Régulation des populations de Nématodes gastro-intestinaux ...

Résultats
nematode infections elicit Th2 immune responses and are almost invariably accompanied by
local and systemic eosinophilia, mucosal mast cell hyperplasia, and local and general specific
antibody responses (mainly IgA, IgE and IgG1) (Urban et al., 1991). Similar features are
described in sheep infected with Haemonchus contortus (Schallig, 2000 ; Lacroux et al.,
2006), Teladorsagia circumcincta (Stear et al., 1995) and with T. colubriformis (Bendixsen et
al., 1995). In our study, mast cell and globule leukocytes hyperplasia, mucosal eosinophilia
and specific antibodies levels are detected at the end of the experiment (17 or 28 dpc) in
previously-infected sheep only. No significant cellular and humoral responses were observed
in the primary-infected group, as well as in uninfected control lambs, suggesting that a first
exposure to the parasite is not sufficient to induce significant Th2-type effector modifications.
The last objective of this study was to measure the effects of recruited cells or
antibodies on parasite establishment, development and fecundity. No differences in the
establishment rate of worms were observed between previously-infected and primary-infected
lambs. Moreover, the parasite development within the host was not delayed during the
secondary infection in contrast to other studies using H. contortus (Schallig et al., 1995 ;
Lacroux et al., 2006) or T. circumcincta infections (Stear et al., 1995). However, a significant
decrease in faecal egg output was observed in previously-infected lambs as soon as 17 dpc,
suggesting a stunting effect on female size and a reduced fecundity as demonstrated in H.
contortus infected lambs (Lacroux et al., 2006). These results corroborate previous
observations stating that young lambs are unable to control total worm burden due a
constitutive immunological hyporesponsiveness (Colditz et al., 1996), but are able to
influence parasite life traits like adult female worm length and then faecal egg output (Stear et
al., 1999). Strong negative correlations were observed between eosinophils, mast cells, a large
range of IgA and IgG antibody responses and the egg excretion at 28 dpc (Table 5),
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