The effect of cycloleucine on SFV A7(74) infection in mice.

Cycloleucine (CL), a non-metabolizable amino acid analogue, was found to reduce thymus and spleen weights in Semliki Forest virus (SFV) strain A7(74) infected and control mice. The maximum effects were seen when three daily doses of CL were given to mice 24 h after an SFV A7(74) infection. In these mice thymus atrophy led to abolition of thymus dependent immune responses and changes in the pathological features of the viral infection--the most striking feature being prevention of demyelination. In addition virus titres in the brains of CL treated infected mice were increased and prolonged. These results show that demyelination following an SFV A7(74) infection is not a result of direct virus action, but of a T-cell mediated mechanism.