Passive transfer of mucosal antibody to Streptococcus equi in the foal

Tumor necrosis factor-α is transferred to equine neonates via colostrum but is not associated with their health status

We followed the hypothesis that equine neonates with reduced transfer of tumor necrosis factor-α (TNFα) are at increased risk of neonatal infection. We investigated TNFα concentrations in colostrum of healthy mares and blood of their neonates in a non-hospitalized population of Warmblood mares where delivery, neonatal adaptation and health was closely monitored by veterinarians. Concentration of TNFα and IgG was determined in colostrum respective milk and in neonatal blood collected immediately after delivery and 18 h thereafter in 97 foals that were assigned to groups failure of passive transfer (FPT; n = 31) and control (CON; n = 66) based on serum IgG concentration at 18 h of age. Foal health was assessed repeatedly during the first 24 h of life. Statistical analysis was done with p < 0.05 indicating significance. There were no significant differences between foal groups FPT and CON regarding age and parity of dams, gestation length (FPT 343 ± 10, CON 340 ± 8 days) and foal sex. Concentrations of TNFα in colostrum at birth and in foals at 18 h varied but did not differ between groups (colostrum FPT 6.1 ± 9.1, CON 9.9 ± 31.5 ng/ml; foal FPT 2.3 ± 5.9, CON 2.4 ± 5.3 ng/ml; n.s.). There was an increase in the mean serum TNFα concentration until 18 h in foals (n.s. between groups). Results of the present study confirm previous findings of TNFα transfer from the mare to the neonate via colostrum but do not suggest that transfer of TNFα via colostrum is important for protection of the neonate against infectious diseases.

Streptococcus equi Subspecies equi

Strangles, caused by the bacteria Streptococcus equi subsp equi, is a highly contagious disease of equids classically characterized by a high fever and enlarged lymph nodes of the head. Diagnostic sampling depends on the stage of the disease. The goal of treating strangles is to control transmission and to eliminate infection while providing future host immunity. Daily temperature checking and isolation of febrile horses is the key to controlling outbreaks. Eradication of this disease will not be possible until S equi carriers are eliminated from the equine population.

A pilot study to investigate the measurement of immunoglobulin A in Welsh Cob and Welsh Pony foals' faeces and their dam's milk

Aims: To determine if an ELISA for measurement of IgA in equine serum could be used to measure concentrations of IgA in foal faeces and to determine correlations with concentrations in the milk of the dam.Methods: Faeces from 20 Welsh Cob and Welsh Pony foals and milk from their dams were collected within 12 hours (Day 0) and at 6 days after parturition (Day 6). On Day 6, faeces could not be collected from 2/20 foals, and milk samples could not be collected from 3/20 mares. An equine IgA ELISA validated for serum and plasma was used to measure concentrations of IgA in all samples in triplicate. The precision of the assay for each sample type was determined using modified CV.Results: IgA was not detectable in 7/20 Day 0 faecal samples and in 2/18 Day 6 faecal samples. For samples with detectable IgA, the mean modified CV was 10.5 (95% CI = 6.0-15.0)% for Day 0 faecal samples, and was 6.8 (95% CI = 4.3-9.4)% for Day 6 faecal samples. Median concentrations of IgA in faeces on Day 0 were lower than concentrations on Day 6 (0.7 mg/g vs. 37 mg/g dry matter; p = 0.003). Concentrations of IgA in milk and faeces on Day 6 were statistically correlated (r = 0.59; p = 0.006).Conclusions and clinical relevance: The IgA ELISA showed acceptable precision when used to estimate concentrations of IgA in foal faeces during the first week of life, but IgA could not be detected in 37% of meconium samples collected on Day 0. This assay may be useful for investigation of the role of maternal milk IgA in the gastrointestinal tract of neonatal foals, but further assessment of both accuracy and precision of the ELISA is required.

Decreased Clinical Severity of Strangles in Weanlings Associated with Restricted Seroconversion to Optimized Streptococcus equi ssp equi Assays

Background

Streptococcus equi ssp. equi causes characteristic clinical signs that are most severe in young horses, including fever, purulent nasal discharge, and lymph node abscessation in the head region.

Hypothesis/Objectives

Clinical, serologic, and microbiologic factors related to unexpectedly mild disease severity in a natural outbreak of strangles in immunologically naïve weanlings were investigated.

Animals

One‐hundred and twelve warmblood weanlings.

