Effect of passive immunization on absorption of antigen through the respiratory tract

Isolated perfused rabbit lungs were insufflated with 125I-labeled bovine serum albumin (125I-BSA) and the accumulation of radioactive BSA and its breakdown products was measured in the blood. The addition of anti-BSA serum to the blood caused a 4- to 6-fold reduction in the amount of 125I-BSA which appeared in the blood following the insufflation. To determine whether this reduction was the result of inhibition of absorption or the reuptake of 125I-BSA antigen-antibody complexes formed in the blood, we infused the 125I-BSA into the anti-BSA containing blood perfusing the lungs. Virtually none of the radioactivity was taken up by the lungs, indicating that the reduced blood levels following insufflation were the result of reduced absorption through the lung resulting from antigen-antibody interaction within the alveolocapillary membrane or the bronchoalveolar secretions.