Thrombospondin-1 promotes hemostasis through modulation of cAMP signaling in blood platelets

Thrombospondin-1 (TSP-1) is released by platelets upon activation and can increase platelet activation, but its role in hemostasis in vivo is unclear. We show that TSP-1 is a critical mediator of hemostasis that promotes platelet activation by modulating inhibitory cyclic adenosine monophosphate (cAMP) signaling. Genetic deletion of TSP-1 did not affect platelet activation in vitro, but in vivo models of hemostasis and thrombosis showed that TSP-1-deficient mice had prolonged bleeding, defective thrombosis, and increased sensitivity to the prostacyclin mimetic iloprost. Adoptive transfer of wild-type (WT) but not TSP-1-/- platelets ameliorated the thrombotic phenotype, suggesting a key role for platelet-derived TSP-1. In functional assays, TSP-1-deficient platelets showed an increased sensitivity to cAMP signaling, inhibition of platelet aggregation, and arrest under flow by prostacyclin (PGI2). Plasma swap experiments showed that plasma TSP-1 did not correct PGI2 hypersensitivity in TSP-1-/- platelets. By contrast, incubation of TSP-1-/- platelets with releasates from WT platelets or purified TSP-1, but not releasates from TSP-1-/- platelets, reduced the inhibitory effects of PGI2. Activation of WT platelets resulted in diminished cAMP accumulation and downstream signaling, which was associated with increased activity of the cAMP hydrolyzing enzyme phosphodiesterase 3A (PDE3A). PDE3A activity and cAMP accumulation were unaffected in platelets from TSP-1-/- mice. Platelets deficient in CD36, a TSP-1 receptor, showed increased sensitivity to PGI2/cAMP signaling and diminished PDE3A activity, which was unaffected by platelet-derived or purified TSP-1. This scenario suggests that the release of TSP-1 regulates hemostasis in vivo through modulation of platelet cAMP signaling at sites of vascular injury.

Analysis of gene transcription and relative abundance of the cys-motif gene family from Campoletis sonorensis ichnovirus (CsIV) and further characterization of the most abundant cys-motif protein, WHv1.6

The cys-motif gene family associated with Campoletis sonorensis ichnovirus contains 10 members, WHv1.6, WHv1.0, VHv1.1, VHv1.4, AHv1.0, A'Hv0.8, FHv1.4, LHv2.8, UHv0.8, and UHv0.8a. The results of this study indicated that, within the encapsidated virion, WHv1.6 is the most abundant cys-motif gene, while the combined AHv genes are the least abundant. During parasitization of Heliothis virescens by Campoletis sonorenis, WHv1.6 transcripts were the mostly highly expressed, while the combined UHv genes had the lowest expression. Further proteomic analysis of WHv1.6 showed that it accumulates at high levels in parasitized plasma by 6 h, and is detectable in the haemocytes, fat body, malpighian tubules, nerve cord and epidermis by 2 days after parasitization. Localization experiments led us to conclude that WHv1.6 interacts with the cell membrane along with other organelles within a virus-infected cell and prevents immunocytes from spreading or adhering to a foreign surface. Similarly to VHv1.4 and VHv1.1, WHv1.6 is able to inhibit the translation of haemocyte and Malpighian tubule RNAs. Our results showed that the expression of cys-motif genes during parasitization is related to the gene copy number of each gene within the encapsidated virion and may also be dependent upon cis-regulatory element activity in different target tissues. In addition, WHv1.6 plays a major role in inhibiting the cellular encapsulation response by H. virescens.

Invited review: the role of caterpillars in mare reproductive loss syndrome: a model for environmental causes of abortion

A new abortigenic disease, now known as mare reproductive loss syndrome (MRLS), significantly affected the horse industry in the Ohio River Valley of the United States in late April and early May of 2001 and 2002. In 2001, approximately 25% of all pregnant mares aborted within several weeks (over 3,000 mares lost pregnancies), and abortion rates exceeded 60% on some farms. Mare reproductive loss syndrome struck hard and without warning, it was caused by something in the environment, it was not transmitted between animals, and it was not associated with any known abortigenic agent or disease. These experiments demonstrated that horses will inadvertently consume Eastern tent caterpillars (ETC) when the insects are present in the pasture or other feedstuffs, and MRLS-type abortions were induced in experimental animals (mares and pigs) by mixing ETC with the feed of the animals. Eastern tent caterpillars are hirsute (hairy) caterpillars, and the only part of the caterpillar that caused MRLS abortions was the cuticle. The experiments revealed that the setae (hairs) embed into the submucosa of the alimentary tract creating microgranulomatous lesions. It is hypothesized that the alimentary tract lesions allow bacteria from the alimentary tract of the mare, principally streptococci, actinobacilli, and to a lesser extent enterococci, to invade the circulatory system of the mare. The bacteria then establish infections in tissues where the immune surveillance of the mare is reduced, such as the fetus and placenta. Fetal and placental fluid bacterial infections lead to fetal death and abortion characteristic of MRLS. Inadvertent ingestion of ETC by pregnant mares causes MRLS. Currently the only known means to prevent MRLS is to avoid exposure of horses, particularly pregnant mares, to ETC and probably most hirsute caterpillars.

