Breastfeeding reduces the risk of severe lower respiratory infections (sLRIs), a leading cause of infant mortality; however, the protective mechanisms remain elusive. Here, we demonstrated that the absence of milk-derived osteopontin (OPN), highly expressed in colostrum, predisposes neonatal mice to viral and bacterial sLRI, consequent to disrupted dendritic cell (DC) hematopoiesis in the developing liver and lung. Amelioration of disease severity by oral OPN supplementation was associated with increased enteric abundance of Lactobacillaceae and elevated levels of serum 3-phenyllactic acid (PLA), a peroxisome proliferator-activated receptor gamma (PPARγ) agonist. Supplementation with PLA or the PPARγ agonist rosiglitazone restored lung DC hematopoiesis via airway epithelium-derived chemokine ligand 25 (CCL25)-mediated recruitment of lymphoid-myeloid primed progenitors and induction of a supportive lung niche. PLA-induced DC hematopoiesis and disease tolerance were attenuated by plasmacytoid DC depletion, immunoneutralization of stem cell factor, or genetic deletion of airway epithelial Flt3L. Our findings elucidate a microbiome-host interaction by which milk OPN confers protection against sLRI.

AIM:To define preschool wheeze profiles to 4-years, identify their early life associations, and impact on wheeze risk at 9-years. METHODS:A latent class analysis of eight wheeze responses (1 month-4 years) and two severity markers (respiratory presentation to emergency department and wheeze with shortness of breath) using data from a pre-birth prospective cohort study. Relative risk ratios (RRR) with 95% confidence intervals were calculated using multinomial logistic regression to examine associations between early life risk factors and wheeze at 9-years. RESULTS:Four distinct preschool wheeze profiles were identified: "never/infrequent" with minimal wheeze (n = 538), "early persistent" wheeze from 3 months to 4 years (n = 83), "transient" from 6 to 18 months (n = 263) and "late-onset" from 18 months to 4 years (n = 148). Relative to "never/infrequent", maternal asthma history was associated with increased risk of all adverse wheeze profiles, the highest for "early persistent" wheeze [RRR 5.06; 2.96-8.67]. Breastfeeding at 6 months decreased the risk of "early persistent" wheeze [RRR 0.53; 0.31-0.90] and at 12 months protected against all adverse wheeze profiles. Eczema, food allergy, aeroallergen and food sensitisation all increased the risk of "early persistent" and "late-onset" wheeze. "Early persistent" [RRR 7.25; 3.92-13.42] and "late-onset" [RRR 3.93; 2.24-6.89] wheeze profiles were associated with increased risk of wheeze at 9-years. CONCLUSIONS:Early life exposures and atopy measures had distinct associations with data-derived preschool wheeze profiles. Maternal asthma and the absence of breastfeeding emerged as unifying risk factors. Investigation of the underlying mechanistic pathways is required to inform novel primary prevention strategies.

Early microbial colonization influences immune development, with lower abundance of human milk oligosaccharide (HMO)-utilizing bifidobacteria linked to immune-related disorder risk. Here, we demonstrate that synbiotic supplementation with Bifidobacterium infantis (LMG 11588) and a blend of six structurally diverse HMOs plus Bifidobacterium lactis (CNCM I-3446) altered gut microbiome composition, changed systemic immune cell-networks, and reduced persistence of a T helper 2 (Th2) bias in formula-fed infants, following a pattern observed in breastfed infants. In preclinical models, synbiotic reduces lower respiratory tract infection (LRI) severity and aberrant type-2 immune responses and confers lasting immune benefits into adulthood. These effects are associated with changes in the circulating metabolome, including increased 12(S)-hydroxyheptadecatrienoic acid (12-HHT), which correlates with improved infection outcomes and phenocopies synbiotic-mediated protection when administered orally. Together, these findings indicate that infant-type synbiotic supplementation during a critical early-life window can imprint immune function and promote disease tolerance.

