Aurothiolates enhance the replication of Semliki Forest virus in the CNS and the exocrine pancreas Martina F Scallan 1 and John K Fazakerley* ,2 1 Department of Microbiology, University College Cork, National University of Ireland; 2 Virus Research Group, University of Edinburgh, EH9 1QH, UK The A7(74) strain of Semliki Forest virus (SFV) is avirulent and the L10 strain virulent in adult mice. A7(74) infection of adult mouse brain gives rise to small discrete foci of infection which, in immunocompetent animals, are cleared within 10 days. In contrast L10 infection results in a widespread and fatal central nervous system infection. Aurothiolates are linear, 2-coordinate complexes in which two ligands are covalently bound on either side of a gold nucleus in a +1 oxidation state (gold (I)). Pretreatment of A7(74) infected mice with two distinct aurothiolates (sodium aurothiomalate and aurothioglucose) resulted in signi®cantly increased brain virus titers, and large con¯uent areas of infection in the brain similar to the pattern of infection seen with the L10 strain. The gold (I) moiety of aurothiolates was demonstrated to be the active component, since thiomalic acid when administered alone had no potentiating effect on the infection. Although both aurothiolates allowed productive replication and spread of A7(74) within the nature mouse brain, enhanced neuronal destruction was not apparent. There were no signi®cant changes in virus distribution in any other tissue except for the exocrine pancreas and the myocardium where widespread infection of the acinar cells and occasional infected myocytes were observed. Keywords: alphavirus; Semliki Forest virus; gold; neurovirulence; neurovirol- ogy Introduction Semliki Forest virus (SFV) is a well characterized neurotropic alphavirus. A number of strains, differ- ing in their virulence for mice have been isolated from mosquitoes. Amongst these is a virulent L10 strain, isolated from a pool of Aedes abnormalis mosquitoes captured in Uganda (Smithburn and Hadow, 1944) and an avirulent strain, A7(74), derived from Aedes argenteopunctatus mosquitoes caught in Mozambique (McIntosh et al, 1961; Bradish et al, 1971). Following intraperitoneal (ip) inoculation into 3 ± 4-week-old mice, L10 produces a lethal encephalitis which results in death within 6 days. In contrast A7(74) causes a subclinical encephalitis characterized by restricted virus repli- cation and survival of infected central nervous system (CNS) neurons (Fazakerley et al, 1993; Amor et al, 1996). Both humoural and cell-mediated immune responses contribute to the clearance of A7(74) from the CNS, but do not account for the focal nature of this infection, since the restricted pattern of infection is also observed in adult mice with severe combined immunode®ciency (SCID) (Fazakerley et al, 1993; Amor et al, 1996). Clearance of A7(74) in immunocompetent mice coincides with the appearance of temporary lesions of CD8 T-cell mediated demyelination within the CNS (Suckling et al, 1978; Fazakerley and Webb, 1987a,b; Subak- Sharpe et al, 1993). Both strains of SFV have been reported to replicate to similar titers in extraneural tissues, predominantly muscle (Pusztai et al, 1971; Amor et al, 1996), producing a plasma viraemia which delivers virus to the CNS. In immunocompetent adult Balb/c mice, foci of A7(74) replication in peripheral tissues are dif®cult to ®nd by immunos- taining or in situ hybridization, but focal infection of skeletal muscle ®bres has been observed in infected SCID mice (Amor et al, 1996). SFV is thought to enter the CNS by passage across cerebral vascular endothelial cells (Pathak and Webb, 1974, 1980). *Correspondence: J Fazakerley, Virus Research Group, University of Edinburgh, Summerhall, Edinburgh EH9 1QP Received 3 December 1998; revised 3 March 1999; accepted 13 April 1999 Journal of NeuroVirology (1999) 5, 392 ± 400 ã http://www.jneurovirology.com 1999 Journal of NeuroVirology, Inc.