Uptake of intravenously administered soluble immune complexes by type I alveolar cells and macrophages in mice.

Mice (C57BL/6, n = 5) were given a single intravenous injection of soluble bovine serum albumin (BSA)-rabbit anti-BSA immune-complexes (IC) prepared at five-fold antigen excess. The mice were sacrificed 15 and 30 min, and 1, 2, 4 and 12 h after injection. Granular immunofluorescence for BSA and rabbit IgG, in a pattern consistent with IC aggregation, was observed in the alveolar walls and in the cytoplasm of alveolar cells. Moderate immunofluorescence was observed 15 min after IC injection and maximal immunofluorescence was observed at 30-60 min which decreased rapidly 2 h after IC administration. Only a trace amount of immunofluorescence was observed at 4 h and none was seen at 12 h. Light microscopic immunoperoxidase staining showed localization of IC in the interstitium of the alveolar septa and in type I alveolar cells and alveolar macrophages. By immunoelectronmicroscopy, the uptake of IC in the cytoplasm of type I alveolar cells and alveolar macrophages was confirmed.