Respiratory syncytial virus (RSV) infection in stem cell transplant (SCT) recipients can lead to pneumonitis, respiratory failure and increased mortality. Given the disease mechanism is not well understood, we developed a novel preclinical model of RSV infection in allogeneic bone marrow transplantation (alloBMT) using pneumonia virus of mice (PVM), a murine homologue of RSV. PVM-infected alloBMT mice showed increased mortality and lung pathology compared to uninfected and syngeneic BMT (synBMT) mice, recapitulating clinical disease. To define the viral-specific cellular immune response, we employed a tetramer directed to PVM RNA polymerase (L1052-1060). Virus-specific CD8 T cell numbers were diminished in infected alloBMT versus synBMT mice, suggesting that in the presence of GVHD mice are unable to mount a virus-specific T cell response. AlloBMT mice showed expansion of terminally exhausted (TOX+PD1+TIM3+) polyclonal CD8 T cells compared to synBMT mice. Despite undetected terminally exhausted PVM-specific CD8 T cells in infected alloBMT mice, these were detected in infected synBMT mice suggesting functional capacity in the absence of GVHD. Lung viral load data showed PVM persisted in alloBMT mice three weeks post-infection compared to synBMT where PVM was cleared in a week. These data demonstrate that during GVHD impaired PVM-specific CD8 T cell immunity leads to a lack of viral control, suggesting a critical role for virus-specific CD8 T cells in RSV-infected SCT patients. Research supported by grant funds awarded by the Australian Infectious Diseases Research Centre. SCH is supported by a University of Queensland Research Training Program Scholarship. Transplantation Immunology (TRAN)

BACKGROUND:Interplay between the maternal diet and gut microbiome may impact fetal immune development and allergic disease risk. This study investigated associations between maternal prenatal urinary metabolites and infant food allergy and then extended to potentially relevant dietary and microbial precursors. METHODS:We investigated 599 mother-infant dyads from an Australian population-derived prebirth cohort. Maternal dietary data and fecal and urine samples were collected in the third trimester. NMR was used to measure prenatal urinary metabolites. Infant food allergy status was determined at 1 year by skin prick allergy testing and food challenge. Regression techniques were used to investigate associations and adjust for pre-specific confounding factors. RESULTS:Higher concentration of hippuric acid in maternal urine, an end-product of dietary polyphenol metabolism, was associated with a lower risk of infant food allergy (odds ratio (OR) 0.62 (95% CI 0.42, 0.93)). Consistent with this, dietary proanthocyanidins, a polyphenol, were positively associated with both higher urinary hippuric acid concentration (0.11 log units, CI 0.01, 0.22) and lower risk of infant food allergy (OR 0.58 (CI 0.36, 0.96)). Maternal carriage of the gut commensal Prevotella copri, previously associated with protection against infant allergic disease, was associated with 21% higher urinary hippuric acid concentrations (CI 4%, 40%, corresponding to 0.19 log units CI 0.04, 0.34); however there was no evidence of mediation. CONCLUSION:Further studies are required to confirm whether higher dietary intake of proanthocyanidins during pregnancy is associated with protection against allergic disease in the infant via gut microbiome production of hippuric precursors and other immune-active metabolites.

Viral-bacterial interactions during co-infection are often synergistic and can increase disease severity. However, emerging evidence indicates that some bacteria can antagonise viral infection, although the host responses driving this process remains unclear. Using infant mice co-infected with the nasopharyngeal inhabitant and pathogen Streptococcus pneumoniae and pneumonia virus of mice (PVM) to model antagonistic interactions, we found that prior bacterial colonisation enhances and prolongs anti-viral immune responses during co-infection, compared with viral infection alone. Transcriptomic, immunological, and histological analyses showed that pneumococcal colonisation prior to PVM infection enhanced and prolonged interferon signalling, increased anti-viral cytokine and chemokine protein levels and CD8+ cell responses. Notably, over 50% of differentially expressed host genes during co-infection were not differentially expressed in either infection alone. Our work shows that bacterial colonisation can modulate host immunity, shaping how the immune system responds to incoming viral infections, which has the potential to open novel therapeutic applications. ### Competing Interest Statement SM and CS have received honoraria from Pfizer and MSD for presentations at symposia or attendance at expert advisory meetings unrelated to this study. National Health and Medical Research Council, https://ror.org/011kf5r70, GNT1182442 Jack Brockhoff Foundation, https://ror.org/02ybsyy31, 4212

Liposomes are being developed as inhalable drug delivery systems, but concerns remain about their impact on the lungs. To better understand the impact of liposomes and their physicochemical properties on alveolar macrophages, the cytokine and chemokine expression profile of rat alveolar Nr8383 macrophages exposed to 0.1 and 1 mg/ml hydrogenated soy phosphatidylcholine (HSPC) liposomes was examined. Expression patterns varied considerably between liposomes in a concentration-dependent manner, with both anti- and pro-inflammatory chemokines/cytokines produced. Uncharged liposomes induce the greatest production of cytokines and chemokines, followed by PEGylated liposomes. The most significant increase in cytokine/chemokine expression was seen for IL-2 (up to 24-fold), IL-4 (up to 5-fold), IL-18 and VEGF (up to 10-fold), while liposome exposure significantly reduced MIP1 expression (5-fold). In summary, we demonstrate that liposome surface properties promote variable patterns of cytokine and chemokine secretion by alveolar macrophages. This suggests that the type of liposome employed may influence the type of immune response generated in the lung and by extension, dictate how inhaled liposomal nanomedicines affect the lungs response to inhaled toxicants and local infections.

