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Epithelial injury calls for a regenerative response from a coordinated network of epithelial stem cells and immune cells. Defining this network is key to preserving the repair process for acute resolution, but also for preventing a remodeling process with chronic dysfunction. We recently identified an immune niche for basal-epithelial stem cells using mouse models of injury after respiratory viral infection. Niche function depended on an early sentinel population of monocyte-derived dendritic cells (moDCs) that provided ligand GPNMB to basal-ESC receptor CD44 for reprogramming towards chronic lung disease. These same cell and molecular control points worked directly in mouse and human basal-ESC organoids, but the findings were not yet validated in vivo in human disease. Further, persistence of GPNMB expression in moDCs and M2-macrophages in mouse models suggested utility as a long-term disease biomarker in humans. Here we show increased expression of GPNMB localized to moDC-macrophage populations in lung tissue samples from long-term Covid, asthma, and COPD. The findings thereby provide initial evidence of a persistent and correctable pathway from acute injury to chronic disease with implications for cellular reprogramming and inflammatory memory.

The stress kinase MAPK13 (aka p38δ-MAPK) is an attractive entry point for therapeutic intervention because it regulates the structural remodeling that can develop after epithelial barrier injury in the lung and likely other tissue sites. However, a selective, safe, and effective MAPK13 inhibitor is not yet available for experimental or clinical application. Here we identify a first-in-kind MAPK13 inhibitor using structure-based drug design combined with a screening funnel for cell safety and molecular specificity. This inhibitor (designated NuP-4) down-regulates basal-epithelial stem cell reprogramming, structural remodeling, and pathophysiology equivalently to Mapk13 gene-knockout in mouse and mouse organoid models of post-viral lung disease. This therapeutic benefit persists after stopping treatment as a sign of disease modification and attenuates key aspects of inflammation and remodeling as an indication of disease reversal. Similarly, NuP-4 treatment can directly control cytokine-stimulated growth, immune activation, and mucinous differentiation in human basal-cell organoids. The data thereby provide a new tool and potential fix for long-term stem cell reprogramming after viral injury and related conditions that require MAPK13 induction-activation.

All living organisms are charged with repair after injury particularly at epithelial barrier sites, but in some cases this response leads instead to structural remodeling and long-term disease. Identifying the molecular and cellular control of this divergence is key to disease modification. In that regard, stress kinase control of epithelial stem cells is a rational entry point for study. Here we examine the potential for mitogen-activated protein kinase 13 (MAPK13) regulation of epithelial stem cells using models of respiratory viral injury and post-viral lung disease. We show that Mapk13 gene-knockout mice handle acute infectious illness as expected but are protected against structural remodeling manifest as basal-epithelial stem cell (basal-ESC) hyperplasia-metaplasia, immune activation, and mucinous differentiation. In corresponding cell models, Mapk13 -deficiency directly attenuates basal-ESC growth and organoid formation. Extension to human studies shows marked induction/activation of basal-cell MAPK13 in clinical samples of comparable remodeling found in asthma and COPD. Here again, MAPK13 gene-knockdown inhibits human basal-ESC growth in culture. Together, the data identify MAPK13 as a control for structural remodeling and disease after epithelial injury and as a suitable target for down-regulation as a disease-modifying strategy.

Epithelial barriers are programmed for defense and repair but are also the site of long-term structural remodeling and disease. In general, this paradigm features epithelial stem cells (ESCs) that are called on to regenerate damaged tissues but can also be reprogrammed for detrimental remodeling. Here we identified a Wfdc21-dependent monocyte-derived dendritic cell (moDC) population that functioned as an early sentinel niche for basal ESC reprogramming in mouse models of epithelial injury after respiratory viral infection. Niche function depended on moDC delivery of ligand GPNMB to the basal ESC receptor CD44 so that properly timed antibody blockade of ligand or receptor provided long-lasting correction of reprogramming and broad disease phenotypes. These same control points worked directly in mouse and human basal ESC organoids. Together, the findings identify a mechanism to explain and modify what is otherwise a stereotyped but sometimes detrimental response to epithelial injury.