The Campoletis sonorensis ichnovirus vankyrin protein P-vank-1 inhibits apoptosis in insect Sf9 cells

The Campoletis sonorensis ichnovirus (CsIV) vankyrin genes encode proteins containing truncated ankyrin repeat domains with sequence homology to the inhibitory domains of NF-kappaB transcription factor inhibitors, IkappaBs. The CsIV vankyrin proteins are thought to be involved in the suppression of NF-kappaB activity during immune response and/or developmental events in the parasitized host. Here we report that when P-vank-1 was expressed stably from Sf9 cells, prolonged survival of these cells was observed after baculovirus infection, UV irradiation, and treatment with the apoptosis-inducing chemical camptothecin compared to untransformed Sf9 cells. Furthermore, P-vank-1 inhibited nuclear and internucleosomal degradation and caspase activity after induction of apoptosis in Sf9 cells stably expressing P-vank-1. This is the first report of a polydnavirus protein with anti-apoptotic function.

A teratocyte gene from a parasitic wasp that is associated with inhibition of insect growth and development inhibits host protein synthesis

After parasitization, some wasps induce hosts prematurely to initiate metamorphic development that is then suspended in a postwandering, prepupal state. Following egression of the parasite larva, the host remains in this developmentally arrested state until death. Teratocytes, cells released at egg hatch from extra-embryonic serosal membranes of some wasp parasites, inhibit growth and development when injected into host larvae independent of other parasite factors (e.g. venom, polydnavirus). Synthesis of some developmentally regulated, abundantly expressed Heliothis virescens host proteins is inhibited in hosts parasitized by Microplitis croceipes and by teratocyte injection. A cDNA encoding a 13.9 kDa protein (TSP14) that inhibited protein synthesis, growth and development was isolated from a protein fraction secreted by teratocytes. TSP14 appears to be responsible, in part, for the teratocyte-mediated inhibition of host growth and development. Interestingly, this cDNA encoded a cysteine-rich amino acid motif similar to that described from Campoletis sonorensis polydnavirus, a mutualistic virus that enables wasp parasitization of lepidopteran larvae. Moreover, TSP14 inhibited protein synthesis in a dose-dependent manner in rabbit reticulocyte lysate and wheat germ extract translation systems. We hypothesize that some wasp parasites inhibit translation as a general means to regulate and redirect lepidopteran host physiology to support endoparasite development.

Two Hyposoter didmator ichnovirus genes expressed in the lepidopteran host encode secreted or membrane-associated serine and threonine rich proteins in segments that may be nested

We present in this work two novel Hyposoter didymator ichnovirus genes expressed in parasitized Spodoptera larvae. These genes, named HdCorfS6 and HdGorfP30, are unrelated and present in two different genome segments, possibly nested, SH-C and SH-G respectively. HdCorfS6 encodes a predicted transmembrane protein, putatively glycosylated. HdCorfS6 transcripts appear to be abundant in lepidopteran host hemocytes compared to the other tissues analyzed. The second gene described, HdGorfP30, is well expressed in hemocytes, but also in other tissues, such as the fat body, nervous system and epidermis. This gene is peculiar since it presents 17 perfectly conserved repeated sequences arranged in tandem arrays. Each of these repeats contains 58% of serine and threonine residues and therefore several potential sites for glycosylation. This mucin-like protein, predicted as highly glycosylated, could be involved in host immune suppression.

Expression and characterization of a novel teratocyte protein of the braconid, Microplitis croceipes (cresson)

Microplitis croceipes wasps overcome host immunity by inducing changes in host physiology using factors derived from the embryo and/or larva. Teratocytes of some parasitic wasps circulate in the host hemolymph after egg hatch and synthesize proteins (TSPs), some of which are secreted to alter host physiology in support of endoparasitoid development. TSPs appear to alter host physiology, at least in part, by inhibiting synthesis of certain proteins. M. croceipes teratocytes synthesize a 13.9 kDa protein (TSP14), which inhibits synthesis of host proteins that are linked to larval growth and development. A cDNA encoding TSP14 was generated by RT-PCR from teratocyte RNA, and cloned into yeast expression vectors to produce sufficient recombinant protein for functional analyses. RecTSP14 was produced using the yeast expression system at a concentration of more than 300 micrograms/L. The recTSP14 inhibited in vitro translation of larval Heliothis virescens RNA, with the activity sensitive to boiling, protein concentration, incubation time, and storage temperatures. Although recTSP14 inhibited translation of some cellular RNAs in vitro, the in vivo incorporation of [35S]-methionine into proteins of selected insect and mammalian cell lines was not inhibited. These findings suggest that recTSP14 entry is cell type-specific and required to inhibit synthesis of target protein(s).

Evidence for a conserved polydnavirus gene family: ichnovirus homologs of the CsIV repeat element genes

In Campoletis sonorensis Ichnovirus (CsIV), the repeat element genes constitute a gene family of 28 members. In the present work, we document the presence of members of this gene family in two additional ichnoviruses, Hyposoter didymator Ichnovirus (HdIV) and Tranosema rostrale Ichnovirus (TrIV). Two repeat element genes, representing at least one functional gene, were identified in TrIV, whereas HdIV was found to contain at least three such genes. In both HdIV and TrIV, the known repeat element genes are encoded on single genome segments, with hybridization studies suggesting the presence of other, related but as yet uncharacterized genes. The HdIV and TrIV repeat element genes are all transcribed in infected caterpillars, although differences exist among genes in levels and in tissue specificity of expression. A heuristic tree was generated indicating that the repeat element genes are more similar within a species of wasp than between species, with TrIV genes being more closely related to the CsIV than to the HdIV genes. These results suggest that the most significant duplication, divergence, and expansion of the repeat element genes occurred after speciation. The finding that repeat element genes form an interspecific family within the genus Ichnovirus supports the view that the proteins they encode play an important role in ichnovirus biology.

