A hybrid stochastic model and its Bayesian identification for infectious disease screening in a university campus with application to massive COVID-19 screening at the University of Liège.

Amid the COVID-19 pandemic, universities are implementing various prevention and mitigation measures. Identifying and isolating infectious individuals by using screening testing is one such a measure that can contribute to reducing spread. Here, we propose a hybrid stochastic model for infectious disease transmission in a university campus with screening testing and its surrounding community. Based on a compartmental modeling strategy, this hybrid stochastic model represents the evolution of the infectious disease and its transmission using continuous-time stochastic dynamics, and it represents the screening testing as discrete stochastic events. We also develop, in a Bayesian framework, the identification of parameters of this hybrid stochastic model, including transmission rates. These parameters were identified from the screening test data for the university population and observed incidence counts for the surrounding community. We implement the exploration of the Bayesian posterior using a machine-learning simulation-based inference approach. The proposed methodology was applied in a retrospective modeling study of a massive COVID-19 screening conducted at the University of Liège in Fall 2020. The emphasis of the paper is on the development of the hybrid stochastic model to assess the impact of screening testing as a measure to reduce spread. The hybrid stochastic model allows various factors to be represented and examined, such as interplay with the surrounding community, variability of the transmission dynamics, the rate of participation in the screening testing, the test sensitivity, the test frequency, the diagnosis delay, and compliance with isolation. The application in the retrospective modeling study suggests that a high rate of participation and a high test frequency are important factors to reduce spread.

Effects of a P-class CpG-ODN administered by intramuscular injection on plasma cytokines and on white blood cells of healthy horses.

Cytosine-phosphate-guanosine (CpG-ODN) has been described as a potent immunostimulatory agent in different species. No study reported the effect of a P-class CpG when administered systemically in healthy horses. The aim of this study was to evaluate the tolerance and the effect of an intramuscularly administered P-class CpG-ODN on hematology and on plasma cytokines (IFN-α, IL-10, TNF-α, IFN-γ) in 8 healthy horses. Intra-muscular CpG-ODN or placebo (PBS) was administered twice at a 7 days-interval. Groups were inversed after 2 months of washout period. A physical examination, complete blood count (CBC) and plasma cytokine measurements were performed from 2 days before injection up to 21 days after injection. P-class CpG-ODN injection was well tolerated with minor side effects. After the first injection a significant transient drop in circulating total leukocytes, lymphocytes and an increase in monocytes were observed. A transient drop in eosinophils was also noted after each CpG injection. P-class CpG-ODN at a dose of 5 mg did not create major side effects in 7 horses, one horse showed transient pyrexia. A redistribution of white blood cells was observed in horses receiving CpG, but no change in plasma cytokines was observed at the indicated dose, route of administration and sampling times.

A molecular approach for the rapid, selective and sensitive detection of Exophiala jeanselmei in environmental samples: development and performance assessment of a real-time PCR assay.

Exophiala jeanselmei is an opportunistic pathogenic black yeast growing in humid environments such as water reservoirs of air-conditioning systems. Because this fungal contaminant could be vaporized into the air and subsequently cause health problems, its monitoring is recommended. Currently, this monitoring is based on culture and microscopic identification which are complex, sometimes ambiguous and time-demanding, i.e., up to 21 days. Therefore, molecular, culture-independent methods could be more advantageous for the monitoring of E. jeanselmei. In this study, we developed a SYBR®green real-time PCR assay based on the internal transcribed spacer 2 from the 18S ribosomal DNA complex for the specific detection of E. jeanselmei. The selectivity (100 %), PCR efficiency (95.5 %), dynamic range and repeatability of this qPCR assay were subsequently evaluated. The limit of detection for this qPCR assay was determined to be 1 copy of genomic DNA of E. jeanselmei. Finally, water samples collected from cooling reservoirs were analyzed using this qPCR assay to deliver a proof of concept for the molecular detection of E. jeanselmei in environmental samples. The results obtained by molecular analysis were compared with those of classical methods (i.e., culture and microscopic identification) used in routine analysis and were 100 % matching. This comparison demonstrated that this SYBR®green qPCR assay can be used as a molecular alternative for monitoring and routine investigation of samples contaminated by E. jeanselmei, while eliminating the need for culturing and thereby considerably decreasing the required analysis time to 2 days.

Development and performance assessment of a qualitative SYBR® green real-time PCR assay for the detection of Aspergillus versicolor in indoor air.