Rhinovirus-induced neutrophil extracellular traps (NETs) contribute to acute asthma exacerbations, however the molecular factors that trigger NETosis in this context remain ill-defined. Here, we sought to implicate a role for IL-33, an epithelial cell-derived alarmin rapidly released in response to infection. In mice with chronic experimental asthma (CEA), but not naïve controls, rhinovirus inoculation induced an early (1 day post infection; dpi) inflammatory response dominated by neutrophils, neutrophil-associated cytokines (IL-1α, IL-1β, CXCL1) and NETosis, followed by a later, type-2 inflammatory phase (3-7 dpi), characterized by eosinophils, elevated IL-4 levels, and goblet cell hyperplasia. Notably, both phases were ablated by HpARI ( Heligmosomoides polygyrus Alarmin Release Inhibitor), which blocks IL-33 release and signalling. Instillation of exogenous IL-33 recapitulated the rhinovirus-induced early phase, including the increased presence of NETs in the airway mucosa, in a PAD4-dependent manner. Ex vivo IL-33-stimulated neutrophils from mice with CEA, but not naïve mice, underwent NETosis, and produced greater amounts of IL-1α/β, IL-4, and IL-5. In nasal samples from rhinovirus-infected people with asthma, but not healthy controls, IL-33 levels correlated with neutrophil elastase and dsDNA. Our findings suggest that IL-33 blockade ameliorates the severity of an asthma exacerbation by attenuating neutrophil recruitment and the downstream generation of NETs.

Lifestyle factors like poor maternal diet or antibiotic exposure disrupt early life microbiome assembly in infants, increasing the risk of severe lower respiratory infections (sLRI). Our prior studies in mice indicated that a maternal low-fibre diet (LFD) exacerbates LRI severity in infants by impairing recruitment of plasmacytoid dendritic cells (pDC) and consequently attenuating expansion of lung regulatory T (Treg) cells during pneumonia virus of mice (PVM) infection. Here, we investigated whether maternal dietary fibre intake influences Treg cell phenotypes in the mediastinal lymph nodes (mLN) and lungs of PVM-infected neonatal mice. Using high dimensional flow cytometry, we identified distinct clusters of regulatory T cells (Treg cells), which differed between lungs and mLN during infection, with notably greater effector Treg cell accumulation in the lungs. Compared to high-fibre diet (HFD)-reared pups, frequencies of various effector Treg cell subsets were decreased in the lungs of LFD-reared pups. Particularly, recruitment of chemokine receptor 3 (CXCR3+) expressing Treg cells was attenuated in LFD-reared pups, correlating with lower lung expression of CXCL9 and CXCL10 chemokines. The recruitment of this subset in response to PVM infection was similarly impaired in pDC depleted mice or following anti-CXCR3 treatment, increasing immunopathology in the lungs. In summary, PVM infection leads to the sequential recruitment and expansion of distinct Treg cell subsets to the lungs and mLN. The attenuated recruitment of the CXCR3+ subset in LFD-reared pups increases LRI severity, suggesting that strategies to enhance pDCs or CXCL9/CXCL10 expression will lower immune-mediated pathogenesis.

A poor maternal diet during pregnancy predisposes the infant to severe lower respiratory tract infections (sLRIs), which, in turn, increases childhood asthma risk; however, the underlying mechanisms remain poorly understood. Here, we show that the offspring of high-fat diet (HFD)-fed mothers (HFD-reared pups) developed an sLRI following pneumovirus inoculation in early life and subsequent asthma in later life upon allergen exposure. Prior to infection, HFD-reared pups developed microbial dysbiosis and low-grade systemic inflammation (LGSI), characterized by hyperneutropoiesis in the liver and elevated inflammatory cytokine expression, most notably granulocyte-colony stimulating factor (G-CSF), interleukin-17A (IL-17A), IL-6 and soluble IL-6 receptor (sIL-6R) (indicative of IL-6 trans-signaling) in the circulation and multiple organs but most prominently the liver. Inhibition of IL-6 trans-signaling using sgp130Fc transgenic mice or via specific genetic deletion of IL-6Ra on neutrophils conferred protection against both diseases. Taken together, our findings suggest that a maternal HFD induces neonatal LGSI that predisposes to sLRI and subsequent asthma via neutrophil-mediated IL-6 trans-signaling.

