Expression of class II MHC antigens on alveolar epithelium in fibrosing alveolitis.

Lung biopsy specimens from eight patients with fibrosing alveolitis with or without connective tissue disease were investigated for the presence of immune deposits and the expression of class II histocompatibility antigens on the alveolar epithelium. Immune deposits were not detected. The alveolar epithelium stained strongly with anti-Ia (HLA-DR) monoclonal antibodies in seven out of eight biopsy specimens from the patients, but not in control lung tissue. Sub- and intra-epithelially localized mononuclear cell infiltrates consisted predominantly of T8-positive (cytotoxic/suppressor) lymphocytes. The expression of class II antigens on the alveolar epithelium and its infiltration with T8 positive cells is consistent with local presentation of self-antigens and an ensuing local immune response.