Immunization of cattle with synthetic peptides derived from the Boophilus microplus gut protein (Bm86)

Selection of reference genes for quantitative RT-PCR studies in Rhipicephalus (Boophilus) microplus and Rhipicephalus appendiculatus ticks and determination of the expression profile of Bm86

Background

For accurate and reliable gene expression analysis, normalization of gene expression data against reference genes is essential. In most studies on ticks where (semi-)quantitative RT-PCR is employed, normalization occurs with a single reference gene, usually β-actin, without validation of its presumed expression stability. The first goal of this study was to evaluate the expression stability of commonly used reference genes in Rhipicephalus appendiculatus and Rhipicephalus (Boophilus) microplus ticks. To demonstrate the usefulness of these results, an unresolved issue in tick vaccine development was examined. Commercial vaccines against R. microplus were developed based on the recombinant antigen Bm86, but despite a high degree of sequence homology, these vaccines are not effective against R. appendiculatus. In fact, Bm86-based vaccines give better protection against some tick species with lower Bm86 sequence homology. One possible explanation is the variation in Bm86 expression levels between R. microplus and R. appendiculatus. The most stable reference genes were therefore used for normalization of the Bm86 expression profile in all life stages of both species to examine whether antigen abundance plays a role in Bm86 vaccine susceptibility.

Results

The transcription levels of nine potential reference genes: β-actin (ACTB), β-tubulin (BTUB), elongation factor 1α (ELF1A), glyceraldehyde 3-phosphate dehydrogenase (GAPDH), glutathione S-transferase (GST), H3 histone family 3A (H3F3A), cyclophilin (PPIA), ribosomal protein L4 (RPL4) and TATA box binding protein (TBP) were measured in all life stages of R. microplus and R. appendiculatus. ELF1A was found to be the most stable expressed gene in both species following analysis by both geNorm and Normfinder software applications, GST showed the least stability. The expression profile of Bm86 in R. appendiculatus and R. microplus revealed a more continuous Bm86 antigen abundance in R. microplus throughout its one-host life cycle compared to the three-host tick R. appendiculatus where large variations were observed between different life stages.

Conclusion

Based on these results, ELF1A can be proposed as an initial reference gene for normalization of quantitative RT-PCR data in whole R. microplus and R. appendiculatus ticks. The observed differences in Bm86 expression profile between the two species alone can not adequately explain the lack of a Bm86 vaccination effect in R. appendiculatus.

Protective efficacy of bacterial membranes containing surface-exposed BM95 antigenic peptides for the control of cattle tick infestations

The Rhipicephalus (Boophilus) microplus BM86 and BM95 glycoproteins are homologous proteins that protect cattle against tick infestations. In this study, we demonstrated that the recombinant chimeric protein comprising tick BM95 immunogenic peptides fused to the A. marginale MSP1a N-terminal region for presentation on the Escherichia coli membrane was protective against R. microplus infestations in rabbits. This system provides a novel and simple approach for the production of tick protective antigens by surface display of antigenic protein chimera on live E. coli and suggests the possibility of using recombinant bacterial membrane fractions for vaccination against cattle tick infestations.

Comparison of predicted binders in Rhipicephalus (Boophilus) microplus intestine protein variants BM86 Campo Grande strain, BM86 and BM95

This paper reports the sequence analysis of Bm86 Campo Grande strain comparing it with Bm86 and Bm95 antigens from the preparations TickGardPLUS and GavacTM, respectively. The PCR product was cloned into pMOSBlue and sequenced. The secondary structure prediction tool PSIPRED was used to calculate alpha helices and beta strand contents of the predicted polypeptide. The hydrophobicity profile was calculated using the algorithms from the Hopp and Woods method, in addition to identification of potential MHC class-I binding regions in the antigens. Pair-wise alignment revealed that the similarity between Bm86 Campo Grande strain and Bm86 is 0.2% higher than that between Bm86 Campo Grande strain and Bm95 antigens. The identities were 96.5% and 96.3% respectively. Major suggestive differences in hydrophobicity were predicted among the sequences in two specific regions.

