Purification of horse immunoglobulin isotypes based on differential elution properties of isotypes from protein A and protein G columns

Purification of IgG against ribonucleoprotein by a homemade immunoaffinity chromatography column for rabies diagnosis

Polyclonal or monoclonal antibodies against rabies virus ribonucleoprotein (RNP) conjugated to fluorescein isothiocyanate (FITC) have been employed for Rabies virus (RABV) antigen detection by the direct fluorescent antibody test (DFA). To date, these biomolecules have been purified by traditional methods such as precipitation by ammonium sulfate or ion exchange chromatography followed by ammonium sulfate precipitation, which allows only for partial detection of the protein of interest. In this study, we aimed to purify anti-RNP polyclonal horse IgG antibodies by cation-exchange chromatography in combination with a homemade immunoaffinity chromatography on RNP immobilized (RNP-IAC). Furthermore, to evaluate the accuracy of the prepared anti-RNP IgG fluorescent antibody in diagnostic purposes, DFA was applied for RABV antigen detection in suspected brain samples of different animal species. The combination of these two techniques made it possible to obtain antibodies with high selectivity and purity. Compared with the performance of the traditional method, anti-RNP IgG antibodies purified by RNP-IAC can be obtained from a smaller volume of hyperimmune serum and with greater avidity. Furthermore, the results obtained by DFA analyses revealed that the prepared anti-RNP IgG fluorescent antibody achieved 100% diagnostic specificity and sensitivity for RABV antigen detection. Thus, two-technique chromatographic, including RNP-IAC technology could be appropriate methods for the purification of polyclonal anti-RNP IgG for the use as a diagnostic reagent for rabies.

PNAG-specific equine IgG1 mediates significantly greater opsonization and killing of Prescottella equi (formerly Rhodococcus equi) than does IgG4/7

Prescottella equi (formerly Rhodococcus equi) is a facultative intracellular bacterial pathogen that causes severe pneumonia in foals 1-6 months of age, whereas adult horses are highly resistant to infection. We have shown that vaccinating pregnant mares against the conserved surface polysaccharide capsule, β-1 → 6-linked poly-N-acetyl glucosamine (PNAG), elicits opsonic killing antibody that transfers via colostrum to foals and protects them against experimental infection with virulent. R. equi. We hypothesized that equine IgG1 might be more important than IgG4/7 for mediating protection against R. equi infection in foals. To test this hypothesis, we compared complement component 1 (C1) deposition and polymorphonuclear cell-mediated opsonophagocytic killing (OPK) mediated by IgG1 or IgG4/7 enriched from either PNAG hyperimmune plasma (HIP) or standard plasma. Subclasses IgG1 and IgG4/7 from PNAG HIP and standard plasma were precipitated onto a diethylaminoethyl ion exchange column, then further enriched using a protein G Sepharose column. We determined C1 deposition by enzyme-linked immunosorbent assay (ELISA) and estimated OPK by quantitative microbiologic culture. Anti-PNAG IgG1 deposited significantly (P < 0.05) more C1 onto PNAG than did IgG4/7 from PNAG HIP or subclasses IgG1 and IgG4/7 from standard plasma. In addition, IgG1 from PNAG HIP mediated significantly (P < 0.05) greater OPK than IgG4/7 from PNAG HIP or IgG1 and IgG4/7 from standard plasma. Our findings indicate that anti-PNAG IgG1 is a correlate of protection against R. equi in foals, which has important implications for understanding the immunopathogenesis of R. equi pneumonia, and as a tool for assessing vaccine efficacy and effectiveness when challenge is not feasible.

Secretory immunoglobulin A and immunoglobulin G in horse saliva

This study aimed to increase the knowledge on salivary antibodies in the horse since these constitute an important part of the immune defence of the oral cavity. For that purpose assays to detect horse immunoglobulin A (IgA) including secretory IgA (SIgA) were set up and the molecular weights of different components of the horse IgA system were estimated. Moreover, samples from 51 clinically healthy horses were tested for total SIgA and IgG amounts in saliva and relative IgG3/5 (IgG(T)) and IgG4/7 (IgGb) content were tested in serum and saliva. Results showed a mean concentration of 74μg SIgA/ml horse saliva and that there was a large inter-individual variation in salivary SIgA concentration. For total IgG the mean concentration was approx. 5 times lower than that of SIgA, i.e. 20μg IgG/ml saliva and the inter-individual variation was lower than that observed for SIgA. The saliva-serum ratio for IgG isotypes IgG3/5 and IgG4/7 was also assessed in the sampled horses and this analysis showed that the saliva-serum ratio of IgG4/7 was in general approximately 4 times higher than that of IgG3/5. The large inter-individual variation in salivary SIgA levels observed for the normal healthy horses in the present study emphasises the need for a large number of observations when studying this parameter especially in a clinical setting. Moreover, our results also indicated that some of the salivary IgG does not originate from serum but may be produced locally. Thus, these results provide novel insight, and a base for further research, into salivary antibody responses of horses.

