Construction, screening and identification of a phage display antibody library against the Eimeria acervulina merozoite

Identification of Eimeria tenella sporozoite immunodominant mimotopes by random phage-display peptide libraries-a proof of concept study

INTRODUCTION

Coccidiosis, caused by parasites of numerous Eimeria species, has long been recognized as an economically significant disease in the chicken industry worldwide. The rise of anti-coccidian resistance has driven a search for other parasite management techniques. Recombinant antigen vaccination presents a highly feasible alternative. Properly identifying antigens that might trigger a potent immune response is one of the major obstacles to creating a viable genetically modified vaccine.

METHODS

This study evaluated a reverse immunology approach for the identification of B-cell epitopes. Antisera from rabbits and hens inoculated with whole-sporozoites of E. tenella were used to identify Western blot antigens. The rabbit IgG fraction from the anti-sporozoite serum exhibited the highest reactogenicity; consequently, it was purified and utilized to screen two random Phage-display peptide libraries (12 mer and c7c mer). After three panning rounds, 20 clones from each library were randomly selected, their nucleotide sequences acquired, and their reactivity to anti-sporozoite E. tenella serum assessed. The selected peptide clones inferred amino acid sequences matched numerous E. tenella proteins.

RESULTS AND CONCLUSIONS

The extracellular domain of the epidermal growth factor-like (EGF-like) repeats, and the thrombospondin type-I (TSP-1) repeats of E. tenella micronemal protein 4 (EtMIC4) matched with the c7c mer selected clones CNTGSPYEC (2/20) and CMSTGLSSC (1/20) respectively. The clone CSISSLTHC that matched with a conserved hypothetical protein of E. tenella was widely selected (3/20). Selected clones from the 12-mer phage display library AGHTTQFNSKTT (7/20), GPNSAFWAGSER (2/20) and HFAYWWNGVRGP (8/20) showed similarities with a cullin homolog, elongation factor-2 and beta-dynein chain a putative E. tenella protein, respectively. Four immunodominant clones were previously selected and used to immunize rabbits. By ELISA and Western blot, all rabbit anti-clone serums detected E. tenella native antigens.

DISCUSSION

Thus, selected phagotopes contained recombinant E. tenella antigen peptides. Using antibodies against E. tenella sporozoites, this study demonstrated the feasibility of screening Phage-display random peptide libraries for true immunotopes. In addition, this study looked at an approach for finding novel candidates that could be used as an E. tenella recombinant epitope-based vaccine.

Immunotherapy With Egg Yolk Eimeria sp.-Specific Immunoglobulins in SPF Leghorn Chicks Elicits Successful Protection Against Eimeria tenella Infection

Avian coccidiosis is the first to most economically important parasite disease affecting poultry industries worldwide. Current prevention measures are largely based upon prophylactic chemotherapy supplemented by the application of live attenuated or wild-type parasite vaccines. However, the rising appearance of drug resistance, consumer's concern for antibiotics use in poultry production and higher manufacturing cost of live vaccines has driven to adopt new technologies aimed at increasing animal health and production efficiency. Supplementing chickens with egg yolk Eimeria sp.-specific immunoglobulins can be a viable alternative to avoid severe outbreaks of the disease. Twelve-week-old SPF White Leghorn chickens were experimentally infected with a large dose of E. tenella. During the prepatent period, the birds were supplemented by oral gavage with 60 or 120 mg/bird of hyperimmune egg yolk Eimeria species-specific immunoglobulins Y (Supracox®, SC) on a daily basis. The animals were euthanized 7 days post-infection (PI) and their passive immune protection was evaluated. Birds treated with 120 mg/bird of SC showed more viability, increased body weight gain (BWG), a normal hematocrit level (HCT), reduced oocyst output per gram of feces (OPG) or cecal tissue (OPGC), and fewer cecal lesions compared to the untreated infected (UI) control group. Birds supplemented with 60 mg/bird of SC did not show any significant difference on BWG, HCT, OPG, OPGC, and cecal lesion score when compared with the UI group. An ELISA test of the SC showed a weak cross-reactivity of IgY toward two asexual zoite stages of E. tenella. Western blot analysis of the sporozoite with SC showed few antigens barely recognized, while more stained bands were detected in the merozoite (≈82, ≈60, ≈54, ≈40, ≈38, ≈27.5, and ≈13 kDa). Oral immunotherapy using egg yolk polyclonal IgYs against Eimeria sp. represents an effective and natural resource against severe E. tenella infection favoring the gradual withdrawal of the anticoccidial drugs and antibiotics.

Selection and characterization of single-chain recombinant antibodies against spring viraemia of carp virus from mouse phage display library

Antibody-displaying phage library was selected after three rounds of panning against spring viraemia of carp virus (SVCV) by phage display technology. Eight positive clones which could produce soluble single-chain fragment variable (scFv) antibody induced by isopropyl-beta-d-thiogalactopyranoside (IPTG) were obtained. Dot blot results showed that the eight scFv antibodies could recognize SVCV. The soluble scFv antibodies showed a molecular weight 29 kD by Western blot. All scFv antibodies could recognize SVCV proteins specifically without cross-reaction with other virus proteins by ELISA. Indirect immunofluorescence results showed that all of these scFv antibodies reacted positively with virus in the SVCV-infected cells. These scFv antibodies will be useful tools to establish immunological detection methods for SVCV.

