Detection of novel fetal polypeptides in human amniotic fluid using two-dimensional gel electrophoresis

We compared the two-dimensional polypeptide pattern of donor-matched samples of mid-gestational amniotic fluid and maternal plasma to identify fetally-derived polypeptides in the amniotic fluid. Ten major polypeptide groups, ranging in molecular mass from 14.6 to 225 Kilodaltons (K), were consistently present in amniotic fluid that were not detected in maternal plasma. Three of these polypeptide complexes have been identified: one is alphafetoprotein, the second is a cellular form of fibronectin, and the third is beta 2-microglobulin. We searched for the remaining seven polypeptides in fetal serum and urine to confirm their fetal origin. Urine contained two polypeptides at 30.5K and 25.5K with mobilities identical to species found in amniotic fluid; the 25.5K polypeptide was also present in cord serum. Possible sources for the remaining 5 components may be the fetal respiratory and gastrointestinal tracts, integument, membranes (amnion and chorion) or the uterus. In addition, developmental changes in amniotic fluid polypeptides were studied by comparing samples obtained at mid-gestation and at term. Three proteins characteristic of mid-gestational amniotic fluid with masses of 185.8K, 38.2K and 25.4K were not detected or were present only at trace levels at term; and new polypeptide groups at approximately 51K, and 18K were observed in late gestation.