The effect of anti-lymphocyte serum on experimental allergic encephalomyelitis in the guinea-pig.

An anti-thymocyte serum completely suppressed the clinical and histological manifestations of experimental allergic encephalomyelitis (EAE) in the guinea-pig. Long-term suppression of EAE was obtained with a relatively short course of treatment (8 days) although tolerance did not develop and the disease recurred in an attenuated form. Early treatment (0–8 days) was as effective as that given later, at a time (10–18 days) when the inflammatory lesion normally develops in the brain and cord. This suggests that the major effect is immunosuppressive rather than anti-inflammatory. A definite protective effect was also demonstrated within 24 hr of giving the serum to paralysed animals, implying a `peripheral' action upon sensitized lymphocytes or some additional anti-inflammatory component. The brain lesions seen in some long term survivors showed more advanced demyelination than is commonly seen in EAE, probably due to the chronicity of the lesion.