Rf. Searle et al., Human amniotic fluid lacks interleukin-2 and interleukin-15 but can interact with the beta-chain of the interleukin-2 receptor, IMMUNOLOGY, 99(3), 2000, pp. 411-417
The present study investigated whether an explanation for the conflicting r
eports on the interleukin-2 (IL-2) status of amniotic fluid is due to the p
resence of IL-15 which shares biological activities with IL-2 and utilizes
the IL-2 receptor beta-chain. Amniotic fluids from 45 normally progressing
pregnancies between 14 and 16 weeks after the last menstrual period were as
sayed for IL-2 and IL-15 by bioassay and enzyme-linked immunosorbent assay
(ELISA). The ability of amniotic fluids to induce cytotoxic T lymphoblastoi
d line-2 (CTLL-2) cell proliferation was demonstrated to be dependent upon
bioassay culture conditions. In serum-free medium each amniotic fluid stimu
lated CTLL-2 proliferation with a mean level of IL-2-like bioactivity of 14
.7 +/- 2.3 ng/ml but amniotic fluids failed to induce CTLL-2 proliferation
in serum-supplemented medium. Treatment with neutralizing anti-IL-2 or anti
-IL-15 antibodies failed to inhibit amniotic fluid-induced CTLL cell prolif
eration in serum-free medium, indicating a lack of IL-2 and IL-15 bioactivi
ty. In contrast, treatment with anti-IL-2 receptor beta-chain antibody sign
ificantly reduced amniotic fluid-induced proliferation. The lack of IL-2 an
d IL-15 activity in amniotic fluids was confirmed using ELISA. Although hig
h levels of IL-15 immunoactivity were detected in all samples, specificity
controls showed a lack of specific IL-15 immunoactivity in amniotic fluid.
Pretreatment of amniotic fluids with 100-500 ng/ml mouse immunoglobulin G a
brogated IL-15 immunoactivity, indicating that amniotic fluid contains mole
cules binding to Fc regions of immunoglobulins and responsible for false EL
ISA positivity. These studies unequivocally show that amniotic fluid lacks
IL-2 and IL-15 but can stimulate CTLL-2 cell proliferation via the IL-2 rec
eptor beta-chain. The absence of IL-2 and IL-15 in normal mid-trimester amn
iotic fluid suggests that the cytokine profile of human pregnancy appears t
o be associated with a bias against type 1 cytokines within the feto-placen
tal unit.