Margherita Profiti

Genetic Heterogeneity of Small Ruminant Lentiviruses Involves Immunodominant Epitope of Capsid Antigen and Affects Sensitivity of Single-Strain-Based Immunoassay

ABSTRACT The pol and gag gene fragments of small ruminant lentivirus field isolates collected in the last decade in Italy were amplified, sequenced, and analyzed. Phylogenetic analysis revealed that the majority of ovine isolates form a distinct cluster more similar to caprine lentivirus prototypes than to the visna virus prototype. These findings confirm and extend those reported by Leroux et al. (Arch. Virol., 142:1125-1137, 1997). Moreover, we observed that a variable region of Gag, included in the fragment analyzed, corresponded to one of the three major capsid antigen epitopes, which suggests that the antibody response to this epitope may be type specific. To test this hypothesis, two recombinant peptides, derived from the Icelandic prototype K1514 and this novel genotype, were expressed and used in an enzyme-linked immunosorbent assay to screen a panel of ovine and caprine sera collected from different geographical locations in Italy. Several sera reacted in a type-specific manner, indicating that in a diagnostic setting the combination of at least these two type-specific peptides is necessary to cover a wide range of infections. Additionally, these results support the hypothesis of cross-species transmission based on the phylogenetic analysis described above. This has implications for the control and eradication of small ruminant lentivirus infections.

Prokaryotic Expression and Antigenic Characterization of Three Recombinant Leishmania Antigens for Serological Diagnosis of Canine Leishmaniasis

ABSTRACT Three recombinant antigens of Leishmania chagasi (= L. infantum) were expressed in prokaryotic systems and evaluated (using a panel of dog sera characterized by parasitological and serological immunofluorescent antibody test [IFAT] techniques) as diagnostic markers of infection. The whole open reading frame encoding K9, the gene fragment encoding the repetitive sequence of K26, and the 3′-terminal gene fragment encoding a single 39-amino-acid subunit of the kinesin-related protein K39 (K39sub) were amplified from L. infantum DNA and cloned into a pGEX-2T expression vector in frame with glutathione S-transferase (GST). The sensitivity and specificity of enzyme-linked immunosorbent assays (ELISAs) using K26 as an antigen (evaluated with sera from 20 parasitologically positive and 20 parasitologically negative dogs) were both 100% (95% confidence interval [CI] = 83.2 to 100). When K9 and K39sub were used, sensitivity was 95% (95% CI = 75.1 to 99.9) and specificity was 100% (95% CI = 83.2 to 100). Using 182 field sera, a good agreement was found between the recombinant K26 ELISA and IFAT (K = 0.92; 95% CI = 0.86 to 0.98) results and between the K9 and K39sub ELISA (used in parallel) and IFAT (K = 0.87; 95% CI = 0.80 to 0.95) results. The results demonstrate that each antigen carries immunodominant epitopes and that their combination may further increase the sensitivity of currently available serological tests.

Molecular and antigenic characterization of a Mycoplasma bovis strain causing an outbreak of infectious keratoconjunctivitis.

An unusually high incidence of infectious keratoconjunctivitis followed by pneumonia and arthritis was observed in beef calves of a managed herd. No Moraxella spp. or bacteria other than Mycoplasma spp. were obtained from conjunctival and nasal swabs. A strategy was designed for characterization of bovine mycoplasmas at species and strain level on the basis of a combination of molecular tools and the immunoblotting method. The strategy made it possible to rapidly assign the bacterium responsible for this outbreak to one of the phylogenetic clusters of bovine mycoplasmas delineated in this study and then to identify it as Mycoplasma bovis. The strain, designated Sar 1, showed a 100% 16S rDNA sequence identity with two European strains (120/81 and MC3386) isolated in Germany and Ireland, respectively, and hosts a vsp gene analog to the vsp A, vsp 422-4, and vsp 422-8 genes of the M. bovis reference strain PG45T and of the field strain 422. The use of a cross-reactive rabbit serum developed against the Mycoplasma agalactiae immunodominant antigen P48 confirmed the molecular findings. The immunological response of calves against M. bovis was also investigated. This is the first report on the occurrence of M. bovis on the Island of Sardinia (Italy).

