Arthropod-transmitted filarial nematodes can survive for in excess of a decade via modulation of the vertebrate host immune system. Although human infection can result in very severe pathology, most infected individuals show remarkably little evidence of this. Analysis of the anti-nematode response indicates that apparently pathology-free individuals have an anti-inflammatory immunological phenotype and it has been suggested that this favours maintenance of host good health. It is considered that parasite-derived molecular secretions contribute to the anti-inflammatory phenotype and we have thus investigated the properties of a filarial nematode glycoprotein secreted in some abundance, ES-62. This molecule shows a plethora of immunomodulatory activities that can be classified as anti-inflammatory. It has been observed in a number of studies that several autoimmune disorders including rheumatoid arthritis (RA) exhibit reduced incidence and severity in geographic regions in which filarial nematodes are transmitted to humans. Furthermore, it has been speculated that these two observations are linked although molecular explanations for such an association have not been forthcoming. Although the aetiology of RA remains unknown a majority of data are consistent with it being mediated via excess pro-inflammatory cytokine production. Given that ES-62 is anti-inflammatory, we hypothesised that it might be able to counter the pathology associated with diseases like RA. Indeed, we found that exposure to ES-62 prevented initiation of collagen-induced arthritis (CIA) in a murine model and also suppressed progression of established disease. Ex vivo analyses demonstrated that these effects correlated with inhibition of TNF-alpha production and inhibition of collagen-specific TH-1 responses. The nematode product was also able to suppress pro-inflammatory cytokine release in vitro in synovial cells derived from RA patients. ES-62 thus constitutes a pathogen-derived immunomodulator with significant therapeutic potential.