Régulation des populations de Nématodes gastro-intestinaux ...

Résultats
experimental protocols, age and breed of experimental animals that could potentially cause
variations in the outcomes of different experiments, the origin for the discrepancy in different
works mentioned above is not clear.
The second objective of our study was to compare the adaptive immune responses in
BBB and INRA 401 lambs. CD4+ T helper cells are involved in the genetic control of sheep
immunity to H. contortus (Gill et al., 1993). Therefore, we hypothesized that the higher
resistance of BBB lambs could arise from a quicker and/or more intense Th2 polarization and
mobilization of Th2 effector cells. Following both initial and secondary infections, a clear
Th2-type immune response characterized by cytokine gene expressions and effector cell
mobilisation was demonstrated in the two breeds and this was consistent with previous data
for the INRA 401 genotype (Lacroux et al., 2006). mRNA cytokine transcriptions for IL-4,
IL-5 and IL-13 were moderately higher at 30 dpc in primary infected and previously-infected
BBB lambs than in their INRA 401 counterparts. As to our knowledge, this is the first work
comparing the cytokine gene expression in resistant and susceptible sheep breeds to H.
contortus infections. Similar works were already reported for Trichostrongylus colubriformis
resistant and susceptible Romney sheep lines (Pernthaner et al., 2005) in which animals of the
resistant category were found to develop stronger Th2-polarised cytokine (IL-5 and IL-13 but
not IL-4) gene expressions than the susceptible lines. Recently, Moreno et al. (2006) have
detected a QTL for resistance to H. contortus on ovine chromosome 5 in the INRA 401 x
Barbados Blackbelly backcross lines. The proximal most likely location of this QTL
corresponded to the IL-3/IL-4/IL-5 region. In this study, IL-5 gene over-expression was
apparent following H. contortus exposure and its level remained high in the Blackbelly sheep
till 30 dpc, while it was down regulated to very low values in INRA 401 lambs. In line with
the persistent IL-5 cytokine gene expression pattern, a higher and long lasting blood
eosinophilia was observed in BBB compared to INRA 401 lambs. Negative correlations were
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