Effects of peripheral blood mononuclear cells on Haemonchus contortus larval motility in vitro

The objective of this experiment was to determine effects of peripheral blood mononuclear cells (PBMC), derived from parasite-resistant St. Croix (STC) and parasite-susceptible Suffolk (SF) sheep, on motility of Haemonchus contortus L₃ stage larvae in vitro. Peripheral blood mononuclear cells were collected from 10 lambs of each breed, 5 naïve and 5 which had received a priming infection with H. contortus. Larval motility was quantified using a MIF Nikon Sweptfield microscope and NIS Elements AR software, and measurements included path length (PL) (μm), velocity (VEL) (μm/s) and acceleration (ACC) (μm/s² ). After 18 h of incubation, PL and VEL were greatest in larvae cultured with SF-derived PMBC and were significantly different from all other groups (P < 0·01). No difference was observed in PL or VEL between larvae exposed to naïve or primed STC-derived PBMC and primed-SF PBMC. Differences in ACC were detected between larvae cultured with primed STC-derived PBMC (10·91 μm/s² ) and naïve SF-derived PBMC (45·7 μm/s² ) (P = 0·035). These data indicate an innate ability of STC-derived PBMC to severely inhibit larval motility.