Myelin basic protein serum factor. An endogenous neuroantigen influencing development of experimental allergic encephalomyelitis in Lewis rats

Age-related concentrations of myelin basic protein serum factor (MBP- SF), an endogenous neuroantigen detected and quantitated by inhibition of binding of rat myelin basic protein (RMBP) antibody with 125I-RMBP reagent antigen and immunochemically indistinguishable from native RMBP in this respect, reach peak levels as high as 21 ng/microliter among 2- 3-wk-old normal suckling Lewis rats. Levels then progressively decline to low, usually undetectable levels of less than or equal to 0.6 ng/microliter MBP-equivalents in adult animals by 7 wk of age. MBP-SF levels are inversely related to the age-related increasing capacity of maturing Lewis rats to develop experimental allergic encephalomyelitis (EAE) after sensitization to MBP of syngeneic, but not xenogeneic, origin. MBP-SF appears to be an endogenous neuroimmunoregulatory product of potential importance for immunologic tolerance to autologous RMBP in Lewis rats.