AbstractMechanisms linking pre-pregnancy obesity to increased preterm birth risk are unclear. Here, we examined the impact of pre-pregnancy obesity on metabolites, Fms-related tyrosine kinase 3 ligand (Flt3L), and proinflammatory cytokine profiles in preterm birth. We used cytokine bead array, ELISA and Gas Chromatography-Mass Spectrometry (GC-MS) to determine cytokine and metabolite profiles in maternal and cord blood samples from 124 pregnant women in Australia, who gave birth at term (n = 86) or preterm (n = 38). Besides the expected variations in birth weight and gestational age, all demographic characteristics, including pre-pregnancy body mass index, were similar between the term and preterm birth groups. Mothers in the preterm birth group had reduced Flt3L (P = 0.002) and elevated IL-6 (P = 0.002) compared with term birthing mothers. Among mothers who gave birth preterm, those with pre-pregnancy obesity had lower Flt3L levels (P = 0.02) compared with lean mothers. Flt3L and IL-6 were similar in cord blood across both groups, but TNFα levels (P = 0.02) were reduced in preterm newborns. Metabolomic analysis revealed significant shifts in essential metabolites in women with pre-pregnancy obesity, some of which were linked to preterm births. Our findings suggest that maternal pre-pregnancy obesity alters the metabolome and reduces Flt3L expression, potentially increasing risk of preterm birth.

Abstract Prostaglandin D2 (PGD2) signals via the DP1 and DP2 receptors. In Phase II trials, DP2 antagonism decreased airway inflammation and airway smooth muscle (ASM) area in moderate-to-severe asthma patients. However, in Phase III, DP2 antagonism failed to lower the rate of exacerbations, and DP2 as a target was shelved. Here, using a preclinical model of chronic experimental asthma, we demonstrate that rhinovirus-induced exacerbations increase PGD2 release, mucus production, transforming growth factor (TGF)-β1 and type-2 inflammation. DP2 antagonism or DP1 agonism ablates these phenotypes, increases epithelial EGF expression and decreases ASM area via increased IFN-γ. In contrast, dual DP1-DP2 antagonism or dual corticosteroid/DP2 antagonism, which attenuates endogenous PGD2, prevented ASM resolution. We demonstrate that DP2 antagonism resolves ASM remodelling via PGD2/DP1-mediated upregulation of IFN-γ expression, and that dual DP2 antagonism/corticosteroid therapy, as often occurred in the human trials, impairs the efficacy of DP2 antagonism by suppressing endogenous PGD2 and IFN-γ production.

Poor maternal diet during pregnancy is a risk factor for severe lower respiratory infections (sLRIs) in the offspring, but the underlying mechanisms remain elusive. Here, we demonstrate that in mice a maternal low-fiber diet (LFD) led to enhanced LRI severity in infants because of delayed plasmacytoid dendritic cell (pDC) recruitment and perturbation of regulatory T cell expansion in the lungs. LFD altered the composition of the maternal milk microbiome and assembling infant gut microbiome. These microbial changes reduced the secretion of the DC growth factor Flt3L by neonatal intestinal epithelial cells and impaired downstream pDC hematopoiesis. Therapy with a propionate-producing bacteria isolated from the milk of high-fiber diet-fed mothers, or supplementation with propionate, conferred protection against sLRI by restoring gut Flt3L expression and pDC hematopoiesis. Our findings identify a microbiome-dependent Flt3L axis in the gut that promotes pDC hematopoiesis in early life and confers disease resistance against sLRIs.

With increasing rates of cesarean section worldwide and international guidelines advising pre-incision antibiotics, neonatal exposure to pre-birth antibiotics is higher than ever before. Emerging evidence has raised concern regarding the impact of such antibiotics on the neonatal intestinal microbiota, immune system development and health conditions later in life. This narrative review investigates current protocols for intrapartum prophylactic antibiotics in cesarean section, how this and other factors may affect the neonatal intestinal microbiota and whether intrapartum antibiotics used for cesarean section are linked to the development of allergic disease.

