Inclusion Criteria:  Men or women, age (18-70 years old), II. Lifelong never-smokers or ex-smokers (< 10 pack years). (1 pack year= 20 cigarettes/day for 1 year).  III. Must be competent to give written informed consent. IV. Female participants of child bearing potential must have a negative urine pregnancy test prior to bronchoscopy.  V Potential participants must meet the safety criteria to have a Spirometry test where necessary.  vi Must meet the safety criteria to have a bronchoscopy.  Asthmatic participants:  VI. Have a physician diagnosis of asthma. VII. All asthma patients will have either bronchodilator reversibility of ≥12% or 200 mL at screening, or historic data confirming bronchodilator reversibility or bronchial hyperreactivity to methacholine (PC20). Those without prior confirmed reversibility will have bronchodilator reversibility testing to salbutamol at screening and the asthma control questionnaire (ACQ) administered. Where reversibility to salbutamol is inconclusive a methacholine challenge will be performed.  VIII. Must have stable disease with no recent flare-ups (within 4 weeks). IX. Oxygen saturations whilst breathing room air must be > 90% (a measure of how well the lungs are providing oxygen to the body).  X. When blowing forcefully into a tube (forced expiratory volume or FEV), the patient must be able to blow out at least one litre of air in the first second (FEV1 > 1Litre).  Non-asthmatic participants:  XI. Have no physician diagnosis of asthma. XII. Have no evidence of any long term lung condition or any other disabling condition and they must not have had a chest infection in the preceding 4 weeks.  Exclusion Criteria:  I. Significant smoking history (>10 pack year). II. Significant lung co-morbidities III. Patient unable to give informed consent IV. History of myocardial infarction within the preceding 6 weeks V. Any subject with asthma who requires home oxygen will not be included for safety reasons