Mr. Strand et Ll. Pech, MICROPLITIS-DEMOLITOR POLYDNAVIRUS INDUCES APOPTOSIS OF A SPECIFIC HEMOCYTE MORPHOTYPE IN PSEUDOPLUSIA-INCLUDENS, Journal of General Virology, 76, 1995, pp. 283-291
Microplitis demolitor polydnavirus (MdPDV) is associated with Micropli
tis demolitor, a parasitic wasp that attacks the larval stage of the l
epidopteran Pseudoplusia includens. Previously, we observed that MdPDV
induced several alterations in the granular cells and plasmato-cytes
of P. includens, the primary haemocytes involved in regulating the cel
lular immune response toward M. demolitor and other parasites. In exam
ining the mechanisms underlying immunosuppression of this host, we fou
nd that MdPDV induced apoptosis of granular cells. Granular cells unde
rwent apoptosis both when virus was injected into the haemocoel of P.
includens larvae and after infection with MdPDV in vitro. Characterist
ics of MdPDV-induced apoptosis included condensation of chromatin, cel
l surface blebbing and fragmentation of DNA into a 200 bp ladder. Alth
ough MdPDV induced changes in the ability of plasmatocytes to adhere t
o foreign surfaces, apoptosis of this morphotype was not observed. Exa
mples from the literature suggest that some viruses promote their own
survival by suppressing apoptosis of host cells. However, since polydn
aviruses are likely to be transmitted vertically, we suggest that MdPD
V promotes its own survival by inducing apoptosis of host immune cells
which would otherwise kill the developing M. demolitor egg.