A monoclonal antibody (IN-1) which neutralizes neurite growth inhibitory proteins in the rat CNS recognizes antigens localized in CNS myelin.

In previous studies two neurite growth inhibiting protein fractions of 35 and 250 kDa were identified in myelin preparations of the rat CNS. These activities were not found in the myelin of PNS. A monoclonal antibody (mAb IN-1) was raised against the 250 kDa protein fraction and selected for its ability to neutralize the inhibitory effect of CNS myelin and of both isolated protein fractions. IN-1 has been shown both in vitro and in vivo to neutralize the inhibitory effect of differentiated oligodendrocytes and CNS white matter. In the present study, the antigens of IN-1 were localized by immunohistochemistry on cryostat sections of the adult rat nervous system. The staining pattern of IN-1 was compared to that of mAbs specific for proteins found in CNS and PNS myelin. These proteins include myelin basic protein, myelin oligodendrocyte glycoprotein, and myelin associated glycoprotein. IN-1 stained white matter and myelinated fibre tracts in the CNS on sections of fresh frozen tissue fixed with 95% ethanol: 5% acetic acid (Clark's solution). Sciatic nerve myelin and spinal roots remained unstained. The staining pattern of IN-1 corresponded most closely to that of a mAb against myelin oligodendrocyte glycoprotein, a protein which occurs exclusively in CNS myelin and on differentiated oligodendrocytes.