Immunological parameters in goats experimentally infected with SRLV genotype E, strain Roccaverano

Genotype E of small ruminant lentivirus has been recently described in goats from different breeds in Italy. Genotype E infection may differ from known genotypes since deletions of dUTPase and VPR proteins have been confirmed in different independent areas and goat breed, and play a key role on virus replication and pathogenesis. In particular, genotype E Roccaverano strain has been described as low pathogenic since does not lead to clinical symptoms in goats. In contrast, classical CAEV infected goats of the same area and breed presented arthritis. In this study, we have used intratracheal and intra-bone marrow routes to establish genotype E persistent infections. Humoral and cellular immune responses elicited in the host against genotype E and genotype B derived antigens were evaluated until 200 days post-inoculation. Compared to genotype B antigen, seroconversion against genotype E GAG P16-25 antigen was detected at 2-3 weeks after inoculation, significantly earlier and at higher titres. Interestingly, antibody avidity did not increase in the course of the experiment neither against P16-25 nor against SU5, both derived from genotype E. T cell proliferation against P25-GST fusion protein antigens derived from genotype E was firstly detected at 15 days post-inoculation and was maintained throughout time until week 20 post-infection, while T cell proliferation against the genotype B P25 was not produced by the end of the experiment at 20 weeks post-inoculation. The strength of reaction was also higher when using P25 E as stimulator antigen. In contrast with antibody and T cell proliferation, cytotoxic-T-lymphocyte (CTL) activity in the circulating lymphocytes (effector cells) using blood-derived macrophages (BDM) as target cells, was not strain specific being surprisingly higher against genotype B infected antigen presenting cells (APCs). This is the first study reporting experimentally induced immunological changes in SRLV genotype E infection and indicates that CTL activity may be the adaptive immune response able to induce protection against heterologous infection.

In vitro properties of small ruminant lentivirus genotype E

Small ruminant lentivirus genotype E lacks the dUTPase subunit and vpr-like gene. Two strains (Roccaverano and Seui) with identical genetic organization have been described, with the env HV1-HV2 domains being the most divergent. Although dUTPase and vpr-like deletions have been involved in the RT fidelity in non dividing cells, both strains were able to replicate efficiently in blood derived macrophages (BDM), while virus production of E1 subtype was reduced or abrogated in replicating fibroblastic-like cells. The transcriptional activity of genotype E was similar in these two cellular populations. When viral pseudotypes were generated with the env of both viruses, Roccaverano pseudotype displayed a paranuclear localization on BDM, suggesting a different mechanism of entry. Polymorphic GAS and TAS sites in the U3 region, further suggest that a population different from classically activated macrophages can be infected by these viruses, opening new insights into lentiviruses with low or null pathogenic potential.

LTR promoter activity of SRLV genotype E, strain Roccaverano

The highly divergent, small ruminant lentivirus (SRLV) genotype E Roccaverano strain has a full genome consisting of 8,418 nucleotides, which lack the entire dUTPase subunit of the pol gene, the vpr-like accessory gene, and the 71-bp repeat of the U3 region within the long terminal repeat (LTR). These deletions affect in reverse transcriptase fidelity in non-dividing cells (dUTPase and vpr-like) and in the regulation of viral replication. Surprisingly, this SRLV strain was able to replicate efficiently in non-dividing cells (i.e., blood-derived macrophages), while replication in fibroblastic-like cells was somewhat restricted. To evaluate whether this observation was due to the presence/absence of specific transcription factors within these fibroblasts, U3 transcriptional activity was measured in the different cell types and revealed that both fibroblasts and macrophages were able to activate the viral promoter in the same manner. Among the transcription factor-binding sites present within the U3 region, the highly conserved Ap4 tandem repeat was shown to be sufficient for LTR promoter activity.

