Characterisation of serum IgG(T) responses to potential diagnostic antigens for equine cyathostominosis.

Cyathostomins are ubiquitous parasitic nematodes of horses. These worms spend substantial periods as intestinal wall stage encysted larvae, which can comprise up to 90% of the total burden. Several million larvae have been reported in individuals. Emergence of these larvae from the gut wall can lead to life-threatening colitis. Faecal egg count tests, increasingly used by horse owners to inform anthelmintic treatments, do not correlate with the intra-host burden of cyathostomins; this represents a key gap in the diagnostic toolbox. Previously, a cyathostomin Gut Associated Larval Antigen was identified as a promising marker for the intra-host stages of infection. Here, cyathostomin Gut Associated Larval Antigen and an additional protein, Cyathostomin Immuno-diagnostic antigen, were investigated to examine their value in providing information on cyathostomin burden. ELISA analyses examined serum IgG(T) responses to recombinant proteins derived from individual cyathostomin species. Receiver Operator Characteristic curve analysis was performed on the ELISA data; proteins with the highest Area Under the Curve values were selected to test protein combinations to investigate which were the most informative in identifying the infection status of individuals. Three cocktail combinations were tested, comprising: (a) Cy-GALA proteins from two species and a Cy-CID protein from a third species (CT3), (b) Cy-GALA proteins from five species (CT5), and (c) all CT5 components, plus a Cy-CID protein from an additional species (CT6). The best predictive values for infection were obtained using CT3 and CT6, with similar values achieved for both. Proteins in CT3 are derived from the most commonly reported species, Cyathostomum catinatum, Cylicocyclus nassatus and Cylicostephanus longibursatus. This combination was selected for future development since it represents a more commercially viable format for a diagnostic test.

Interaction between anthelmintic treatment and vaccine responses in ponies naturally infected with cyathostomins.

Anthelmintics and vaccines are commonly given concurrently in routine equine management, but it is unknown to what extent an interaction between the two exists. Cyathostomins can modulate the local immune response by stimulating a type 2 helper T cell (Th2) response. In addition, anti-inflammatory effects of ivermectin have been found in rodent models. It is unknown whether these anti-inflammatory effects affect the acute phase response elicited by commonly used vaccines. This study evaluated how the acute phase inflammatory response, leukocyte expression of pro-inflammatory cytokines, and vaccine-specific titers induced by simultaneous injection of three vaccines (West Nile Virus, Equine Herpes Rhinopneumonitis, and Keyhole Limpet Hemocyanin) were modulated by concurrent administration of ivermectin or pyrantel pamoate in ponies naturally infected with cyathostomins. Mixed-breed yearling ponies were blocked by gender and fecal strongyle egg count, then randomly assigned to three treatment groups: ivermectin (n=8), pyrantel pamoate (n=8), and control (n=7). All ponies received vaccinations intramuscularly on days 0 and 29, and anthelmintics were administered on the same days. Whole blood, serum and plasma samples were collected one, three and 14 days after each vaccination. Samples were analyzed for concentrations of acute phase reactants (haptoglobin, serum amyloid A, fibrinogen and iron), mRNA expression levels of cytokines (interleukin (IL)-1ß, IL-4, IL-10, tumor necrosis factor (TNF)-α and interferon (IFN)-γ) in leukocytes, and vaccine-specific antibody titers. A marked acute-phase response was noted following both vaccinations. In contrast, the pattern of change in cytokine expression was less pronounced and more variable. Statistical differences were observed between groups for haptoglobin, fibrinogen, IL-1ß, IL-4, and IL-10, but differences were generally small and none of the vaccine titers were different between the groups. Taken together, the study found some signs of modulation of immunologic or inflammatory responses to the administered vaccines, when anthelmintics were administered concurrently, but these are unlikely to have practical implications for vaccination routines.

Estimation of genetic parameters for resistance to gastro-intestinal nematodes in pure blood Arabian horses.

Equine internal parasites, mostly cyathostomins, affect both horse welfare and performance. The appearance of anthelmintic-resistant parasites creates a pressing need for optimising drenching schemes. This optimization may be achieved by identifying genetic markers associated with host susceptibility to infection and then to drench carriers of these markers. The aim of our study was to characterise the genetics of horse resistance to strongyle infection by estimating heritability of this trait in an Arabian pure blood population. A population of 789 Arabian pure blood horses from the Michalów stud farm, Poland were measured for strongyle egg excretion twice a year, over 8 years. Low repeatability values were found for faecal egg counts. Our analyses showed that less than 10% of the observed variation for strongyle faecal egg counts in this population had a genetic origin. However, additional analyses highlighted an age-dependent increase in heritability which was 0.04 (±0.02) in young horses (up to 3 years of age) but 0.21 (±0.04) in older ones. These results suggest that a significant part of the inter-individual variation has a genetic origin. This paves the way to a genomic dissection of horse-nematode interactions which might provide predictive markers of susceptibility, allowing individualised drenching schemes.

