Compositions for treating autoimmune, allergic, or atopic disease comprising a compound that inhibits hyaluronan synthesis and a pharmaceutically acceptable carrier are described. In some embodiments, the compound that inhibits hyaluronan synthesis is 4-methylumbelliferone or a metabolite of 4-methylumbelliferone. Methods for treating autoimmune diabetes, multiple sclerosis and/or autoimmune demyelination, including administering to the subject a composition having a compound in an amount effective to inhibit hyaluronan synthesis in a mammalian subject, are also described.