The effect of several naturally occurring dietary flavonoids including quercetin, naringin, hesperetin, and catechin on the infectivity and replication of herpes simplex virus type 1 (HSV-1), polio-virus type 1, parainfluenza virus type 3 (Pf-3), and respiratory syncytial virus (RSV) was studied in vitro in cell culture monolayers employing the technique of viral plaque reduction. Quercetin caused a concentration-dependent reduction in the infectivity of each virus. In addition, it reduced intracellular replication of each virus when monolayers were infected and subsequently cultured in medium containing quercetin. Preincubation of tissue culture cell monolayers with quercetin did not affect the ability of the viruses to infect or replicate in the tissue culture monolayers. Hesperetin had no effect on infectivity but it reduced intracellular replication of each of the viruses. Catechin inhibited the infectivity but not the replication of RSV and HSV-1 and had negligible effects on the other viruses. Naringin had no effect on either the infectivity or the replication of any of the viruses studied. Thus, naturally occurring flavonoids possess a variable spectrum of antiviral activity against certain RNA (RSV, Pf-3, polio) and DNA (HSV-1) viruses acting to inhibit infectivity and/or replication.

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We studied the appearance of IgE in the respiratory tract in 42 infants and young children with various forms of respiratory illness after infection by respiratory syncytial virus (RSV). IgE was bound to exfoliated nasopharyngeal epithelial cells in most patients with RSV infection during the acute phase of infection, regardless of the form of illness. However, the continued presence of cell-bound IgE was more common in patients with RSV-induced bronchiolitis or asthma than in patients with mild upper-respiratory-tract illness or pneumonia due to RSV. Persistence of IgE was also apparently related to the incidence of previous episodes of wheezing in patients or their families. The production of IgE and the subsequent release of chemical mediators of bronchospasm may contribute to the pathogenesis of acute illness due to RSV; persistence of IgE in the respiratory tract may explain the recurrent episodes of wheezing that occur in many patients after RSV-induced bronchiolitis.