Summary Severe lower respiratory infection (sLRI) are a major cause of infant morbidity and mortality, and predispose to later chronic respiratory diseases such as asthma. Poor maternal diet during pregnancy is a risk factor for sLRI in the offspring. Here we demonstrate in mice that a maternal low-fibre diet (LFD) disrupts plasmacytoid and conventional dendritic cell (DC) hematopoiesis in the offspring, predisposing to sLRI and subsequent asthma. The LFD alters the composition of the maternal milk microbiome and assembling infant gut microbiome, ablating the induction of a developmental wave of the non-redundant DC growth factor Flt3L by neonatal intestinal epithelial cells. Therapy with a propionate-producing bacteria isolated from the milk of high-fibre diet-fed mothers, or supplementation with propionate, confers protection against sLRI by restoring gut Flt3L expression and pDC hematopoiesis. Our findings identify a microbiome-dependent Flt3L axis in the gut that regulates pDC hematopoiesis in early life and confers disease resistance.

Major histocompatibility complex (MHC) II is dynamically expressed on mucosal epithelial cells and is induced in response to inflammation and parasitic infections, upon exposure to microbiota, and is increased in chronic inflammatory diseases. However, the regulation of epithelial cell–specific MHC II during homeostasis is yet to be explored. We discovered a novel role for IL-22 in suppressing epithelial cell MHC II partially via the regulation of endoplasmic reticulum (ER) stress, using animals lacking the interleukin-22-receptor (IL-22RA1), primary human and murine intestinal and respiratory organoids, and murine models of respiratory virus infection or with intestinal epithelial cell defects. IL-22 directly downregulated interferon-γ–induced MHC II on primary epithelial cells by modulating the expression of MHC II antigen A α (H2-Aα) and Class II transactivator (Ciita), a master regulator of MHC II gene expression. IL-22RA1-knockouts have significantly higher MHC II expression on mucosal epithelial cells. Thus, while IL-22–based therapeutics improve pathology in chronic disease, their use may increase susceptibility to viral infections.

AbstractBreastfeeding facilitates vertical transmission of microbes from mothers to infants. Milk microbiome composition is strongly influenced by maternal diet, and this affects which taxa are likely to colonize the infant gut with consequences for host health and immune development. At present, it is unclear how diet influences the composition of the milk microbiome and why these microbes lead to different health outcomes for the infant. Here, we used metagenomics and metabolomics to link microbially-mediated immunoregulatory traits and metabolites to individual milk microbial taxa, and determine how the representation of these traits changes with maternal dietary fiber content. We assembled and annotated genomes accounting for 90% of the milk microbial communities from breastfeeding mice fed high or low-fiber chow. Diverse carbohydrate and fatty acid content in high-fiber milk was associated with diverse microbes harboring multiple glycoside hydrolases and high redundancy of immunoregulatory metabolite pathways. Low dietary fiber, by contrast, produced milk enriched in amino acids and a low-diversity peptide degrading microbiome with limited immunoregulatory traits. Our study indicates that complex milk carbohydrate availability drives assembly of a diverse milk microbiome, and by extension a diverse set of immunoregulatory functions inheritable by the breastfeeding infant. Collectively, our findings highlight how the mother’s diet influences the composition of the milk microbiome and the potential vertical transmission of immunoregulatory traits from mother to infant.

