Characterization of a galectin-like activity from the parasitic nematode, Haemonchus contortus, which modulates ovine eosinophil migration in vitro

Abstract

The development of eosinophilia is a characteristic feature of helminth infection, although the exact nature of the interaction between eosinophils and parasites remains to be fully defined. Previously, it has been reported that Haemonchus contortus and other nematodes produce eosinophil-specific chemoattractants. This paper describes studies aimed at isolating and identifying the factor(s) responsible. Initial studies showed that soluble extracts of infective larvae (L3) of H. contortus provoked a chemokinetic, rather than chemotactic, response in ovine bone marrow eosinophils in vitro. This activity was inhibited by lactose to a markedly greater extent than sucrose suggesting a galectin-like identity. Lactose affinity chromatography of soluble H. contortus extracts resulted in the isolation a specific bound fraction which retained biological activity. SDS-PAGE gel electrophoresis indicated a single Coomassie-stained band at between 31 and 41 kDa. Subsequent, mass spectrometric analysis confirmed that the bound fraction contained a mixture of nematode galectins. The results confirm that H. contortus larvae produce several galectin-like proteins, at least one of which demonstrates eosinophil chemokinetic activity in vitro. The possibility of the parasite-derived factor mimicking the mammalian galectin-9, a known eosinophil chemokine, is discussed.

Introduction

The development of systemic and local tissue eosinophilia is characteristic of the host immune response towards helminth infection (Sanderson, 1992, Jones, 1993). However, opinion is divided on the role of eosinophils during infection, in terms of both their protective effect (Behm and Ovington, 2000, Meeusen and Balic, 2000, Klion and Nutman, 2004) and their ability to mediate inflammation (Lee and Lee, 2005, Jacobsen et al., 2007). Evidence for a protective role derives mainly from in vitro studies on parasite killing in the presence of eosinophils or their granular components (Butterworth and Thorne, 1993, Butterworth, 1984, Rainbird et al., 1998). As yet, there are few confirmatory data from in vivo infections to support such an effector role. More recent studies, using transgenic and/or IL-5 knockout rodent models to alter eosinophil production and recruitment, have yielded mixed and often contradictory results with respect to disease establishment and outcome (Dent et al., 1997, Behm and Ovington, 2000, Meeusen and Balic, 2000, Klion and Nutman, 2004, Galioto et al., 2006). Ablation of systemic and/or tissue eosinophilic responses have been associated with reduced, enhanced or unaffected severity of infection generally depending on the particular parasite and experimental situation being studied.

In atopic conditions, the development of pathology is strongly linked to eosinophils and their products (Walsh, 1999). There is also some evidence suggesting that eosinophils may contribute to pathogenesis during parasitic infection (Hall et al., 1998, Nickdel et al., 2001). Moreover, it has previously been shown that a number of ovine parasitic gastro-intestinal nematodes produce a factor(s) that promote eosinophil migration in vitro (Wildblood et al., 2005). This raises the possibility that helminths may actively promote eosinophil recruitment and activation, and utilize resulting tissue damage to aid their survival within the host. For example, eosinophil-mediated mucosal damage, such as that seen in the asthmatic lung, could result in impaired absorption and, therefore, an enhanced nutrient supply for developing worms, and/or could provide a favourable microenvironment for their establishment. The aim of this study was to attempt to characterize and identify eosinophil chemoattractant(s) produced by the infective third stage larvae (L3) of Haemonchus contortus.