POLYDNAVIRUSES OF HYMENOPTERAN ENDOPARASITOIDS KNOCK OUT THE HOST INSECT IMMUNE-RESPONSE

The insect immune system reacts against invading microorganisms and pa rasites with the recruitment of haemocytes and with humoral response. Cellular immune reactions involve phagocytosis, nodule formation and e ncapsulation by different types of haemocytes whereas insect cell-free antibacterial immunity depends on the production of a number of pepti des and proteins, among which lysozyme, cecropins and attacins represe nt the major group of immune proteins. Polydnaviruses from certain hym enopterous parasitoids interfere with both host immunity and host deve lopment. These immunosuppressive viruses exhibit an intimate genetic r elationship with the parasitoid since viral sequences are integrated w ithin the parasitoid chromosomal DNA. The viral genes expression in pa rasitized host induces immunosuppression and alters development of the host insect. The parasitoids developing in the host body cavity knock out the insect immune system, inducing a decline in cellular and humo ral components of the immune system so that parasitoid eggs are not re cognized as foreign and thereby are not encapsulated. Polydnaviruses c arrying parasitoids escape the host immune response and may develop wi thin the insect host whereas other invaders are normally destroyed by defense factors of insect haemolymph.