Myelin basic protein serum factor (MBP-SF) in adult lewis rats: A method for detection and evidence that MBP-SF influences the appearance of antibody to MBP in animals developing experimental allergic encephalomyelitis

MBP-SF, a prominent serum factor in suckling Lewis rats, that additively inhibits the binding of¹²⁵I-labeled and unlabeled MBP to syngeneic Lewis rat anti-MBP, has now been found in low but significant amounts in adult Lewis rats using a new and more sensitive radioimmunoassay procedure. The serum factor appears to delay the time of appearance of free circulating anti-MBP antibody in immunized rats by at least a day, but the disappearance curve of MBP-SF is immediately joined by the antibody time-response curve, both elements appearing to be mutually antagonistic. The generation of significant amounts of anti-MBP antibody appears to begin on the 8th day after immunization even though free antibody does not become measurable until the 9th day. From the nature of the timing of events leading to EAE, in which the 9th day is also critical, it is therefore conceivable that MBP-SF may function as the proposed endogenous autoneurotolerogen of Orgad and Cohen and that its efficient removal by anti-MBPat least a day before anti-MBP actually becomes detectable sets the stage for the subsequent cellular immune reactions that signal EAE.