The expression and activity of 5-LOX in the large intestine of horses harbouring encysted cyathostomin larvae.

Leukotrienes are products of the arachidonic acid metabolism and act as potent inflammatory mediators modulating the immune response and various physiological processes. This study evaluated the expression and activity of 5-lipoxygenase (5-LOX), the enzyme that catalyzes the first two steps in the biosynthesis of leukotrienes, in horses infected by larval cyathostomins. Tissue samples from dorsal and ventral colon, and from the cecum were collected from 16 horses slaughtered for human consumption. Samples were analyzed to estimate the burdens of encysted cyathostomin larvae and adult luminal stages, and then processed for the evaluation of biochemical parameters. No significant differences were found in the protein expression and enzymatic activity of 5-LOX between animals harbouring only adult parasites and negative horses. The protein expression and enzyme activity of 5-LOX were significantly higher in horses harbouring encysted larvae in comparison with horses free of encysted larvae. Although preliminary, these results indicate that 5-LOX is an important mediator in the course of horse cyathostominosis and further studies are warranted to unveil the possible role this enzyme plays in the pathogenesis of horse cyathostominosis, and its potential as a diagnostic marker.

Development of Strongylus vulgaris-specific serum antibodies in naturally infected foals.

Strongylus vulgaris is regarded as the most pathogenic helminth parasite infecting horses. Migrating larvae cause pronounced endarteritis and thrombosis in the cranial mesenteric artery and adjacent branches, and thromboembolism can lead to ischemia and infarction of large intestinal segments. A recently developed serum ELISA allows detection of S. vulgaris-specific antibodies during the six-month-long prepatent period. A population of horses has been maintained at the University of Kentucky without anthelmintic intervention since 1979, and S. vulgaris has been documented to be highly prevalent. In 2012, 12 foals were born in this population, and were studied during a 12-month period (March-March). Weekly serum samples were collected to monitor S. vulgaris specific antibodies with the ELISA. Nine colts underwent necropsy at different time points between 90 and 300 days of age. At necropsy, Strongylus spp. and Parascaris equorum were identified to species and stage and enumerated. Initial statistical findings indicate a significant interaction between foal age and ELISA results (p<0.042). All foals had initial evidence of S. vulgaris-directed maternal antibodies transferred in the colostrum, but then remained ELISA negative during their first three months of life. Foals born in February and March became ELISA positive at about 12 weeks of age, while those born in April and May went positive at about 15 and 21 weeks, respectively. Foal date of birth was significantly associated with ELISA results (p<0.0001). This could be explained by birth date-dependent differences in parasite exposure. One foal remained ELISA-negative throughout the course of 30 weeks during the study. A significant association was found between ELISA values and larval S. vulgaris burdens (p<0.0001) as well as a three-way interaction between S. vulgaris, S. edentatus, and P. equorum burdens (p<0.001). A plateau with a subsequent decline in ELISA values corresponded with S. vulgaris larvae leaving the bloodstream and migrating back to the intestine.

Isolation of potentially useful antigens from cyathostomin third-stage larvae by using a fast protein liquid chromatography one-step method.

Three major protein complexes (51, 29, and 15 kDa, named P1 to P3, respectively) were resolved by gel filtration of the excretory/secretory antigens collected from a mixture of horse cyathostomin third-stage larvae (L3s). The potential application for the detection of infected horses was assessed with an enzyme-linked immunosorbent assay (ELISA) by the comparison of the serological and copromicroscopical results. The value of the area under the receiver operating characteristic (ROC) curve was higher than 0.9 when the three peaks were used. Elevated values (>90%) for the sensitivity, specificity, and the positive-likelihood ratio were also observed for all the antigen complexes. A significant increment in the IgG antibody levels 4 weeks prior to the observation of eggs in the feces of weanlings naturally infected was recorded. Our results indicate that the evaluation of chemotherapy is possible by using immunoenzymatic probes and fast protein liquid chromatography (FPLC)-purified antigens. Data collected in the present investigation indicate that FPLC isolation offers a very helpful one-step method for collecting antigens with diagnostic potential to be employed in immunoenzymatic probes.

