Effect of particle size on phagocytosis of latex particles by guinea-pig polymorphonuclear leucocytes

The effect of the size of foreign particles on phagocytosis by guinea-pig polymorphonuclear leucocytes (PMNs) was investigated using latex particles having approximately the same surface potentials but different sizes. Two types of latexes with different negative surface potentials, those having amino groups (Ami-latexes) and those having carboxylic acid groups (Ca-latexes), were used in this experiment. Since Ca-latexes had different surface potentials for different particle sizes, the carboxylic acid groups were modified by the carbodiimide method to make the surface potentials almost equal. Phagocytosis was estimated by the rate of oxygen consumption. It was found that the phagocytosis reached its maximum when the latex particle size was about 0.5 microns. This finding was plausibly explained by considering the two probabilities that a latex particle comes into contact with a PMN surpassing a potential barrier and the contact takes place at certain receptor areas favourable to phagocytosis on the PMN surface.