Currently, contamination of indoor environment by fungi and molds is considered as a public health problem. The monitoring of indoor airborne fungal contamination is a common tool to help understanding the link between fungi in houses and respiratory problems. Classical analytical monitoring methods, based on cultivation and microscopic identification, depend on the growth of the fungi. Consequently, they are biased by difficulties to grow some species on certain culture media and under certain conditions or by noncultivable or dead fungi that can consequently not be identified. However, they could have an impact on human health as they might be allergenic. Since molecular methods do not require a culture step, they seem an excellent alternative for the monitoring of indoor fungal contaminations. As a case study, we developed a SYBR® green real-time PCR-based assay for the specific detection and identification of Aspergillus versicolor, which is frequently observed in indoor environment and known to be allergenic. The developed primers amplify a short region of the internal transcribed spacer 1 from the 18S ribosomal DNA complex. Subsequently, the performance of this quantitative polymerase chain reaction (qPCR) method was assessed using specific criteria, including an evaluation of the selectivity, PCR efficiency, dynamic range, and repeatability. The limit of detection was determined to be 1 or 2 copies of genomic DNA of A. versicolor. In order to demonstrate that this SYBR® green qPCR assay is a valuable alternative for monitoring indoor fungal contamination with A. versicolor, environmental samples collected in contaminated houses were analyzed and the results were compared to the ones obtained with the traditional methods.

Real-time PCR for quantification in soil of glycoside hydrolase family 6 cellulase genes.

UNLABELLED: Cellulose is the main structural component of the cell walls of higher plants, representing c. 35-50% of a plant's dry weight; after decomposition and transformation, and constituting a large part of soil organic matter. Telluric micro-organisms able to use cellulose as carbon and energy sources for growth are widely distributed in the environment, but the factors controlling the rate of cellulose degradation are not well understood. In this study, we have developed a quantitative real-time PCR (qPCR) primer set to quantify the glycoside hydrolase family 6 (GH6 family) cellulase genes in soil samples. The qPCR assays were linear over 8 orders of magnitude and sensitive down to 10 copies per assay. qPCR analysis of contrasted soil samples showed densities between 2·47 × 10(7) and 1·48 × 10(10) copies per gram of soil. Cloning and sequencing of the PCR products from environmental DNA confirmed both specific amplification (more than 96%) and the wide diversity targeted by the primer set, throughout nearly all the GH6 family, including sequences of bacteria and fungi. SIGNIFICANCE AND IMPACT OF THE STUDY: Telluric micro-organisms able to use cellulose as carbon and energy sources for growth are widely distributed in the environment, but the factors controlling the rate of cellulose degradation are not well understood. The objective of our study was to develop a qPCR for rapid quantification of GH6 cellulase genes in soil. This qPCR could be applied to study the potential for cellulose degradation in different soils in order to better understand the factors controlling the stability of the soil organic matter.

Correlations between PAH bioavailability, degrading bacteria, and soil characteristics during PAH biodegradation in five diffusely contaminated dissimilar soils.

The natural biodegradation of seven polycyclic aromatic hydrocarbons (PAHs) by native microorganisms was studied in five soils from Normandy (France) from diffusely polluted areas, which can also pose a problem in terms of surfaces and amounts of contaminated soils. Bioavailability tests using cyclodextrin-based extractions were performed. The natural degradation of low molecular weight (LMW) PAHs was not strongly correlated to their bioavailability due to their sorption to geosorbents. Conversely, the very low degradation of high molecular weight (HMW) PAHs was partly correlated to their poor availability, due to their sorption on complexes of organic matter and kaolinites or smectites. A principal component analysis allowed us to distinguish between the respective degradation behaviors of LMW and HMW PAHs. LMW PAHs were degraded in less than 2-3 months and were strongly influenced by the relative percentage of phenanthrene-degrading bacteria over total bacteria in soils. HMW PAHs were not significantly degraded, not only because they were less bioavailable but also because of a lack of degrading microorganisms. Benzo[a]pyrene stood apart since it was partly degraded in acidic soils, probably because of a catabolic cooperation between bacteria and fungi.

Analysis of gene expression in canine idiopathic pulmonary fibrosis.

