other pneumococcal disease phenotypes such as OM. Here, we used an infant mouse model, human middle ear epithelial cells, and a series of reverse-engineered influenza viruses to investigate how IAV promotes bacterial OM. Our data suggest that the influenza virus HA facilitates disease by inducing a proinflammatory response in the middle ear cavity in a replication-dependent manner. Importantly, our findings suggest that it is the inflammatory response to IAV infection that mediates pneumococcal replication. This study thus provides the first evidence that inflammation drives pneumococcal replication in the middle ear cavity, which may have important implications for the treatment of pneumococcal OM.

Respiratory syncytial virus infection augments NOD2 signaling in an IFN-ß-dependent manner in human primary cells.

Respiratory syncytial virus (RSV) is a major cause of lower respiratory tract infections in infants, with remarkable variability in disease severity. An exaggerated proinflammatory response and influx of leukocytes is part of the pathogenesis of severe RSV disease. Here, we show an increase in proinflammatory cytokine production by human immune cells after stimulation with RSV and muramyl dipeptide (MDP), which is recognized by nucleotide-binding oligomerization domain containing 2 (NOD2). PBMCs from Crohn's disease patients homozygous for the 3020insC mutation in the NOD2 gene did not show a synergistic response to stimulation with RSV and MDP, suggesting that NOD2 is essential for the observed synergy. Further experiments aimed at identifying the viral ligand indicated that viral RNA plays an essential role in the recognition of RSV. Stimulation with RSV or Poly(I:C) induced IFN-ß expression, which resulted in an increased expression of the viral receptors TLR3 and RIG-I, as well as an increased NOD2 expression. Our data indicate that IFN-ß induction by viral RNA is an essential first step in the increased proinflammatory response to MDP. We hypothesize that the enhanced proinflammatory response to MDP following RSV infection may be an important factor in determining the outcome of the severity of disease.