Myelin basic protein-related proteins in mouse brain and immune tissues.

Brain and immune system tissues express myelin basic protein (MBP) mRNAs that contain novel exons upstream of those of the classic MBPs. We have generated antisera against a recombinant protein that includes the deduced sequence for one of the predicted species of the new MBP-related protein, hemopoietic HMBPR1. We report here the presence of multiple proteins reactive to the antisera in a range of tissues. The principal finding is that the antisera recognize a family of proteins of approximately 25 kDa that are restricted to brain, thymus, and spleen, the only tissues in which the new MBP-related transcripts are present. These antisera also detect other proteins of apparent molecular mass consistent with other isoforms of predicted MBP-related proteins. The expression of MBP-related proteins in immune system tissues may be important for self-tolerance to CNS MBPs and the initiation of immune-associated demyelinating diseases.