ANTIGENIC TARGETS AUTOIMMUNE SENSORINEURAL HEARING LOSS

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DESCRIPTION: (Adapted from applicant's description) Autoimmune sensorineural hearing loss (AISNHL) in man may be the result of antibodies to inner ear antigens. A monoclonal antibody KHRI-3 that binds to supporting cells in the organ of Corti and a 68 kD protein in guinea pig inner ear extracts causes hearing loss and loss of outer hair cells in the guinea pig. In sera from 50-60% of patients with AISNHL we found antibodies with similarities to KHRI-3. We will test the hypothesis that patients with AISNHL have antibody to a 68 kD inner ear antigen, that this antigen is expressed on supporting cells in the organ of Corti, and that the same antigen is also expressed in human inner ear. We will test a second hypothesis that human autoantibodies and KHRI-3 bind to the same inner ear protein, that this protein is distinct from heat shock protein 70 (HSP-70), that the inner protein can be affinity purified on a KHRI-3 column, sequenced, and that the gene for this protein can be cloned, sequenced, expressed in vitro and used as an antigenic substrate for detecting antibodies in patients with AISNHL. Preliminary results show that human sera with antibodies to a 68 kD guinea pig inner ear antigen also bind to supporting cells in the guinea pig inner ear. Human inner ear tissue can specifically absorb this antibody reactivity. A 68 kD protein immunoprecipitated from guinea pig inner ear extracts by KHRI-3 is stained by AISNHL sera, but not by normal donors' sera and not by antibodies to HSP-70. These preliminary data support our hypotheses and suggest that an immunoaffinity column prepared with KHRI-3 antibodies will isolate a protein of sufficient purity for amino acid sequencing. Based on the sequence we will screen inner ear libraries, isolate and clone the gene for the inner protein, express the full length cDNA in an in vitro translation system, and test whether this material can be used as a substrate for detecting AISNHL antibodies. If we are successful this could lead to a rational, accurate test for AISNHL and a better understanding of the mechanism of autoimmune damage to the inner ear.