Distribution of immunocompetent cells in the endolymphatic sac

To better understand the role of immunocompetent cells in the defense mechanism of the inner ear, the distribution patterns of those cells were investigated in the endolymphatic sac (ES) of mice maintained in three different conditions: germ-free (GF), specific pathogen-free (SPF), and conventional (CV). In another experiment, the recruitment of lymphocyte subsets was examined in the ES of SPF rats undergoing a perilymphatic antigen challenge after systemic presensitization. In the ES of GF mice, no immunocompetent cells were found. In the ES of SPF and CV mice, cells positive for IgG, IgA, IgM, and Lyt-1 were present in much smaller numbers than in the nasal mucosa. Cells positive for Lyt-2 were not seen in the ES of any mice. In the ES of rats that underwent a perilymphatic antigenic stimulation after a systemic presensitization, B lymphocyte subsets (positive for IgG, IgA, IgM) were mobilized in increased numbers, and T cell subsets (helper/inducer and suppressor) were also found 1 week after perilymphatic antigen challenge. These results taken together suggest that the ES is not originally equipped to possess immunocompetent cells and mount an immune response, but that once it has been activated with the inner ear antigenic stimuli, the ES can be the active site of a local immune response of the inner ear.