The influence of the shape of dust particles on the rate of phagocytosis in vitro.

Abstract

Phagocytosis of the dust particles is one of the most striking phenomena observed in histological sections of lungs exposed to the effects of dusts. Therefore, a number of authors who tried to explain the mechanism of the origin of silicosis paid special attention to the question of phagocytosis. Some of them were of the opinion (Fenn, 1922) that the rate of phagocytosis was indirectly propor tional to the danger of various kinds of dusts. Fenn's results support this hypothesis as far as the effects of coal dust and quartz are concerned. On the other hand, Franks and Watt (1934) and Kasten (1939) found that these two kinds of dusts of biologically different efficiency were phagocytosed, roughly in the same degree, in an in vitro experiment. Further experiments by Policard (1948) have not led to general agreement on this problem. The lack of agreement may be caused partly by the variety of tissues used (embryonic lung tissue, spleen, sus pensions of leucocytes), partly by differences in the state of the dusts, or perhaps to inadequacy in the methods of estimating the degree of phagocytosis. Recent work shows that in addition to the effect of the chemical properties of the dust some physical properties may to some extent control its biological efficiency (King, Mohanty, Harrison, and Nagel schmidt, 1953). Some of the later work supports the hypothesis propounded by Fenn (1922) on the in direct relation between the harmfulness of dusts and the degree by which they are phagocytosed. Thus J?tten and Marwyck (1952) showed that protective dusts, which in animal experiments diminish the silicotic effectiveness of quartz, increase at the same time the efficiency by which quartz is phagocytosed in experiments in vitro. The know ledge of factors which may determine the rate of phagocytosis of quartz dusts appears therefore to be of great importance, and the shape of the quartz particles may be one of these determining factors. Material and Methods Our first objective was to ascertain the degree of dependence of the rate of phagocytosis on the shape of phagocytosed particles. The shape of particles was characterized by the relation of the minimum to the maximum dimension of their projection under the micro scope, and each of these extreme dimensions had its own distribution in the given sample of dusts. An ideal arrangement of the experiment would have been one in which the rate of phagocytosis of particles for different ranges of ratios of extreme dimensions could have been ascertained. Since, however, such an experiment was not feasible, we proceeded in such a way that the particles were distributed into two groups : (1) the long particles where the length exceeds the width, and (2) the round ones , where both of these dimensions are approximately equal. Since such a determination can to a certain extent be considered subjective, a control was established by repeated classifications of particles from different sub-samples taken from the same principal sample. The ratios between the number of particles of the first and the second group in each sub-sample agreed well. The study was carried out in cultures of macrophages derived from the spleen of 14-day chicken embryos culti vated in hanging drops. The degree of phagocytosis was evaluated with a phase-contrast microscope. Reproducible doses of dusts were achieved by methods already described by Lengerov?, Lenger, Esslov? Tuscany, and Volfov? (1956). The cultures were made on coverslips, dust being suspended in a diluted embryonic extract. Instead of normally hollow-ground slides, glasses with planparallel bottoms, which do not disturb observa tions through the phase-contrast microscope, were used. The distribution of the particle sizes was such that 99-4% did not exceed 5/x. Nr For both shapes investigated the relation, Z = ?,