AMNIOTIC FLUID CLARA CELL PROTEIN CONCENTRATION IN NORMAL PREGNANCY, A MARKER OF FETAL AIRWAY GROWTH OR FETAL LUNG MATURATION? † 1355

Abstract

Clara cells protein (CCP) is a lung secretory protein of 16 KD molecular mass that is synthesized by nonciliated bronchial and bronchiolar cells including Clara cells. This protein is produced in the developing fetal airways and can be quantified in amniotic fluid (AF) as early as 15-16 weeks of gestation. The concentration of CCP in AF increases progressively with advancing gestation and has been suggested as a marker of growth of the fetal airways (Pediatr Res 36:771, 1994). However, whether the changes of CCP in AF are also related to the process of fetal lung maturation is unclear. We measured CCP by RIA in 98 AF samples obtained by amniocentesis between 25 and 41 weeks of gestation, from pregnancies without conditions that accelerate or delay fetal lung maturation, and determined its relationship with other known markers of this process. These were the lecithin/sphingomyelin (L/S) ratio determined by thin layer chromatography (TLC), and the concentrations of saturated phosphatidylcholine (Sat PC) measured by TLC after exposure to osmium tetroxide and surfactant protein A (SP-A) quantified by ELISA. With advancing gestational age (GA) the AF concentration of CCP increased slightly(R=0.27, p = 0.006), but more pronounced increases of the L/S ratio (R=0.58, p<0.00001), Sat PC (R=0.45, p <0.0001) and SP-A (R=0.60, p<0.00001) were found. There were extremely weak correlations of CCP with the L/S ratio(R2=0.09, p=0.008) and the AF concentration of Sat PC (R2=0.08, p=0.004), but not with the AF concentration of SP-A (R2=0.02, p=0.10). Using multiple linear regression, the ability to predict changes in the AF concentration of CCP using GA, L/S, Sat PC and SP-A as independent variables was poor (F=3.82, R2=0.19, p=0.007). Conversely, SP-A, Sat PC and GA accounted for most of the variation of the L/S ratio (F=34.71, R2=0.61, p<0.000001). These data suggest that the concentration of CCP in AF has a poor correlation with known indices of fetal lung maturation and probably reflects primarily the development of the fetal airways. (Supported in part by FONDECYT-1930854).