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 this case the proteins are referred to as Golli-MBP proteins and result from the use of 3 exons not utilized in the nervous system, resulting in larger proteins with unique N-terminal regions.
Much evidence has suggested that immune reactions to myelin sheathes is the cause of multiple sclerosis (MS, 3). One hypothesis is that MS is caused by viral infections in early life which generate immune responses which later attack myelin. One candidate immunogen is MBP, and some similarity is seen between MBP and certain viral sequences (4). Detection of MBP in blood or CSF may be a biomarker of demyelination in MS and other damage and disease states (e.g. 5).
In the central nervous system there are four different forms of the protein made by alternate transcription from a single gene, the protein products having molecular weights of 21.5, 20.5, 18.5, and 17.2kDa in humans. The mammalian gene has 7 exons, and in humans exons 2 and 5 are either included or not, producing these four proteins. The single gene of rodents also produces 4 different proteins, but of slightly different sizes, 21.5, 18.5, 17 and 14kDa. In this case the homologous exons are utilized differently: exons 2 and 6 are either inserted or not. Sequence alignments of both human and rodent isotypes can be downloaded from here. We have found that MCA-7G7 and our chicken antibody, CPCA-MBP, stain all four transcripts on blots, whereas our mouse monoclonal MCA-7D2 binds only the 21.5 kDa and 18.5kDa isotypes. here.
Above: Immunofluorescent analysis of rat brain stem section stained with mouse mAb to Myelin Basic Protein (MBP), MCA-7G7, dilution 1:5,000 in green, and costained with rabbit pAb to neurofilament NF-H, RPCA-NF-H, dilution 1:2,000 in red. The MBP antibody stains oligodendrocytes and the myelin sheathes around axons. In this high magnification view it is clear that the NF-H antibody labels axons within the myelin sheathes. Mouse select image for larger view.
Above: Blots of 20µg crude rat brain homogenate blotted with 2 MBP antibodies; MCA-7G7 (left lane) at 1:5,000 and MCA-7D2 (right lane) also at 1:5,000 dilution. MCA-7G7 bind all four rat transcripts running at 21.5kDa, 18.5kDa, 17kDa and 14kDa, while the alternate EnCor antibody MCA-7D2 binds only the two largest transcripts. We can conclude MCA-7G7 binds the core region of MBP while MCA-7D2 binds to the sequence encoded by exon 2 of the MBP gene. A sequence alignment of the human and rat MBP alternate transcripts is here.
Above: Rat mixed neuron/glial cultures stained with Myelin Basic Protein monoclonal antibody MCA-7G7 (red). Blue is a DNA stain. Note that the Myelin Basic Protein antibody stains an oligodendrocyte and some membrane shed from this cell. Other cells in the field include neurons, astrocytes, microglia and fibroblasts, all of which are completely negative with this antibody. Mouse select image for larger view.
A sequence alignment of the four CNS MBP isotypes in human and rat can be downloaded here.
1. Eylar EH, et al. Basic A1 protein of the myelin membrane. The complete amino acid sequence. J. Biol. Chem. 246:5770-84 (1971).
2. Marty MC, et al. The myelin basic protein gene is expressed in differentiated blood cell lineages and in hemopoietic progenitors. PNAS 99:8856-61 (2002).
3. Libbey JE, Fujinami RS. Experimental Autoimmune Encephalomyelitis as a Testing Paradigm for Adjuvants and Vaccines. Vaccine 29:3356–62 (2011).
4. Wucherpfennig KW, Strominger JL. Molecular mimicry in T cell-mediated autoimmunity: Viral peptides activate human T cell clones specific for myelin basic protein. Send toCell 80:695-705 (1995).
5. Berger RP, et al. Serum neuron-specific enolase, S100B, and myelin basic protein concentrations after inflicted and noninflicted traumatic brain injury in children. J. Neurosurg. 103:61-8 (2005).
