TABLE 1.

Comparative susceptibilities of NEJ F. gigantica and F. hepatica to killing by PLCs of F. hepatica-infected or F. gigantica-infected ITT sheep following incubation with homologous or heterologous Fasciola-immune serum^a

Incubation	% Viable NEJ parasites
Fh PLCs + Fh NEJ + NS	95 ± 4†
Fh PLCs + Fh NEJ + Fh IS	95 ± 4†
Fh PLCs + Fh NEJ + Fg IS	93 ± 4†
Fg PLCs + Fh NEJ + NS	92 ± 4†
Fg PLCs + Fh NEJ + Fh IS	93 ± 4†
Fg PLCs + Fh NEJ + Fg IS	94 ± 4†
Fg PLCs + Fg NEJ + NS	88 ± 8†
Fg PLCs + Fg NEJ + Fh IS	58 ± 15‡
Fg PLCs + Fg NEJ + Fg IS	43 ± 17‡
Fh PLCs + Fg NEJ + NS	92 ± 3†
Fh PLCs + Fg NEJ + Fh IS	49 ± 13‡
Fh PLCs + Fg NEJ + Fg IS	48 ± 4‡

^aEach of three replicate wells containing 20 to 30 NEJ F. gigantica (Fg) or F. hepatica (Fh) parasites and PLCs (E/T ratio of 2 × 10⁵ cells to 1 NEJ parasite) in 1 ml of medium was incubated for 3 days with either serum from Fasciola-naive ITT sheep (NS) or immune serum (IS) from Fasciola-infected ITT sheep. The viability of the NEJ parasites was then assessed at 72 h as the ability to reduce the tetrazolium salt MTT. Results are the mean ± standard deviation obtained with PLCs from five ITT sheep. For each incubation, mean values followed by the same symbol († or ‡) could not be significantly differentiated by the Dunnett multiple-comparison test at P < 0.05. No significant killing was observed with F. gigantica or F. hepatica NEJ liver flukes incubated with naive-sheep serum or immune serum alone (data not shown). F. gigantica PLCs were obtained from F. gigantica-infected ITT sheep; F. hepatica PLCs were obtained from F. hepatica-infected ITT sheep.