Intact human fetal membranes (amnion, chorion and decidua) were incuba
ted with I-125-labelled cytokines added to the fetal or maternal sides
of the membrane. The transfer of I-125-labelled interleukin-6 (IL-6),
I-125-labelled tumour necrosis factor cr. (TNF-alpha), I-125-labelled
interleukin-1 alpha (IL-1 alpha) and I-125-labelled interleukin-1 bet
a (IL-1 beta) was determined by measurement of radioactivity in a gamm
a counter and the integrity of the cytokines was assessed by acid prec
ipitation and by radioimmunoassay. IL-1 alpha and IL-1 beta were trans
ferred through human fetal membranes in both feto-maternal and materno
-fetal directions at similar rates. Only 2-4% of the cytokine original
ly added appeared to be intact on the opposing side of the membrane af
ter 24 h of culture. Transfer of intact TNF-alpha (5-7%) and IL-6 (8-1
7%) was greater than that of the IL-I isomers. Low but variable amount
s of the four cytokines tested may be transferred through the human fe
tal membrane. This finding suggested that concentrations of cytokines
in amniotic fluid would not reflect those produced by decidua if the f
etal membranes are intact.