The expression of βgalactosidase in lung, thymus, and lymph nodes 24 hours after ovalbumin aerosol challenge. Frozen sections of lung, thymus, and lymph nodes from untreated or ovalbumin aerosol-challenged (OVA 24 hours) mice were stained with X-gal overnight followed by counter-stain with eosin. Shown are results from a representative experiment.