Canine distemper virus causes apoptosis of vero cells

Apoptosis of Vero cells infected with two canine distemper virus (CDV) vacc ine strains was detected using TdT (terminal deoxynucleotidyl transferase)- mediated dUTP nick end-labelling (TUNEL), flow cytometric analysis, agarose gel electrophoresis and electron microscopy (EM). By TUNEL, apoptotic cell s were found in CDV-Onderstepoort (CDV-Ond)-infected cells. DNA fragments i solated from infected cells were separated by agarose gel electrophoresis a nd a 'ladder' pattern appeared. EM observations demonstrated that the cells undergoing cytopathic effect (CPE) possessed morphological characteristics of apoptotic cells. Flow cytometric analysis indicated that CDV could indu ce apoptosis of Vero cells, but the percentages of the apoptotic cells were correlated with the CPE types. The strain showing the cell-rounding type o f CPE produced a much higher percentage of apoptotic cells than CDV-Ond wit h the syncytium type of CPE (P < 0.01). It was concluded that CDV vaccine s trains could induce apoptosis of Vero cells and the apoptosis was virus str ain-dependent and cell-dependent The mechanism remains to be studied.