Vaccine potential of a tick vitellin-degrading enzyme (VTDCE)

VTDCE (Vitelin-Degrading Cysteine Endopeptidase) is a peptidase with an active role in Rhipicephalus (Boophilus) microplus embryogenesis. VTDCE is found in the tick's eggs and was shown to be the most active protein in vitellin (VT) hydrolysis of the three peptidases already characterized in R. microplus eggs (Boophilus Yolk pro-cathepsin (BYC), Tick Heme Binding Aspartic Proteinase (THAP) and VTDCE). VTDCE activity was assessed in vitro using the natural substrate and a synthetic substrate (N-Cbz-Phe-Arg-MCA). The activity was inhibited by anti-VTDCE antibodies. In the present study, it was shown that VTDCE acts differently from BYC and THAP in VT hydrolysis and that the vaccination of bovines with VTDCE induces a partial protective immune response against R. microplus infestation. Immunized bovines challenged with R. microplus larvae presented an overall protection of 21%, and a reduction in the weight of fertile eggs of 17.6% was observed. The data obtained indicate that VTDCE seems to be important for tick physiology, and that it induces partial protective immune response when inoculated in bovines. This suggests that VTDCE can be useful to improve the protective capacity observed for other antigens.

Expression of recombinant Rhipicephalus (Boophilus) microplus, R. annulatus and R. decoloratus Bm86 orthologs as secreted proteins in Pichia pastoris

Background

Rhipicephalus (Boophilus) spp. ticks economically impact on cattle production in Africa and other tropical and subtropical regions of the world. Tick vaccines constitute a cost-effective and environmentally friendly alternative to tick control. The R. microplus Bm86 protective antigen has been produced by recombinant DNA technology and shown to protect cattle against tick infestations.

Results

In this study, the genes for Bm86 (R. microplus), Ba86 (R. annulatus) and Bd86 (R. decoloratus) were cloned and characterized from African or Asian tick strains and the recombinant proteins were secreted and purified from P. pastoris. The secretion of recombinant Bm86 ortholog proteins in P. pastoris allowed for a simple purification process rendering a final product with high recovery (35–42%) and purity (80–85%) and likely to result in a more reproducible conformation closely resembling the native protein. Rabbit immunization experiments with recombinant proteins showed immune cross-reactivity between Bm86 ortholog proteins.

Conclusion

These experiments support the development and testing of vaccines containing recombinant Bm86, Ba86 and Bd86 secreted in P. pastoris for the control of tick infestations in Africa.

Synthetic vaccine (SBm7462) against the cattle tick Rhipicephalus (Boophilus) microplus: preservation of immunogenic determinants in different strains from South America

The synthetic vaccine SBm7462 is based on three immunogenic epitopes (4822, 4823 and 4824) contained within protein Bm86 derived from the Australian Yeerongpilly strain of the tick Rhipicephalus (Boophilus) microplus. Twenty strains of the tick originating from Brazil, Argentina, Colombia and Uruguay were analysed in order to identify differences compared with sequences present in components of vaccine SBm7462. For each parasite population, three cDNA fragments containing the nucleotides coding for the epitopes 4822, 4824 and 4823 were sequenced, and the amino acid sequences were deduced and compared with those of the homologous bm86 gene. The results indicate that the epitope sequences of vaccine SBm7462 are conserved in the South American populations of the tick. The conservation of such sequences is very important for the immunological response of different populations of R. (B.) microplus.

A synthetic bmti n-terminal fragment as antigen in bovine immunoprotection against the tick Boophilus microplus in a pen trial

Cattle tick control remains a serious problem in cattle farms worldwide, due to the limited success achieved with chemicals. Although the use of vaccines for tick control may open possibilities for an integrated approach, the search for other protective antigens is still necessary to improve control. Boophilus microplus is a rich source of BmTIs, serine proteinase inhibitors that are present throughout the tick's lifecycle. The present paper reports a pen trial conducted to evaluate the performance of a synthetic BmTI N-terminal fragment as antigen against the tick in bovines. The trial was conducted with two groups of eight crossbred cattle under controlled infestation: one group was vaccinated with BmTI peptide using saponin as adjuvant and the other was kept as control. Challenge was performed with 15,000 larvae. The specific IgG response was measured by ELISA, with successful outcomes for vaccinated animals. Vaccination resulted in an 18.4% level of efficacy when compared with the control group.