The effects of Strongylus vulgaris parasitism on eosinophil distribution and accumulation in equine large intestinal mucosa.

REASONS FOR PERFORMING STUDY: Eosinophilic granulocytes have been associated with parasite or immune-mediated diseases, but their functions in other disease processes remain unclear. Cause and timing of eosinophil migration into the equine gastrointestinal mucosa are also unknown. OBJECTIVE: To determine the effects of intestinal parasitism on eosinophils in equine large intestinal mucosa. METHODS: Large intestinal mucosal samples were collected from horses and ponies (n = 16) from the general veterinary hospital population, ponies (n = 3) raised in a parasite-free environment, ponies experimentally infected with 500 infective Strongylus vulgaris larvae and treated with a proprietary anthelmintic drug (n = 14), and a similar group of ponies (n = 7) that received no anthelmintic treatment. Total eosinophil counts and eosinophil distribution in the mucosa were determined by histological examination. A mixed model analysis was performed and appropriate Bonferroni adjusted P values used for each family of comparisons. P<0.05 was considered significant. RESULTS: There was no difference in large intestinal mucosal eosinophil counts and eosinophil distribution between ponies infected with S. vulgaris and those raised in a parasite-free environment. Experimental infection with S. vulgaris, with or without subsequent anthelmintic treatment, did not change eosinophil counts, and counts were similar to those for horses from the general population. CONCLUSIONS: Migration of eosinophils to the equine large intestinal mucosa appears to be independent of exposure to parasites. Large intestinal mucosal eosinophils may have more functions in addition to their role in defence against parasites.

The involvement of mast cells and mast cell proteinases in the intestinal response to equine cyathostomin infection.

Cyathostomins (Cyathostominae) are regarded as the most pathogenic equine nematode worldwide. These nematodes are difficult to control in equine populations due to emerging anthelmintic resistance and evasion of encysted larval cyathostomins to regular modern anthelmintics. Mast cells and their proteinases have been shown to play a role in the mammalian immune response to nematode infections. Involvement of mast cells and mast cell proteinases in the equine immune response to cyathostomin infection is proposed. A technique was established to perform immunohistochemical staining using polyclonal rabbit anti-equine mast cell proteinase-1 (eqMCP-1) and anti-equine tryptase on formalin-fixed large intestinal sections, from horses classified as cyathostomin positive and negative at the time of death based upon larval enumeration. Quantitative analysis of antibody labelled mast cells was used to detect mast cell proteinases in equine large intestinal sections positive and negative for cyathostomin larvae. This demonstrated an increase in equine tryptase labelled mucosal and submucosal mast cells in cyathostomin positive horses. This study has established an immunohistochemical technique to demonstrate mast cell proteinases in formalin-fixed large intestinal sections. This technique may be used to determine possible involvement of mast cells and their proteinases in the equine immune response to cyathostomin larvae. Further studies are required to define a specific role.

Small strongyle infection: consequences of larvicidal treatment of horses with fenbendazole and moxidectin.

The study was undertaken to evaluate adverse effects of larvicidal treatment in horses naturally infected with cyathostomins. Out of 24 ponies kept on pasture, four animals were housed in September and anthelmintically cured to serve as worm-free controls (group C-0). The others were housed in December. Eight animals each were treated 8 weeks later with 5 x 7.5mg/kg fenbendazole (FBZ) or 1 x 0.4 mg/kg moxidectin (MOX). Four animals remained untreated (group C-i). Two, 4, 6 and 14 days after the end of treatment two animals of each of the treated groups were necropsied together with group C-0 and C-i animals. Infected animals before treatment showed weight loss, eosinophilia, increased plasma protein and globulin contents. Treatment was followed by weight gain and temporal plasma protein and globulin increase. Proportions of CD4+ and CD8+ T lymphocytes in the peripheral blood did not differ between the groups before treatment but dropped significantly temporally after FBZ treatment. Group C-0 was worm-free at necropsy. Group C-i animals contained variable numbers of luminal and tissue cyathostomins. Histological sections showed larval stages in the lamina propria und submucosa surrounded by macrophages. Either treatment was effective against luminal parasites and reduced the number of larvae in the bowel wall beginning 4-6 days after FBZ and 6-14 days after MOX treatment. Histologically, as a first reaction after FBZ application T lymphocytes accumulated around morphologically intact L4 in the submucosa. Subsequently T lymphocytes associated with eosinophils infiltrated the submucosa. Parasites became enclosed by granulomas with eosinophils adhering to and invading the larvae which started to disintegrate on day 4. Later on, particularly on day 14 inflammation extended into the mucosa and was frequently associated with ulcerations. Third stage larvae in general and L4 in the lamina propria, however, seemed not to be affected until day 14 and even then, parasites did usually not generate extensive inflammation. After MOX treatment severe morphologically detectable alterations of tissue larvae could not be observed earlier than day 14. Different from FBZ treatment, larvae disintegrated and were obviously resorbed without causing severe inflammation in the gut wall. In conclusion treatment with either drug was efficacious against tissue larvae of cyathostomins but there may be different clinical consequences: in contrast to MOX effects, killing of larvae due to FBZ was associated with severe tissue damage, which clinically may correspond to reactions caused by synchronous mass emergence of fourth stage larvae, i.e., may mimic larval cyathostominosis.

