Possible role for toll-like receptors in interaction of Fasciola hepatica excretory/secretory products with bovine macrophages

Alternative activation of macrophages (Mφ) during helminth infection is a characteristic feature of the host immune response. Alternatively activated macrophages (AAMφ) are distinguished from others by high arginase 1 (Arg-1) activity, low nitric oxide (NO), and high interleukin 10 (IL-10) production. In murine models, these cells have been shown to possess anti-inflammatory properties. They have also been implicated in exacerbating a subsequent infection with a secondary pathogen. In this study we used cattle experimentally infected with Fasciola hepatica to monitor the kinetics of IL-4 and IL-10 over the course of infection. Using naïve Mφ in vitro, we examined the effects of exposure to F. hepatica excretory/secretory products (FhepES) alone or in combination with IL-4. Our results suggest that FhepES may work in combination with IL-4 to produce AAMφ. The effects of FhepES on the subsequent responses to lipopolysaccharide (LPS) and purified protein derivative from Mycobacterium bovis (PPD-B), which are bovine Toll-like receptor 4 (TLR4) and TLR2 antagonists, respectively, were also examined. We found that Mφ stimulated with FhepES together with LPS or PPD-B have reduced NO or gamma interferon production, respectively. The ability of FhepES to produce AAMφ was found to be heat labile and partially dependent on glycan residues. A possible role for TLR recognition is discussed.