IMPAIRMENT OF MULTICYCLE INFLUENZA-VIRUS GROWTH IN VERO (WHO) CELLS BY LOSS OF TRYPSIN ACTIVITY

We demonstrated that influenza virus replication in Vero (WHO) cells, a subline of African green monkey kidney cells, is impaired by rapid i nactivation of trypsin in the culture fluids. Trypsin inactivation was caused by a factor secreted by Vero cells into the media. Repeated ad dition of trypsin to the culture medium of influenza virus-infected Ve ro cells restores the multicycle growth pattern of influenza A virus s trains, allowing high yields to be obtained at a low multiplicity of i nfection. These findings may permit efficient use of Vero (WHO) cells in the production of influenza vaccines.