Alpha-fetoprotein subfractions in amniotic fluid identified by a modification of the method of concanavalin A, lentil lectin or phytohemagglutinin-E affinity crossed-line immunoelectrophoresis.

Using a modified method of concanavalin A (Con A), lentil lectin (LCH) or phytohemagglutinin-E (PHA-E) affinity crossed-line immunoelectrophoresis, alpha-fetoprotein (AFP) subfractions were studied in 33 samples of human amniotic fluid obtained between 41 and 287 days of gestation. Fetal tissues (yolk sac, liver, stomach and small intestine) obtained from a fetus of 68 days' gestation were incubated for 24 hours and AFP subfractions in the culture fluid examined. AFP in control amniotic fluids yielded two subfractions (types a and b) with Con A, three subfractions (types A, B and C) with LCH, and four subfractions (types W, X, Y and Z) with PHA-E. Serial changes of AFP subfractions in the amniotic fluid, as well as in the incubation study, indicated that the yolk sac and the gastrointestinal tract were responsible for the production of the Con A non-reactive subfraction (type b), the LCH weakly-reactive subfraction (type B) and the PHA-E reactive subfraction (types W and X), at an early stage of gestation. The Con A reactive subfraction (type a), LCH reactive subfraction (type A), PHA-E weakly-reactive subfraction (type Y) and PHA-E non-reactive subfraction (type Z) were assumed to be produced mainly by yolk sac, liver or gastrointestinal tract. We also found that the LCH non-reactive subfraction (type C) was synthesized either by liver or by the gastrointestinal tract at an early stage of gestation. At term, type a of Con A, type C of LCH and types Y and Z of PHA-E were the main subfractions in amniotic fluid, assumed to be produced by the fetal liver.