G2/M arrest caused by actin disruption is a manifestation of the cell size checkpoint in fission yeast

In budding yeast, actin disruption prevents nuclear division. This has been explained as activation of a morphogenesis checkpoint monitoring the integrity of the actin cytoskeleton. The checkpoint operates through inhibitory tyrosine phosphorylation of Cdc28, the budding yeast Cdc2 homolog. Wild-type Schizosaccharomyces pombe cells also arrest before mitosis after actin depolymerization. Oversized cells, however, enter mitosis uninhibited. We carried out a careful analysis of the kinetics of mitotic initiation after actin disruption in undersized and oversized cells. We show that an inability to reach the mitotic size threshold explains the arrest in smaller cells. Among the regulators that control the level of the inhibitory Cdc2-Tyr15 phosphorylation, the Cdc25 protein tyrosine phosphatase is required to link cell size monitoring to mitotic control. This represents a novel function of the Cdc25 phosphatase. Furthermore, we demonstrate that this cell size-monitoring system fulfills the formal criteria of a cell cycle checkpoint.

Relationships between polydnavirus gene expression and host range of the parasitoid wasp Campoletis sonorensis

To evaluate the relationship between immune suppression and host range six lepidopteran species were parasitized by the ichneumonid parasitoid Campoletis sonorensis. Parasitism inhibited the growth of permissive hosts (Heliothis virescens, Helicoverpa zea, and Trichoplusia ni), whereas growth of semi-permissive (Spodoptera exigua, Agrotis ipsilon) and non-permissive hosts (Manduca sexta) was not significantly affected. The 29-36 kDa ovarian protein (OP), responsible for transient immunosuppression in the permissive host H. virescens, bound to and was endocytosed by hemocytes of permissive and non-permissive hosts. Expression of the cysteine-rich polydnavirus gene, VHv1.4, was detected in all the hosts, but declined only in semi- and non-permissive hosts at later times after parasitization. The VHv1.4 protein bound to hemocytes of permissive and semi-permissive hosts, but did not bind to hemocytes of the non-permissive host, M. sexta. Melanization of larval hemolymph was severely inhibited by parasitism in permissive hosts, but was unaffected in M. sexta. In the semi-permissive host, A. ipsilon, hemolymph melanization was transiently inhibited while viral genes were expressed. In conclusion, C. sonorensis OP transiently inhibits encapsulation in all hosts that were tested. The host range of C. sonorensis seems to be determined by whether or not the C. sonorensis ichnovirus (CsIV) is able to establish persistent infections of parasitized larvae to provide long-term suppression of host immunity.

A gene encoding a polydnavirus structural polypeptide is not encapsidated

Polydnaviruses are symbiotic viruses associated with some parasitic Hymenoptera that are vertically transmitted as proviruses within wasp genomes. To study this symbiotic association a gene encoding an abundant Campoletis sonorensis polydnavirus virion protein was characterized. This gene is not encapsidated but resides in the wasp genome where it is expressed only during virus replication. Immunolocalization studies detected the encoded 44-kDa protein only in oviduct tissue with ultrastructural studies detecting epitopes between or on virion envelopes. Expression and localization of the 44-kDa protein are consistent with its being a viral structural protein but localization of the gene only within the wasp genome is atypical, raising the possibility that this protein is adventitiously packaged during virion assembly. To address this possibility, quantitative dot blot and genomic Southern blot hybridizations were performed to determine whether the copy number of the p44 gene increased disproportionately during replication, as would be expected for a gene encoding a virion protein. The copy number of the p44 gene increases in tissues supporting virus replication but is unchanged in other tissues, suggesting that this gene is amplified in replicative cells. The data indicate that genes encoding polydnavirus virion proteins may be distributed between wasp and encapsidated viral genomes.

Parasitism-linked block of host plasma melanization

When parasitized by the Ichneumonid parasitoid Campoletis sonorensis, larvae of the Noctuid moth, Heliothis virescens, are unable to mount an effective immune response against parasitoid eggs. Defensive melanization of plasma and cellular encapsulation of parasite eggs are dramatically inhibited by infection with the symbiotic immunosuppressive C. sonorensis ichnovirus (CsIV). This study demonstrates that the CsIV-mediated inhibition of melanization is associated with reduction in the enzymatic activity and protein titer of key enzymes in the melanization pathway, phenoloxidase, dopachrome isomerase, and DOPA decarboxylase. Inhibition of the synthesis of key melanization enzymes leads to reductions in the melanization substrates l-dihydroxyphenylalanine, N-acetyldopamine, and N-beta-alanyl dopamine from millimolar to nanomolar levels in parasitized larvae. By contrast, concentration of a precursor catecholamine, dopamine, rises fourfold in these larvae. Thus in CsIV-infected larvae, enzymatic deficiencies in the melanization pathway lead to reduced concentrations of specific enzyme substrates, causing failure of melanization in parasitized insects.

Cloning and expression of a gene encoding a Campoletis sonorensis polydnavirus structural protein

Polydnaviruses are the only known group of mutualistic viruses. They are required for successful parasitization in many braconid and ichneumonid parasitoids. The intimacy of this mutualistic association is indicated by the integration and vertical transmission of polydnaviruses in wasp genomes and by their asymptomatic, developmentally regulated replication. The evolution of this mutualism raises several interesting issues that require a better understanding of the viral genome and viral replication. To develop probes for virus replication and morphogenesis, we have begun to characterize several viral structural proteins. A 699 bp cDNA encoding the p12 viral structural protein was cloned and sequenced. The p12 gene localizes to viral segment Y and encodes a predicted protein of 92 amino acids that does not encode a signal peptide and is unrelated to known peptide or nucleic acid sequences. The p12 mRNA is detected at the onset of virus replication. mRNA titers increase with increasing rates of virus replication. Polyclonal antisera raised against histidine-tagged p12 protein expressed in bacteria reacted specifically with the p12 polypeptide in Western blots of CsPDV virions. The p12 polypeptide was not detected in non-replicative wasp or lepidopteran tissues by Western blot analyses but was readily detected in protein extracts of wasp ovaries. The data indicate that the p12 gene is a viral gene encoding a virion protein and provides a specific probe for virus replication that will be useful for studying the evolution of this group of mutualistic viruses.

