Accelerated response to reinoculation in experimental allergic encephalomyelitis: clinical study

An attack of experimental allergic encephalomyelitis is generally thought to confer resistance to a second attack. Nevertheless, some authors have produced second attacks, sometimes with an anamnestic shortening of the incubation period. In addition, second attacks of experimental allergic encephalomyelitis with accelerated onsets following reinoculation were found in every experiment when histopathologic rather than clinical criteria were employed. In the present work, we found that clinical signs with accelerated onset were also found in each experiment provided that the first attack was produced with the aid of Freund's complete adjuvant and provided that the reinoculation stimulus was the highly potent combination of rat spinal cord and carbonyl iron. Whatever the potency of the reinoculation, and regardless of the occurrence of an accelerated onset, the eventual outcome was a decreased severity and mortality of the second attack of experimental allergic encephalomyelitis. The new data demonstrate that accelerated onset is not necessarily an indication of increased severity.