F 344 rats were given vitamin A for four consecutive days and then their alveolar macrophages (AM Ø) were obtained by bronchopulmonary lavage of the lung. Compared with unstimulated AM Ø, AM Ø from rats given vitamin A had more numerous and longer cytoplasmic projections, and these projections had many knobs on their sides and tip.
The AM Ø became attached to syngeneic mammary adenocarcinoma cells at many focal points and the tumor cells then lost surface microvilli around the contact zones. Detachment of the knobs from the projections on AM Ø was often observed in areas of close association between AM Ø and tumor cells. The detached knobs were 250 nm in diameter, gave a positive reaction for acid phosphatase, and frequently became attached to the surface of tumor cells. Then, many of the tumor cells in the vicinity of AM Ø exhibited cytolytic changes.
It is concluded that the cytotoxicity of stimulated AM Ø is due to their attachment to the surface of tumor cells and their release of particles with acid phosphatase activity into the narrow space between the cells, and then to uptake of these particles by susceptible tumor cells.
Alveolar macrophage Cytoplasmic projection Knobs
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