The effect of trophoblasts on T lymphocytes: possible regulatory effector molecules--a proteomic analysis

Tolerance of T lymphocytes at the feto-maternal interface is necessary to sustain normal pregnancy. The present investigation aimed to observe the regulatory effects on T lymphocytes by human trophoblasts and to explore possible effector molecules.

Conditioned media was made by trophoblast culture or villous explant culture for T lymphocyte proliferation and proteomic analysis. Lymphocyte proliferation was tested by thymidine incorporation. Messenger RNA for indoleamine 2,3- dioxygenase (IDO) was detected by RT-PCR and tryptophan was assayed. The protein profile of conditioned media was assessed with shotgun mass-spectrometry and the identified proteins were bioinformatically analyzed. Human chorionic gonadotropin (HCG), human chorionic somatomammotropin (HCS), interleukin (IL)-2, 4, 10 and tumor necrosis factor (TNF)-alpha were assayed with radioimmunoassay (RIA).

T Lymphocyte proliferation was inhibited by conditioned medium in a dose-dependent manner. Inhibition of IDO during previous conditioning or addition of tryptophan to the conditioned medium partly restored T lymphocyte proliferation. mRNA for IDO was expressed in trophoblasts and chorionic villi. The concentrations of tryptophan were 19.01 and 3.79 micromol/L in unconditioned and conditioned media respectively. By proteomic procedures, 548 proteins were found in placenta-conditioned medium. Among these proteins were some proteins inhibiting T lymphocytes including HCG, HCS, AFP, pregnancy-specific beta 1-glycoprotein (SP1), glycodelin, transforming growth factor beta2, thrombospondin-1, pigment epithelium-derived factor (PEDF), galectin-1, and macrophage migration inhibitory factor. HCG and HCS were also detected with RIA, however, no interleukins were detected in conditioned media with RIA or proteomic analysis.

Trophoblasts inhibit T lymphocyte through IDO-mediated tryptophan depletion and placenta-derived immunoregulatory factors. Immunological tolerance at maternal-fetal interface represents a synergistic effect of these substances and a complex mechanism involving endocrine and immune networks.