IN-VIVO BINDING AND HEARING-LOSS AFTER INTRACOCHLEAR INFUSION OF KHRI-3 ANTIBODY

The IgG1 mouse monoclonal antibody (MAb) KHRI-3, binds to an antigen o f 65-68 kDa expressed on inner ear supporting cells in guinea pigs. We previously showed [Nair et al. (1995) Monoclonal antibody induced hea ring loss. Hear. Res. 83, 101-113] that mice carrying the KHRI-3 hybri doma develop high frequency hearing loss and loss of hair cells in the basal turn suggesting that this MAb causes immune-mediated sensorineu ral hearing loss. To evaluate the specificity of this effect, sterile KHRI-3 and control IgG1 preparations were infused directly into the gu inea pig cochlea using Alzet(R) mini-osmotic pumps. Assessments includ ed: (1) hearing, measured by click auditory brain stem responses (ABRs ); (2) in vivo antibody binding; and (3) the structural integrity of t he organ of Corti. Nine animals were infused with KHRI-3 preparations and 5 controls were infused with control IgG1. Four guinea pigs given KHRI-3 developed 25-55 dB hearing loss. Control animals showed no diff erence from baseline. In vivo binding of KHRI-3 was detected in the or gan of Corti in 6 of the 9 animals, including all 4 that had hearing l oss. No staining was observed with control antibody. Confocal microsco py revealed that the in vivo KHRI-3 antibody binding pattern was ident ical to that obtained by incubating fixed tissue in vitro with KHRI-3. Histologic examination revealed an increased frequency of hair cell l oss in KHRI-3 treated ears when compared to either the contralateral e ars of the same guinea pigs or the IgG1 treated ears of control animal s. The lesions in the infused ears of guinea pigs were scattered throu ghout the cochlea from base to apex. These experiments demonstrate the following points: (1) Antibodies can be chronically infused directly into the cochlea of living animals. (2) The KHRI-3 antibody binds to l ive supporting cells within the organ of Corti. (3) Infusion of an inn er ear specific antibody affects auditory function. (4) The infusion o f irrelevant antibody had no effect on the structure or function of th e ear. This system provides an animal model for further studies of ant ibody-induced sensorineural hearing loss.