Human amniotic fluid lacks interleukin‐2 and interleukin‐15 but can interact with the β‐chain of the interleukin‐2 receptor

• Published in: Immunology 2000-03, Vol.99 (3), p.411-417
• Main Authors: Searle, R. F., Bromage, S. J., Palmer, J., Curry, J. E., Lang, A. K.
• Format: Article
• Language: English
• Subjects: Amniotic Fluid - immunology; Amniotic Fluid - metabolism; Antibodies, Blocking - pharmacology; Biological Assay; Cytotoxicity Tests, Immunologic; Enzyme-Linked Immunosorbent Assay; Female; Humans; interleukin 2 receptors; Interleukin-15 - analysis; Interleukin-2 - analysis; Interleukins - analysis; Lymphocyte Activation; Original; Pregnancy; Pregnancy Trimester, Second; Receptors, Interleukin-2 - metabolism
• ISSN: 0019-2805; 1365-2567
• DOI: 10.1046/j.1365-2567.2000.00978.x

Summary The present study investigated whether an explanation for the conflicting reports on the interleukin‐2 (IL‐2) status of amniotic fluid is due to the presence of IL‐15 which shares biological activities with IL‐2 and utilizes the IL‐2 receptor β‐chain. Amniotic fluids from 45 normally progressing pregnancies between 14 and 16 weeks after the last menstrual period were assayed for IL‐2 and IL‐15 by bioassay and enzyme‐linked immunosorbent assay (ELISA). The ability of amniotic fluids to induce cytotoxic T lymphoblastoid line‐2 (CTLL‐2) cell proliferation was demonstrated to be dependent upon bioassay culture conditions. In serum‐free medium each amniotic fluid stimulated 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 proliferation in serum‐free medium, indicating a lack of IL‐2 and IL‐15 bioactivity. In contrast, treatment with anti‐IL‐2 receptor β‐chain antibody significantly reduced amniotic fluid‐induced proliferation. The lack of IL‐2 and IL‐15 activity in amniotic fluids was confirmed using ELISA. Although high 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 abrogated IL‐15 immunoactivity, indicating that amniotic fluid contains molecules binding to Fc regions of immunoglobulins and responsible for false ELISA 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 receptor β‐chain. The absence of IL‐2 and IL‐15 in normal mid‐trimester amniotic fluid suggests that the cytokine profile of human pregnancy appears to be associated with a bias against type 1 cytokines within the feto–placental unit.