Idiopathic pulmonary fibrosis (IPF) in dogs is a rare disease of unknown aetiology, seen in terrier breeds, particularly the West Highland white terrier (WHWT). The aim of this study was to determine pulmonary gene expression in canine IPF in order to gain insights into the pathogenesis of the disease and to identify possible biomarkers. Microarray analyses were conducted to determine gene expression profiles in the lungs of dogs with IPF and control dogs of various breeds. More than 700 genes were identified as having greater than two-fold difference in expression between the two groups. The significant biological functions associated with these genes were related to cellular growth and proliferation, developmental processes, cellular movement, cell to cell signalling and interaction, and antigen presentation. Altered levels of expression were confirmed by quantitative reverse transcriptase PCR for genes encoding chemokine (C-C) ligand (CCL) 2 (+4.9 times), CCL7 (+6.8 times), interleukin 8 (+4.32 times), chemokine (C-X-C) ligand 14 (+3.4 times), fibroblast activation protein (+4.7 times) and the palate, lung and nasal associated protein (PLUNC, -25 times). Serum CCL2 concentrations were significantly higher in WHWTs with IPF (mean 628.1 pg/mL, interquartile range 460.3-652.7 pg/mL) than unaffected WHWTs (mean 344.0 pg/mL, interquartile range 254.5-415.5 pg/mL; P=0.001). The results support CCL2 as a candidate biomarker for IPF in dogs.

Cytokine and transcription factor expression by Aspergillus fumigatus-stimulated peripheral blood mononuclear cells in dogs with sino-nasal aspergillosis.

The causal agent of sino-nasal aspergillosis is usually Aspergillus fumigatus, which is a saprophytic and ubiquitous fungus that causes a severe rhinosinusitis in apparent healthy dogs. Affected dogs do not have systemic immuno-suppression. It has been shown previously that dogs affected by this disease have local over-expression of interleukin (IL)-10 and Th1 cytokines in nasal mucosal tissue. The aim of the present study was to assess the response of peripheral blood mononuclear cells (PBMC) from affected and unaffected dogs to antigen-specific stimulation with heat-inactivated Aspergillus spp. conidia, by quantifying gene expression for specific Th1, Th2, Th17 and Treg cytokines and their related transcription factors. Quantification of IL-4 and IFN-γ protein in culture supernatant was performed by enzyme-linked immunosorbent assay (ELISA). PBMC from dogs with SNA produced adequate mRNA encoding IFN-γ and IFN-γ protein. The expression of IL-17A mRNA was significantly greater in PBMC of affected compared with unaffected dogs. The amount of IL-10 mRNA in PBMC from affected dogs decreased after antigen-specific challenge. These results suggest that the incapacity of affected dogs to clear these fungal infections is not related to a defect in Th1 immunity or to an overwhelming regulatory reaction, but rather to an uncontrolled pro-inflammatory reaction driven by Th17 cells.

Myeloid hypoxia-inducible factor 1α prevents airway allergy in mice through macrophage-mediated immunoregulation.

Hypoxia-inducible factor (HIF) has important roles in promoting pro-inflammatory and bactericidal functions in myeloid cells. Conditional genetic ablation of its major subunit Hif1α in the myeloid lineage consequently results in decreased inflammatory responses in classical models of acute inflammation in mice. By contrast, we report here that mice conditionally deficient for Hif1α in myeloid cells display enhanced sensitivity to the development of airway allergy to experimental allergens and house-dust mite antigens. We support that upon allergen exposure, MyD88-dependent upregulation of Hif1α boosts the expression of the immunosuppressive cytokine interleukin (IL)-10 by lung interstitial macrophages (IMs). Hif1α-dependent IL-10 secretion is required for IMs to block allergen-induced dendritic cell activation and consequently for preventing the development of allergen-specific T-helper cell responses upon allergen exposure. Thus, this study supports that, in addition to its known pro-inflammatory activities, myeloid Hif1α possesses immunoregulatory functions implicated in the prevention of airway allergy.

Interactions between ethylenediaminetetraacetic acid (EDTA) and iron absorption pathways, in the Caco-2 model.

UNLABELLED: EDTA is a well known enhancer of iron absorption; however, the precise way of absorption of iron ingested in presence of EDTA is not known; some data suggest it could use a passive, non regulated paracellular way. Iron (sulphate or gluconate) absorption by Caco-2 cells was assessed in presence of EDTA. EDTA did not change the apical uptake of iron; transport in the basal chamber increased by 98% for FeSO4 and 95% for Fe gluconate. By contrast, intracellular storage decreased by 31% for FeSO4 and 64% for Fe gluconate. In addition EDTA induced a significant increase of permeability of the cell monolayer assessed by a decrease of transepithelial electrical resistance: 314+/-34 Omegacm(-2) to 235+/-57 Omegacm(-2) for sulphate, 414+/-33 Omegacm(-2) to 223+/-36 Omegacm(-2) for gluconate; iron free control: 410+/-10 Omegacm(-2). CONCLUSIONS: These results suggest that in presence of EDTA iron absorption occurs mainly by the paracellular instead of the regulated cellular way, that could potentially enhance its toxicity.