Clinical signs and hematologic, cytokine, and plasma nitric oxide alterations in response to Strongylus vulgaris infection in helminth-naïve ponies.

The objective of this study was to determine the effect of infection with Strongylus vulgaris on serum cytokines and plasma nitric oxide (NO) concentrations in helminth-naive ponies. Group 1 (n = 21) was given 500 S. vulgaris L3 larvae and group 2 (n = 7) received a saline control. Ponies were monitored daily for clinical signs, and blood was collected for complete blood cell counts and serum cytokines (TNF, IL-1, IL-6) quantification. Group 1 ponies were depressed, anorexic, and febrile for variable periods of time. Plasma NO was increased on day 21 in group 1 and on days 9 and 21 in group 2. Significant increases in total white blood cell counts, fibrinogen, and plasma protein concentrations in group 1 were found. Significant decreases in red blood cell counts and packed cell volume were also noted in group 1. There were no differences in serum cytokines across time in either group of ponies. Despite the lack of proinflammatory cytokine induction with the apparent inflammatory response to S. vulgaris there is evidence of a potential role of NO.

Mast cell and eosinophil mucosal responses in the large intestine of horses naturally infected with cyathostomes.

From December 1998 to March 2000, caecum and ascendant colon of 42 horses naturally infected with cyathostomes were collected during routine necropsy or from a local slaughterhouse. Changes in the numbers of mucosal and submucosal mast cells (MMC and SMMC), intraepithelial, mucosal and submucosal eosinophils (IE, ME and SME) in the large intestine were investigated by histochemical techniques in relation to the worm burdens. The effect of age was examined in three subgroups: 6-24-month-old horses (group 1), 2-10-year-old horses (group 2) and horses more than 10 years of age (group 3). No globule leucocytes were detected in any sections. No significant variations with breed or sex were observed in cell counts. The main variations were higher eosinophil counts in groups 2 and 3 and a marked increase of the MMC counts in the oldest horses (group 3). For each cell type, the infiltration was homogeneous and generalised along the large intestine. In the whole horse sample, the IE numbers were the only parameters that correlated with the MMC and SMMC counts. Very few significant relationships were found between mast cells and eosinophils in groups 1 and 3, whereas numerous positive correlations were recorded in group 2. In the whole horse sample, several correlations were found between different cell counts and cyathostome burdens. The numbers of larvae, adult worms, and the total worm burdens were related to some of the tissular eosinophil counts while the percentage of early third stage larvae (EL3) was linked to mast cell densities. These relations between cells and worm populations showed variations with age. In group 1, most of the significant associations were found between eosinophil counts (IE and SME) and the total numbers of larvae and worms; in group 2, they were noticed between the three eosinophil types and the total cyathostome burdens. In group 3, a MMC hyperplasia was observed and correlations were mostly recorded between these MMC and the total numbers of adult worms or the percentage of EL3. Several associations were also detected between eosinophils (mainly ME and/or IE) and different cyathostome burdens. These variations in the relationship between inflammatory cells and cyathostomes seemed to be consistent with the cellular changes observed among the three age groups. These results suggest that eosinophil and mast cell infiltrations quantified in the large intestine wall might be associated with cyathostome infection.

The development of naturally acquired cyathostome infection in ponies.

Groups of animals of different ages and experience of previous parasite exposure were allowed to graze a single pasture for 5 weeks in autumn (7 October to 11 November). There was evidence that previous exposure modified cyathostome development, as acquired burdens in foals which had previously grazed were smaller and developed more slowly than those of helminth-naive animals of the same age. The burdens acquired by yearling and adult ponies were of a similar size to those of the previously grazed foals, but the incidence of arrested development was higher in the younger groups of foals and yearlings when compared with adults. Further evidence of an effect of age on cyathostome development was that the level of faecal egg output of the adult ponies was lower than in the groups of young animals.