Methods

Prospective longitudinal observational study of a natural outbreak of strangles. The entire cohort was examined at the peak of the outbreak by deep nasal swabs for culture and quantitative PCR (qPCR) for the presence of S. equi and clinically and serologically in a sequential manner by an optimized ELISA from the index case throughout the outbreak until resolution. Descriptive statistics were calculated and comparisons made using a nondirectional Wilcoxon signed‐rank test.

Results

Outbreak morbidity was 53%, with 9 of 14 horses culture positive and 26 of 53 horses qPCR positive for S. equi lacking clinical signs characteristic of strangles. By resolution, 91 of 112 had seroconverted to Antigen A by ELISA but seroconversion to antigen C (part of the SeM protein) was minimal. Sequencing of the isolates detected no alterations in the SeM protein, but identified a 61 bp deletion in the gene SEQ_0402.

Conclusions and Clinical Importance

Absence of clinical signs alone in naïve horses may be an insufficient criterion to release horses from strangles quarantine measures. Restricted seroconversion to antigen C may have been associated with decreased clinical severity. The role of a minor gene deletion in SEQ_0402 in the virulence of S. equi warrants further investigation.

Cytokine levels in colostrum and in foals' serum pre- and post-suckling

The purpose of this study is to investigate the presence of IL-4, IL-8, IL-13 and IFN-γ in equine colostrum and in foals' serum. Samples were obtained from 14 mares and their healthy foals. Soon after parturition, 10ml of colostrum was collected, filtered, centrifuged and frozen until assayed. Blood samples were obtained from each foal at birth (TO) and again after 24h (T24), after which they were frozen until assayed. Serum IgG was measured at 24h of age with an immunoturbidimetric quantitative method. Cytokine concentration was determined using commercially available ELISA tests. Statistical analyses revealed a significant difference in serum concentration of IL-4 at T0 and at T24 (p<0.05) and a significant correlation between the serum IL-4 at T24 and colostral IL-4. These results suggest the absorption of IL-4 from colostrum. The presence of IL-8 in the pre-suckle foal's serum may be due to an endogenous production. With the exception of two samples, there was no IL-13 detected in the foals' serum at birth and remained undetectable in 8/14 samples after 24h. This cytokine was also undetectable in four colostrum samples, where its concentration showed a wide range and a high standard deviation. IFN-γ was present in both the colostrum and in the foals serum at birth.

Immunogenicity of an electron beam inactivated Rhodococcus equi vaccine in neonatal foals

Rhodococcus equi is an important pathogen of foals that causes severe pneumonia. To date, there is no licensed vaccine effective against R. equi pneumonia of foals. The objectives of our study were to develop an electron beam (eBeam) inactivated vaccine against R. equi and evaluate its immunogenicity. A dose of eBeam irradiation that inactivated replication of R. equi while maintaining outer cell wall integrity was identified. Enteral administration of eBeam inactivated R. equi increased interferon-γ production by peripheral blood mononuclear cells in response to stimulation with virulent R. equi and generated naso-pharyngeal R. equi-specific IgA in newborn foals. Our results indicate that eBeam irradiated R. equi administered enterally produce cell-mediated and upper respiratory mucosal immune responses, in the face of passively transferred maternal antibodies, similar to those produced in response to enteral administration of live organisms (a strategy which previously has been documented to protect foals against intrabronchial infection with virulent R. equi). No evidence of adverse effects was noted among vaccinated foals.

Cloning, expression and characterization of SeM protein of Streptococcus equi subsp. equi and evaluation of its use as antigen in an indirect ELISA

Strangles is an economically important horse disease caused by Streptococcus equi subsp. equi. The diagnosis can be confirmed either directly by bacterial isolation and PCR or by ELISA, which is an indirect method based on the detection of serum antibodies. The aim of this study was to clone, express and characterize the SeM protein of Streptococcus equi subsp. equi, evaluate its use as antigen in indirect ELISA and determine its performance to distinguish sera of negative, vaccinated and positive animals. This was initially performed by cloning the gene encoding the SeM protein and its expression in Escherichia coli. Subsequently, the protein produced was characterized and used as antigen in ELISA. Serum samples for evaluation were taken from 40 negative foals, 46 horses vaccinated with a commercial vaccine against strangles and 46 horses diagnosed with the disease. The test showed high specificity and sensitivity, allowing discrimination between negative and positive, positive and vaccinated animals, and vaccinated animals and negative sera. Thus, it was concluded that the protein produced rSeM, which can be used as antigen for disease diagnosis, and the described ELISA might be helpful to evaluate the immune status of the herd.

