Localization of the human 64kD autoantigen D1 to myofibrils in a subset of extraocular muscle fibers

Purpose. To evaluate the tissue-specific expression pattern of the 64kD human autoantigen D1, a tropomodulin-related protein that may be involved in thyroid-associated ophthalmopathy. Methods. Recombinant 64kD human autoantigen D1 was generated in a bacterial expression system and used to immunize rabbits. Specific antibodies were affinity-purified and used for Western blots on normal and hyperthyroid rat and rabbit tissue, and immunofluorescence localization on cryosections of rat tissue. Results. Anti-64kD human autoantigen D1 antibodies recognize specifically a similar to 70kD polypeptide in western blots of extraocular muscle, sternothyroid muscle, and smooth muscle. Immunofluorescence staining demonstrates that the 64kD human autoantigen D1 localizes to myofibrils in slow fibers from rat extraocular and sternothyroid muscle. The level of this protein is not altered in extraocular muscles from hyperthyroid rabbits. Conclusions. The 64kD human autoantigen D1 is expressed in slow fibers of extraocular and sternothyroid muscles as a component of myofibrils, and is not upregulated in conditions of hyperthyroidism.