An acute inflammatory response is a complex, coordinated process that occurs in distinct phases. The initial stage requires plasma proteins and the expression of chemokines and/or cytokines to initiate the recruitment of innate inflammatory cells. Next, the infiltrating leukocytes (eg, neutrophils, eosinophils, monocytes) attempt to kill the invading pathogen, often indiscriminately, and so collateral damage to host cells is unavoidably incurred. Last comes the resolution phase, which is mediated primarily by tissue-resident and recruited macrophages that produce growth factors such as TGF-β, to facilitate tissue remodeling and repair. An additional layer of specialty may arise as part of this process whereby effector classes or immune modules (ie, type 1, type 2, and type 17 immunity) are induced so that the effector response is tailor-made to defeat the invading pathogen and adaptive immune memory is established. Beyond this paradigm, type 2 immunity may arise in the latter stages of the inflammatory response to counterregulate type 1 inflammation (ie, to limit the collateral damage) and to initiate tissue remodeling and repair.1Gieseck 3rd, R.L. Wilson M.S. Wynn T.A. Type 2 immunity in tissue repair and fibrosis.Nat Rev Immunol. 2018; 18: 62-76Crossref PubMed Scopus (566) Google Scholar Critically, the various phases of inflammation and immune modules must be tightly regulated and occur sequentially to promote the favored outcome, namely, tissue homeostasis and the restoration of tissue function. In the context of allergic asthma, the acute inflammatory response that is initiated in response to an environmental trigger is aberrant and dysregulated, and by perturbing tissue function and compounding the existing airway remodeling, it causes the ensuing loss of asthma control. Respiratory virus infections are the main trigger of acute exacerbations of asthma. Optimal viral killing and clearance necessitates type 1 immunity, and yet, the immunologic landscape in the asthmatic airway is typically biased toward type 2 inflammation (Fig 1). Thus, a counterregulatory “handbrake” is already in place at the start of the infection in asthmatic patients. This inhibitory pressure is evident in human airway epithelial cells (AECs) when assessed ex vivo: AECs from patients with asthma show an impaired production of type I and type III interferons and increased viral load in response to rhinovirus infection.2Wark P.A. Johnston S.L. Bucchieri F. Powell R. Puddicombe S. Laza-Stanca V. et al.Asthmatic bronchial epithelial cells have a deficient innate immune response to infection with rhinovirus.J Exp Med. 2005; 201: 937-947Crossref PubMed Scopus (1040) Google Scholar,3Werder R.B. Zhang V. Lynch J.P. Snape N. Upham J.W. Spann K. et al.Chronic IL-33 expression predisposes to virus-induced asthma exacerbations by increasing type 2 inflammation and dampening antiviral immunity.J Allergy Clin Immunol. 2018; 141: 1607-1619.e9Abstract Full Text Full Text PDF PubMed Scopus (54) Google Scholar Mechanistic studies have demonstrated that this phenotype can be driven by IL-4, IL-13, IL-33, prostaglandin D2, and TGF-β, firmly establishing the inhibitory role of type 2 immunity on antiviral immunity in the airway mucosa.3Werder R.B. Zhang V. Lynch J.P. Snape N. Upham J.W. Spann K. et al.Chronic IL-33 expression predisposes to virus-induced asthma exacerbations by increasing type 2 inflammation and dampening antiviral immunity.J Allergy Clin Immunol. 2018; 141: 1607-1619.e9Abstract Full Text Full Text PDF PubMed Scopus (54) Google Scholar, 4Bedke N. Sammut D. Green B. Kehagia V. Dennison P. Jenkins G. et al.Transforming growth factor-beta promotes rhinovirus replication in bronchial epithelial cells by suppressing the innate immune response.PLoS One. 2012; 7e44580Crossref PubMed Scopus (68) Google Scholar, 5Werder R.B. Lynch J.P. Simpson J.C. Zhang V. Hodge N.H. Poh M. et al.PGD2/DP2 receptor activation promotes severe viral bronchiolitis by suppressing IFN-lambda production.Sci Transl Med. 2018; 10eaoo0052Crossref Scopus (40) Google Scholar AECs are an important first line of host defense; however, plasmacytoid dendritic cells (pDC) are highly specialized antiviral cells; they possess the key machinery to rapidly sense virus-associated molecular patterns (eg, single-stranded or double-stranded RNA) and the ability to produce prodigious amounts of type I interferons and chemokines to initiate type 1 immunity. As has been shown with AECs, pDCs obtained from patients with asthma elicit impaired interferon responses to virus stimulation, and intriguingly, this phenotype can be recapitulated by the cross-linking of FcεRIα, the high-affinity receptor for IgE.6Gill M.A. Bajwa G. George T.A. Dong C.C. Dougherty II, Jiang N. et al.Counterregulation between the FcepsilonRI pathway and antiviral responses in human plasmacytoid dendritic cells.J Immunol. 2010; 184: 5999-6006Crossref PubMed Scopus (250) Google Scholar Significantly, omalizumab (anti-IgE) treatment of children with mild-to-moderate asthma increases IFN-α release from rhinovirus-stimulated PBMCs, and this response is linked to a reduction in exacerbations.7Teach S.J. Gill M.A. Togias A. Sorkness C.A. Arbes Jr., S.J. Calatroni A. et al.Preseasonal treatment with either omalizumab or an inhaled corticosteroid boost to prevent fall asthma exacerbations.J Allergy Clin Immunol. 2015; 136: 1476-1485Abstract Full Text Full Text PDF PubMed Scopus (426) Google Scholar These findings suggest that the targeting of type 2 inflammation not only restores asthma control but also decreases exacerbation susceptibility by derepressing antiviral immunity. Eosinophils are a key effector cell of type 2 inflammation, and their targeting via IL-5 neutralization or IL-5Rα blockade decreases exacerbation frequency. However, whether eosinophils contribute to asthma pathogenesis by suppressing antiviral immunity has remained unknown. In this issue of the Journal of Allergy and Clinical Immunology, Dill-McFarland et al provide compelling evidence that eosinophils dampen pDC antiviral immunity.8Dill-McFarland K.A. Schwartz J.T. Zhao H. Shao B. Fulkerson P.C. Altman M.C. et al.Eosinophil-mediated suppression and anti-IL-5 enhancement of plasmacytoid dendritic cell interferon responses in asthma.J Allergy Clin Immunol. 