ABSTRACT
Three subpopulations of A/Hong Kong/1/68 (H3N2) influenza virus differing from one another in biological properties obtained by elution from DEAE-Sephadex with phosphate buffer containing increasing concentrations (0.1, 0.5 and 1 mol/l) of NaCl, were used to induce persistent infection of L929 mouse fibroblast cells. In the course of 25 passages, cell destruction occurred only at low passage levels, especially in the LA-68/0.5 and LA-68/all. sublines. The proliferating activities of LA-68/0.1 and LA-68/1.0 were higher than those of the other two sublines. The size of cell nuclei in all infected sublines was increased. Influenza virus antigen was demonstrated by immunofluorescence in cells of all sublines. The virus was recovered irregularly and only at some passage levels: after 2, 2 and 5 chick embryo passages from the LA-68/0.5, LA-68/0.1 and LA-68/1.0 cells, respectively. The viruses recovered from the LA-68/1.0 subline possessed the lowest haemagglutinating activity against various animal erythrocytes.