Respiratory viruses, including severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2), can trigger chronic lung disease that persists and even progresses after expected clearance of infectious virus. To gain an understanding of this process, the current study examined a series of consecutive fatal cases of coronavirus disease 2019 (COVID-19) that came to autopsy at 27 to 51 days after hospital admission. In each patient, a stereotyped bronchiolar-alveolar pattern of lung remodeling was identified with basal epithelial cell hyperplasia, immune activation, and mucinous differentiation. Remodeling regions featured macrophage infiltration and apoptosis and a marked depletion of alveolar type 1 and 2 epithelial cells. This pattern closely resembled findings from an experimental model of post-viral lung disease that requires basal-epithelial stem cell growth, immune activation, and differentiation. Together, these results provide evidence of basal epithelial cell reprogramming in long-term COVID-19 and thereby yield a pathway for explaining and correcting lung dysfunction in this type of disease., (Copyright © 2023 American Society for Investigative Pathology. Published by Elsevier Inc. All rights reserved.)

Background: Early-life severe respiratory syncytial virus (RSV) bronchiolitis is a risk factor for childhood asthma. Because azithromycin may attenuate airway inflammation during RSV bronchiolitis, we evaluated whether it would reduce the occurrence of post-RSV recurrent wheeze., Methods: We prospectively enrolled 200 otherwise healthy 1- to 18-month-old children hospitalized with RSV bronchiolitis in this single-center, double-blind, placebo-controlled study and randomly assigned them to receive oral azithromycin (10 mg/kg daily for 7 days, followed by 5 mg/kg daily for 7 days) or placebo. Randomization was stratified by recent open-label antibiotic use. The primary outcome was the occurrence of recurrent wheeze, defined as a third episode of post-RSV wheeze over the following 2 to 4 years., Results: As an indication of the biologic activity of azithromycin, nasal wash interleukin-8 levels, at day 14 after randomization, were lower among azithromycin-treated participants (P<0.01). Despite evidence of biologic activity, azithromycin did not reduce the risk of post-RSV recurrent wheeze (47% in the azithromycin group vs. 36% in the placebo group; adjusted hazard ratio, 1.45; 95% confidence interval [CI], 0.92 to 2.29; P=0.11). Azithromycin also did not modify the risk of recurrent wheeze among participants already receiving other antibiotic treatment at the time of enrollment (hazard ratio, 0.94; 95% CI, 0.43 to 2.07). There was a potential signal among antibiotic-naïve participants who received azithromycin to have an increased risk of recurrent wheeze (hazard ratio, 1.79; 95% CI, 1.03 to 3.1)., Conclusions: Azithromycin therapy for 14 days during acute severe RSV bronchiolitis did not reduce recurrent wheeze occurrence over the following 2 to 4 years. Our data suggest no benefit of azithromycin administration with the goal of preventing recurrent wheeze in later life. (Funded by the National Heart, Lung, and Blood Institute; ClinicalTrials.gov number, NCT02911935.).