Polydnavirus-mediated inhibition of lysozyme gene expression and the antibacterial response

Parasitism of lepidopteran host larvae by hymenopteran parasitoids impairs the cellular immune response via expression of polydnavirus genes. Encapsulation of parasitoid eggs is thereby prevented. Parasitized insects are susceptible to opportunistic infections, suggesting that additional components of the immune system are affected. Insects normally respond to infection by inducing the synthesis of an array of antibacterial factors, including cecropins and lysozyme via a NFkappaB/lkappaB-like signal transduction pathway. To characterize the effects of PDVs on the antibacterial immune response, plasma antibacterial activities were assayed in H. virescens larvae infected with the C. sonorensis PDV. Plasma lysozyme activity in Heliothis virescens was reduced in parasitized and PDV-infected larvae after immune challenge. To examine the regulation of lysozyme after CsPDV injection, the Heliothis virescens lysozyme cDNA was cloned. In contrast to plasma lysozyme activity, the 1.1 kb lysozyme mRNA was induced in fat body and haemocytes by known elicitors. The data suggest that CsPDV, like some other viruses, regulates host cell gene expression at the level of translation. We propose that the immunodeficiencies caused by CsPDV injection are caused, in part, by the targeted translational inhibition of specific humoral immune response transcripts.

Homologous sequences in the Campoletis sonorensis polydnavirus genome are implicated in replication and nesting of the W segment family

Polydnaviruses (PDVs) are double-stranded DNA viruses with segmented genomes that replicate only in the oviducts of some species of parasitic wasps and are required for the successful parasitization of lepidopteran insects. PDV DNA segments are integrated in the genomes of their associated wasp hosts, and some are nested; i.e., smaller segments are produced from and largely colinear with larger segments. To determine the internal structure of nested viral segments, the first complete nucleotide sequence of a PDV genome segment and its integration locus was determined. By restriction mapping, Southern blot, and sequence analyses, we demonstrated that the Campoletis sonorensis PDV segment W is integrated into wasp genomic DNA. DNA sequence analysis revealed that proviral segment W terminates in two 1,185-bp direct long terminal repeats (LTRs) in the wasp chromosome, while only one LTR copy is present in the extrachromosomal (viral) W. The results suggest that terminal direct repeats are a general feature of PDV DNA segment integration but that the homology and size of the repeats can vary extensively. Segment W contains 12 imperfect direct repeats of six different types between 89 bp and 1.9 kbp with 65 to 90% homology. The orientation and structure of the repeats suggest that W itself may have arisen through sequence duplication and subsequent divergence. Mapping, hybridization, and sequence analyses of cloned R and M demonstrated that these segments are nested within segment W and that internal imperfect direct repeats of one type are implicated in the homologous intramolecular recombination events that generate segments R and M. Interestingly, segment nesting differentially increases the copy number of genes encoded by segment W, suggesting that the unusual genomic organization of PDVs may be directly linked to the unique functions of this virus in its obligate mutualistic association with parasitic wasps.

Expression, assembly, and proteolytic processing of Helminthosporium victoriae 190S totivirus capsid protein in insect cells

The dsRNA genome (5.2 kbp) of Helminthosporium victoriae 190S totivirus (Hv190SV) consists of two large overlapping open reading frames (ORFs). The 5' proximal ORF codes for the capsid protein (CP) and the 3' ORF codes for an RNA-dependent RNA polymerase. Although the capsid of Hv190SV is encoded by a single gene, it is composed of two major closely related polypeptides, either p88 and p83 or p88 and p78. Whereas p88 and p83 are phosphoproteins, p78 is nonphosphorylated. Expression of the CP ORF in insect cells generated both p78 and p88 which assembled into virus-like particles. The finding that p78, p83, and p88 share a common N-terminal amino acid sequence is consistent with the determination that N-terminal, but not C-terminal, CP deletions were incompetent for assembly. Evidence was obtained that p78 is derived from p88 via proteolytic cleavage at the C-terminus. Proteolytic processing may play a regulatory role in the virus life cycle since it leads to dephosphorylation of CP and a subsequent decrease in virion transcriptional activity.

Promoter analysis of a cysteine-rich Campoletis sonorensis polydnavirus gene

Promoter activity of the Campoletis sonorensis polydnavirus (CsPDV) WHv1.6 gene was analysed by transient transfection assays in insect cell culture using constructs expressing the CAT gene. Deletions of the WHv1.6 gene promoter were used to define promoter regions important for expression. Progressive deletion of the regions upstream of the TATA box reduced the promoter activity, whereas deletions eliminating the TATA box abolished promoter activity. Cis-activating elements were detected up to 1 kb upstream of the WHv1.6 transcription initiation site (TIS). Promoter elements increasing transcription were detected between -444 and -550 bp and between -831 and -1035 bp relative to the TIS. Analysis of the 3' flanking sequences of the WHv1.6 gene indicated that the polyadenylation signals were the only important elements affecting expression in the constructs. Comparison of promoter regions of four cysteine-rich CsPDV genes revealed homologous sequences that may be important for transcriptional regulation of polydnavirus gene expression in parasitized Heliothis virescens larvae.