Decreasing traits of fecal immunoglobulin A in neonatal and weaning piglets

The concentration of fecal secretory immunoglobulin A (sIgA) in neonate and weaning piglets was measured daily from 1 day after birth to 50 days of age. The concentration of fecal sIgA started from the level of 10(4) microg/g wet feces 1 day after birth and then increased to a maximal value of up to 10(5) microg/g within a few days of birth. The values constantly declined to between 10(1) and 10(2) microg/g for the next 10 days and were relatively constant until weaning. The level of sIgA in the feces remained very low until at least 50 days of age. The vulnerability of pre- or post-weaning piglets can be explained, at least in part, by this low level of sIgA in the intestine.

A common theme in interaction of bacterial immunoglobulin-binding proteins with immunoglobulins illustrated in the equine system

The M protein of Streptococcus equi subsp. equi known as fibrinogen-binding protein (FgBP) is a cell wall-associated protein with antiphagocytic activity that binds IgG. Recombinant versions of the seven equine IgG subclasses were used to investigate the subclass specificity of FgBP. FgBP bound predominantly to equine IgG4 and IgG7, with little or no binding to the other subclasses. Competitive binding experiments revealed that FgBP could inhibit the binding of staphylococcal protein A and streptococcal protein G to both IgG4 and IgG7, implicating the Fc interdomain region in binding to FgBP. To identify which of the two IgG Fc domains contributed to the interaction with FgBP, we tested two human IgG1/IgA1 domain swap mutants and found that both domains are required for full binding, with the CH3 domain playing a critical role. The binding site for FgBP was further localized using recombinant equine IgG7 antibodies with single or double point mutations to residues lying at the CH2-CH3 interface. We found that interaction of FgBP with equine IgG4 and IgG7 was able to disrupt C1q binding and antibody-mediated activation of the classical complement pathway, demonstrating an effective means by which S. equi may evade the immune response. The mode of interaction of FgBP with IgG fits a common theme for bacterial Ig-binding proteins. Remarkably, for those interactions studied in detail, it emerges that all the Ig-binding proteins target the CH2-CH3 domain interface, regardless of specificity for IgG or IgA, streptococcal or staphylococcal origin, or host species (equine or human).

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.

Occurrence of IgE in foals: Evidence for transfer of maternal IgE by the colostrum and late onset of endogenous IgE production in the horse

IgE is the key antibody involved in type I allergies. Allergen mediated crosslinking of IgE bound to high affinity Fcepsilon-receptors on mast cells and basophils stimulates cellular degranulation and release of inflammatory mediators and cytokines. In this report, we demonstrate that IgE antibodies can be transferred from the mother to offspring in horses via the colostrum. We found a clear correlation between the IgE concentration in colostrum and the total IgE concentration in foal sera on day 2 after birth (r(sp)=0.83). Maternal IgE was detected in foal sera by ELISA and on peripheral blood leukocytes of foals by flow cytometry. Both serum and cell membrane-bound IgE were undetectable in newborn foals before colostrum uptake and peaked on days 2-5 after birth. Cell-bound IgE became undetectable at 2 months after birth. Serum IgE disappeared from the circulation within the first 3-4 months of age. These kinetics suggest that the IgE antibodies which are detectable in foals during the first 4 months after birth are of maternal origin only. The endogenous IgE production was found to begin at 9-11 months of age, when IgE could be detected on peripheral blood leukocytes and in foal sera again. After 18 months of life, the total IgE concentrations in foal sera were comparable to those detected in their dams. The late onset of endogenous IgE production offers an explanation for observations that IgE mediated allergies are generally not observed in horses before puberty. The roles of the passively transferred maternal IgE in newborn foals are not yet known, but could be manifold, ranging from passive immunity and induction of immunoregulatory functions to determinative influences of maternal IgE on the antibody repertoire in the offspring.

Immunoglobulins and immunoglobulin genes of the horse

Antibodies of the horse were studied intensively by many notable immunologists throughout the past century until the early 1970's. After a large gap of interest in horse immunology, additional basic studies on horse immunoglobulin genes performed during the past 10 years have resulted in new insights into the equine humoral immune system. These include the characterization of the immunoglobulin lambda and kappa light chain genes, the immunoglobulin heavy chain constant (IGHC) gene regions, and initial studies regarding the heavy chain variable genes. Horses express predominately lambda light chains and seem to have a relatively restricted germline repertoire of both lambda and kappa chain variable genes. The IGHC region contains eleven constant heavy chain genes, seven of which are gamma heavy chain genes. It is suggested that all seven genes encoding IgG isotypes are expressed and have distinct functions in equine immune responses.

