Effect of infection with bovine respiratory syncytial virus on pulmonary clearance of an inhaled antigen in calves.

OBJECTIVE

To evaluate the effect of infection with bovine respiratory syncytial virus (BRSV) on clearance of inhaled antigens from the lungs of calves.

ANIMALS

Eleven 6- to 8-week-old Holstein bull calves.

PROCEDURES

Aerosolized (99m)technetium ((99m)Tc)-labeled diethylene triamine pentacetate (DTPA; 3 calves), commonly used to measure integrity of the pulmonary epithelium, and (99m)Tc-labeled ovalbumin (OA; 8 calves), commonly used as a prototype allergen, were used to evaluate pulmonary clearance before, during, and after experimentally induced infection with BRSV or sham inoculation with BRSV. Uptake in plasma (6 calves) and lung-efferent lymph (1 calf) was examined.

RESULTS

Clearance of (99m)Tc-DTPA was significantly increased during BRSV infection; clearance of (99m)Tc-OA was decreased on day 7 after inoculation. Clearance time was correlated with severity of clinical disease, and amounts of (99m)Tc-OA in plasma and lymph were inversely correlated with clearance time. Minimum amounts of (99m)Tc-OA were detected at time points when pulmonary clearance of (99m)Tc-OA was most delayed.

CONCLUSIONS AND CLINICAL RELEVANCE

BRSV caused infection of the respiratory tract with peak signs of clinical disease at 7 or 8 days after inoculation. Concurrently, there was a diminished ability to move inhaled protein antigen out of the lungs. Prolonged exposure to inhaled antigens during BRSV infection may enhance antigen presentation with consequent allergic sensitization and development of chronic inflammatory lung disease.

IMPACT FOR HUMAN MEDICINE

Infection of humans with respiratory syncytial virus early after birth is associated with subsequent development of allergic asthma. Results for BRSV infection in these calves suggested a supportive mechanism for this scenario.