Physiological and immunological effects of chronic antigen exposure in immunized guinea pigs.

Antigenic tolerance was induced in previously sensitized guinea pigs by challenging with ovalbumin (OA) aerosol 1 h/day, 5 days/week for 6 weeks. Reactivity was assessed visually and by lung mechanics. Sera from tolerant and sensitized animals showed comparable titers of antigen-specific antibody by passive cutaneous anaphylaxis with 6-hour, 4-day (heated serum) and 7-day sensitizations. In vitro contractile responses of airway smooth muscle revealed comparable histamine responses in sensitized and tolerant guinea pigs but decreased OA sensitivity in smooth muscle from tolerant animals. Although lung histamine content was equivalent in the two groups, antigen-induced histamine release from chopped lung preparations was significantly less in tolerant animals at a low antigen concentration. We conclude that antigen-induced histamine release is impaired in tolerant animals.