Helenalin reduces Staphylococcus aureus infection in vitro and in vivo.

Staphylococcus (S.) aureus is a major udder pathogen causing bovine mastitis. Some pro-inflammatory cytokines, including tumor necrosis factor-alpha (TNF-alpha), enhance extracellular and intracellular growth of S. aureus, indicating that the inflammatory process favors S. aureus infection. Helenalin is a sesquiterpene lactone with potent anti-inflammatory properties. This study was designed to evaluate the effects of helenalin on S. aureus infection. First, in vitro experiments were conducted. These studies revealed that proliferation of S. aureus in bovine mammary epithelial MAC-T cells treated in the presence or absence of TNF-alpha was markedly reduced in the presence of helenalin. Secondly, in vivo effects of helenalin were investigated. Lactating mice treated in the presence or absence of helenalin were challenged by the intramammary route with S. aureus and the bacteria in the mammary glands were counted 12 h after infection. Significantly less numbers of bacteria were recovered from the infected glands of helenalin-treated mice compared with untreated mice. Moreover, histological examination of mammary tissue from helenalin-treated mice that were challenged with S. aureus indicated that helenalin is able to significantly reduce leukocyte infiltration in the mammary gland following S. aureus inoculation. Our results show that helenalin reduces S. aureus intracellular growth and experimental S. aureus infection. We conclude that helenalin may be of potential interest in the treatment of S. aureus-induced mastitis in the bovine species.

Prolactin-induced activation of nuclear factor kappaB in bovine mammary epithelial cells: role in chronic mastitis.

We sought to determine whether prolactin (PRL) could influence the neutrophilic inflammation that characterizes chronic mastitis. Most of the genes encoding inflammatory proteins depend on the nuclear factor kappaB (NF-kappaB) for their expression. We addressed the hypothesis that immunomodulatory activities of PRL might arise from an increase in NF-kappaB activity. MAC-T cells, a bovine mammary epithelial cell line, were stimulated with increasing concentrations of bovine PRL (1, 5, 25, 125, and 1,000 ng/mL). Level of NF-kappaB binding activity was measured and mRNA was evaluated for IL-1beta, IL-6, IL-8, granulocyte-macrophage colony-stimulating factor (GMCSF), IFN-gamma, and tumor necrosis factor (TNF)-alpha, cytokines known to require NF-kappaB for their maximal transcription. Prolactin activated NF-kappaB; maximal NF-kappaB activation was weaker with PRL than with TNF-alpha at 30 or 180 min poststimulation. In addition, PRL significantly amplified, in a dose-dependent manner, mRNA expression of IL-1beta, IL-6, IL-8, GMCSF, and TNF-alpha. We measured PRL concentrations in blood and milk from healthy and chronic mastitis-infected cows, and studied the relationship between the PRL concentration and the degree of inflammation in the mammary gland as indirectly assessed by somatic cell counts (SCC). Plasma PRL did not differ significantly between healthy and chronic mastitis-affected cows (63.7 and 67.5 ng/mL, respectively). Milk PRL concentration was significantly increased in chronic mastitis-affected quarters with the highest SCC, and had a positive significant correlation between SCC, as well as between the number of neutrophils present in milk samples. The present findings show that PRL promotes an inflammatory response in bovine mammary epithelial cells via NF-kappaB activation, and suggest a role for PRL in the pathogenesis of chronic mastitis.

Iron availability and consumption of tea, vervain and mint during weaning in Morocco.

