Anti-Myelin Proteolipid Protein Peptide Monoclonal Antibodies Recognize Cell Surface Proteins on Developing Neurons and Inhibit Their Differentiation

Using a panel of monoclonal antibodies (mAbs) to myelin proteolipid protein (PLP) peptides, we found that in addition to CNS myelin, mAbs to external face but not cytoplasmic face epitopes immunostained neurons in immature human CNS tissues and in adult hippocampal dentate gyrus and olfactory bulbs, that is neural stem cell niches (NSCN). To explore the pathobiological significance of these observations, we assessed the mAb effects on neurodifferentiation in vitro. The mAbs to PLP 50–69 (IgG(1κ) and IgG(2aκ)), and 178–191 and 200–219 (both IgG(1κ)) immunostained live cell surfaces and inhibited neurite outgrowth of E18 rat hippocampal precursor cells and of PC12 cells, which do not express PLP. Proteins immunoprecipitated from PC12 cell extracts and captured by mAb-coated magnetic beads were identified by GeLC-MS/MS. Each neurite outgrowth-inhibiting mAb captured a distinct set of neurodifferentiation molecules including sequence-similar M6 proteins and other unrelated membrane and extracellular matrix proteins, for example integrins, Eph receptors, NCAM-1, and protocadherins. These molecules are expressed in adult human NSCN and are implicated in the pathogenesis of many chronic CNS disease processes. Thus, diverse anti-PLP epitope autoantibodies may inhibit neuronal precursor cell differentiation via multispecific recognition of cell surface molecules thereby potentially impeding endogenous neuroregeneration in NSCN and in vivo differentiation of exogenous neural stem cells.