Serum Surfactant Proteins A and D as Prognostic Factors in Idiopathic Pulmonary Fibrosis and Their Relationship to Disease Extent

TLDR

Idiopathic pulmonary fibrosis is a progressive, life‑threatening interstitial lung disease of unknown cause, and current noninvasive methods, including high‑resolution CT, inadequately predict reversible versus irreversible disease activity. The study aimed to evaluate serum surfactant proteins A and D as semiquantitative markers of disease extent and as predictors of pulmonary function decline and survival over a three‑year follow‑up. Serum SP‑A and SP‑D were quantified by ELISA in 52 IPF patients, and their levels were correlated with high‑resolution CT findings, yearly pulmonary function deterioration, and three‑year survival outcomes. Serum SP‑A and SP‑D concentrations correlated with reversible alveolitis but not with irreversible fibrosis; SP‑D additionally tracked parenchymal collapse and the rate of pulmonary function decline, and higher levels predicted mortality, suggesting that combined SP‑A/SP‑D assays could aid in forecasting IPF progression and patient outcomes.

Abstract

Idiopathic pulmonary fibrosis (IPF) is a progressive, life-threatening, interstitial lung disease of unknown etiology. For optimal therapeutic management of IPF an accurate tool is required for discrimination between reversible and irreversible types of the disease. However, such noninvasive tools are few, and even with high-resolution computed tomography (HRCT), which is the most trusted method for doing so, the nature of the disease activity in IPF cannot always be accurately predicted. The aims of the present study were to assess the values of surfactant protein (SP)-A and SP-D in semiquantifying the extent of disease in IPF and in predicting deterioration in restrictive pulmonary function and survival over a follow-up period of 3-yr. SP-A and SP-D in sera were measured with enzyme-linked immunosorbent assays as previously described. Fifty-two IPF patients were studied to evaluate the association between serum SP-A and SP-D and disease extent on HRCT, deterioration in pulmonary function, and survival during 3 yr of follow-up. Both SP-A and SP-D concentrations were significantly correlated with the extent of alveolitis (a reversible change), whereas they did not correlate with the progression of fibrosis (an irreversible change). The SP-D concentration, unlike that of SP-A, was also related to the extent of parenchymal collapse and the rate of deterioration per year in pulmonary function. The concentrations of SP-A and SP-D in patients who died within 3 yr were significantly higher than in patients who were still alive after 3 yr. We propose that assays of SP-A and SP-D in sera from IPF patients are useful tools for understanding some pathologic characteristics of the disease, that SP-D may be a good predictive indicator of the rate of decline in pulmonary function, and that a combination of the assays for SP-A and SP-D may be helpful in predicting the outcome of patients with IPF.