BACKGROUND/AIMS: Iron deficiency impairs growth and psychomotor development of infants. In Morocco, infusions are introduced very early in infant diet, and could contribute to iron deficiency, due to their high polyphenol content. METHODS: The availability of tea, mint and vervain infusions was assessed using an in vitro model of digestion and dialysis. Two gastric pHs were used: pH 4 as in the first week life, and pH 2.5 as in older infants. Six repetitions of each experiment were made. The total polyphenol content of infusions was measured. RESULTS: At pH 4 and at pH 2.5, iron availability was decreased by tea and vervain, and increased by mint and ascorbic acid. At both pHs it was increased by addition of ascorbic acid to tea and vervain. In addition, at pH 2.5 it was increased by addition of ascorbic acid to mint. The highest value was observed in the presence of both ascorbic acid and mint (33.1 +/- 4.1%). In any case, iron availability was higher at pH 2.5 than at pH 4 (with single compounds or combinations with ascorbic acid). The polyphenol contents (mg/l) of tea, vervain and mint infusions were 2,236.1, 771.1, and 16.5. CONCLUSIONS: Tea and vervain infusions inhibited iron availability. In contrast, mint improved it; vitamin C helped in preventing these inhibiting properties. It could be proposed to discourage tea and vervain drinking at early weaning and to replace them by mint infusion, or at least to promote the consumption of vitamin C-rich fruit juice to counteract these inhibiting effects.

Cysteinyl-leukotrienes contribute to sputum eosinophil chemotactic activity in asthmatics.

BACKGROUND: Cysteinyl-leukotrienes are lipid derived mediators involved in asthma. They are able to stimulate eosinophil chemotaxis in vitro. Induced sputum from asthmatics has been shown to contain eosinophil chemotactic activity. The purpose of our study was to evaluate the contribution of cysteinyl-leukotrienes to sputum eosinophil chemotactic activity in asthmatics and to seek whether there might be differences between asthmatics free of inhaled corticosteroids vs those regularly receiving this treatment. METHODS: Twenty-two patients (11 corticosteroid free, mean FEV1 99% predicted, 11 corticosteroid-treated, mean FEV1 77% predicted) recruited from our asthma clinic underwent a sputum induction. Sputum was processed according to standard procedure. Eosinophil chemotactic activity contained in the fluid phase was assessed using Boyden microchamber model and expressed as chemotaxis index (CI). Cysteinyl-leukotrienes were measured in sputum supernatant by ELISA and their role in sputum eosionophil chemotactic activity was evaluated by using montelukast, a selective antagonist of a cys-LT1 receptor. RESULTS: Cysteinyl-leukotrienes were well detectable in sputum supernatants from both steroid-naive (247 +/- 42 pg/ml) and steroid-treated (228 +/- 26 pg/ml) asthmatics. Sputum eosinophil chemotactic activity was indiscriminately present in both corticosteroid-naive (CI: 2.61 +/- 0.22) and corticosteroid-treated (2.98 +/- 0.35) asthmatics. Montelukast (100 microM) significantly inhibited the eosinophil chemotactic activity in both groups achieving a mean inhibition of 54.2 +/- 9.2% (P < 0.001) and 64.7 +/- 7.8% (P < 0.001) in steroid-naive and steroid-treated asthmatics respectively. CONCLUSION: Cysteinyl-leukotrienes actively participate in sputum eosinophil chemotactic activity found in asthmatics irrespective of whether they are or not under treatment with inhaled corticoids.

[Control of gene transcription as a new therapeutic target in asthma]. / Le contrôle de la transcription génique en tant que nouvelle cible thérapeutique dans le traitement de l'asthme.

The recent advances in the knowledge of the molecular mechanisms underlying asthma have lead to a significant improvement of the current treatments of the disease and opened new perspectives for the development of therapeutic alternatives to inhaled corticosteroids. The selective targeting of transcription factors controlling the expression of the genes implicated in the pathogenesis of asthma is one of these privileged strategies. This review aims at describing the most promising new therapeutic targets in the control of asthmatic inflammation at the gene transcription level.

Delayed neutrophil apoptosis in bovine subclinical mastitis.