Severe respiratory syncytial virus (RSV) bronchiolitis in early life is a significant risk factor for future recurrent wheeze (RW) and asthma. The goal of the Azithromycin to Prevent Wheezing following severe RSV bronchiolitis II (APW-RSV II) clinical trial is to evaluate if azithromycin treatment in infants hospitalized with RSV bronchiolitis reduces the occurrence of RW during the preschool years. The APW-RSV II clinical trial is a double-blind, placebo-controlled, parallel-group, randomized trial, including otherwise healthy participants, ages 30 days-18 months, who are hospitalized due to RSV bronchiolitis. The study includes an active randomized treatment phase with azithromycin or placebo for 2 weeks, and an observational phase of 18-48 months. Two hundred participants were enrolled during three consecutive RSV seasons beginning in the fall of 2016 and were randomized to receive oral azithromycin 10 mg/kg/day for 7 days followed by 5 mg/kg/day for an additional 7 days, or matched placebo. The study hypothesis is that in infants hospitalized with RSV bronchiolitis, the addition of azithromycin therapy to routine bronchiolitis care would reduce the likelihood of developing post-RSV recurrent wheeze (≥3 episodes). The primary clinical outcome is the occurrence of a third episode of wheezing, which is evaluated every other month by phone questionnaires and during yearly in-person visits. A secondary objective of the APW-RSV II clinical trial is to examine how azithromycin therapy changes the upper airway microbiome composition, and to determine if these changes are related to the occurrence of post-RSV RW. Microbiome composition is characterized in nasal wash samples obtained before and after the study treatments. This clinical trial may identify the first effective intervention applied during severe RSV bronchiolitis to reduce the risk of post-RSV RW and ultimately asthma., (© 2021 The Authors. Published by Elsevier Inc.)

Background: Sex differences exist in asthma susceptibility and severity. Accumulating evidence has linked airway microbiome dysbiosis to asthma, and airway microbial communities have been found to differ by sex. However, whether sex modifies the link between airway microbiome and asthma has not been investigated., Objective: To evaluate sex effects in the association between airway microbiome and asthma., Methods: We analyzed induced sputum samples from 47 subjects (n = 23 patients with asthma and n = 24 normal controls) using 16S ribosomal RNA gene sequencing methods. The bacterial composition was analyzed for sex differences. Bacterial associations with asthma were assessed for each sex at the core taxa and genus levels., Results: The microbiome in induced sputum differed in women vs men at the community level. A total of 5 core bacterial taxa were found in all samples. No sex-specific core taxa were detected. The most abundant core taxon, Streptococcus salivarius, was significantly enriched in women than in men (P = .02). Within each sex, individuals with relatively lower abundance of S salivarius were more likely to have asthma (P = .006). For both sexes, increased Lactobacillus species were found in sputum samples of patients with patients compared with normal controls (adjusted P = .01). Haemophilus species were associated with asthma in men and not in women., Conclusion: The airway microbiome differed by sex, and sex effects exist in the association of airway microbial markers and asthma. Future airway microbiome studies may yield better resolution if the context of specific sex is considered. The airway microbiome is a potential mechanism driving sex differences in asthma., (Copyright © 2020 American College of Allergy, Asthma & Immunology. Published by Elsevier Inc. All rights reserved.)

Background: Infants with severe respiratory syncytial virus (RSV) bronchiolitis have an increased risk of recurrent wheezing and asthma. We aimed to evaluate the relationships between regulatory T cell (Treg) percentage and cytokine production of in vitro-stimulated CD4+ T cells during acute bronchiolitis and the development of recurrent wheezing in the first 3 years of life., Methods: We obtained peripheral blood from 166 infants hospitalized with their first episode of RSV-confirmed bronchiolitis. Granzyme B (GZB) expression, and interleukin-10, interferon-γ, tumor necrosis factor-α (TNF-α), IL-4, and IL-5 production by in vitro anti-CD3/CD28- and anti-CD3/CD46-activated CD4+ T cells, and percentage of peripheral Treg (CD4+CD25 hi Foxp3 hi ) cells were measured by flow cytometry. Wheezing was assessed every 6 months. Recurrent wheezing was defined as three or more episodes following the initial RSV bronchiolitis., Results: Sixty-seven percent (n = 111) of children had wheezing after their initial RSV infection, with 30% having recurrent wheezing. The percentage of peripheral Treg (CD4+CD25 hi Foxp3 hi ) cells was not significantly different between the wheezing groups. Decreased TNF-α production from anti-CD3/CD28- and anti-CD3/CD46- activated CD4+ T cells was observed in the recurrent wheezers, compared with nonwheezers (p = .048 and .03, respectively). There were no significant differences in the GZB+ CD4+ T cells and production of other inflammatory cytokines between these groups., Conclusions: We demonstrated lower TNF-α production by in vitro stimulated CD4+ T cells during severe RSV bronchiolitis in children that subsequently developed recurrent wheezing, compared with children with no subsequent wheeze. These findings support the role of CD4+ T cell immunity in the development of subsequent wheezing in these children., (© 2019 The Authors. Immunity, Inflammation and Disease published by John Wiley & Sons Ltd.)