2022; 150: 666-675Abstract Full Text Full Text PDF PubMed Scopus (8) Google Scholar Rhinovirus-stimulated pDCs secreted markedly less IFN-α and CXCL10 when cocultured directly and indirectly (separated by a transwell system) with eosinophils or the supernatants of IL-3–stimulated eosinophils. The same inhibitory effect was observed when the pDCs were stimulated with a synthetic Toll-like receptor-7 agonist, suggesting that the attenuated IFN-α response is not an inhibitory effect of the active virus. To identify the soluble factor mediating the suppressive effect, Dill-McFarland et al8Dill-McFarland K.A. Schwartz J.T. Zhao H. Shao B. Fulkerson P.C. Altman M.C. et al.Eosinophil-mediated suppression and anti-IL-5 enhancement of plasmacytoid dendritic cell interferon responses in asthma.J Allergy Clin Immunol. 2022; 150: 666-675Abstract Full Text Full Text PDF PubMed Scopus (8) Google Scholar analyzed the eosinophil-derived supernatants, detecting eosinophil cationic protein, eosinophil-derived neurotoxin (EDN), and TGF-β1 but not major basic protein, eosinophil peroxidase, IL-4, IL-5, or IL-13. Exogenous EDN or TGF-β1, but not eosinophil cationic protein, attenuated rhinovirus-induced IFN-α release by pDCs (Fig 1), although the effect was only partial and not as striking as that of the eosinophil supernatant, suggesting that other as yet identified soluble factors may also contribute to the suppressive effect on pDC responsiveness. Candidates include TNF-α, IL-33, IL-25, and other isoforms of TGF-β.9Lynch J.P. Werder R.B. Simpson J. Loh Z. Zhang V. Haque A. et al.Aeroallergen-induced IL-33 predisposes to respiratory virus-induced asthma by dampening anti-viral immunity.J. Allergy and Clin. Immunol. 2016; 138: 1326-1337Abstract Full Text Full Text PDF PubMed Scopus (73) Google Scholar To strengthen their observations clinically, Dill-McFarland et al8Dill-McFarland K.A. Schwartz J.T. Zhao H. Shao B. Fulkerson P.C. Altman M.C. et al.Eosinophil-mediated suppression and anti-IL-5 enhancement of plasmacytoid dendritic cell interferon responses in asthma.J Allergy Clin Immunol. 2022; 150: 666-675Abstract Full Text Full Text PDF PubMed Scopus (8) Google Scholar then compared the pDC responses of patients with asthma treated with or without therapies targeting IL-5 or its receptor, IL-5Rα. Although the study was limited by its small sample size, pDC-derived IFN-α production was markedly greater in those individuals receiving an eosinophil-ablating therapy. This effect was associated with increased IFN-α and IFN-γ responses at baseline, as assessed by global gene expression in the pDCs. Interestingly, the inflammatory response gene set was upregulated in response to rhinovirus but not in those patients on anti–IL-5 or anti–IL-5Rα (mepolizumab or benralizumab) therapy, suggesting that the loss of autocrine interferon signaling switches pDC function towards a more proinflammatory phenotype. pDC can produce proinflammatory cytokines such as IL-6, TNF-α, and IL-17A, and have been proposed to be deleterious in some asthma studies. Moreover, an interesting observation in this study is that pDCs positively enhance at least some eosinophil functions, such as EDN release, which warrants further investigation, as it suggests an indirect mechanism of pDC self-regulation. Another important function of pDCs is their intrinsic ability to promote the differentiation and expansion of regulatory T cells, which calibrate the inflammatory response to limit immunopathology.10Lynch J.P. Werder R.B. Loh Z. Sikder M.A.A. Curren B. Zhang V. et al.Plasmacytoid dendritic cells protect from viral bronchiolitis and asthma through semaphorin 4a-mediated T reg expansion.J Exp Med. 2018; 215: 537-557Crossref PubMed Scopus (53) Google Scholar Regulatory T-cell function is typically perturbed in asthma, but whether type 2 mediators such as TGF-β and EDN contribute to this phenotype via indirect effects on pDC function remains to be explored. A limitation of the study by Dill-McFarland et al8Dill-McFarland K.A. Schwartz J.T. Zhao H. Shao B. Fulkerson P.C. Altman M.C. et al.Eosinophil-mediated suppression and anti-IL-5 enhancement of plasmacytoid dendritic cell interferon responses in asthma.J Allergy Clin Immunol. 2022; 150: 666-675Abstract Full Text Full Text PDF PubMed Scopus (8) Google Scholar is the cross-sectional design in assessing the effect of the biologics in vivo. A longitudinal design including preintervention and postintervention analyses is needed to verify a role for eosinophils in suppressing antiviral immunity. Moreover, the question remains as to how eosinophil-derived factors affect the function of circulating pDCs. The in vitro coculture model used by Dill-McFarland et al8Dill-McFarland K.A. Schwartz J.T. Zhao H. Shao B. Fulkerson P.C. Altman M.C. et al.Eosinophil-mediated suppression and anti-IL-5 enhancement of plasmacytoid dendritic cell interferon responses in asthma.J Allergy Clin Immunol. 2022; 150: 666-675Abstract Full Text Full Text PDF PubMed Scopus (8) Google Scholar is perhaps more representative of the lung mucosa, where both pDC and eosinophils (or their contents) might encounter one other. But in the in vivo setting, are peripheral blood eosinophils regulating the transcriptome or epigenome of circulating pDCs, or is this phenotype a consequence of an altered cytokine microenvironment in the bone marrow (which is the site of pDC development and a reservoir of CD4+ TH2 cells)? One thing is for sure: the new wave of biologics for the treatment of asthma look set to go beyond attenuating pathogenic type 2 immunity for which they were primarily designed. They show the potential to remove the handbrake impairing antiviral immunity, thus restoring the lung microenvironment to a healthy state and breaking the cycle of dysregulated inflammation. Eosinophil-mediated suppression and anti–IL-5 enhancement of plasmacytoid dendritic cell interferon responses in asthmaJournal of Allergy and Clinical ImmunologyVol. 150Issue 3PreviewVirus-induced IFN-α secretion by plasmacytoid dendritic cells (pDCs) is negatively impacted by IgE and has been linked to asthma exacerbations. Eosinophils, another contributor to type 2 inflammation, are also associated with asthma severity. Full-Text PDF

