Hyperthermic pre-conditioning promotes measles virus clearance from brain in a mouse model of persistent infection

Nervous tissue subjected to hyperthermic pre-conditioning is resistance to numerous insults although in vitro, the same treatment can increase gene expression and cytopathic effect of neurotropic paramyxoviruses, including measles virus (MV). The present work determined whether the in vivo relationship between hyperthermic pre-conditioning and MV infection would be to increase neuropathogenicity or, conversely, to promote clearance. Balb/c mice 36 h of age were exposed to a 41 degrees C hyperthermic treatment for 30 min. Intracranial inoculation of mice with Edmonston MV was performed at 6 h following the heat treatment, a time point exhibiting elevated levels of the major inducible 70-kDa heat shock protein in brain, a hallmark of pre-conditioning. Forty-seven percent of the non-heated animals supported a persistent cytopathic infection at 21-day post infection (PI) based upon the quantitative detection of viral RNA in brain using real time RT-PCR. Cytopathic effect in the infected brains was proportionate to viral RNA burden. In contrast, infected stress conditioned mice lacked significant cytopathic effect and clearance was demonstrated in 95% of the animals. Analysis of shorter post-infection intervals showed that levels of viral RNA in brain were equivalent between stress conditioned and non-conditioned mice at 2 and 7 days PI, with clearance being first evident in both groups at 14 days. The temporal onset and progression of clearance was correlated to splenocyte blastogenic responsiveness to purified MV antigen but not the production of MV-specific antibody. Collectively, these results support the hypothesis that stress conditioning enhances the efficacy of cell-mediated immune responses known to mediate viral clearance from brain.