Myelin Basic Protein (MBP) is one of the major proteins of the myelin sheath surrounding axons in the nervous system. Since it is of relatively low molecular weight and high abundance the protein sequence was determined from purified protein over 30 years ago (1). The protein is made by oligodendrocytes in the central nervous system, so antibodies to MBP are good markers of this cell type. However, transcripts from the same gene are also expressed in certain hematopoetic lineage cells (2). In the mammalian central nervous system there are four different forms of the protein made by alternate transcription from a single gene, which have molecular weights of 21.5, 20.5, 18.5, and 17.2 kDa in humans. The single gene of rodents also produces 4 different proteins, but of slightly different sizes, 21.5, 18.5, 17 and 14 kDa. Sequence alignments of both sets of isotypes can be downloaded from here. We characterized our antibodies on rat spinal cord homogenates and detected the four bands expected for that species. As shown below, MAB-10660 shows preferential binding for the two higher molecular weight isoforms of 21.5 kDa and 18.5 kDa in the rat. The HGNC name for this protein is MBP.