Schematic representation of the sensitization and challenge protocols. For the acute challenge protocol (a), mice were sensitized and boosted on days 1 and 7 with OVA, received a single aerosol challenge of either OVA or PBS on day 14, and were studied on day 15. For the chronic challenge protocol (b), mice were sensitized and boosted on days 1 and 7, received repeated aerosol challenge of either OVA or PBS on days 14–20, and were studied on day 21. IP, intraperitoneally; OVA, ovalbumin.