MARKER PROTEINS IN THE PARTICULATE FRACTION OF 3RD-TRIMESTER AMNIOTIC-FLUID

The present clinical evaluation of fetal lung maturity relies largely on the determination of the amniotic surfactant phospholipids phosphot idylglycerol, lecithin, and sphingomyelin, but there are many Salse ne gatives as well as false positives among diabetics. The use of other c omponents of lung surfactant, namely, the hydrophobic surfactant prote ins (SPs) has long been suggested as an alternative to the classical a ssay, but tests based on the detection of immunoreactive SP-A have not proved superior or supplanted phospholipid ratios as an index. This r eport investigates the proteins in a fraction of third-trimester human amniotic fluid (the particulate fraction) enriched in the SP complexe s that form the surfactant monolayer. The proteins were analyzed by tw o-dimensional polyacrylamide gel electrophoresis and visualized by sil ver staining and immunoblotting. Eight proteins are of particular inte l est. Three novel proteins (termed AFPP-1, AFPP-4, and AFPP-8) and th e alpha-fetoprotein/human serum albumin complex (AFPP-7) can be detect ed throughout the 28- to 38-week gestational window. The protein that is referred to as AFPP-2 could be identified as SP-A on the basis of i mmunologic cross-reactivity as well as size and charge characteristics . The time course of appearance of AFPP-2 was also followed in patient s with Rh isoimmunization syndrome and was found to be the same as tha t seen for SP-A. The SP-A was detected as at least five major charged isoforms with multiple subisoforms of different molecular weight and c an be distinguished from a related set of proteins (AFPP-5) that appea r with a different time course but are possible precursors. Two other proteins (AFPP-3, AFPP-6), which are detectable inconsistently bear so me similarity to others reported previously but not extensively charac terized. These results define both constant and variable proteins of t he particulate fraction of the amniotic fluid and indicate that certai n protein isoforms are changing throughout the third trimester. These data enhance the possibility of the utilization of these proteins as m arkers of lung maturity in conditions such as maternal diabetes.