The different effector function capabilities of the seven equine IgG subclasses have implications for vaccine strategies

Recombinant versions of the seven equine IgG subclasses were expressed in CHO cells. All assembled into intact immunoglobulins stabilised by disulphide bridges, although, reminiscent of human IgG4, a small proportion of equine IgG4 and IgG7 were held together by non-covalent bonds alone. All seven IgGs were N-glycosylated. In addition IgG3 appeared to be O-glycosylated and could bind the lectin jacalin. Staphylococcal protein A displayed weak binding for the equine IgGs in the order: IgG1 > IgG3 > IgG4 > IgG7 > IgG2 = IgG5 > IgG6. Streptococcal protein G bound strongly to IgG1, IgG4 and IgG7, moderately to IgG3, weakly to IgG2 and IgG6, and not at all to IgG5. Analysis of antibody effector functions revealed that IgG1, IgG3, IgG4, IgG5 and IgG7, but not IgG2 and IgG6, were able to elicit a strong respiratory burst from equine peripheral blood leukocytes, predicting that the former five IgG subclasses are able to interact with Fc receptors on effector cells. IgG1, IgG3, IgG4 and IgG7, but not IgG2, IgG5 and IgG6, were able to bind complement C1q and activate complement via the classical pathway. The differential effector function capabilities of the subclasses suggest that, for maximum efficacy, equine vaccine strategies should seek to elicit antibody responses of the IgG1, IgG3, IgG4, and IgG7 subclasses.

Vaccine potential of novel surface exposed and secreted proteins of Streptococcus equi

Streptococcus equi, a clonal descendent of an ancestral S. zooepidemicus, causes equine strangles, a highly contagious purulent lymphadenitis of the head and neck. The aim of this study was to evaluate as vaccine components novel surface exposed or secreted S. equi proteins identified in an expression gene library with sera from resistant horses. Six proteins expressed by S. equi CF32 but not by S. zooepidemicus 631 were used to vaccinate one group of eight ponies. A second pony group was immunized with five adhesin and other proteins encoded by genes of Linkage Gr 1. All ponies made strong serum antibody responses to each protein as measured by ELISA but none were resistant to subsequent comingling challenge with S. equi CF32. These results in combination with evidence that recovered horses rapidly clear intranasally inoculated S. equi and do not make detectable serum antibody responses to its surface proteins suggest that acquired immune-mediated tonsillar clearance and not serum antibody must be stimulated by an effective strangles vaccine.

Effect of pepsin digestion on the antivenom activity of equine immunoglobulins

Enzyme digestion of animal-derived sera followed by antibody purification is a classical process used to prepare snake antivenoms worldwide. In this work, we have studied the effect of the harsh conditions prevailing during the digestion step on the activity of the final product, F(ab')(2). To this purpose, the recovery of the activity of anti-Bothrops hyperimmune equine plasma was determined after pepsin digestion under different sets of processing conditions. The balance between pH level and reaction time was found to be critical, reflecting a compromise between complete cleavage of immunoglobulins and strong denaturation of the F(ab')(2) fragments. For pH in the range 2.8-3.2, 30-65% of the initial activity was lost depending mainly on the processing time, as determined by a competition ELISA technique. Pepsin digestion was also carried out with purified immunoglobulins from the same plasma. SDS PAGE run on the digested immunoglobulins allowed us to verify that the lightest isotypes were more resistant to digestion than the heavier ones. In conclusion, for equine F(ab')(2) antivenom production, it seems convenient to carry out digestion at pH values sufficiently low to ensure that total IgG breakdown is achieved in the shortest time compatible with precise operation in the production scale.

Thiophilic paramagnetic particles as a batch separation medium for the purification of antibodies from various source materials

A preparation of thiophilic agarose-based paramagnetic particles (T-Gel) has been developed with physical characteristics (particle size and particle density) that facilitate its use as a batch separation medium suitable for the large-scale purification and isolation of immunoglobulins. The medium was used to extract immunoglobulins from a wide range of starting materials, including sera, ascites fluid, tissue culture medium, and whole blood. None of these starting materials required pretreatment such as clarification by centrifugation or filtration prior to antibody extraction. The antibody purity obtained using T-Gel compared well with that obtained using protein A agarose column chromatography. Yields were approximately 30 mg of immunoglobulins per milliliter of T-Gel, and little was required in the way of specialist equipment. The method is uncomplicated and involves a roll mix extraction overnight, followed by magnetic separation to facilitate supernatant removal and subsequent washing of the particles. Elution of bound antibodies was carried out at neutral pH to yield a concentration of immunoglobulins that was approximately 7 mg/ml. The method was found to be applicable to antibody purification from the blood serum of seven different mammalian species and for all immunoglobulin classes.

Hydrolysis of DNA by 17 snake venoms

DNA hydrolysis caused by venoms of 17 species of snakes was studied by different methodologies. Endonucleolytic activity was tested by incubation of the venoms with the plasmid pBluescript and subsequent visualization of the electrophoretic patterns in 1% agarose gels stained with ethidium bromide. DNA was sequentially degraded, from supercoiled to opened circle, to linear form, in a concentration dependent manner. The highest hydrolytic activity was observed in Bothrops (B.) neuwiedii and Naja (N.) siamensis venoms. Exonucleolytic activity was analyzed on pBluescript digested with SmaI or EcoRI. All venoms caused complete hydrolysis after 2 h of incubation. SDS-PAGE analysis in gels containing calf thymus DNA showed that the hydrolytic bands were located at approximately 30 kDa. DNA degradation was studied by radial hydrolysis in 1% agarose gels containing calf thymus DNA plus ethidium bromide and visualized by UV light. Venom of B. neuwiedii showed the highest activity whereas those of B. ammodytoides and Ovophis okinavensis (P<0.05) showed the lowest activity. Antibodies against venom of B. neuwiedii or N. siamensis neutralized the DNAse activity of both venoms. In conclusion, venom from different snakes showed endo- and exonucleolytic activity on DNA. The inhibition of DNA hydrolysis by EDTA and heterologous antibodies suggests similarities in the structure of the venom components involved.