Altermatt, H JH JAltermattGerber, H AH AGerberGaeng, DDGaengMüller, ChristophChristophMüller0000-0002-3921-8678Arnold, WWArnold2024-10-112024-10-111992-12https://boris-portal.unibe.ch/handle/20.500.12422/87463Despite numerous scientific efforts, the etiology of otosclerosis still remains unknown. Pathogenically, there are several signs of a chronic inflammatory process of the bony otic capsule. In this study, we tried to characterize the components of chronic inflammation by immunohistochemical techniques. Within otosclerotic lesions a mixed cellular infiltrate can be observed, consisting of lymphocytes, macrophages and plasma cells. Macrophages which are capable of presenting antigen in association with major histocompatibility antigens (MHC) class I and class II to CD8(+)-, and CD4(+)-T cells, respectively, were found in otosclerotic lesions based on their expression of the MAC387 antigen. Furthermore, HLA-DR positive cells and complement C3 have been found in resorption lacunae of otosclerotic lesions. Several osteoblasts and chondrocytes in active otosclerotic lesions reveal a strong surface expression of beta-2-microglobulin, indicating an increased MHC class I antigen expression in active otosclerotic lesions. In agreement with recently published data we found that a large fraction of the lymphoid cells are antigen-primed T-cells expressing an alpha/beta T-cell receptor in association with CD3 molecules on their surfaces. CD4+ lymphocytes which functionally represent lymphokine-secreting cells are activated through the specific recognition of antigen, presented in context with MHC class II molecules such as HLA-DR. Therefore, the presence of MHC class II positive cells are crucial for the initiation of a local immune response. Thus, our observation of HLA-DR positive cells in otosclerotic lesions is of particular interest.(ABSTRACT TRUNCATED AT 250 WORDS)de500 - Science::570 - Life sciences; biology600 - Technology::610 - Medicine & healtharticle1493967