Streptococcus pneumoniae (the pneumococcus) is a leading cause of pneumonia in children under 5 years of age. Coinfection by pneumococci and respiratory viruses enhances disease severity. Little is known about pneumococcal coinfections with respiratory syncytial virus (RSV). Here, we developed a novel infant mouse model of coinfection using pneumonia virus of mice (PVM), a murine analogue of RSV, to examine the dynamics of coinfection in the upper respiratory tract, an anatomical niche that is essential for host-to-host transmission and progression to disease. Coinfection increased damage to the nasal tissue and increased production of the chemokine CCL3. Nasopharyngeal pneumococcal density and shedding in nasal secretions were increased by coinfection. In contrast, coinfection reduced PVM loads in the nasopharynx, an effect that was independent of pneumococcal strain and the order of infection. We showed that this "antagonistic" effect was absent using either ethanol-killed pneumococci or a pneumococcal mutant deficient in capsule production and incapable of nasopharyngeal carriage. Colonization with a pneumococcal strain naturally unable to produce capsule also reduced viral loads. The pneumococcus-mediated reduction in PVM loads was caused by accelerated viral clearance from the nasopharynx. Although these synergistic and antagonistic effects occurred with both wild-type pneumococcal strains used in this study, the magnitude of the effects was strain dependent. Lastly, we showed that pneumococci can also antagonize influenza virus. Taken together, our study has uncovered multiple novel facets of bacterial-viral coinfection. Our findings have important public health implications, including for bacterial and viral vaccination strategies in young children. IMPORTANCE Respiratory bacterial-viral coinfections (such as pneumococci and influenza virus) are often synergistic, resulting in enhanced disease severity. Although colonization of the nasopharynx is the precursor to disease and transmission, little is known about bacterial-viral interactions that occur within this niche. In this study, we developed a novel mouse model to examine pneumococcal-viral interactions in the nasopharynx with pneumonia virus of mice (PVM) and influenza. We found that PVM infection benefits pneumococci by increasing their numbers in the nasopharynx and shedding of these bacteria in respiratory secretions. In contrast, we discovered that pneumococci decrease PVM numbers by accelerating viral clearance. We also report a similar effect of pneumococci on influenza. By showing that coinfections lead to both synergistic and antagonistic outcomes, our findings challenge the existing dogma in the field. Our work has important applications and implications for bacterial and viral vaccines that target these microbes.