Never give up Contents Chapter 1Introduction and outline of the thesis Chapter 2Etiology and immunopathogenesis of sarcoidosis: Novel insights Chapter 3Clinical observations: is metal or silica associated sarcoidosis a new trigger-related phenotype? Chapter 4Immunoreactivity to metal and silica associates with sarcoidosis in Dutch patients Chapter 5Simultaneous testing of immunological sensitization to multiple antigens in sarcoidosis reveals an association with inorganic antigens specifically related to a fibrotic phenotype Chapter 6Latent tuberculosis infection associates with cardiac involvement in patients with sarcoidosis Chapter 7Presence of Propionibacterium acnes in granulomas associates with a chronic disease course in Dutch sarcoidosis patients Chapter 8Detection of Propionibacterium acnes in granulomas of patients with either hypersensitivity pneumonitis or vasculitis reveals that its presence is not unique for sarcoidosis Chapter 9Elevated serum amyloid A levels are not specific for sarcoidosis but associate with a fibrotic pulmonary phenotype Chapter 10 Summary and general discussion Appendix Nederlandse samenvatting Affiliations of the authors Dankwoord List of publications Curriculum Vitae