Polydnavirus infection inhibits translation of specific growth-associated host proteins

The wasp Campoletis sonorensis injects a polydnavirus (CsPDV) along with its egg during parasitization of Heliothis virescens larvae. CsPDV protects the wasp egg and larvae by selectively disabling the host's cellular immune response, and by altering host physiology, growth, and development. Among the changes in host physiology brought about by CsPDV infection is a rapid, and specific decline in the translation of fat body mRNAs encoding selected major plasma proteins. Translational inhibition of the synthesis of all storage protein monomers, p82 (Riboflavin binding hexamer), and p74/p76 (arylphorin), occurs upon infection with CsPDV. Moreover, the prewandering peak of the plasma enzyme juvenile hormone esterase (JHE) was blocked by CsPDV injection. Northern blotting of fat body mRNA demonstrated that transcript levels of storage proteins were not affected by infection. Plasma titers of the iron binding proteins transferrin (p72) and ferritin (p24/26), and of the plasma juvenile hormone binding protein (p25) were not changed by CsPDV infection. That storage protein and JHE synthesis are translationally suppressed, while the synthesis of other plasma proteins continues apace, suggests that CsPDV infection may lead to translational discrimination among available mRNAs in CsPDV infected fat bodies. The effect of this translational discrimination is to shunt host resources away from larval growth and adult development, which presumably makes them available to the developing endoparasitoid.

Purification and analysis of a polydnavirus gene product expressed using a poly-histidine baculovirus vector

The VHv1.1 polydnavirus gene has been implicated in suppressing the encapsulation response in parasitized insects [Li and Webb (1994) J. Virol. 68, 7482-7489]. In order to characterize this gene product and to further our analysis of its immunosuppressive function, we expressed the VHv1.1 using a custom-designed C-terminal poly-histidine baculovirus vector which allows for high expression and single-step purification of the protein. The 34 kDa VHv1.1 protein was expressed in baculovirus-infected cell cultures and in H. virescens larvae. Highly enriched preparations of the secreted VHv1.1 protein were obtained after affinity chromatography using a NTA-(Ni2+) resin. Characterization with purified preparations of the VHv1.1 protein established that the protein is N-glycosylated, containing glycogroups which are PNGase F-sensitive but Endo H-resistant. The recombinant VHv1.1 protein bound to hemocytes in vitro and in vivo and was endocytosed in a manner similar to the native protein produced in CsPDV-infected larvae.

Expression and hemocyte-targeting of a Campoletis sonorensis polydnavirus cysteine-rich gene in Heliothis virescens larvae

The polydnavirus associated with the parasitic wasp Campoletis sonorensis is injected into the lepidopteran insect, Heliothis virescens, during parasitization, after which viral gene products suppress the cellular immune system of the hosts. Four related cysteine-rich polydnavirus gene have been identified in parasitized H. virescens larvae and grouped into a family. In this study, we investigated the expression and hemocyte targeting of the cysteine-rich VHv1.4 protein. Full-length and truncated VHv1.4 proteins were produced in a bacterial expression system, and the purified proteins were used to raise polyclonal antisera. In immunoblots the VHv1.4 protein was detected in parasitized insects as early as 6 h and throughout the entire course of parasitism. The VHv1.4 protein appeared predominantly in the plasma fraction of hemolymph from parasitized larvae, suggesting that this protein is secreted. The VHv1.4 protein expressed from a recombinant baculovirus was secreted in two lepidopteran cell lines and in larvae injected with the recombinant virus. Digestion with endoglycosidases suggests that the VHv1.4 protein is glycosylated at multiple N-glycosylation sites. Immunofluorescence assays showed that the VHv1.4 protein binds to the hemocytes, most notably the granulocytes, in H. virescens larvae. After binding, the VHv1.4 protein was internalized, probably by endocytosis. Specific binding of the VHv1.4 to granulocytes implies an important function in the suppression of host cellular encapsulation response.

Expression of polydnavirus genes under polydnavirus promoter regulation in insect larvae infected with baculovirus recombinants

We have evaluated the use of baculoviruses to deliver Campoletis sonorensis polydnavirus (CsPDV) genomic DNA into lepidopteran larvae to facilitate the identification of functional CsPDV genes. Genomic fragments consisting of regulatory (promoter) and coding sequences for two CsPDV genes (VHv1.1 and WHv1.6) were used to generate CsPDV-baculovirus recombinants and evaluate the expression of genes under the regulation of the CsPDV promoters. Northern blot and primer extension studies established that CsPDV genes were expressed under the control of their own promoters in these CsPDV-baculovirus recombinants. Transcripts were detected as early as 4 h post-infection indicating that temporal activity of CsPDV promoters was retained. The VHv1.1 gene product as expressed from CsPDV-baculovirus recombinants was identical in size and in functional properties to that produced in CsPDV-infected insects. CsPDV-baculovirus recombinants may be useful for the screening and characterization of polydnavirus genes with functional activities that can only be evaluated in insect larvae.

