LAUSR

Parasite-resistant St. Croix sheep generate a potent neutrophilic response to larval stages of Haemonchus contortus. Protective neutrophil responses can be best characterized by increased neutrophil infiltration to the abomasum within the first 3 days of infection. These data indicate breed differences in neutrophil chemotaxis and response to H. contortus infection. The purpose of this study was to determine differences in neutrophil chemotaxis by H. contortus third-stage larval (L3) antigen (HcLA). Suffolk (SUF) and St. Croix (STC) neutrophils were isolated and applied to matrigel-coated clearview inserts, and placed into a reservoir containing H. contortus HcLA, Interleukin-8 (IL-8), or complete media. Neutrophil chemotaxis plates were incubated (37°C, 5% CO2) in an Incucyte S3 live cell imaging system for 24 hours, and measurements taken hourly. Neutrophils from STC migrated towards HcLA quicker than SUF neutrophils, and this migration occurred as early as 3 hours (10% and 4% respectively, P < 0.001). The difference in breed chemotaxis increased over time, where 28% of STC neutrophils migrated at 14 hours compared with 13% of SUF cells at the same time. By 24 hours, 37% of STC neutrophils migrated towards HcLA while the percentage of migrating SUF neutrophils remained the same (13%). Positive control for neutrophil chemotaxis was IL-8, and 37% of STC neutrophils achieved migration at 7 hours compared with 26% SUF neutrophils. By 24 hours, IL-8 induced neutrophil chemotaxis was similar in both breeds (STC 47%, SUF 41%). Taken together, these data indicate that delayed responses in neutrophil chemotaxis may contribute to H. contortus establishment in parasite-susceptible hosts. Thus, indicating that neutrophil response to H. contortus infection is a critical component to full host protective immunity.