Ostertagia ostertagi mediates early host immune responses via macrophage and Toll like receptor pathways.

Ostertagia ostertagi is an abomasal parasite with significant economic impact on the cattle industry. Early host immune responses are poorly understood. Herein, we examined time course expression of Toll like receptors (TLRs) in peripheral blood mononuclear cells (PBMC) during infection where PBMC macrophages (MΦ) generated both pro- and anti-inflammatory responses when incubated with excretory secretory products (ESP) from fourth stage larvae (OoESP-L4) or adult worms (OoESP-Ad). First, changes in cell morphology clearly showed that both OoESP-L4 and OoESP-Ad activated PBMC-MΦ in vitro resulting in suppressed CD40 and increased CD80 expression. Expression of mRNAs for TLRs 1, 4, 5 and 7 peaked 7 days post infection (dpi) (early L4), decreased by 19 dpi (post emergent L4 and adult), then increased at 27 dpi (late adults). The pro-inflammatory cytokine TNF-α (transcript and protein) increased in the presence of OoESP-Ad, and the anti-inflammatory cytokine IL-10 (protein) decreased in the presence of OoESP-L4 or OoESP-Ad; however, IL-10 mRNA was up-regulated, and IL-6 (protein) was down-regulated by OoESP-L4. When PBMC-MΦ were treated with ligands for TLR4 or TLR5 in combination with OoESP-Ad, the transcripts for TNF-α, IL-1, IL-6 and IL-10 were significantly down-regulated relative to treatment with TLR4 and TLR5 ligands only. However, the effects of TLR2 ligand and OoESP-Ad were additive but only at the lower concentration. We propose that O. ostertagi L4 and adult worms utilize competing strategies via TLRs and MΦ to confuse the immune system which allows the worm to evade the host innate responses.