KL-6, a human MUC1 mucin, is expressed early in premature lung.

KL-6, one of the MUC1 antigens, is a mucin-like high-molecular-weight glycoprotein, which is strongly expressed on type II pneumocytes. Serum levels of KL-6 have been shown to correlate with activity of interstitial pneumonia (IP). During embryonic development, MUC1 expression coincides with the onset of epithelial sheet and glandular formation. To investigate the potential role of KL-6 in lung morphogenesis, we examined KL-6 expression by immunohistochemistry on autopsied lung tissue specimens of 35 neonates and infants with gestational age from 23 to 40 weeks. Hyaline membranes (HMs) were detected in 13 of 35 cases. Simultaneously, antibody against surfactant protein A (SP-A) was employed in the study which is a distinct marker for type II pneumocytes. In all cases studied with gestational age above 23 weeks, staining for KL-6 was strongly positive in alveolar epithelial cells and in HMs found in 13 cases, whereas immunoreaction for PE10 varied depending on gestational age and duration of postnatal survival. Our findings suggest that KL-6 is expressed earlier in premature lung and may act as an important factor contributing to morphogenesis and function of developing lung in early gestation.