Régulation des populations de Nématodes gastro-intestinaux ...

Résultats
reinforcing the role of these immune effectors in decreasing the faecal egg output. Eosinophils
and mast cells are considered to play an important role in the response against gastrointestinal
nematode infections (Douch et al., 1986 ; Dawkins et al., 1989 ; Pfeffer et al., 1996 ; Balic et
al., 2000), as these cell types may kill infective larvae by releasing toxic proteins against the
target parasite, as least in vitro (Butterworth et al., 1975 ; Capron et al., 1984 ; Rainbird et al.,
1998). Traditionally the effector responses seems to act against incoming larvae and influence
their expulsion. In our study, as no differences in worms establishment are recorded, these
cells could also have a role on established parasites. Similarly, IgA and IgG antibodies could
have a direct effect i) on the immune rejection of incoming larvae (Harrison et al., 2003) and
ii) on established parasites by neutralizing or inactivating vital metabolic enzymes (Gill et al.,
1993) or by interfering with the worm’s ability to feed (Smith, 1988).
In conclusion, two successive one-month long T. colubriformis infections in young
lambs are sufficient to induce the mobilization of Th2 cellular and antibody responses, to
reduce the faecal egg excretion and then the larval contamination of pastures. Nevertheless
using this immunization protocol, no reduction of the total worm burden, nor modifications of
parasite development, are demonstrated, so benefits at the individual level remain limited. No
clear polarization of the immune response can be ruled out when considering a whole given
group, but individual variability observed in the previously-infected sheep for IL-5 mRNA
transcription, cellular and antibody responses, plead nevertheless for a Th2-type pathway
orientation. Repetitive or higher exposures may be required to initiate a strong Th2 protective
immune response in young INRA 401 lambs.
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