Pneumonia in weanlings

Lower respiratory tract infection is common in weanling- and suckling-aged animals. Increased susceptibility to disease in this age group can result from a delay in the establishment of a competent immune system and environmental factors, such as overcrowding, shipping, and sales. S zooepidemicus and R equi are the two most common bacterial isolates. S equi is primarily a disease of the lymph nodes and upper respiratory tract. Viral agents can compromise the natural defense mechanisms of the respiratory tract, resulting in secondary bacterial infections. The acute respiratory distress syndrome is one of unknown etiology and high mortality.

Passive transfer of maternal immunoglobulin isotype antibodies against tetanus and influenza and their effect on the response of foals to vaccination

Influenza and tetanus-specific antibodies of the IgG sub-isotypes are posively transferred to foals via colostrum and inhibit their response to inactivated influenza vaccines and tetanus toxoid. High titres of influenza antibodies of IgGa and IgGb subisotypes and tetanus antibodies of the IgGa, IgGb and IgG(T) subisotypes were detected in postsucking serum samples collected from foals born to mares that had received booster doses of multicomponent vaccines during the last 2 months of gestation. Thereafter, titres declined in an exponential manner but were still detectable in all foals at age 26 weeks, regardless of whether they had been vaccinated prior to age 26 weeks. Mean +/- s.e. half-life of decline of influenza IgGa antibodies (27.0 +/- 2.3 days) was significantly shorter than that of influenza IgGb antibodies (39.1 +/- 2.7 days; P<0.005). Tetanus IgGa and IgGb antibodies declined with half-lives of 28.8 +/- 3.0 and 34.8 +/- 5.1 days, respectively. Titres of tetanus IgG(T) antibodies were substantially higher than those of influenza IgG(T) antibodies in postsucking samples and remained so through age 26 weeks, declining with a half-life of approximately 35 days. Postsucking titres of tetanus and influenza antibodies of the IgA isotype were low and declined rapidly to undetectable levels. Yearlings showed significant increases in titre of influenza IgGa, IgGb and IgG(T) subisotype antibodies but no increase in influenza IgA antibodies in response to 2 doses of multicomponent vaccines containing tetanus toxoid and inactivated influenza A-1 and A-2 antigens. Yearlings also showed strong tetanus IgGa, IgGb and IgG(T) subisotype responses to one dose of vaccine and a substantial further rise in titre in response to administration of a second dose 3 weeks later, but failed to show an increase in titre of tetanus IgA antibodies. The influenza and tetanus IgGa, IgGb and IgG(T) subisotype responses of 6-month-old foals to vaccination followed the same pattern as those shown by yearlings but titres were generally lower. In contrast, 3-month-old foals failed to show increases in titre of either influenza or tetanus IgG subisotypes in response to 2 doses of vaccine and generally needed 1-3 additional booster doses of vaccine to achieve titres similar to those achieved by yearlings after 2 doses. Based on the finding that maternal antibodies exert a significant inhibitory effect on the response of foals to tetanus toxoid and inactivated influenza antigens, it is recommended that primary immunisation of foals born to vaccinated mares should not commence before age 6 months.

Investigations towards an efficacious and safe strangles vaccine: submucosal vaccination with a live attenuated Streptococcus equi

As part of a search for a safe and efficacious strangles vaccine, several different vaccines and different vaccination routes were tested in foals. The degree of protection was evaluated after an intranasal challenge with virulent Streptococcus equi by clinical, postmortem and bacteriological examinations. Inactivated vaccines containing either native purified M-protein (500 microg per dose) or whole S equi cells (10(10) cells per dose) administered at least twice intramuscularly at intervals of four weeks, did not protect against challenge. Different live attenuated S equi mutants administered at least twice at intervals of four weeks by the intranasal route were either safe but not protective or caused strangles. In contrast, a live attenuated deletion mutant administered intramuscularly, induced complete protection but also induced unacceptable local reactions at the site of vaccination. Submucosal vaccination in the inner side of the upper lip with the live attenuated mutant at > or =10(8) colony-forming units per dose, appeared to be safe and efficacious in foals as young as four months of age. The submucosal vaccinations caused small transient swellings that resolved completely within two weeks, and postmortem no vaccine remnants or other abnormalities were found at the site of vaccination.

Immunoglobulin isotypes in sera and nasal mucosal secretions and their neonatal transfer and distribution in horses

OBJECTIVE

To determine concentrations of IgA and IgG subclasses in serum, colostrum, milk, and nasal wash samples of adult horses and foals.

ANIMALS

Seven 2-year-old Welsh ponies, 27 adult mixed-breed horses, and 5 Quarter Horse mares and their foals.

