Clinical significance of serum levels of a carbohydrate antigen, sialyl SSEA-1, in patients with fibrosing lung disease.

Serum levels of sialyl SSEA-1 antigen, a carbohydrate antigen, were measured by radioimmunoassay in 142 patients with nonmalignant lung diseases. In 20 of 41 patients with fibrosing lung disease, either idiopathic or associated with collagen disease, the serum sialyl SSEA-1 levels were abnormally elevated. In patients with other lung diseases, the serum levels were almost within normal limits, less than 38.0 units/ml. In fibrosing lung disease the serum levels ranged from 13.8 to 147.0 units/ml and were largely concurrent with the degree of disease activity. The therapeutic effects of corticosteroid, which were evaluated with clinical-radiographic-physiologic scores and survivals in the patients with elevated serum levels, were significantly lower than those of the patients with the normal range of antigen levels. An immunohistochemical study performed on autopsied lungs from five patients with fibrosing lung disease indicated that the antigen was selectively expressed in the pulmonary epithelial cells that covered the remodeling alveolar septi in the lungs. No antigen was detectable by immunostaining in normal pulmonary epithelium among five normal lungs. From these findings, it is thought that the elevated levels of serum sialyl SSEA-1 may be derived from proliferating epithelial cells that were dominant in the late stage of fibrosing lung disorders. The measurements of serum sialyl SSEA-1 in patients with fibrosing lung disease may be clinically useful in establishing the degree of disease activity that has an influence on patient prognosis and therapeutic response.