Canine distemper virus induces early stages of apoptosis in in vitro culture of canine peripheral blood mononuclear cells

Abstract

Canine distemper virus (CDV) has been described to induce apoptosis in lymphoid tissues, lymphoid cells, and the cerebellum of naturally infected dogs. The immunosuppression stage established from CDV infection is not always associated with virus detection in damaged cells. Examining the host response at the early stages of immunosuppression, especially the expression of activators and/or inhibitors of apoptosis processes, can provide an important understanding of how the immune responses to CDV are orchestrated. For this purpose, canine peripheral blood mononuclear cells (PBMC) collected from healthy dogs were cultured and infected by the CDV vaccine strain (Onderstepoort). After 24 h post-infection (p.i.), early events of apoptosis were detected by search for annexin V™ and ApoTrace™ markers. The expression of mRNA of Bax, BCl-2, caspase-3, 8 and 9, and also survivin genes was performed in infected and uninfected canine PBMC at 24 h p.i. by real-time polymerase chain reaction. The vaccine strain induced loss of PBMC viability with the expression of annexin™ V FITC and Apo-Trace™ FITC in more than 80% of infected cells compared to the control group (P < 0.001) at 24 h p.i. The initiation of early apoptosis after 24h post-infection contrasts with higher expression of mRNA of survivin and BCl-2, two major anti-apoptotic proteins (p < 0.0002). PBMC infected by CDV increased survivin and BCL-2 gene transcription, concomitant to a reduced level of Bax, caspase 3, 8 and 9. This is the first description of survivin expression, an anti-apoptotic mediator, induced by CDV infection on in vitro cultured canine PBMC.