Vaccination of cattle with TickGARD induces cross-reactive antibodies binding to conserved linear peptides of Bm86 homologues in Boophilus decoloratus

Vaccines based on recombinant Bm86 gut antigen from Boophilus microplus are a useful component of integrated control strategies against B. microplus infestations of cattle. The capacity of such vaccines to control heterologous infestations by two African tick species was investigated. The mean weight of engorged female ticks and mean egg mass per tick were significantly reduced in B. decoloratus infestations, but there was no effect of the vaccine against adult Rhipicephalus appendiculatus. We cloned, sequenced and expressed two Bm86 homologues (Bd86) from B. decoloratus. Amino acid sequence identity between Bd86 homologues (Bd86-1 and Bd86-2) and Bm86 was 86% and 85%, respectively, compared to 93% identity between the variants. Native Bd86 protein in B. decoloratus tick mid-gut sections and recombinant Bd86-1 reacted strongly with sera from TickGARD vaccinated cattle. TickGARD can therefore protect against a heterologous tick species with multiple antigen sequences. Epitope mapping using sera from TickGARD-vaccinated cattle identified two linear peptides conserved between the Bd86 homologues and Bm86. These epitopes represent candidate synthetic peptide vaccines for control of Boophilus spp. and the pathogens transmitted by these tick vectors.

Anti-tick vaccines

There is now abundant evidence that vaccination with defined protein antigens is able to induce significant immunity to tick infestation. In a limited number of cases, this immunity has been duplicated by vaccination with recombinant antigens, a critical step on the pathway to commercial vaccine production. The existence of two commercial vaccines has allowed a number of field studies showing that the existing products can make an important contribution to an integrated approach to the control of ticks in the field. Under most circumstances however, the use of a tick vaccine as the single, stand alone control technology is likely to require more efficacious vaccines than those currently available. Increases in efficacy are most likely to come through the discovery of additional, effective vaccine antigens. The number of antigens with demonstrated effect is increasing, though only slowly, while the number of potential antigens that remain to be evaluated is increasing more quickly. There is limited, though convincing, evidence that some of these antigens will show effective cross-species protection, though in a poorly understood and unpredictable way. The groundwork has been laid; the potential of the field is still to be effectively exploited.

Considerations on the effect of anti-sandfly antibodies on biological parameters of Lutzomyia longipalpis (Lutz & Neiva, 1912) (Diptera: Psychodidae: Phlebotominae)

The immunization of vertebrate hosts with vector components may be an alternative for the control of diseases transmitted by insects. In the present study we evaluated the effects of anti-sandfly antibodies on some of the biological parameters of female Lutzomyia longipalpis, a vector of visceral leishmaniasis. Rabbits were immunized with extracts of gut from blood-fed (GB) or sugar-fed (GS) females, carcass of sugar-fed (CS) or blood-fed (CB) females, and with repeated sandfly bites (BITE). Immune sera showed increased antibody titers compared to pre-immunized animals, and specific bands were detected by Western Blot. An analysis of biological parameters revealed a decline in fecundity in the group of females fed on rabbits immunized with GB and BITE. Longevity and mortality were studied in females with oviposition (parous) and without oviposition (nulliparous). Nulliparous females that fed on rabbits immunized with bites died in the highest percentage. A mortality analysis after egg laying revealed a peak on the fifth day in all the groups, but females fed on rabbit subjected to repeated bites showed a shift towards the third day.