Antigenic variability of ovine lentivirus isolated in Italy

S. Rosati1*, M Profiti1, E. Grego, M.L. Carrozza2, M. Mazzei3 and P. Bandecchi3 1Dipartimento di Produzioni Animali Epidemiologia ed Ecologia, Università di T orino; 2Scuola Normale Superiore, Pisa; 3Dipartimento di Patologia Animale, Università di Pisa *Correspondence: Dipartimento di Produzioni Animali, Epidemiologia ed EcologiaFacoltà di Medicina veterinaria V ia L eonardo da V inci, 44 10095 Grugliasco (TO), Italy e-mail: sergio.rosati@unito.it

Expression and antigenic characterization of bubaline herpesvirus 1 (BuHV1) glycoprotein E and its potential application in the epidemiology and control of alphaherpesvirus infections in Mediterranean water buffalo

Bubaline herpesvirus 1 (BuHV1) is a member of ruminant alphaherpesviruses antigenically related to bovine herpesvirus 1 (BoHV1). The impact of BuHV1 infection in infectious bovine rhinotracheitis control program is difficult to establish, due to the lack of specific diagnostic test. The ectodomain of glycoprotein E of BuHV1 was expressed as recombinant secreted protein and used in indirect ELISA as well as in a discriminatory test using the BoHV1 counterpart. A panel of monoclonal antibodies was produced against BuHV1; 6 out of 7 anti-gE monoclonal antibodies specifically recognized the BuHV1 gE. Results indicated BuHV1 gE as a sensitive marker of infection compared to seroneutralization (SN) test or blocking ELISA. When BoHV1 and BuHV1 gEs were immobilized in different wells of the same ELISA microplate, bovine and water buffalo sera were more reactive against the respective infecting virus. About one third of seropositive buffaloes with no history of contact with cattle and having higher SN titres, reacted in BoHV1 gE blocking ELISA, possibly because of steric hindrance. Since in two occasions BuHV1 was also isolated from water buffalo scoring gB+/gE+ BoHV1 blocking ELISA, we conclude that the combination of the two blocking ELISAs is not suitable to differentiate between BoHV1 and BuHV1.

Small ruminant lentivirus genotype B and E interaction: Evidences on the role of Roccaverano strain on reducing proviral load of the challenging CAEV strain.

Live attenuated vaccines provide the most consistent protective immunity in experimental models of lentivirus infections. In this study we tested the hypothesis that animals infected with a naturally attenuated small ruminant lentivirus field strain of genotype E may control a challenge infection with a virulent strain of the caprine arthritis encephalitis virus (CAEV-CO). Within genotype E, Roccaverano strain has been described as attenuated since decreased arthritic pathological indexes were recorded in Roccaverano-infected animals compared to animals of the same breed infected with genotype B strains. Moreover, under natural conditions, animals double-infected with genotypes B and E appear less prone to develop SRLV-related disease, leading to a putative protective role of Roccaverano strain. Here we present evidence that goats experimentally infected with the avirulent genotype E SRLV-Roccaverano strain control the proviral load of a pathogenic challenge virus (CAEV-CO strain) more efficiently than naïve animals and appear to limit the spread of histological lesions to the contralateral joints.

Characterization of caprine herpesvirus 1 (CpHV1) glycoprotein E and glycoprotein I ectodomains expressed in mammalian cells

Caprine herpesvirus 1 (CpHV1) is a member of ruminant alphaherpesviruses antigenically related to the prototype bovine herpesvirus 1 (BoHV1). Although cross reactivity between the two viruses involves many structural glycoproteins, the use of two competitive BoHV1 ELISAs detecting anti gB and gE antibodies has been proposed for CpHV1 infection, resulting mainly in a gB+/gE- reactivity and leading to suppose that CpHV1 gE may represent an useful target for the development of specific diagnostic test. Since CpHV1 gE gene has been only partially characterized so far, in this study the genome fragment of the short unique unit (Us) encompassing gI and gE gene was amplified and sequenced. Gene fragments encoding the ectodomain of both glycoproteins were subcloned into pSECTag2/Hygro and expressed in HEK293T cells as secreted form in serum free medium. Due to the lack of specific monoclonal antibodies (Mabs), the same recombinant glycoproteins were obtained from BoHV1 and used as positive control with a panel of specific gE and gI Mabs as well as in some ELISA assays. Results clearly indicate that the ectodomain of CpHV1 gE, immobilized on solid face in an indirect ELISA format, represents a sensitive and specific marker of infection, when compared with neutralization test, with absence of very low degree of cross-reactivity with BoHV1 gE counterpart, while the use of CpHV1 gI-ELISA or a combination of gE/gI complex did not significantly improve the sensitivity of the assay. In addition, in the rare event in which cross species barrier occurs for both viruses from their natural host to other species, the use of both BoHV1 and CpHV1 gE in a comparative assay may be proposed.