HUMAN SURFACTANT PROTEINS A1 AND A2 ARE DIFFERENTIALLY REGULATED DURING DEVELOPMENT AND BY SOLUBLE FACTORS

An RT-PCR method for the relative quantitation of the mRNAs for human surfactant protein (SP) Al and SP-A2 was developed, verified, and then utilized to determine the relative levels of these mRNAs in fetal and adult lung samples in vivo, as well as in cultured human fetal lung e xplants and H441 cells. For the cultured tissue and cells, we assessed the effects of a variety of soluble factors known to modulate total S P-A. Comprehensive analysis revealed many significant findings, includ ing the following: both mRNAs were expressed as early as 15 wk of gest ation; throughout midgestation, SP-A1 was present at higher levels tha n SP-A2, with an average ratio of 30:1. In the adult lung, SP-A1 mRNA was present at lower levels than SP-A2, with a ratio of 0,4:1, whereas in H441 cells, the ratio was 0.85:1. In fetal lung cultured for 4 day s, both mRNAs increased, with a greater increase in SP-A2 (97-fold) th an in SP-A1 (15-fold), resulting in a final ratio of 4:1. Differential regulation was demonstrated for 8-(4-chlorophenylthio)-cAMP, interfer on (IFN)-gamma, tumor necrosis factor-alpha, and transforming growth f actor (TGF)-beta in the human fetal lung explant system, with SP-A2 be ing more affected, and for IFN-gamma and TGF-beta in the H441 cells, w here SP-A1 showed greater regulation. Of the soluble factors tested, I FN-gamma and TGF-beta had the most potent and consistent effects in bo th systems.