Interleukin-13 induces paralysis of Haemonchus contortus larvae in vitro.

AIMS: Interleukin-13 (IL-13) is a Th2-associated cytokine that typically induces gut contractility and mucus secretion to eliminate helminth parasites from the digestive tract. Little evidence exists of IL-13's direct effect on Haemonchus contortus larvae (L3) and thus was the objective of this study. METHODS: To test effects of IL-13 on H contortus, L3 were treated with ovine recombinant (r) IL-13 (1 µg/mL); motility and morbidity were assessed. Monocytes isolated from H contortus-resistant St. Croix (STC) and susceptible Suffolk (SUF) sheep were treated with anti-IL-13 blocking antibody to elucidate differences in host immune response. RESULTS: rIL-13 treatment reduced L3 speed (27 µm/s) and distance (7.5 µm) compared to untreated L3 (speed: 94 µm/s; distance: 27 µm) (P < .001). Comparison of larval speed to known paralytic levamisole (LEV) revealed no difference between treatments (rIL13: 23 µm/s; LEV 27 µm/s). Additionally, rIL-13 had no effect on larval morbidity. Blocking IL-13 reduced monocyte-driven larval morbidity (0.13 µmol/L ATP) and increased larval motility (88 µm/s; 27 µm) compared to larvae treated with STC-monocytes alone (0.07 µM ATP; 34 µm/s; 8 µm) (P < .05). CONCLUSIONS: These data indicate IL-13 has a dual capability paralysing L3 and contributing to monocyte-driven larval morbidity, and also indicate breed differences.