Materials and methods for using multivalent molecules (e.g., antibodies) to modulate cellular function. A molecule can be targeted to a particular type of cell, either through direct binding to an epitope on the surface of the cell, or through a linker that recognizes both the multivalent molecule and a marker on the cell surface. The invention provides a chimeric polypeptide comprising a first amino acid sequence and a second amino acid sequence, wherein the first amino acid sequence comprises an WIC Class I peptide sequence, and where the second amino acid sequence comprises an epitope to which a multivalent molecule binds, including wherein the multivalent molecule is an IgM antibody, including antibody hIgM22. The invention provides a linker molecule for targeting IgM antibody, including antibody hIgM22, to a cell in the oligodendrocyte lineage.