Analysis of aluminium-silicate storage foci in the lungs.

A single dose of 60 mg bentonite dust of 0-2 microns particle size suspended in physiological saline was given to CFY rats intratracheally. The effect of bentonite on the lungs was investigated by electron microscope and electron beam X-ray microanalysis 3 and 6 months later. Two cell types were observed within the so-called bentonite storage foci: the majority of the cells building up the storage foci were dark (type I), while the other cells, especially on the periphery of the foci were light with vacuolized cytoplasm (type II). The type I cells contain inclusions consisting of electron dense and electron lucent layers with high Si and Al content, while type II cells contain only small amounts of Al and Si. The inclusions lying with or without a coating, limiting lamella in the cytoplasm were shown to be bentonite deposits on the basis of their structure and composition. Both cell types derive from macrophages, are poor in organelles and exhibit minimal mitotic activity. The bentonite clearance of the storing cells is supposed to be relatively long.