Evaluation of reverse transcriptase polymerase chain reaction for the detection of eastern equine encephalomyelitis virus during vector surveillance

A reverse transcriptase polymerase chain reaction (RT-PCR) assay was evaluated for the detection of eastern equine encephalomyelitis virus (EEEV). EEEV was detected by amplification of a 416-bp PCR product from within the E2 gene. Internal restriction endonuclease digestion and hybridizations to EEEV RNA demonstrated that the PCR product was amplified from EEEV. PCR amplifications from serial dilutions of an EEEV isolate identified by a neutralization test and titered by an infectious assay in cell culture indicated that this RT-PCR assay detected viral RNA at concentrations below 1 plaque forming unit(PFU) per reaction. The performance of the PCR assay in detection of EEEV was compared with an infectious assay detection procedure (IA/IFA) as part of the New Jersey 1993 vector surveillance program. During 1993, 7,007 field-collected Culiseta melanura (Coquillett) were assayed in 522 pools by both RT-PCR and IA/IFA. EEEV was detected in 95 pools by RT-PCR and 17 pools by IA/IFA; all IA/IFA positive pools were also positive by RT-PCR. During the 1993 field season, RT-PCR consistently detected virus at enzootic foci earlier that IA/IFA and in greater numbers of mosquito pools. The data indicated that viral RNA may be present earlier and in more mosquitoes than indicated by IA/IFA.

Isolation and characterization of a member of the cysteine-rich gene family from Campoletis sonorensis polydnavirus

The endoparasitic wasp Campoletis sonorensis injects a symbiotic polydnavirus into its host Heliothis virescens. Viral gene expression protects the wasp egg and larva from encapsulation by host haemocytes. Three related C. sonorensis polydnavirus (CsPDV) genes, which are expressed in parasitized H. virescens, have been previously isolated and grouped into a cysteine-rich gene family. In this report, a CsPDV gene encoding an abundant 1.4 kb mRNA expressed in parasitized insects was isolated and mapped to viral segment V (15.2 kb) by Southern blotting and PCR. The VHv1.4 cDNA is 1338 bp long and has an ORF that encodes 322 amino acids with two complete and one partial cysteine motifs. Similar to other characterized CsPDV cysteine motifs, the VHv1.4 motifs are also characterized by six cysteines at conserved positions and variable inter-cysteine amino acids. DNA sequence analyses show that the VHv1.4 gene shares regions of significant identity (73-97%) with the VHv1.1 gene, a member of the cysteine-rich gene family. The VHv1.4 and the VHv1.1 proteins are 62% identical overall; at the N termini including the signal peptide and the N-terminal cysteine motif the identity is greater (90%). Unlike other CsPDV cysteine-rich genes, the VHv1.4 cDNA has two conserved domains (77% identical in nucleotides, 55% identical in amino acids) that presumably result from the duplication of a portion of the gene. The VHv1.4 gene has four introns with splicing sites located at positions similar to VHv11.1 introns. Introns 2 and 3, located in the first and second domains respectively, have greater identity (97%) than the flanking exon sequences (77%). We propose, based on the evidence presented in this paper, that the VHv1.4 gene is a new member of the cysteine-rich polydnavirus gene family.

Interaction of a wasp ovarian protein and polydnavirus in host immune suppression

During parasitization of Heliothis virescens, Campoletis sonorensis deposits an egg along with venom, polydnavirus particles (CsPDV), and ovarian proteins (OPs). Oviposited eggs are not encapsulated, while washed eggs are encapsulated rapidly by H. virescens. Early protection from encapsulation is afforded by a group of 29-36 kD OP glycoforms. These glycoforms are endocytosed by host hemocytes within 30 min post-parasitization (pp) and disrupt hemocyte spreading behavior and egg encapsulation through at least 24 h p.i. Purified CsPDV does not protect eggs from encapsulation early, but disrupts hemocyte spreading and egg encapsulation from 24 h through at least 5 days p.i. Functional activity of CsPDV appears to be correlated with time-dependent accumulation of virus-specific proteins in parasitized insects. We propose that the fast-acting 29-36 kD OP protects Campoletis eggs from encapsulation until accumulation of CsPDV proteins which sustain immunosuppression.

Apparent functional role for a cysteine-rich polydnavirus protein in suppression of the insect cellular immune response

Polydnaviruses suppress the cellular immune response and inhibit growth and development in their lepidopteran host, allowing survival of their endoparasitic hymenopteran host. Characterization of genes disrupting insect physiological systems is a major objective in the study of polydnaviruses. Recently, a cysteine-rich gene family encoding a motif composed of invariable cysteine residues flanking hypervariable intercysteine amino acids was described (S.D. Dib-Hajj, B.A. Webb, and M.D. Summers, Proc. Natl. Acad. Sci. USA 90:3765-3769, 1993). They noted similarities to the positive selection pressure for mutations within the vertebrate major histocompatibility complex (MHC) class II genes and speculated that this class of polydnavirus genes may target and disrupt the insect immune system. To study the functional activity of this family of predicted cysteine-rich proteins, the VHv1.1 gene product was produced from bacterial and baculovirus expression systems. Polyclonal antiserum produced from the bacterial fusion protein reacted with a 30-kDa protein from hemocytes, cell-free plasma, and fat body of parasitized larvae. Immunofluorescence analysis of hemocytes from parasitized insects detected the 30-kDa protein bound to granulocytes and plasmacytes. To assay the functional activity of the 30-kDa VHv1.1 protein, a recombinant baculovirus was constructed allowing in vivo expression of the 30-kDa polydnavirus protein from infected insects. Expression of the VHv1.1 protein from the baculovirus system reduced the encapsulation response to washed wasp eggs relative to controls. The experimental evidence demonstrates that Campoletis sonorensis polydnavirus-infected cells secrete VHv1.1 into the hemolymph, where it binds to hemocytes and is associated with the inhibition of the cellular immune response.

