A study to investigate the underlying molecular characteristics of allergic asthma

Group 1: Subjects with mild to moderate allergic asthma (n=20)who are controlled on inhaled corticosteroids will be asked to withdraw their inhaled corticosteroids (ICS) immediately following a 2 week run-in prior to an 8 week observational period. Subjects will visit the clinic every two weeks where their asthma status will be assessed. Group 2: Subjects who have attended the severe asthma clinic at the John Hunter Hospital and are deemed suitable under current PBS guidelines for add on therapy for difficult asthma with omalizumab (Xolair) will be recruited to an observational study during their 6 month Xolair trial. Xolair administration will follow standard therapeutic guidelines and be administered every 2 or 4 weeksby the Xolair clinic nurse. The dose of omalizumab for each patient is detrmined by IgE levels and body weight. Frequency of dosing is determined by clinical status as assessed by the supervising physician. For the purposes of this study this group of subjects will be seen once per month only. If omalizumab is administered fortnightly, subjects enrolled in this study will be seen every second omalizumab injection. Group 3: Healthy control volunteers will be recruited (n=20) to provide induced sputum and bloods samples for comparison to groups 1 & 2. The length of study involvement for this group will be dependent on the availablility of the subject to attend a post-baseline clinic visit if the subject catches a cold. These subjects will remain on stand-by and will be considered active participants until either the subject expresses an unwillingness to be involved in the study or the investigators obtain sufficient data to complete the study.