Precipitin response of the mitogen produced by Strongylus vulgaris arterial larvae.

The precipitin response of the mitogen produced by Strongylus vulgaris arterial larvae was investigated. IgG (T) from the sera of horses naturally infected with S. vulgaris adults and arterial larvae recognised the presence of two antigenic components of the mitogenic fractions. The results obtained seem to confirm that these antigens are immunogenic in stimulating the production of increased levels of IgG(T) in infected animals, and showed that the procedures could be used as immunological tools in the diagnosis of S. vulgaris infection.

Role of the eosinophil in serum-mediated adherence of equine leukocytes to infective larvae of Strongylus vulgaris.

The adherence of equine leukocytes to Strongylus vulgaris infective larvae (L3) in the presence of normal and immune sera was examined in vitro. Immune sera promoted adherence of buffy coat cells from ponies with S. vulgaris-induced eosinophilia (eosinophilic ponies) to S. vulgaris L3. However, eosinophils in the buffy coat cells were the predominant adherent cell type. Studies using leukocyte populations enriched for eosinophils, neutrophils, and mononuclear cells from eosinophilic ponies support the observations using buffy coat cells that eosinophils were the main effector cells. Adherent eosinophils from eosinophilic ponies immobilized L3. Neutrophils were less adherent and did not immobilize L3. Mononuclear cells failed to adhere. Normal eosinophils from strongly-naive ponies did not immobilize S. vulgaris L3 in the presence of immune serum, suggesting the in vivo activation of eosinophils in eosinophilic animals. Immune serum promoted less adherence of buffy coat cells to Strongylus edentatus or mixed species of Cyathostominae L3, suggesting that the serum-mediated cellular adherence phenomenon was species-specific. Normal serum promoted less cellular adherence to S. vulgaris L3 than immune serum. The adherence mediated by normal serum was removed by heat inactivation, suggesting that this nonspecific phenomenon was a complement-mediated reaction. Immune globulins promoted reactions similar to that seen using heat-inactivated immune serum, whereas normal globulins did not promote adherence. Immune globulins absorbed with pieces of S. vulgaris adult worms did not promote the adherence of buffy coat cells to S. vulgaris L3, suggesting that adult and L3 stages share antigens important in this phenomenon that resulted in the removal of specific adherence antibody during absorption.

Immune responses of pony foals during repeated infections of Strongylus vulgaris and regular ivermectin treatments.

Ten helminth-free pony foals divided into three groups were used in this study. Eight foals were each experimentally infected per os with 50 Strongylus vulgaris infective larvae weekly for 4 weeks, at which time one foal died of acute verminous arteritis. The remaining seven foals subsequently received 50 S. vulgaris infective larvae every 2 weeks for an additional 20 weeks. Four of the infected foals remained untreated (Group 1) and three of the infected foals were given ivermectin at 8, 16 and 24 weeks post initial infection (Group 2). Two foals served as controls (Group 3). Foals in Group 1 developed eosinophilia, which was sustained throughout the course of infection. A mild eosinophilia also developed in Group 2 foals; however, the eosinophil numbers were markedly reduced for 3 weeks after each ivermectin treatment. Only foals in Group 1 developed significant (P less than 0.05) hyperproteinemia, hyperbetaglobulinemia and a reversal of the albumin/globulin (A/G) ratio 4 weeks after initial infection. Significant (P less than 0.05) IgG anti-S. vulgaris ELISA titers developed in foals in Groups 1 and 2 3 weeks after infection and were sustained for the duration of the experiment. Western blot analysis of soluble somatic antigens of S. vulgaris adult female and male worms probed with sera from foals in Groups 1 and 2 revealed only subtle differences between these animals. The blastogenic reactivity of peripheral blood mononuclear cells (PBMC) to phytohemagglutinin and concanavalin A was not significantly different between groups. Peripheral blood mononuclear cells from foals in Groups 1 and 2 developed significant (P less than 0.05) blastogenic reactivity to S. vulgaris soluble adult somatic antigen when examined at 25 weeks after infection. Mesenteric lymph node cells from foals in Group 2, although not statistically significant, were more reactive to antigen than were the mesenteric lymph node cells from foals in Group 1 when examined at 27 weeks after infection. These results suggest that significant alterations in the immune response of ponies to S. vulgaris does not occur after intravascular killing of larvae by ivermectin treatments.

