The Effects of Omalizumab (Anti-IgE) on the Late-phase Response to Nasal Allergen Challenge

This is a randomized, placebo-controlled, double-blind, parallel group design study that includes 3.5 months of treatment with omalizumab or placebo and a 3 month follow-up. All subjects will be cat allergic. Twenty four subjects (1:1 randomization) will undergo a cat allergen nasal challenge prior to treatment and another challenge after 2 months of treatment or when their blood basophils become hyporesponsive to cat allergen in vitro. A second group of 10 subjects (1:1 active:placebo), will not undergo nasal challenges. This group will participate in an ancillary study in which the effects of omalizumab on gene expression profiles in peripheral blood cells will be studied.