Tenascin immunoreactivity in cryptogenic fibrosing alveolitis

Tenascin is a hexameric extracellular matrix (ECM) glycoprotein which has been demonstrated to have a temporal relationship with active scar formation in adult tissues. We hypothesized that this ECM protein might therefore serve to identify areas of active scarring in lung biopsies from patients with cryptogenic fibrosing alveolitis (CFA). The distribution of tenascin was examined in open lung biopsies from ten patients with CFA, six patients with sarcoidosis, and six pulmonary resection specimens from patients with no evidence of interstitial lung disease, using an immunohistochemical technique. Immunoreactive tenascin was not identified in histologically normal control lung parenchyma and was only focally found around large aggregates of granulomas in sarcoidosis. In the CFA, tenascin production was demonstrated in minimally damaged alveolar walls and areas of active disease but not in end-stage scarred lung. There was considerable local heterogeneity of staining within cases, which did not appear to relate to the density of the local inflammatory infiltrate. Large plaques of tenascin were noted to be particularly associated with hyperplastic type II alveolar epithelial lining cells, which are recognized to produce fibrogenic cytokines. The examination of tenascin expression in open lung biopsies from patients with CFA may be useful in assessing fibrogenic activity and may thus provide additional prognostic information.