Background: Our objective was to determine those characteristics associated with reversibility of airflow obstruction and response to maximal bronchodilation in children with severe asthma through the Severe Asthma Research Program (SARP)., Methods: We performed a cross-sectional analysis evaluating children ages 6 to 17 years with nonsevere asthma (NSA) and severe asthma (SA). Participants underwent spirometry before and after 180 µg of albuterol to determine reversibility (≥12% increase in FEV 1 ). Participants were then given escalating doses up to 720 µg of albuterol to determine their maximum reversibility., Results: We evaluated 230 children (n = 129 SA, n = 101 NSA) from five centers across the United States in the SARP I and II cohorts. SA (odds ratio [OR], 2.08, 95% confidence interval [CI], 1.05-4.13), second-hand smoke exposure (OR, 2.81, 95%CI, 1.23-6.43), and fractional exhaled nitric oxide (FeNO; OR, 1.97, 95%CI, 1.35-2.87) were associated with increased odds of airway reversibility after maximal bronchodilation, while higher prebronchodilator (BD) FEV 1 % predicted (OR, 0.91, 95%CI, 0.88-0.94) was associated with decreased odds. In an analysis using the SARP III cohort (n = 186), blood neutrophils, immunoglobulin E (IgE), and FEV 1 % predicted were significantly associated with BD reversibility. In addition, children with BD response have greater healthcare utilization. BD reversibility was associated with reduced lung function at enrollment and 1-year follow-up though less decline in lung function over 1 year compared to those without reversibility., Conclusions: Lung function, that is FEV 1 % predicted, is a predictor of BD response in children with asthma. Additionally, smoke exposure, higher FeNO or IgE level, and low peripheral blood neutrophils are associated with a greater likelihood of BD reversibility. BD response can identify a phenotype of pediatric asthma associated with low lung function and poor asthma control., (© 2019 Wiley Periodicals, Inc.)

Background: Studies evaluating circulating dendritic cells (DCs) and natural and induced regulatory T cells (nTregs, iTregs) are often obtained at a single time point and difficult to interpret without understanding their intrinsic day-to-day biologic variability., Methods: We investigated the day-to-day variability in quantifying DCs, nTregs (FoxP3(+)CD25(+)CD4(+)) and cytokine production by iTregs (granzyme B-GZB, Th1/2 cytokines following CD3 plus CD46 in vitro activation) from peripheral blood mononuclear cells (PBMCs) collected on three consecutive days in healthy adults. Intraclass correlation coefficients (ICCs) were used to evaluate intra-individual variability., Results: In 10 healthy adults, the %PBMCs of plasmacytoid (pDC) and myeloid (mDC1 and mDC2) were 0.27 ± 0.12, 0.22 ± 0.10, and 0.02 ± 0.02, with ICC 0.91, 0.90, and 0.17 respectively. Natural Tregs (3.27 ± 1.27% CD4(+) cells) had an ICC of 0.86. Inducible Tregs (GZB-positive, 35.3 ± 17.7% CD4(+) cells) had an ICC of 0.77. The ICCs for IL-10, TNF-α, IFN-γ, IL-4, and IL-5 production by iTregs were 0.49, 0.63, 0.68, 0.74, and 0.82, respectively. There were no significant changes in ICC (<0.1) after adjusting for age, gender and atopy except for IL-4. Substantial variability for iTregs was determined for the control condition (PBS with IL-2)., Conclusions: No meaningful day-to-day biologic variability was observed for the quantification of nTregs, pDC and mDC1 in normal adults; however, there was substantial variability in measuring mDC2 proportions and iTreg production of IL-10. These results suggest obtaining an average of several measurements over time to determine the most representative value of these biologic measures., (Copyright © 2016 Elsevier B.V. All rights reserved.)

