Régulation des populations de Nématodes gastro-intestinaux ...

1. INTRODUCTION
Résultats
Due to the emergence of anthelmintic resistance in parasite populations (Sangster,
1999 ; Jackson and Coop, 2000) and increased public concern about chemical residues in
animal products, the knowledge of immune mechanisms involved in gastrointestinal
helminthic infections has become of crucial importance for their control in sheep. The
characterization of the underlying immune response to parasitic infections is also a
prerequisite for the development of alternative and effective control strategies such as
vaccination or selective breeding for resistance.
Immune response to gastrointestinal nematodes has been extensively studied in
rodents models where protective immunity against these parasites is dependent on the
activation of CD4+ T helper cells, and on the Th2 polarization of the immune response (Urban
et al., 1992 ; Finkelman et al., 1997 ; Else and Finkelman, 1998). Similar features are also
encountered in natural human nematode gut infections (Cooper et al., 2000 ; Quinnell et al.,
2004). In sheep, the nature of the immune response towards gastrointestinal helminths, like
the existence of a true Th1/Th2 dichotomy, were discussed (Brown et al., 1998 ; Gill et al.,
2000). In a previous study, we have shown that 5-6 months old INRA 401 lambs developed
an unequivocal Th2 immune response following an experimental H. contortus infection. This
response was characterized by high levels of Th2 cytokines mRNA transcription (IL-4, IL-5
and IL-13), and a rapid and intense mobilization of cellular (mast cells, eosinophils and
globule leukocytes) and humoral Th2 effectors (Lacroux et al., 2006). The intensities of these
immune effectors were negatively correlated to the development of worms, the size and the
fecundity of females and to the egg excretion (Lacroux et al., 2006). However, data
concerning the polarization of the immune response in Trichostrongylus colubriformis
infections in sheep are more conflicting and most of them are coming from infections in
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