The mechanism by which complement is activated by MBP—and other self-antigens such as thyroglobulin (TG) [47]–remains to be elucidated, but the presence of MBP-reactive antibodies in normal human serum and in serum from MS patients [48,49] suggests that immune complexes containing MBP activate complement through the classical pathway leading to tagging of MBP with fragments of complement component 3. This evidence concerns the gene MBP and myeloid sarcoma.