Levels and plasmatic distribution of protein S were studied on umbilical cordplasmas from 25 normal full-term newborns (N) and 15 normal fetuses (F) between20 and 30 weeks of gestation.
Samples from fetuses were collected for antenatal diagnosis by direct puncture of the umbilical vein under high resolution real-time ultrasound. Total protein S(PS) level was determined using Laurell rocket immuno-electrophoresis (Diagnostica Stago, Asnifcres-France). Free PS wasmeasured using this latter method, afterprecipitation of C4b-BP-bound-PS by polyethylene glycol (PEG). Normal pool plasma, treated as well, was considered as the reference curve. C4b-binding protein (C4b-BP) determinations were conducted by Laurell rocket immunoelectrophoresis. The qualitative distribution of free PS and C4b-BP-bound-PS in plasma was also assessed by crossed-immunoelectrophoresis(CIE). Results (mean - SD) were expressed in percentage, in relation to healthy adults values (n = 15). Low levels of total PS were obtained in all fetuses (16.4 ±4.2) and newborns (36.4 ±9.5) as compared to adults (91.6 ± 12.2). Free protein S level was also decreased both in fetuses (22.2 ±6.0) and newborns (48.5 ± 12.1 versus 89.4 ± 26.3 in adults). At these stages of development, the ratio Free PS / Total PS (both values were obtained according to a reference curve performed with a normal adult pool plasma untreated by PEG) was significantly higher as compared to normal adults (0.82 ±0.07 in F, 0.64 ±0.17 in N and 0.39 ±0.11 in A, p‹0.001, Student t test). The predominance of
free PS was also visualized in the CIE patterns. These data may be explained by undetectable C4b-BP in 21-week old fetuses (‹2% in 10 cases). After the 26th week of gestation C4b-BP level was 7.8 ±7.4 ‹n=5) and reached a value of 19.2 ±15.6 in newborns (adults = 95.7 ±14.7). In human fetus and newborn, PS essentially circulates under free form and this might compensate the decrease of the total PS level.