Release of Arboviruses from Cells Cultivated with Low Ionic Strength Media

Abstract

Discussion and Summary

The present study indicates that production of CHIK and DEN-1 viruses in BHK-21 cells were inhibited by lowering NaCl concentrations of culture media. The inhibitory effect was reversed rapidly (within 30 sec) by placing the cells in normal medium. By changing the media from normal to low NaCl concentrations, the inhibition of virus release again took place within short periods of time. In this manner, the inhibition of virus release and its recovery could be repeated practically indefinitely in a particular culture. The effect was due to the ionic strength rather than osmolarity of media. No substances other than the salt such as amino acids or culture medium ingredients were regarded to be involved.

While the present data are compatible with those previously reported with viruses of Sindbis (3) and polio (2), some unique findings were obtained in our electron microscopic studies. The cells cultured in low ionic strength media did not reveal characteristic pictures of viral budding from the cell surface membrane as commonly seen in cells cultured in normal media. In spite of it, the “precursor particles” (8, 9) were observed in the cells cultured in low ionic strength media as in normally cultured cells. As generally accepted (7-12), the group A arboviruses acquire their outer coat from the cell surface membrane of host cells during the budding stage. The ionic strength seems to influence this process, altering certain biochemical and/or biophysical conditions of the cell membrane structures. This may have a significant relation with the mechanism of virus release from host cells such as observed with Western equine encephalitis virus in chick embryo cells (13) or Venezuelan equine encephalitis virus in KB cells (14).