PROCEDURE

Serum was obtained from ponies and adult horses. Colostrum and milk were obtained from mares and serum and nasal wash samples from their foals immediately after parturition and on days 1, 7, 14, 28, 42, and 63. Nasal wash samples were also obtained from 23 adult horses. Concentrations of immunoglobulins were determined by use of inhibition ELISA. To determine transfer of maternal isotypes to foals, concentrations in colostrum and milk were compared with those in foal serum. Serum half-lives of isotypes in foals were also determined.

RESULTS

IgGb was the most abundant isotype in serum and colostrum from adult horses, whereas IgA was the predominant isotype in milk. The major isotype in nasal secretions of adult horses and foals > or = 28 days old was IgA, but IgGa and IgGb were the major isotypes in nasal secretions of foals < or = 14 days old. Serum half lives of IgGa, IgGb, IgG(T), and IgA in foals were 176, 32, 21, and 3.4 days, respectively.

CONCLUSIONS AND CLINICAL RELEVANCE

The early immunoglobulin repertoire of neonatal foals comprised IgGa, IgG(T), and IgA; endogenous synthesis of IgGb could not be detected until 63 days after birth. The restricted repertoire of immunoglobulins in foals may influence humoral immune responses to vaccination.

Strangles

The etiology, epizootiology, pathogenesis, and clinical presentation of strangles are described. Streptococcus equi, the causative organism, is highly host-adapted to Equidae and shows no antigenic variation. Protective immunity apparently is mediated by a combination of serum opsonic and nasopharyngeal mucosal humoral responses. Vaccines based on M protein or inactivated bacterial suspensions may reduce the clinical attack rate by 50%, a level of protection much lower than that produced during recovery from strangles.

Studies of antigenic components in acid extracts of group C streptococci with special reference to Streptococcus equi

For the determination of a species-specific antigen of Streptococcus (S.) equi, acid extracts of group C streptococcal strains from horses (S. equi, S. zooepidemicus, S. equisimilis) were investigated using polyacrylamide gel electrophoresis and the immunoblotting technique. Using sera of horses suffering from strangles as well as sera from horses with respiratory infection of unknown etiology, Western blotting yielded more or less multiple banding reactions with bands in the 70, 54, 42, 40, and 31-28 kd molecular weight ranges against extracts of all of the 3 different bacterial species. However, an antigen found in this study at 18-16 kd which was highly sensitive to trypsin, proved to react specifically and regularly only with the serum of horses exposed to S. equi. The specificity of the reaction was assured by antisera of rabbits and horses vaccinated against S. equi, S. zooepidemicus or S. equisimilis, respectively, and by cross absorption of a serum originating from a mare recovered from strangles with Lancefield group C and group G streptococci as well as a strain of S. pyogenes. According to Western blot results on 180 serum pairs from horses with clinical signs of respiratory infection, 15.6% of which gave positive reactions, the 18-16 kd antigen appears as a marker suitable for qualitative testing of horse sera for antibodies to S. equi.

Molecular analysis of the M protein of Streptococcus equi and cloning and expression of the M protein gene in Escherichia coli

A Streptococcus equi gene bank was constructed in the bacteriophage lambda gt11 cloning vector, and hybrid phage plaques were screened with S. equi M protein antiserum. A hybrid phage expressing the S. equi M protein (lambda gt11/SEM7) was identified and lysogenized into Escherichia coli Y1089. The cloned M protein appeared in immunoblots as three polypeptides with relative molecular weights of 58,000, 53,000, and 50,000. When reacted with S. equi M protein antiserum in an agar double-diffusion assay, the cloned M protein formed a line of identity with a protein in an acid extract of S. equi. Furthermore, lambda gt11/SEM7 protein inhibited opsonization of S. equi by antiserum to S. equi M protein. In addition, the recombinant protein expressed determinants of the antigen in the immune complexes of purpura hemorrhagica. Native M protein obtained from S. equi and recombinant M protein showed very similar molecular weight distributions on immunoblots, appearing as multiple closely spaced bands with molecular weights ranging from 52,000 to 60,000. Antisera prepared separately against each of the acid-extracted polypeptides shown to be important in serum bactericidal responses (molecular weight, 29,000) and nasopharyngeal local antibody responses (molecular weights, 41,000 and 46,000) of the horse each reacted with all three polypeptides in an acid extract. Moreover, antisera against protoplasts and against recombinant M protein of S. equi also reacted with these polypeptides. These results suggest that the entire M protein molecule of S. equi is present in these preparations and that the fragments in acid extracts carry overlapping segments.