Studies on the inactivation of encephalitogenic myelin basic protein by serum

This study confirms previous reports that myelin basic protein loses its encephalitogenic activity when incubated in normal serum at 37 degrees C. The mechanisms for this was studied. 125I-labelled human myelin basic protein was rapidly degraded by normal guinea pig serum to low molecular weight products as shown by polyacrylamide gel electrophoresis. An intermediate product of molecular weight about 6000 daltons was seen. Plasma had a much lower degradative activity than serum; the half life of myelin basic protein was 3.8 hours in plasma compared with 12 minutes in serum. Serum degraded myelin basic protein was no longer capable of suppressing experimental allergic encephalomyelitis in the guinea pig nor of eliciting delayed-type hypersensitivity in guinea pigs sensitized to myelin basic protein.