Chronic pulmonary inflammation modulates the fate of proteins administered by the respiratory tract

The systemic appearance of radioiodinated proteins (¹²⁵I-OA and ¹³¹I-HSA) administered via the respiratory route was studied in normal rabbits and in rabbits with BCG-induced chronic granulomatous pulmonary inflammation. The proteins were administered by i.t. injection into intact rabbits and into rabbits with tracheal cannulas or as an aerosol into isolated perfused lungs. The results showed that radioactivity appeared in the circulation as two fractions, one that was precipitable with 5% TCA and therefore protein-bound and one that was soluble in TCA. In both intact and tracheostomized animals, significantly more protein-bound radioactive iodine was detected in the circulation of BCG-treated animals than in normal animals as early as 15 min after i.t. injection, and the differences persisted from 2 to 4 hr. However, in the isolated perfused lung, in which the only route for protein uptake into the circulation was the alveolocapillary barrier, only minimal differences in blood protein levels were observed as compared to normal BCG-inflamed lungs. This study suggests that chronic pulmonary inflammation promotes the absorption of i.t.-injected protein into the circulation, and that the route of enhanced uptake into blood is not the alveolocapillary membrane.