Purification and antigenicity of two recombinant forms of Boophilus microplus yolk pro-cathepsin expressed in inclusion bodies

The tick Boophilus microplus is a bovine ectoparasite present in tropical and subtropical areas of the world and the use of vaccines is a promising method for tick control. BYC is an aspartic proteinase found in eggs that is involved in the embryogenesis of B. microplus and was proposed as an important antigen in the development of an anti-tick vaccine. The cDNA of BYC was amplified by PCR and cloned for expression in two forms with and without thioredoxin fusion protein (Trx), coding recombinant proteins named rBYC-Trx and rBYC, respectively. Expression, solubility, and yields of the two forms were analyzed. The recombinant proteins were expressed in inclusion bodies (IBs) and three denaturant agents (N-lauroyl sarcosine, guanidine hydrochloride, and urea) were tested for IBs solubilization. The N-lauroyl sarcosine solubilized 90.4 and 92.4% of rBYC-Trx and rBYC IBs, respectively, and was the most efficient denaturant. Two recombinant forms were affinity-purified by Ni2+-Sepharose under denaturing conditions. After dialysis, the yield of soluble protein was 84.1% for r-BYC-Trx and 5.9% for rBYC. These proteins were immune-reactive against sera from rabbit, mouse, and bovine previously immunized with native BYC, which confirms the antigenicity of the recombinant BYCs expressed in the Escherichia coli system.

Characterization of three Ixodes scapularis cDNAs protective against tick infestations

cDNA expression library immunization (ELI) and analysis of expressed sequenced tags (EST) in a mouse model of tick infestations was used to identified cDNA clones that affected I. scapularis. Three protective antigens against larval tick infestations, 4F8, with homology to a nucleotidase, and 4D8 and 4E6 of unknown function, were selected for further characterization. All three antigens were expressed in all I. scapularis stages and localized in adult tick tissues. 4D8 was shown to be conserved in six other tick species. Based on immunization trials with synthetic polypeptides against larvae and nymphs and on artificial feeding experiments of adults, these antigens, especially 4D8, appear to be good candidates for continued development of a vaccine for control of tick infestations and may be useful in a formulation to target multiple species of ticks.

Synthetic peptide vaccination in cattle: induction of strong cellular immune responses against peptides derived from the Mycobacterium bovis antigen Rv3019c

Fully synthetic peptide vaccines possess attractive cost and safety attributes. However, peptide vaccines that induce cell-mediated immunity require both selection of appropriate peptides and the development of adjuvant formulations supporting the induction of cellular immunity. An adjuvant formulation composed of emulsigen and the synthetic CpG motif containing ODN2007 was tested in cattle for its ability to induce cellular immunity after peptide vaccination, and compared to Rv3019c DNA vaccination. Peptides from the protective Mycobacterium bovis antigen Rv3019c were included into the vaccine on the basis of their frequent and strong recognition by T cells from M. bovis infected or BCG vaccinated cattle. Following peptide vaccination, strong IFN-gamma and proliferative T cell responses were observed. Proliferative, but no significant IFN-gamma responses were induced by DNA vaccination. Peptide vaccination boosted responses primed by DNA vaccination. In conclusion, emulsigen and CpG motif containing ODN constitute a promising adjuvant formulation to deliver peptides to veterinary species.

Use of biodegradable PLGA microspheres as a slow release delivery system for the Boophilus microplus synthetic vaccine SBm7462

The synthetic anti-Boophilus microplus vaccine SBm7462 derived from the tick intestinal protein, Bm86, induced a protective immune response when emulsified in saponin and used in cattle. Using a mice model, and with the objective of improving the vaccine by continual peptide release, it was encapsulated in PLGA 50:50 microspheres and inoculated in BALB/c mice to assess the immunological response by detection of anti-peptide IgGs. Comparative studies were made with the peptide emulsified in saponin and with another synthetic vaccine, and the microsphere/peptide was characterized for efficiency of encapsulation, in vitro release profile, morphology, size, peptide integrity after encapsulation and stability in different pHs. The findings showed that saponin enhances a better immune response from SBm7462 and that the PLGA 50:50 microspheres are suitable for use with this peptide.

