Ultrastructural changes of the rabbit lung tissue during sensitization to antigens

In order to specify the ultrastructure of changes induced in the rabbit lung tissue during sensitization to antigens - previously studied by conventional methods -, two groups of rabbits were weekly sensitized by intramuscular injections, the first group with complete Freund adjuvant (CFA) only, the second with CFA to which human gammaglobulin was added. Fragments from caudal lobes harvested six days after the 3rd, 4th and 5th injections were processed for electron microscopy. This investigation confirmed the general process of cell accumulation within alveolar walls, interlobular areas and bronchial subepithelial layers previously appreciated histochemically and morphometrically. The predominating cells in both rabbit groups were histiocytes (macrophages) of local and blood origin; a monocyte marginating an alveolar capillary was evidenced. In the rabbits sensitized with CFA only, histiocytes were largely accompanied by lymphocytes; between them some relationships may be ultrastructurally observed. An increased number of fibrils and fibroblasts was also seen in this group. The animals sensitized with CFA containing human gamma-globulin showed active plasmoblasts and plasma cells among histiocytes; this picture corresponded to the high increase of serum precipitins. These ultrastructural changes form the basis on which hypersensitivity reactions may be challenged experimentally and during human immune chronic lung diseases.