A B S T R A C T

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A B S T R A C T Idiopathic pulmonary fibrosis (IPF) is a progressive disease of lung parenchyma characterized by a chronic inflammatory cellular infiltration and varying degrees of interstitial fibrosis. Current data indicate that the severity of fibrosis and the degree of cellularity determine, in part, the prognosis of IPF and the response to therapy. Whereas lung biopsy gives the best assessment of fibrosis and cellularity, physiologic studies are used to stage and monitor the disease process. To determine which physiologic studies correlate best with severity of fibrosis and degree of cellularity, these parameters were graded in lung biopsies of 23 patients with IPF and compared with a variety of physiologic studies.Although vital capacity, total lung capacity, and diffusing capacity are commonly used as objective monitors of the disease process, none of these parameters correlated with either the severity of fibrosis or the degree of cellularity in biopsy specimens. In contrast, almost all parameters of lung distensibility correlated with the morphologic assessment of degree of fibrosis; compliance had the best correlation. Parameters of distensibility, however, correlated poorly with the degree of cellularity.In comparison, gas exchange during exercise correlated with both morphologic parameters; the exercise-induced changes in arterial oxygen pressure per liter of oxygen consumed had a high correlation with the degree of fibrosis (r = 0.89; P < 0.001) and correlated to a lesser extent with the degree of cellularity (r = 0.56; P = 0.009). In contrast, neither the resting arterial oxygen tension nor the arterial oxygen tension at

Cellular and immunoglobulin components of bronchoalveolar fluid recovered by bronchoscopic lavage were evaluated in 32 control patients, 10 normal volunteers, and 60 patients with the following interstitial lung diseases: idiopathic pulmonary fibrosis, pulmonary fibrosis associated with collagen-vascular disease, eosinophilic granuloma, sarcoidosis, and hypersensitivity pneumonitis. The percentage of lymphocytes distinguished two general disease categories: those with increased lymphocytes (sarcoidosis and hypersensitivity pneumonitis); and those with normal lymphocytes (idiopathic pulmonary fibrosis, pulmonary fibrosis associated with collagen-vascular disease, and eosinophilic granuloma). Patients in all five disease categories had elevated IgG levels and percentages of neutrophils compared with control patients, with the highest proportion of neutrophils found in idiopathic pulmonary fibrosis. Immunoglobulin levels also helped distinguish among patient groups, in that patients with hypersensitivity pneumonitis had lavage IgG/albumin ratios greater than 1, whereas patients with sarcoidosis had ratios less than 1; and with infrequent exceptions, the finding of IgM in lavage fluid was limited to patients with hypersensitivity pneumonitis.

To test the hypothesis that idiopathic pulmonary fibrosis (IPF) is mediated through collagenase present in the lower respiratory tract, we used the fiberoptic bronchoscope to obtain fluid from the lower respiratory tract of 24 patients with IPF, 18 controls and nine patients with sarcoidosis. The fluid was analyzed for a variety of enzymes, including collagenase. Fifteen of 21 patients with IPF showed collagenase activity, whereas normal controls and patients with sarcoidosis showed none (P greater than 0.001, for all comparisons). In two patients with IPF who were re-evaluated after eight to 24 months, the collagenase activity was persistent. Fluid from patients with IPF also contained elevated levels of a non-specific neutral protease (P greater than 0.01 compared with controls), but there was no elastase activity in fluid from patients with IPF or from controls. The collagenase found in lavage fluid in IPF cleaved lung collagen into collagenase-specific TCA and TCB fragments. We conclude that in IPF the collagen of the lung is subjected to sustained lysis, followed by disordered resynthesis, and that the presence of active collagenase in the lower respiratory tract is a specific feature of the alveolitis associated with this disease.