Immunologic and hematologic responses in ponies with experimentally induced Strongylus vulgaris infection.

Immunologic and hematologic responses were examined in 4 ponies with experimentally induced Strongylus vulgaris infection and in 5 helminth-free ponies. Two ponies were inoculated with 200 larvae and 2 were inoculated with 700 larvae of S vulgaris and then were reinoculated with the same numbers of larvae 34 weeks later. Initial response of the ponies inoculated with S vulgaris was S vulgaris antigen-induced lymphocyte response that developed 1.5 to 3 weeks after inoculation and did not persist. Development of antigen-reactive lymphocytes was followed sequentially by a biphasic complement-fixing antibody response, then biphasic eosinophilia. Antibody titer to S vulgaris antigen was higher in ponies inoculated with 700 larvae, compared with that in ponies given 200 larvae of S vulgaris. Also, the second peak in antibody titer and in absolute number of eosinophils was observed earlier in ponies inoculated with 700 larvae, compared with ponies inoculated with 200 S vulgaris larvae, and subsided before or from about 24 weeks after inoculation. The prepatent period for S vulgaris infection was 24 to 25 weeks. After reinoculation with S vulgaris, a degree of increased lymphocyte responsiveness was apparent but, by 17 weeks after reinoculation, only the primary peak in the absolute number of eosinophils indicated an anamnestic response. Essentially, antibody was not detectable after reinoculation.

Immunity and potential of vaccination.

This article will focus on current information available on the equine immune response to helminth parasites as it relates to acquired resistance, hypersensitivity reactions, and vaccine development.

Turbidimetric measurement of IgG(T) in the serum of healthy Thoroughbreds and ponies.

The turbidimetric analysis of IgG(T) in the serum of horses is described. Reference values are provided for 'worm-free' ponies (2.6 +/- 0.7 g/litre), stabled Thoroughbreds two years old and over (4.1 +/- 1.3 g/litre), grazing Thoroughbred broodmares (7.1 +/- 2.4 g/litre) and regularly wormed adult and young ponies grazing pasture contaminated with intestinal parasite eggs and larvae.

In vitro induction of lymphocyte responsiveness by a Strongylus vulgaris-derived mitogen.

Proliferation in vitro of peripheral blood lymphocytes both from horses infected with Strongylus vulgaris and from helminth-free ponies was observed in the presence of extracts of the fourth and fifth stage larvae and adults of S. vulgaris. In addition, S. vulgaris extracts induced transformation in cultures of peripheral blood lymphocytes from sheep and dogs and in mouse spleen cell cultures. Nylon wool non-adherent, T cell enriched fractions of lymphocytes from both mice and horses were stimulated by the S. vulgaris larval mitogen while no proliferation was observed in cultures containing nylon wool adherent, B cell enriched fractions. Macrophage co-operation appeared not to be necessary for S. vulgaris mitogen-induced transformation of spleen cells. The S. vulgaris mitogen stimulated a subpopulation of mouse spleen cells different from those responsive to PHA, Con A and LPS. These cells might be T helper cells since B cells were stimulated to proliferate in the presence of both T cells and S. vulgaris larval mitogen. In addition, the supernatant of in vitro cultured larvae of S. vulgaris induced slight, but significant transformation of equine peripheral blood lymphocytes. Therefore, it is possible that the S. vulgaris mitogen released by both viable parasites and degenerating larvae might induce T cell dependent production of immunoglobulin in vivo and account for the beta-globulinaemia, of which IgG(T) is a major component, in S vulgaris infected horses.

Antibody responses of ponies to initial and challenge infections of Strongylus vulgaris.

An indirect fluorescent antibody assay (IFA) was developed using Strongylus vulgaris third stage larvae (L3) as antigens. Observations using the IFA indicate that a species-specific antibody response to S. vulgaris L3 develops in S. vulgaris-infected ponies and that some surface L3 antigens are shared by adult worms. Sequential antibody levels against S. vulgaris were measured in strongyle-naive and in immune ponies following initial and challenge infections using the IFA and an indirect hemagglutination assay (IHA). Antibody levels measured by IFA increased faster following initial infections than did levels measured by IHA. Antibody levels appear to increase following challenge infections of immune ponies when measured with the IFA, but not with the IHA. Significant differences in antibody titers were not seen between ponies which developed colic following challenge infections and those that did not develop colic. Antibodies were not detectable in ponies unexposed to larval migrations, but which received surgical implantation of S. vulgaris adults into the cecum.