Immune Responses in Rats Sensitized with Aerosolized Antigen

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Abstract
Rats of BN × Wi/Fu strain were immunized by aerosol exposure to 0.001–1% of ovalbumin (OA) without using any adjuvant for 2- or 1-week periods with 4-week intervals. The immunization, particularly with the highest dose, induced antibody formation of IgE, measured with RAST, and of IgG and IgA, measured with ELISA. Regional lymph node cells from immunized animals showed spontaneous proliferation which was suppressed by syngeneic spleen cells. The cell mixture could be stimulated by addition of specific antigen or mitogen, while cultures of peripheral lymph node cells showed a less consistent increase in lymphoblast formation. Histological examination of the lungs of immunized animals revealed a rapid onset of inflammation with accumulations of mononuclear cells and also increased numbers of mast cells. There was some dose-response relationship between antigen concentration and cell accumulations. The immunization also seemed to induce differentiation of epithelial cells to mucous cells. Intravenous provocation of animals immunized with 0.01–1% OA aerosol resulted in clinical bronchial reactivity assessed as increased transpulmonary pressure. This airway response was attenuated by pretreatment with indomethacin. Animals immunized with 1% OA did, however, not respond to challenge. These animals showed a decreased response to serotonin compared with nonimmunized controls. In summary, the described animal model seems to provide a tool for studies of the asthmatic reaction.