Severe infection with respiratory syncytial virus (RSV) during infancy is strongly associated with the development of asthma. To identify genetic variation that contributes to asthma following severe RSV bronchiolitis during infancy, we sequenced the coding exons of 131 asthma candidate genes in 182 European and African American children with severe RSV bronchiolitis in infancy using anonymous pools for variant discovery, and then directly genotyped a set of 190 nonsynonymous variants. Association testing was performed for physician-diagnosed asthma before the 7th birthday (asthma) using genotypes from 6,500 individuals from the Exome Sequencing Project (ESP) as controls to gain statistical power. In addition, among patients with severe RSV bronchiolitis during infancy, we examined genetic associations with asthma, active asthma, persistent wheeze, and bronchial hyperreactivity (methacholine PC20) at age 6 years. We identified four rare nonsynonymous variants that were significantly associated with asthma following severe RSV bronchiolitis, including single variants in ADRB2, FLG and NCAM1 in European Americans (p = 4.6x10-4, 1.9x10-13 and 5.0x10-5, respectively), and NOS1 in African Americans (p = 2.3x10-11). One of the variants was a highly functional nonsynonymous variant in ADRB2 (rs1800888), which was also nominally associated with asthma (p = 0.027) and active asthma (p = 0.013) among European Americans with severe RSV bronchiolitis without including the ESP. Our results suggest that rare nonsynonymous variants contribute to the development of asthma following severe RSV bronchiolitis in infancy, notably in ADRB2. Additional studies are required to explore the role of rare variants in the etiology of asthma and asthma-related traits following severe RSV bronchiolitis.

Background: Vitamin D deficiency at birth has been reported as a risk factor for respiratory syncytial virus (RSV) lower respiratory tract infection during the first year of life. Limited data are available on whether an infant's vitamin D status is associated with the severity of acute RSV bronchiolitis., Methods: Infants < 1 year of age and hospitalized with their first episode of RSV bronchiolitis were enrolled into the RSV Bronchiolitis in Early Life II cohort. We investigated the relationships between vitamin D status at enrollment and the following indicators of bronchiolitis severity: duration of hospitalization, lowest oxygen saturation measured during hospitalization, and bronchiolitis severity score., Results: Among the 145 enrolled infants, the median (quartile 1 [Q1], Q3) serum 25-OH-VitD level was 36.8 (29.8, 42.3) ng/mL, with 14 infants (9.7%) having deficient serum vitamin D levels (25-OH-VitD <20 ng/mL). Vitamin D-deficient infants were younger than infants with 25-OH-VitD ≥ 20 ng/mL (2.8 vs 4.5 months, respectively; P = .04) and were less likely to consume infant's formula (42.9% vs 87.0%, respectively; P < .01). The following indicators of acute bronchiolitis severity did not differ between infants who were vitamin D-deficient and nondeficient: duration of hospitalization (P = .53), lowest oxygen saturation (P = .45), and bronchiolitis severity score (P = .97), even after adjusting for age, and for infant's formula consumption., Conclusions: Among this cohort of infants that were hospitalized for RSV bronchiolitis, vitamin D status at the time of bronchiolitis was not associated with indicators of acute bronchiolitis severity.

