Characterization of ovine monocyte activity when cultured with Haemonchus contortus larvae in vitro.

ABSTRACT

AIMS: The objective of this study was to identify and characterize cell populations within ovine peripheral blood mononuclear cells (PBMCs) associated with Haemonchus contortus (Hc) larval morbidity and impairment in vitro. METHODS AND RESULTS: Monocytes and lymphocytes were separated from PBMC from parasite-resistant St. Croix (STC) sheep and parasite-susceptible Suffolk (SUF) sheep. Cells were cultured with Hc third stage larvae (L3) for 9 h. Larval morbidity was assessed using ATP concentration. Activation status was determined through gene expression analysis and enzyme inhibition. Enzymes arginase-1 (Arg1) and inducible nitric oxide synthase (iNOS) were inhibited using BEC (S-(2-boronoethyl)-I-cysteine) and 1400W (N-(3-(aminomethyl)benzyl)acetamidine), respectively. Larval ATP was lower when cultured with STC-derived monocytes (0.015 µmol/L ATP) compared to SUF-derived monocytes (0.067 µmol/L ATP) (P < .001), or lymphocytes from either breed (STC 0.085 µmol/L, SUF 0.112 µmol/L ATP) (P < .001). SUF-derived monocytes displayed higher expression of M1 genes, whereas STC-derived monocytes displayed M2 genes continuously. Inhibition of Arg1 decreased monocyte function in both breeds, whereas iNOS inhibition restored SUF-derived monocyte function. CONCLUSIONS: Together, these data indicate STC-derived monocytes favour M2 phenotype when exposed to L3, where SUF-derived monocyte function resembled M1 phenotype and described potential for improving Suffolk sheep through modulating inflammatory responses.