Biogenesis, structure, and immune-suppressive effects of virus-like particles of a Drosophila parasitoid, Leptopilina victoriae.
Drosophila melanogaster larvae are attacked by virulent strains of parasitoid wasps. Females of Leptopilina heterotoma produce virus-like particles (VLPs) that efficiently destroy lamellocytes, a major larval immune effector cell type. We report here that L. victoriae, a closely related wasp species, also produces VLPs that trigger immune suppression responses in fly hosts. We compare the ability of immune suppression of the two parasitoids using a mutant host strain hopscotch(Tumorous-lethal) (hop(Tum-l)). hop(Tum-l) larvae have two defects of hematopoietic origin: overproliferation of hemocytes and constitutive encapsulation of self-tissue by lamellocytes. The encapsulation phenotype is suppressed weakly by L. victoriae and strongly by L. heterotoma. In vitro studies on hop(Tum-l) lamellocytes show that VLP-containing fluid from either wasp species induces lamellocyte lysis, but with different kinetics. Previously undocumented precursors of L. victoriae VLPs are synthesized in the long gland and are first visible within canals connecting secretory cells to the long gland lumen. VLP assembly occurs in the lumen. VLPs show multiple electron-dense projections surrounding a central core. Maturing particles appear segmented, singly or in arrays, embedded in the reservoir matrix. In sections, mature particles are pentagonal or hexagonal; the polygon vertices extending into spikes. Our results suggest that L. victoriae is likely to promote immune suppression by an active mechanism that is mediated by VLPs, similar to that used by L. heterotoma.
Morales
Jorge
J
Biology Program, The Graduate School and University Center of The City University of New York, 365 Fifth Avenue, New York, NY 10016, USA.
Chiu
Hsiling
H
Oo
Thiri
T
Plaza
Rosemary
R
Hoskins
Sally
S
Govind
Shubha
S
D000818:Animals; D004330:Drosophila / Q000276:immunology / Q000469:parasitology*; D005088:Exocrine Glands / Q000033:anatomy & histology / Q000378:metabolism; D005260:Female; D006434:Hemocytes / Q000187:drug effects*; D006652:Histological Techniques; D007108:Immune Tolerance / Q000187:drug effects / Q000276:immunology*; D019476:Insect Proteins / Q000096:biosynthesis* / Q000276:immunology / Q000633:toxicity; D007814:Larva / Q000276:immunology / Q000469:parasitology; D013045:Species Specificity; D014863:Wasps / Q000276:immunology / Q000378:metabolism*
D019476:Insect Proteins