In vitro pre-exposure ofHaemonchus contortusL3 to blood eosinophils reduces their establishment potential in sheep

Abstract

-Different authors have reported that eosinophils are capable of immobilising infective larvae of different species of nematodes in vitro. However, classifying larvae as mobile or immobile is so subjective that it does not always mean all apparently immobile larvae are dead or those that are mobile are capable of surviving further immune responses if administered to their natural hosts. The objective of this experimental study was therefore to substantiate the role of eosinophils in the killing of Haemonchus contortus infective larvae by comparing the infectivity in sheep of larvae that had been incubated with eosinophil-enriched cell suspensions with control larvae. Since it was not possible to isolate pure eosinophils from sheep blood, we were compelled to evaluate the effects of other blood cells contaminating our eosinophil-enriched suspensions. Although eosinophils and neutrophils were the only cells found adherent to H. contortus infective larvae in vitro, induced eosinophils in the presence of immune serum were primarily responsible for the drastic reduction in larval motility compared to the minor effects of neutrophils and mononuclear cells. Corresponding reductions in faecal egg count and worm numbers were observed when the incubated larvae were transferred intra-abomasally to sheep. Interestingly, the proportion of larvae that failed to establish was much higher following incubation with induced eosinophils compared with other cells or with immune serum alone. Although this study did not address the in vivo role of eosinophils in sheep, the results strongly indicate that sheep blood eosinophils have a larval killing potential in vitro, and a larval mobility test alone may not fully explain the level of damage inflicted on the larvae.Haemonchus contortus / eosinophils / in vitro / intra-abomasal / sheep

Effects of peripheral blood mononuclear cells on Haemonchus contortus larval motility in vitro

“…Previous studies culturing immune cells with H. contortus larvae demonstrated that eosinophils and not PBMC are capable of severely reducing larval motility . Furthermore, the authors reported that larvae with prior exposure to eosinophils had lower infectivity in the host.…”

Haemonchus contortus P-Glycoproteins Interact with Host Eosinophil Granules: A Novel Insight into the Role of ABC Transporters in Host-Parasite Interaction

“…However purification of an eosinophil cell population from sheep blood remains challenging. For example Terefe et al [22] reported that a single Percoll gradient (1.090 g/ml) allowed the purification of sheep eosinophils with a purity ranging from 43 to 63%. In the present work, we optimized this approach using two gradient Percoll densities in combination with cell sorting that resulted in a cell population containing 95% eosinophils.…”

“…Exposure of infective H. contortus larvae to host eosinophils in vitro reduces their ability to establish a subsequent infection in vivo , making this species an appropriate model to investigate the interaction beetween eosinophils and the parasite [22]. We have previously developed an egg based assay where fluorescent rhodamine-123 transport out of H. contortus eggs is mediated by Pgp [23], [24].…”

Increased susceptibility to Haemonchus contortus infection by interleukin‐5 modulation of eosinophil responses in sheep

“…In general, sheep can develop resistance with repeated infection and eosinophils are implicated as a major resistance mechanism . In vitro assays have demonstrated that eosinophils can inhibit the motility of L3 larvae with visible lesions appearing in the cuticle of the L3 and reduced infectivity . In immunized animals, a negative association between eosinophils and faecal egg count (FEC) has been demonstrated and eosinophils are observed surrounding the H contortus larvae in abomasal tissues .…”