Background: Atopic asthma is characterized by intermittent exacerbations triggered by exposure to allergen. Exacerbations are characterized by an acute inflammatory reaction in the airways, with recruitment of both innate and adaptive immune cells. These cell populations as well as soluble factors are critical for initiating and controlling the inflammatory processes in allergic asthma. Detailed data on the numbers and types of cells recruited following allergen challenge is lacking. In this paper we present an extensive phenotypic analysis of the inflammatory cell infiltrate present in the bronchoalveolar lavage (BAL) fluid following bronchoscopically directed allergen challenge in mild atopic asthmatics., Methods: A re-analysis of pooled data obtained prior to intervention in our randomized, placebo controlled, double blinded study (costimulation inhibition in asthma trial [CIA]) was performed. Twenty-four subjects underwent bronchoscopically directed segmental allergen challenge followed by BAL collection 48 hours later. The BAL fluid was analyzed by multi-color flow cytometry for immune cell populations and multi-plex ELISA for cytokine detection., Results: Allergen instillation induced pro-inflammatory cytokines (IL-6) and immune modulating cytokines (IL-2, IFN-?, and IL-10) along with an increase in lymphocytes and suppressor cells (Tregs and MDSC). Interestingly, membrane expression of CD30 was identified on lymphocytes, especially Tregs, but not eosinophils. Soluble CD30 was also detected in the BAL fluid after allergen challenge in adult atopic asthmatics., Conclusions: After segmental allergen challenge of adult atopic asthmatics, cell types associated with a pro-inflammatory as well as an anti-inflammatory response are detected within the BAL fluid of the lung.

Rationale: T lymphocytes are important in the pathogenesis of allergic asthma. Costimulation through CD28 is critical for optimal activation of T cells, and inhibition of this pathway with CTLA4Ig has been shown to be effective in preventing airway inflammation and hyperresponsiveness in animal models of asthma. Abatacept, a humanized version of CTLA4Ig, has been approved for treatment of rheumatoid arthritis, providing the opportunity to test whether inhibition of costimulation is an effective strategy to treat people with asthma., Objectives: To determine if 3 months of treatment with abatacept reduced allergen-induced airway inflammation in people with mild atopic asthma., Methods: Randomized, placebo-controlled, double-blinded study. Bronchoscopically directed segmental allergen challenge was performed on 24 subjects followed by bronchoalveolar lavage 48 hours later. Subjects were randomized 1:1 to receive abatacept or placebo, followed by a second allergen challenge protocol after 3 months of study drug., Measurements and Main Results: There was no significant reduction in allergen-induced eosinophilic inflammation in the abatacept-treated group compared with placebo (17.71% ± 17.25% vs. 46.39% ± 29.21%; P = 0.26). In addition, we did not detect an effect of abatacept on FEV1, provocative concentration of methacholine sufficient to induce a 20% decline in FEV1, or asthma symptoms. Subjects treated with abatacept had an increased percentage of naive and a corresponding decrease in memory CD4(+) T cells in the blood compared with placebo., Conclusions: Inhibition of CD28-mediated costimulation with abatacept does not seem to alter the inflammatory response to segmental allergen challenge or clinical measures of asthma symptoms in people with mild atopic asthma. Clinical trial registered with ClinicalTrials.gov (NCT 00784459).

Background: The development of asthma after respiratory syncytial virus (RSV) bronchiolitis has been demonstrated in case-control studies, although the determinants of post-RSV asthma remain undefined., Objectives: We sought to evaluate the potential determinants of physician-diagnosed asthma after severe RSV bronchiolitis during infancy., Methods: We enrolled 206 children during an initial episode of severe RSV bronchiolitis at 12 months of age or less in a prospective cohort study and followed these children for up to 6 years. In a subset of 81 children, we analyzed CCL5 (RANTES) mRNA expression in upper airway epithelial cells., Results: Forty-eight percent of children had physician-diagnosed asthma before the seventh birthday. Independent determinants significantly associated with increased risk for physician-diagnosed asthma by the seventh birthday included maternal asthma (odds ratio [OR], 5.2; 95% CI, 1.7-15.9; P = .004), exposure to high levels of dog allergen (OR, 3.2; 95% CI, 1.3-7.7; P = .012), aeroallergen sensitivity at age 3 years (OR, 10.7; 95% CI, 2.1-55.0; P = .005), recurrent wheezing during the first 3 years of life (OR, 7.3; 95% CI, 1.2-43.3; P = .028), and CCL5 expression in nasal epithelia during acute RSV infection (OR, 3.8; 95% CI, 1.2-2.4; P < .001). White children (OR, 0.19; 95% CI, 0.04-0.93; P = .041) and children attending day care (OR, 0.18; 95% CI, 0.04-0.84; P = .029) had a decreased risk of physician-diagnosed asthma., Conclusions: Approximately 50% of children who experience severe RSV bronchiolitis have a subsequent asthma diagnosis. The presence of increased CCL5 levels in nasal epithelia at the time of bronchiolitis or the development of allergic sensitization by age 3 years are associated with increased likelihood of subsequent asthma., (Copyright © 2012 American Academy of Allergy, Asthma & Immunology. Published by Mosby, Inc. All rights reserved.)

