Endogenous Sp35 is a negative regulator for neuronal survival, axon regeneration, oligodendrocyte differentiation and myelination. Molecules that block endogenous Sp35 function, such anti-Sp35 antibodies can be used as therapeutics for the treatment of neuron and oligodendrocyte dysfunction. The present invention provides antibodies specific for Sp35, and methods of using such antibodies as antagonists of endogenous Sp35 function. The invention further provides specific hybridoma and phage library-derived monoclonal antibodies, nucleic acids encoding these antibodies, and vectors and host cells comprising these antibodies. The invention further provides methods of promoting oligodendrocyte survival and myelination in a vertebrate, comprising administering to a vertebrate in need of such treatment an effective amount of an anti-Sp35 antibody.