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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 development of respiratory syncytial virus (RSV)-specific IgE and the release of histamine in nasopharyngeal secretions from 79 infants with various forms of respiratory illness due to RSV. RSV-IgE was measured by an enzyme-linked immunosorbent assay; specificity was confirmed by appropriate blocking experiments. Histamine content in the secretions was determined by fluorimetric methods. RSV-IgE was detectable in only one of 19 patients with RSV infection without wheezing, but was detectable in the majority of 60 patients with wheezing (P less than 0.01). Titers of RSV-IgE were significantly higher in patients with wheezing (P less than 0.05). Histamine was detectable in secretions of some patients with all forms of illness but was detected significantly more often (P = 0.05) and in higher concentrations in patients with wheezing. Peak titers of RSV-IgE and concentrations of histamine correlated significantly with the degree of hypoxia (P less than 0.001). Formation of RSV-specific IgE and release of histamine may adversely affect the outcome of RSV infection.

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