The HuD paraneoplastic protein shares immunogenic regions between PEM/PSN patients and several strains and species of experimental animals.

Patients with small-cell carcinoma of the lung and paraneoplastic encephalomyelitis develop antibodies (anti-Hu) against HuD, a member of a family of neuronal specific RNA-binding proteins, which are also expressed by the tumor. In order to determine if the human HuD paraneoplastic antigen shares immunogenic regions between patients and several strains and species of animals, we immunized animals with HuD and several deletion constructs of this protein. All immunized animals developed high titers of anti-HuD antibodies, comparable to the antibody titers found in paraneoplastic patients. Using immunohistochemistry and Western blot analysis of human and mouse cerebral cortex, the pattern of reactivity of these antibodies could not be differentiated from the human paraneoplastic anti-Hu antibodies. None of the immunized animals developed neurologic symptoms. Western blot analysis of HuD deletion constructs demonstrated that the first and second RNA binding domains were the main immunodominant regions, and that the animal immune response was both strain and species dependent.