Equine immunity to parasites

Cytokine responses to various larval stages of equine strongyles and modulatory effects of the adjuvant G3 in vitro

AIMS

To generate different larval stages of Strongylus vulgaris and to study cytokine responses in cultures of eqPBMC exposed to defined larval stages of S. vulgaris and cyathostomins with the aim to understand the early immune reaction to these parasites.

METHODS AND RESULTS

EqPBMC were exposed to S. vulgaris larvae (L3, exsheated L3 and L4) and cyathostomin L3 and analysed for cytokine gene expression. Procedures for decontamination, culturing and attenuation of larvae were established. Transcription of IL-4, IL-5 and IL-13 was induced by both S. vulgaris and cyathostomin L3. Moulting of S. vulgaris from L3 to L4 stage was accompanied by a shift to high expression of IL-5 and IL-9 (exsheated L3 and L4) and IFN-γ (L4 only). In parallel, the adjuvant G3 modified the cytokine profile induced by both parasites by reducing the expression of IL-4, IL-5 and IL-10 while concomitantly enhancing the expression of IFN-γ.

CONCLUSION

The L4 stage of S. vulgaris generated a cytokine profile different from that induced by the earlier L3 stage of S. vulgaris and cyathostomins. This diversity depending on the life cycle stage will have implications for the choice of antigen and adjuvant in future vaccine design.

Prevalence of strongyle nematodes in naturally infected ponies of different ages and during different seasons of the year in Louisiana

One hundred and seventeen ponies were surveyed for the seasonal prevalence of strongyloid parasites, particularly cyathostomes, and for host- and age-related differences in these infections. For 56 ponies, all stages of the cyathostome life cycle, both mucosal and luminal, were enumerated. Total numbers of cyathostomes and percentage of developing larvae (DL) encysted in the mucosa remained constant in all 4 seasons of the year, whereas a significant increase in the percentage of adults in the cyathostome population occurred in fall. In yearling ponies, encysted early third-stage larvae constituted a significantly lower percentage of the cyathostome population, and DL and adults formed a significantly higher percentage, compared with those stages in older ponies, 2-5 yr of age. More species of cyathostomes were present in yearling ponies than in older ponies. Significant differences occurred in fecal egg counts at different seasons of the year, even though adult cyathostome and large strongyle numbers remained constant. Twenty-four species of cyathostomes were found year-round, and 2 rare species were found in only 2 or 3 seasons of the year. Prevalences for these 24 species were not significantly different during any season, although 5 species had significant differences in intensity levels of infection in certain seasons of the year. Three species of large strongyle (strongylinae) adults had significant seasonal variations in intensities. These were Strongylus edentatus and S. vulgaris, which occurred in significantly higher numbers in summer and fall, and Triodontophorus brevicauda, which was more numerous in spring and summer. Fourth- and fifth-stage larvae of S. vulgaris recovered from the mesenteric vasculature were significantly more numerous in winter and spring than in other seasons.

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.