Neuron- and myelin-specific monoclonal antibodies recognizing cell-surface antigens of the central and peripheral nervous system

Immunohistochemical screening of monoclonal antibodies raised against Triton X-114-treated synaptic membranes revealed two monoclonal antibodies, namely BM88 and BM72, with characteristic binding specificities in the central and peripheral nervous systems of the pig. Monoclonal antibody BM88 was exclusively associated with neuronal elements while BM72 was myelin-specific. Thus, in the central nervous system, immunostaining with BM88 was observed throughout the gray matter of all regions of the forebrain and spinal cord tested. In the peripheral nervous system, BM88 strongly labelled the perikarya and processes of dorsal root ganglion neurons as well as the myelinated and unmyelinated neuronal processes of the dorsal roots; BM88 immunoreactivity was also detected in neuronal cell bodies and fibres of the enteric ganglia. In addition, BM88 immunolabelled the cell-surface of cultured neurons derived from brain. In mixed cultures the staining was uniformly distributed on the perikarya and along the neurites of these cells. However, in neuron-enriched cultures where 95% of the cells were immunochemically identified as neurons, the staining of the neuronal surface membrane was patchy. This phenomenon was independent of days in culture and suggested that the distribution of the BM88 antigen on the cell surface of neurons may be regulated by neuron glia interactions. By Western blotting, the antigen recognized by BM88 in brain membrane fractions which had undergone reducing sodium dodecyl sulphate/polyacrylamide gel electrophoresis was shown to be a 22,000 mol. wt polypeptide. When extracted with Triton X-114 this polypeptide partitioned into the detergent-rich phase, a property typical of an amphipathic membrane protein. In non-reducing conditions BM88 bound to a band with a molecular weight of 43,000. These results show that the BM88 antigen is composed of two polypeptide chains of equal molecular weight linked by disulphide bridges. Monoclonal antibody BM72 recognized a myelin-associated antigen in the central and peripheral nervous system. Immunohistochemical evidence suggested a cell-surface location for this antigen. By solid phase radioimmunoassay, monoclonal antibody BM88 was shown to cross-react with brain membrane fractions from pig, rabbit and rat while BM72 recognized only a pig membrane antigen. Both monoclonal antibodies BM88 and BM72 may be used as specific cellular markers in the nervous system.