*3.5. Homology with Host SOD Facilitates Immune Evasion*

Western blot analysis of rFhSOD1 and rFhSOD3 probed with pooled sera from experimentally infected sheep demonstrated that these proteins are not immunogenic during *F. hepatica* infection (Figure 7A–D). These results were confirmed by analysis of individual sheep sera collected at 0, 3, 7, 11, 15, and 23 WPI by ELISA against rFhSOD1 and rFhSOD3, using the immunogenic cathepsin peptidase, rFhCL1, as a positive control (Figure 7E).

**Figure 7.** Antibody responses to recombinant FhSOD1 and FhSOD3 in experimentally infected sheep. (**A**–**C**) Recombinant (1 ug/well) FhSOD1 and FhSOD3 were transferred to a nitrocellulose membrane and probed with pooled sera from experimentally infected sheep (**A**) pre-infection (negative control), (**B**) 7 weeks post-infection (WPI), and (**C**) 20 WPI. (**D**) Recombinant FhSOD1 and FhSOD3 were probed with anti-SOD1 and anti-SOD3 polyclonal antibodies raised in rabbits (positive control). Lane 1; recombinant FhSOD1, lane 2; recombinant FhSOD3, lane 3; recombinant FhCL1 zymogen mutant (positive control), M; molecular weight in kDa (Precision Plus Protein Dual, Bio-Rad. (**E**) The optical density of IgG antibodies to rFhSOD1, rFhSOD3 and rFhCL1 from experimentally infected sheep 0, 3, 7, 11, 15 and 25 WPI.
