Respiratory syncytial virus (RSV) is the major viral cause of severe pulmonary disease in young infants worldwide. However, the mechanisms by which RSV causes disease in humans remain poorly understood. To help bridge this gap, we developed an ex vivo/in vitro model of RSV infection based on well-differentiated primary pediatric bronchial epithelial cells (WD-PBECs), the primary targets of RSV infection in vivo. Our RSV/WD-PBEC model demonstrated remarkable similarities to hallmarks of RSV infection in infant lungs. These hallmarks included restriction of infection to noncontiguous or small clumps of apical ciliated and occasional nonciliated epithelial cells, apoptosis and sloughing of apical epithelial cells, occasional syncytium formation, goblet cell hyperplasia/metaplasia, and mucus hypersecretion. RSV was shed exclusively from the apical surface at titers consistent with those in airway aspirates from hospitalized infants. Furthermore, secretion of proinflammatory chemokines such as CXCL10, CCL5, IL-6, and CXCL8 reflected those chemokines present in airway aspirates. Interestingly, a recent RSV clinical isolate induced more cytopathogenesis than the prototypic A2 strain. Our findings indicate that this RSV/WD-PBEC model provides an authentic surrogate for RSV infection of airway epithelium in vivo. As such, this model may provide insights into RSV pathogenesis in humans that ultimately lead to successful RSV vaccines or therapeutics.

BackgroundHuman respiratory syncytial virus (RSV) causes severe respiratory disease in infants. Airway epithelial cells are the principle targets of RSV infection. However, the mechanisms by which it causes disease are poorly understood. Most RSV pathogenesis data are derived using laboratory-adapted prototypic strains. We hypothesized that such strains may be poorly representative of recent clinical isolates in terms of virus/host interactions in primary human bronchial epithelial cells (PBECs).MethodsTo address this hypothesis, we isolated three RSV strains from infants hospitalized with bronchiolitis and compared them with the prototypic RSV A2 in terms of cytopathology, virus growth kinetics and chemokine secretion in infected PBEC monolayers.ResultsRSV A2 rapidly obliterated the PBECs, whereas the clinical isolates caused much less cytopathology. Concomitantly, RSV A2 also grew faster and to higher titers in PBECs. Furthermore, dramatically increased secretion of IP-10 and RANTES was evident following A2 infection compared with the clinical isolates.ConclusionsThe prototypic RSV strain A2 is poorly representative of recent clinical isolates in terms of cytopathogenicity, viral growth kinetics and pro-inflammatory responses induced following infection of PBEC monolayers. Thus, the choice of RSV strain may have important implications for future RSV pathogenesis studies.

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1 In a placebo controlled study (six healthy male subjects), the effects of UK-52,046 (0.4 pLg kg-1 i.v.) and prazosin (0.25 mg i.v.) on baroreflex function were compared, at doses which produced antagonism to phenylephrine, but which had no effect on supine blood pressure.2 Baroreflex function [AR-R interval ms mm Hg-1 change in SBP] was assessed following increases in systolic blood pressure (SBP) with phenylephrine and during the Valsalva manoeuvre.3 At these doses neither UK-52,046 nor prazosin had an effect on supine SBP or heart rate; however following prazosin, standing SBPs at 5 s (69.7 ± 7.6 mm Hg) and at 3 min (65.5 ± 11.7 mm Hg) were less than the respective pre-treatment (P < 0.05) values (96.0 + 2.9, 110.3 ± 6.2 mm Hg) and placebo (82.7 ± 5.6, 98.7 ± 11.1 mm Hg). UK-52,046 had no significant effects on standing SBP at 5 s or 3 min. At 5 s, pre-and post-treatment R-R intervals (584 ± 26, 541 ± 27 ms respectively) were not significantly different with prazosin, but at 3 min the post-treatment R-R interval following prazosin (519 ± 17 ms) was less (P < 0.05) than the pre-treatment value (658 ± 36 ms).4 UK-52,046 had no effect on baroreflex sensitivity (12.7 ± 1.3 ms mm Hg'l) compared with placebo (17.9 ± 2.7 ms mm Hg-1). Following prazosin baroreflex sensitivity (9.9 ± 1.5 ms mm Hg-1) was reduced (P < 0.05) compared with both the pre-treatment value (16.6 ± 1.8 ms mm Hg-1) and placebo.5 The results of this study suggest that the different effects of UK-52,046 and prazosin on baroreflex function, standing BP and heart rate may be due to less extensive blockade of peripheral vascular otl-adrenoceptors by UK-52,046.

The effects of rilmenidine, a new centrally acting antihypertensive agent, on a number of tests of autonomic function were investigated in six healthy male volunteers. Baroreflex function (delta RR interval [in milliseconds] with each millimeter of mercury change in systolic blood pressure) was determined in response to changes in pressure after injections of phenylephrine and nitroglycerin. Reflex cardiovascular responses to handgrip and standing, as well as during deep breathing and the Valsalva maneuver, were also investigated. Rilmenidine produced a dose-dependent decrease in blood pressure that was not accompanied by an increase in heart rate. Under conditions of low basal sympathetic activity, rilmenidine enhanced parasympathetic tone during the early reflex heart rate changes that occur immediately after standing and during deep breathing, as well as baroreflex heart rate responses to phenylephrine. During a test of sympathetic function, standing blood pressure, and heart rate after 3 minutes, rilmenidine reduced sympathetic tone.