[Granule-accumulation in VERO cells used for determination of antitoxin titration by micro cell culture method: I. Influence of mouse serum].

When the titration of diphtheria antitoxin of mouse serum was carried out by micro cell culture method using VERO cells, a large number of granules were observed in the cells. In order to examine the influence of this phenomenon on the titration of antitoxin, kinetics of the granule-accumulation was investigated. The granule-accumulation occurred in the cells in the culture medium to which either immunized or normal mouse serum was added. The granule-rich cells appeared at the dilution of the serum less than 1:32 and increased in number with the concentration of the serum. After 4 days of incubation 88% of the cells showed granule-accumulation when undiluted serum was added. Besides the mouse serum, those from guinea-pigs, horses, fetal calves and humans were examined. However, intensive accumulation of granules such as shown with mouse serum was not observed. From these results it was suggested that mouse serum might have some unknown mechanism which caused the remarkable accumulation of granules in VERO cells. The nature of granule and influence of this phenomenon on the titration of diphtheria antitoxin will be presented in an accompanying paper.