The effect of IgG and IgG fragments on the absorption of inhaled antigens across the air-blood barrier of isolated perfused rabbit lungs.

The absorption of inhaled soluble protein antigens across the alveolocapillary membrane can be inhibited by passive immunization in isolated rabbit lungs. The present study was carried out to determine the immunoglobulin class and structural features (Fc-receptor binding, divalent antigen binding) required to effect the inhibition. Isolated rabbit lungs from unimmunized rabbits were perfused with autologous blood to which whole antiserum, IgG or IgG fragments specific for either ovalbumin (OA) or human serum albumin (HSA) was added. The lungs were insufflated with an aerosol containing 125I-OA and 131I-HSA and blood samples were analysed for 125I and 131I in trichloracetic acid (TCA)-precipitable and TCA-soluble forms for 4 hr after insufflation. Whole antiserum and the IgG immunoglobulin fraction of the whole antiserum were equally effective in inhibiting the antigen absorption, indicating that the IGG antibody is sufficient for the effect. The F(ab')2 and Fab' fragments of the IgG molecule were as effective as native IgG, indicating that the antigen-binding site is the only structural requirement and that Fc-receptor and divalent antigen binding are not required.