SURFACTANT PROTEIN A2 GENE-EXPRESSION BY HUMAN AIRWAY SUBMUCOSAL GLAND-CELLS

To determine whether human airway submucosal glands produce and secret e surfactant proteins, we examined their protein and gene expression i n submucosal glands from trachea and bronchi obtained from operated an d autopsied lungs within 4 h of death. Using a monoclonal antibody (PE -10) against surfactant protein A (SP-A), a positive immunoperoxidase stain was observed over serous cells of submucosal glands in histologi c sections of airway walls. Measurement of SP-A in culture medium samp les using single-step enzyme-linked immunosorbent assay showed a signi ficant secretion of SP-A by isolated submucosal glands (1.2 +/- 0.08 n g/ml/h, SEM, n = 40). In gene expression experiments by reverse transc ription-polymerase chain reaction, the SP-A complementary DNA (cDNA) s egment was amplified from isolated submucosal glands, indicating the p resence of SP-A messenger RNA (mRNA) in airway submucosal glands. Bron chial superficial epithelial cells failed to show the presence of SP-A mRNA. No cDNA segment of SP-B, SP-C, or SP-D cDNA was amplified from isolated submucosal glands or superficial epithelial cells, whereas al l were amplified from alveolar tissue. Furthermore, in contrast to the control alveolar tissue, which expressed both SP-A1 and SP-A2 genes, SP-A2 gene transcript alone was detected in isolated submucosal glands by Southern analysis that included the digestion of the amplified SP- A cDNA fragment with the restriction enzyme Apa I. These findings indi cate that human airway submucosal gland cells can transcribe the SP-A2 gene and produce SP-A protein in a manner different from peripheral a irways and alveoli, playing a role in the airway defense mechanism.