Selection of binding targets in parasites using phage-display and aptamer libraries in vivo and in vitro

Parasite infections are largely dependent on interactions between pathogen and different host cell populations to guarantee a successful infectious process. This is particularly true for obligatory intracellular parasites as Plasmodium, Toxoplasma, and Leishmania, to name a few. Adhesion to and entry into the cell are essential steps requiring specific parasite and host cell molecules. The large amount of possible involved molecules poses additional difficulties for their identification by the classical biochemical approaches. In this respect, the search for alternative techniques should be pursued. Among them two powerful methodologies can be employed, both relying upon the construction of highly diverse combinatorial libraries of peptides or oligonucleotides that randomly bind with high affinity to targets on the cell surface and are selectively displaced by putative ligands. These are, respectively, the peptide-based phage display and the oligonucleotide-based aptamer techniques. The phage display technique has been extensively employed for the identification of novel ligands in vitro and in vivo in different areas such as cancer, vaccine development, and epitope mapping. Particularly, phage display has been employed in the investigation of pathogen–host interactions. Although this methodology has been used for some parasites with encouraging results, in trypanosomatids its use is, as yet, scanty. RNA and DNA aptamers, developed by the SELEX process (Systematic Evolution of Ligands by Exponential Enrichment), were described over two decades ago and since then contributed to a large number of structured nucleic acids for diagnostic or therapeutic purposes or for the understanding of the cell biology. Similarly to the phage display technique scarce use of the SELEX process has been used in the probing of parasite–host interaction. In this review, an overall survey on the use of both phage display and aptamer technologies in different pathogenic organisms will be discussed. Using these techniques, recent results on the interaction of Trypanosoma cruzi with the host will be highlighted focusing on members of the 85 kDa protein family, a subset of the gp85/TS superfamily.

Rapid isolation of single-chain antibodies from a human synthetic phage display library for detection of Bacillus thuringiensis (Bt) Cry1B toxin

Single chain variable fragment antibody (scFv) is capable of binding its target antigens and is one of the most popular recombinant antibodies format for many applications. In this study, a large human synthetic phage displayed library (Tomlinson J) was employed to generate scFvs against Cry1B toxin by affinity panning. After four rounds of panning, six monoclonal phage particles capable of binding with the Cry1B were isolated, sequenced and characterized by Enzyme-Linked Immunosorbent Assay (ELISA). Two of the identified novel anti-Cry1B scFvs, namely H9 and B12, were expressed in Escherichia coli HB2151 and purified by Ni metal ion affinity chromatography. Sodium dodecyl sulfate polyacrylamine gel electrophoresis (SDS-PAGE) indicated that the relative molecular mass of scFv was estimated at 30 kDa. The purified scFv-H9 was used to develop an indirect competitive enzyme-linked immunosorbent assay (ic-ELISA) for Cry1B toxin. The linear range of detection for standards in this ic-ELISA was approximately 0.19-1.1 μg mL⁻¹ and 50% inhibition of control (IC₅₀) was 0.84 μg mL⁻¹ for Cry1B. The affinity of scfv-H9 was (1.95±0.12) × 10⁷ M⁻¹ and showed cross-reactivity with Cry1Ab toxin and Cry1Ac toxin (8.53% and 7.58%, respectively), higher cross-reactivity (12.8%) with Cry1C toxin. The average recoveries of Cry1B toxin from spiked leaf and rice samples were in the range 89.5-96.4%, and 88.5-95.6%, respectively, with a coefficient of variation (C.V) less than 6.0%. These results showed promising applications of scfv-H9 for detecting Cry1B toxin in agricultural and environmental samples.

Distinct immunoregulatory properties of macrophage migration inhibitory factors encoded by Eimeria parasites and their chicken host

Macrophage migration inhibitory factor (MIF) is a proinflammatory cytokine that plays an important role in host defense against a variety of microorganisms including protozoan parasites. Interestingly, some microbial pathogens also express a MIF-like protein, although its role in disease pathogenesis is not well understood. The aim of this study was to compare an Eimeria-encoded MIF (E.MIF) protein with chicken MIF (C.MIF) on the basis of their structural, immunological, and biological properties. E.MIF and C.MIF proteins, each with a glutathione S-transferase epitope tag, were expressed in Escherichia coli or COS-7 cells and purified by glutathione affinity chromatography. Rabbit antisera against the purified proteins demonstrated their mutual immunological cross-reactivity on Western blots, and immunolocalized intracellular native E.MIF to the Eimeria schizont, merozoite, and oocyst life cycle stages. HD11 chicken macrophages treated in vitro with C.MIF recombinant protein expressed increased levels of transcripts encoding interleukin-6 (IL-6), IL-17, and tumor necrosis factor superfamily member 15 (TNFSF15), but decreased levels of IL-8 transcripts, compared with cells treated with the PBS control; similar treatment with E.MIF only down-regulated IL-8 transcripts. Unlike recombinant E.MIF, C.MIF exhibited in vitro chemotactic activity for HD11 cells. Conversely, E.MIF, but not C.MIF, enhanced protection against experimental Eimeria infection, compared with the PBS control. These studies provide evidence for overlapping structural and antigenic properties, but distinct immunoregulatory roles, of E.MIF and C.MIF.