AN EVALUATION OF METHODS FOR THE CONCENTRATION AND PURIFICATION OF INFLUENZA VIRUS.

The concentration and purification of influenza virus by means of differential centrifugation in a vacuum type centrifuge, by adsorption on and elution from adult chicken red cells, by elution of the precipitate formed on freezing and thawing of allantoic fluid, by adsorption on and elution from embryonic chick red cells, and by combinations of the first method with each of the three succeeding methods, have been studied. Over-all yields of virus of about 50 to 70 per cent were obtained by these methods and combinations of methods except for somewhat lower yields when adsorption on and elution from adult chicken red cells was employed. However, the purified products obtained by methods involving only the use of red cells or the freezing and thawing technique were found to contain about 80 per cent of non-virus protein. The purified products obtained when differential centrifugation was used either alone or in combination with any one of the other methods were found to be indistinguishable and to consist of a fairly homogeneous component having a sedimentation constant of about 600 S. Such preparations possessed about 22,000 chicken red cell agglutinating units per mg. of protein nitrogen and solutions containing only about 10(-14) gm. of the materials gave 50 per cent infectivity end points in chick embryos. The Sharples centrifuge was found to be almost as efficient as the vacuum type centrifuge for the concentration and purification of influenza virus and, because of its larger capacity, is recommended for the preparation of purified virus on a large scale.