Plasmacytoid dendritic cells (pDC) play a crucial role in antiviral immunity and promoting Th1 polarization, possibly protecting against development of allergic disease. Examination of the relationship between peripheral blood plasmacytoid DC levels and manifestations of asthma and atopy early in life. We have isolated peripheral blood mononuclear cells (PBMC) from 73 children (mean age +/- SD: 6.6 +/- 0.5 yr old) participating in the RSV Bronchiolitis in Early Life (RBEL) study. Flow cytometry was performed on PBMC detecting DC surface-markers: Blood Dendritic Cell Antigens (BDCA) 1, 3, and 2 which identify myeloid type 1, type 2, and plasmacytoid cells, respectively. Total serum IgE, peripheral eosinophil count, and allergy skin tests were documented. About 45% (n = 33) of study participants had physician-diagnosed asthma by 6 yr of age. These children had significantly lower quantities (mean +/- SD) of plasmacytoid DC than their non-asthmatic counterparts (1020 +/- 921 vs. 1952 +/- 1170 cells per 10(6) PBMC, p = 0.003). We found significantly lower numbers of myeloid dendritic cells in children with asthma (3836 +/- 2472 cells per 10(6) PBMC) compared with those without asthma (4768 +/- 2224 cells per 10(6) PBMC, p = 0.02); however, this divergence was not significant after adjusting for covariates of age, gender, race, skin test reactivity, smoke exposure, and daycare attendance. We did not identify any direct association between DC levels and markers of atopy: skin test reactivity, peripheral eosinophilia, and IgE level. Children who are diagnosed with asthma after severe RSV bronchiolitis appear to have a relative deficiency of plasmacytoid DC in peripheral blood.

Background: Immune response after viral infection usually involves T(H)1-mediated response; however, severe respiratory syncytial virus (RSV) infection appears to be associated with the development of asthma, a T(H)2-predominant phenotype., Objective: To understand the early and subsequent immunologic response to a serious RSV infection in children over time., Methods: A total of 206 previously healthy infants hospitalized with severe RSV bronchiolitis were enrolled in a prospective cohort called the RSV Bronchiolitis in Early Life study. Peripheral blood T cells were obtained immediately after RSV infection and at 2, 4, and 6 years of age, stimulated with phorbol 12-myristate 13-acetate and ionomycin, and analyzed for IL-2, IL-4, IL-13, and IFN-gamma by flow cytometry and real-time PCR., Results: Of the children, 48% (n = 97) developed asthma (physician-diagnosed), and 48% (n = 97) had eczema by age 6 years; 32% (n = 48 of 150) developed allergic sensitization by 3 years of age. Children with asthma had lower IL-13 expression at 6 years of age than those without (P = .001). IFN-gamma, IL-2, and IL-4 levels did not differ by asthma or eczema status during follow-up (all P > .05). Allergic sensitization was not associated with differences in cytokine levels during follow-up (all P > .05)., Conclusion: Severe RSV infection early in life is associated with a high incidence of asthma and eczema. Contrary to expectations, subsequent immunologic development in those who developed asthma, eczema, or allergic sensitization was not associated with a T(H)2 phenotype in the peripheral blood.