LOCALIZATION OF A PULMONARY AUTOANTIGEN IN CRYPTOGENIC FIBROSING ALVEOLITIS

Background - Cryptogenic fibrosing alveolitis (CFA) is believed to hav e an immunological pathogenesis with a persisting inflammatory reactio n to an as yet unidentified pulmonary antigen(s). A high frequency of IgG autoantibodies has previously been found in the plasma of patients with CFA to an extractable 70-90 kDa lung antigen by Western blotting . Preliminary immunohistochemical studies with patient IgG had indicat ed that the target protein(s) might be associated with alveolar epithe lial lining cells which have previously been suggested as the site of immunological attack in CFA. Methods - In order to confirm this findin g immunohistochemical analysis and Western blotting were performed on a human type II alveolar cell line (A549) using CFA patient plasma. In order to study further the distribution of the antigen, antibodies we re raised in a rabbit to the partially purified 70-90 kDa CFA lung pro tein. Results - The results showed that the human CFA autoantibody rec ognised a 70-90 kDa protein with a cytoplasmic distribution present in the A549 cells, confirming previous observations. The immune rabbit I gG recognised a protein of similar molecular weight by Western blottin g of protein derived from lung biopsy samples of patients with CFA and A549 cells. In addition it immunoprecipitated protein(s) of this mole cular weight from lung biopsy protein extracts from patients with CFA. The precipitated protein(s) were found to crossreact with the autoant ibody found in the plasma of patients with CFA. Immunohistochemical an alysis with the immunised rabbit antibody revealed positive staining o f type I and II alveolar epithelial lining cells in CFA. A similar pat tern of epithelial staining was also observed with the rabbit IgG on b iopsy specimens of lung from patients with sarcoidosis and control lun g tissue, although this was more focal and less intense. No positive s taining was seen on sections from a number of nonpulmonary tissues (co lon, Liver, kidney, tonsil, lymph node, skin, cervix). Cytoplasmic sta ining of the A549 cell line was also detected. Conclusions - The 70-90 kDa protein recognised by autoantibodies in patients with CFA is asso ciated with pulmonary epithelial lining cells. The immune rabbit IgG p roduced appears to recognise antigen by Western blotting and immunohis tochemical staining of lung tissue in a similar pattern to the patient autoantibodies. Immunohistochemical data obtained with this antibody suggest that the putative autoantigen against which patients with CFA mount a humoral immune response may be endogenous and specific to the lung.