Polydnavirus infection inhibits synthesis of an insect plasma protein, arylphorin

The wasp Campoletis sonorensis injects a segmented, double-stranded DNA polydnavirus (CsPDV) along with its egg during parasitization of Heliothis virescens larvae. After parasitization, CsPDV protects the wasp egg and larva by selectively disabling the host's cellular immune response. Other host physiological systems including growth and development are affected to the apparent benefit of the parasite. To begin the characterization of the biochemical effects and mode of action of CsPDV on host growth, the titre of a developmentally regulated insect storage protein, arylphorin, was studied. Parasitized or virus-infected insects had substantially less circulating arylphorin than control insects. Fat bodies from parasitized larvae also synthesized less arylphorin in vitro. However, Northern blots of total RNA from parasitized and non-parasitized, control insects showed that the arylphorin transcript level was unaffected by parasitization suggesting a biochemical block at the translational level. In vitro translation followed by immunoprecipitation of arylphorin indicated that the mRNA was present and translatable at equal levels in both parasitized and control insects. Injection of purified virus elicited the response observed in naturally parasitized larvae, demonstrating that the effect on arylphorin synthesis is mediated, either directly or indirectly, by polydnavirus gene product(s).

Evidence for an early immunosuppressive role for related Campoletis sonorensis venom and ovarian proteins in Heliothis virescens

Shared epitopes among venom, ovarian, and viral proteins may indicate that related proteins have similar functional roles during parasitization of Heliothis virescens by Campoletis sonorensis. Venom and ovarian proteins are introduced directly into the hemolymph during parasitization where they may target hemocytes or other components of the immune system. Polydnavirus expression has been detected in hemocytes, fat body, and other tissues but has not been detected earlier than 4 h after parasitization. Therefore, effects on hemocytes at times earlier than 4 h may not be caused by polydnavirus proteins synthesized in the parasitized insect. Visualization of hemocyte F-actin with fluorescently labeled phallicidin indicated that a dramatic alteration of plasmatocyte and granulocyte cytoskeletons occurred within 1.5 h after parasitization. The predominant non-viral proteins in the ovary introduced during parasitization were immunologically related to venom and viral envelope proteins. These ovarian proteins persist in the hemolymph. Antisera to the ovarian proteins bound to granulocytes and to plasmatocytes to a lesser degree, suggesting that ovarian proteins may be involved in early suppression of the host's immune response after parasitization.

Structure and evolutionary implications of a "cysteine-rich" Campoletis sonorensis polydnavirus gene family

For successful parasitization, the female Campoletis sonorensis endoparasitic wasp injects a polydnavirus into its host, Heliothis virescens, during oviposition. Viral gene expression induces immunosuppression and alters development of the host. We report here that three abundantly expressed genes, VHv1.1, WHv1.0, and WHv1.6, describes a polydnavirus "cysteine-rich" gene family which may be important in inducing these host manifestations. These genes have a similar primary gene structure and their proteins contain cysteine motifs characteristic of snail ion-channel ligands, the omega-conotoxins. Like the omega-conotoxins, the intercysteine amino acid residues are hypervariable with only three identical amino acids in all motifs. The conservation of this domain in the three viral genes may reflect an important functional role for these viral proteins in the parasitization of H. virescens. The three genes also contain introns similar in sequence at comparable positions in their 5' untranslated leaders and coding sequences. VHv1.1 contains two cysteine motifs, and each motif is interrupted by an intron at the same position as in the cysteine motifs of WHv1.0 and WHv1.6. Intron 2 sequences of WHv1.0 and WHv1.6 are 92% identical, while the immediately flanking exon sequences encoding the cysteine motifs are only 76% identical. This provides an example of nuclear pre-mRNA introns which are more conserved than flanking exons among members of a gene family.

Stimulation of polydnavirus replication by 20-hydroxyecdysone

During oviposition the endoparasitic wasp Campoletis sonorensis, introduces a polydnavirus into parasitized insects where viral gene expression is required for endoparasite survival. The polydnavirus is integrated into wasp chromosomal DNA and replicates only in the ovary. Ecdysteroids regulate the developmental expression of many insect genes and may regulate polydnavirus replication. Direct verification of viral replication was performed by dot blot hybridization and by amplifying DNA sequences containing the viral integration site; this 'junction' fragment cannot be amplified from integrated virus. Thoracic ligations and in vitro ecdysteroid treatments of wasp ovaries support the hypothesis that polydnavirus DNA replication is regulated by ecdysteroid during parasite development.

Venom and viral expression products of the endoparasitic wasp Campoletis sonorensis share epitopes and related sequences

Endoparasitic wasps of lepidopteran insects must induce changes in host immunity and development to survive. Depending on the species, this may require wasp venom proteins and/or a polydnavirus. We describe an immunological and genetic relationship between the Campoletis sonorensis polydnavirus and the wasp's venom gland. Monoclonal antibodies raised against venom glands recognized epitopes conserved on several polydnavirus proteins and on multiple wasp oviduct and venom proteins. The viral envelope proteins had molecular masses of 16, 20, 45, and 50 kDa, while a complex of at least five immunoreactive venom-gland and soluble oviduct proteins ranged in size from 24 to 36 kDa. Since the conserved epitopes were present on the viral envelope, neutralization assays were performed. Monoclonal antibodies added to purified virus blocked the normal viral inhibition of host growth and development. To determine whether venom mRNA and viral genes were also related, venom-related cDNA clones were isolated from the wasp oviduct with a venom-gland cDNA probe. Venom-related viral clones were then identified and selected from a viral genomic library and from a parasitized Heliothis virescens cDNA library. Venom-related mRNAs were expressed in the venom gland, the oviduct, and the parasitized host. We propose that the immunological relationship between venom and viral proteins, and the hybridization of venom and viral genes, may reflect an evolutionary relationship in which venom gene homologs were incorporated into the viral genome, thereby allowing viral expression of venom-related genes and enhancing parasite survival.