Bovine subclinical mastitis can be defined as a moderated inflammatory disease characterized by a persistent accumulation of neutrophils in milk. As GMCSF-mediated delay of neutrophil apoptosis contributes to the accumulation of inflammatory cells at the site of inflammation in many human diseases, we sought to determine whether subclinical mastitis in cows is also associated with a GMCSF-dependent increase in milk-neutrophil survival. We first addressed the hypothesis that GMCSF delays bovine neutrophil apoptosis by activation of the signal transducer and activator of transcription (STAT) family members STAT3 and STAT5, which are critical regulators of the expression of various Bcl-2 family proteins. Granulocyte-macrophage colony-stimulating factor significantly delayed apoptosis of blood neutrophils obtained from healthy cows. In these cells, GMCSF activated STAT5, but not STAT3, and induced an increase in the mRNA of the antiapoptotic Bcl-2 member, Bcl-xL. Granulocyte-macrophage colony-stimulating factor-dependent STAT5 activation and up-regulation of Bcl-xL mRNA were blocked by the Jak inhibitor, AG-490. This inhibition was associated with abrogation of the prosurvival effect of GMCSF, demonstrating a key role for STAT5 in delayed neutrophil apoptosis. We further found that GMCSF expression was increased in milk cells from cows affected with subclinical mastitis. Neutrophils from these cows demonstrated a significant delay of apoptosis as compared with neutrophils obtained from healthy cows and were unresponsive to GMCSF. Active STAT5 complexes were detected in these neutrophils. Finally, in the presence of AG-490, apoptosis was induced and a time-dependent down-regulation of Bcl-xL mRNA was observed in milk neutrophils from mastitis-affected cows. These results indicate that neutrophil survival is enhanced in milk of subclinical mastitis-affected cows and suggest a role for a GMCSF-activated STAT5 signaling pathway in this phenomenon. This pathway could thus represent a target for the control of persistent accumulation of neutrophils in the bovine mammary gland.

Imbalance between lipoxin A4 and leukotriene B4 in chronic mastitis-affected cows.

Persistent accumulation of inflammatory cells in the udder, with neutrophils being the predominant cell type, is a characteristic feature of chronic mastitis in dairy cows. Leukotriene (LT) B4 is a potent chemotactic agent, known to induce recruitment and accumulation of neutrophils in the bovine mammary gland. The LTB4-stimulated neutrophil functional responses are closely opposed by lipoxin (LX) A4, which promotes the resolution of inflammation. We thus hypothesized that the chronic inflammation of the udder could be associated with an unfavorable ratio between these two eicosanoids and that the persistence of neutrophil accumulation could be due to an increase in LTB4 synthesis and/or an impaired LXA4 production. In an attempt to verify this hypothesis, we first measured LXA4, LTB4, and their ratio in the milk of healthy and acute and chronic mastitis-affected quarters. Next, we studied the relationships between these variables and the degree of udder inflammation as assessed by somatic cell count measurement. The LTB4 concentration was low in healthy quarters, drastically increased in acute mastitis, and reached intermediate levels in chronic mastitis-affected quarters. However, whereas LXA4 concentration was highly increased in acute mastitis, healthy and chronic quarters had similarly low values. The LXA4:LTB4 ratio was thus significantly lower in chronic mastitis-affected cows. The LTB4 concentrations measured in chronic quarters were highly correlated to somatic cell count and to milk neutrophil and macrophage numbers. A weaker correlation was observed between LXA4 and these variables. For both eicosanoids, the highest correlation was observed with the number of neutrophils. These results show the existence of an LXA4:LTB4 imbalance in chronic mastitis-affected cows because of low LXA4 concentrations. Further studies are needed to determine whether administration of LX or stable analogs could have therapeutic potential in the control of chronic bovine mastitis.

[Value of induced sputum in the investigation of asthma]. / Intérêt des expectorations induites dans l'exploration de l'asthme.

INTRODUCTION: The technique of induced expectoration generates sputum by the inhalation of hypertonic saline. On account of its non-invasive character, its simplicity, its relative harmlessness, its cost effectiveness and its reproducibility this technique, that appeared in the early 1990's, has rapidly established itself as the technique of choice in the investigation of bronchial inflammation in asthma. STATE OF THE ART: We present the results of our studies that have contributed to the validation of the technique at the methodological level and to the exploitation of the cellular contents as much as the fluid phase of the expectorations in characterising bronchial inflammation in asthmatics. Our results confirm an infiltration of the airways of asthmatics with eosinophils that appears to be proportional to the severity of the illness. We evaluate the effect of inhaled steroids and of theophylline on sputum eosinophilia and bronchial reactivity and discuss the role of eosinophils on bronchial hyperreactivity. Finally we discuss the use of induced expectoration in clinical practice in asthma. PERSPECTIVES: The analysis of induced sputum could well become a valuable tool in the clinical evaluation and monitoring of asthma in the same way as symptoms and abnormalities of lung function. CONCLUSIONS: Induced expectoration has certainly contributed to the understanding of the cellular and molecular mechanisms of asthma as well as the role of bronchial inflammation in the clinical manifestations of the disease.