A theoretical analysis of codon adaptation index of the Boophilus microplus bm86 gene directed to the optimization of a DNA vaccine

DNA vaccines utilize host cell molecules for gene transcription and translation to proteins, and the interspecific difference of codon usage is one of the major obstacles for effective induction of specific and strong immune response. In an attempt to improve codon usage effects of DNA vaccine on protein expression, a quantitative study was conducted to clarify the relationship of codon usage in the tick gene bm86 and its potential expression in bovine cells. The calculated relative synonymous codon usage (RSCU) and codon adaptation index (CAI) values of bm86 from Boophilus microplus and a set of 14 highly expressed genes from Bos taurus indicated that some codons utilized frequently in bm86 are rarely used in B. taurus genes and vice versa. The different translational efficiencies obtained suggested that after DNA vaccination using the wild bm86 gene, the protein Bm86 would be expressed in bovines, but it would not be the optimum sequence. However, using the codon-optimized bm86 gene to bovines, whose sequence was theoretically designed, would probably improve the level of the immune response generated against ticks.

Assessment of duration of immunity in crossbred cattle immunized with glycoproteins isolated from Hyalomma anatolicum anatolicum and Boophilus microplus

To develop immunoprophylactic measures against multi-tick infestation, two glycoproteins of 34 and 29 kDa were isolated from the larvae of Hyalomma anatolicum anatolicum and Boophilus microplus, respectively, and assessed for their efficacy against experimental challenge infestations. The synergistic effect of the antigens in the presence of incomplete Freund's adjuvant was found to confer protection (DT%) in animals against 56.48% of larvae and 52% of adults of H. a. anatolicum, while the effect was 40% against adults of B. microplus. The efficacy (E%) of the antigens in combination against larvae and adults of H. a. anatolicum was calculated as 70% and 64.3%, respectively, and 63% against adults of B. microplus. A direct correlation between anti-glycoprotein antibody response and protection against infestation was observed. Western blot analysis detected specific antigen in the sera of animals of group A. The antigens in combination with incomplete Freund's adjuvant could protect animals from H. a. anatolicum and B. microplus infestations for at least 30 weeks. The possibility of employing the vaccination strategy in Indian conditions is discussed.

TICKCIDAL EFFECT OF MONOCLONAL ANTIBODIES AGAINST HEMOCYTES, OM21, IN AN ADULT FEMALE TICK, ORNITHODOROS MOUBATA (ACARI: ARGASIDAE)

In the present study, monoclonal antibodies (mAbs) against adult Ornithodoros moubata hemocytes were established. Afterward, artificial feeding was performed to assess the tickcidal effect of fetal bovine serum meal containing each mAb. As a result, Om21 showed the strongest tickcidal effect on adult female O. moubata. The reactivity of various tick cells and organs, including the hemocyte, midgut, trachea, ovary, fat body, and muscle, to Om21 was then examined by an indirect immunofluorescent antibody test and by immunoelectron microscopy. Om21 reacted with not only hemocytes but also with fat body cells, epidermis, cuticle of the trachea, connective tissue of the muscle, and the basement membrane of the midgut, trachea, fat body, oocyte, and epidermis. These results suggest that Om21 passing through the midgut epithelium induced a tickcidal effect on hemocytes or various organs. However, the target of Om21 could not be identified in the present study. The antihemocyte mAb produced in this study, Om21, may be useful for the immunological control of ticks.

Cloning, expression and partial characterization of a Haemaphysalis longicornis and a Rhipicephalus appendiculatus glutathione S-transferase

The ticks Haemaphysalis longicornis and Rhipicephalus appendiculatus are important parasites worldwide. The current method for control of cattle ticks involves the use of chemicals. Nevertheless, parasite resistance is an ever increasing global problem. Glutathione S-transferases (GSTs) play a central role in detoxication of xenobiotic and endogenous compounds. Several authors have noted that an increase in GST activity is associated with resistance to insecticides and acaricides. In the present study, we report the cloning and expression of GST cDNAs from H. longicornis and R. appendiculatus. In addition, we determine the effect of three acaricides (ethion, deltamethrin and diazinon) on the enzymatic activity of rGSTs.