Exposure of hay fever subjects to an indoor environmental grass pollen challenge system

A new indoor nasal allergen challenge system has been developed which allows subjects with hay fever to be exposed to pre-determined concentration of grass pollen grains in the immediate environment. Thirteen subjects were exposed during the winter months to an atmosphere containing approximately 1000 grains/m3 for 30 min. No changes in nasal airway patency or symptoms of nasal congestion were recorded. It was necessary to increase the pollen concentration to approximately 9000 and 35 000 grains/m3 in two subjects and six subjects respectively, before a positive response was recorded. This response was reproducible in all subjects. Administration of intra-nasal sodium cromoglycate before exposure significantly inhibited the decrease in nasal airway patency and when administered 1 min before exposure totally abolished symptoms of nasal congestion. This new challenge system may therefore be used as an in vivo screen to assess the potential therapeutic value of drugs in hay fever under controlled conditions.