Effects of systemic and local immunization on alveolar epithelial permeability to protein in the rat

This study aimed to characterize the effect on alveolar epithelial permeability to protein as a result of immunization when animals were reexposed to antigen. Antigen (bovine serum albumin [BSA]) and a related bystander protein (human serum albumin [HSA]) were intratracheally instilled into lungs of immunized rats and their passages across the alveolar epithelium were measured as serum levels 16 h after instillation. Nonimmunized control rats showed similar passages of both BSA and HSA. In rats intradermally immunized against BSA, BSA was undetectable in serum, whereas serum levels of HSA were markedly increased compared with those in control rats. In rats immunized with BSA intratracheally, serum levels of both BSA and HSA were unchanged compared with those in control rats. Serum titers of specific IgG antibodies (anti-BSA) were measured and were higher in intradermally immunized animals than in intrapulmonary immunized animals, whereas no anti-BSA antibodies were detected in nonimmunized control rats. Anti-BSA antibodies were detected only in lavage fluid from intradermally immunized rats. These findings suggest that presence of specific antibodies locally in the lungs may increase alveolar epithelial permeability to protein. This finding may have clinical implications, e.g., for sensitive asthmatics, since increased nonspecific permeability caused by local immune-related inflammation may result in further allergies.