Regulation of expression of arylphorin and female-specific protein mRNAs in the tobacco hornworm, Manduca sexta

Two non-cross-hybridizing cDNA clones were isolated from a lambda gt11 cDNA library prepared from Day 2 fifth instar female fat body of Manduca sexta and shown by hybrid selection to code respectively for the two storage proteins arylphorin and female-specific protein (FSP). Analysis of the developmental expression of arylphorin showed its presence during the feeding phases of the penultimate (fourth) and final (fifth) larval instars and its absence during the molt. Abdominal ligation of larvae followed by infusion of Grace's medium showed that this amino acid-rich medium was able to maintain arylphorin expression in fourth instar larvae, but not continued high expression in fifth instar larvae. This nutrient medium however was sufficient to allow initiation of expression in newly ecdysed fifth larval abdomens. Infusion of 5 micrograms 20-hydroxyecdysone (20HE) caused a significant reduction of arylphorin RNA in ligated fourth larval abdomens, whereas 50 micrograms was required in Day 2 fifth larval abdomens to suppress this RNA. Thus, both the lack of incoming nutrients and the rising titer of ecdysteroid contribute to the loss of arylphorin mRNA at the molts and at wandering. By contrast, FSP mRNA was first detected in females on Day 2 of the fifth instar, but not in males until wandering, and then was present throughout the prepupal period. In females allatectomy caused the precocious appearance of FSP mRNA which was prevented by application of 10 micrograms methoprene, a juvenile hormone analog. Expression of FSP mRNA in males however appeared to be independent of hormonal milieu.

Synthesis of two storage proteins during larval development of the tobacco hornworm, Manduca sexta

Studies of synthesis and accumulation of the two storage proteins arylphorin and female-specific protein (FSP) during the final two larval instars of the tobacco hornworm showed both stage and temporal specificity. Arylphorin was present in both stages, but its synthesis ceased during the molt, during starvation, and at the wandering stage, and then resumed about 24 hr after the onset of feeding. During the larval molt about 25% of injected iodinated arylphorin was incorporated into the newly forming fifth instar cuticle. The cessation of arylphorin synthesis was mimicked by exposure of the fat body to 1 microgram/ml 20-hydroxyecdysone (20HE) in complete Grace's medium or to dilutions of Grace's medium greater than 50%. Lower concentrations of 20HE were ineffective, indicating that the cessation of synthesis in vivo was likely due to a combination of lack of excess nutrients and the hormonal milieu. The female-specific protein was not synthesized until the final larval instar, appearing first in females on Day 2 and later in males at the time of wandering, with synthesis continuing throughout the prepupal period. In vitro studies showed that this protein was synthesized as a 620-kDa protein, and then during secretion a 730-kDa immunoreactive form also appeared. Synthesis of FSP was inhibited by exposure of Day 2 fat body to 1 microgram/ml 20HE for 24 hr. Ligation followed by 20HE infusion showed that the disappearance of FSP from the hemolymph during the prepupal period was controlled by the rising ecdysteroid titer.

Identification of factors limiting the accurate measurement of plasma D-penicillamine in rheumatoid arthritis patients

Free and total reduced concentrations of D-penicillamine have been measured in the plasma of rheumatoid arthritis patients by HPLC and electro-chemical detection. A reverse-phase ion-pair separation in conjunction with a dual porous graphite electrode satisfied the requirements of robustness, sensitivity, selectivity and suitable retention time. Plasma levels measured between 1.5 and 3 h after an oral dose, were less than 0.3 to 57.6 mumol/L and 0.6 to 85.0 mumol/L (n = 26) for free and total reduced drug concentrations, respectively. Sources of error in the accurate measurement of peak plasma D-penicillamine levels were identified as oxidative loss and alteration in the free to protein-bound ratio in the period following sample collection.

Iron binding proteins and their roles in the tobacco hornworm, Manduca sexta (L.)

Manduca sexta larvae accumulate large amounts of iron during their larval feeding period. When 59Fe was fed to 5th instar larvae, it was evenly distributed among the hemolymph, gut and carcass until the cessation of feeding. By pupation 95% of the labelled iron was found in the fat body. In the adult a significant portion of this iron was found in flight muscle. Studies of the hemolymph disclosed two iron-containing proteins. The first was composed of a single polypeptide chain of 80 kD, containing one atom of iron. This protein bound ionic iron in vitro and was able to transfer this iron to ferritin when incubated with fat body in vitro. Therefore, it appeared to serve a transport function. The second protein had a molecular weight of 490 kD with subunits of 24 and 26 kD and contained 220 micrograms of iron/mg protein. Its chemical and ultrastructural characteristics were those of ferritin. These studies demonstrate the presence of both a transport protein and a unique circulating ferritin in Manduca sexta, the latter serving a storage function during development and possibly also a transport function.

A potential systematic error in using lysivane as inhibitor in the measurement of amniotic fluid acetylcholinesterase by the Ellman method

The measurement of low levels of cholinesterase or acetylcholinesterase by the Ellman method requires correction for a non-enzymatic increase in absorption at 412 millimicron that is due both to non-enzymatic hydrolysis of the acetylthiocholine substrate and to modification of the colour reagent. The rate of increase in absorption is dependent on temperature and pH. Addition of an acidic solution of lysivane to the assay solution for selective measurement of amniotic fluid acetylcholinesterase gives rise to a shift in pH; the use of methanol is suggested as an easier method of dissolving the inhibitor and does not affect the pH of the assay, obviating any need to redetermine the background absorption. There is, however, no improvement in ability of the method to predict pregnancies associated with neural-tube defects.