Background Prostaglandin E2 (PGE₂) is a key modulator of dendritic cells (DCs) function, and cornea-derived transforming growth factor beta 2 (TGF-β₂) promotes generation of phenotypically and functionally immature DCs. Therefore, this study was carried out to investigate whether PGE₂ is involved in the suppressive effect on DCs maturation mediated by corneal stroma cells (CSCs) and whether PGE₂ and TGF-β₂ have synergistic effect in this immunosuppressive mechanism.
Methods  Bone marrow-derived DCs (BM-DCs), splenic T cells and CSCs culture supernatant were obtained from mice via various protocols. After that, the level of PGE₂ in CSCs culture supernatant was analyzed by enzyme-linked immunosorbent assay. Then, immature BM-DCs pretreated by EP₂ receptor antagonist AH6809 or dimethyl sulfoxide were induced to mature BM-DCs in the presence of lipopolysaccharide, with or without CSCs culture supernatant. In parallel experiments, neutralizing TGF-β₂ antibody or normal goat IgG was added into the supernatant. Next, the cellular surface markers for DCs maturation, including CD80, CD86 and major histocompatibility complex class II (MHC II), were analyzed by flow cytometry, the capability to stimulate the proliferation of T lymphocytes was evaluated by allogeneic mixed lymphocyte reactions and the function of endocytosis was assessed by fluorescein isothiocyanate -dextran uptake.
Results Higher concentration of PGE₂ was detected in CSCs culture supernatant than in the fresh medium. In addition, after treated with the supernatant in the mature stage, compared with control group, BM-DCs displayed lower expression of CD80, CD86 and MHC II, lower T cell stimulatory capacity and higher endocytosis function. However, after application of AH6809, BM-DCs partially regained the T cell stimulatory capacity and expression of CD86 and MHC II, but partially lost endocytic activity. Moreover, after application of AH6809 and neutralizing TGF-β₂ antibody, the result of statistical analysis indicated that there was statistical difference of interaction in expression of MHC II and T cell stimulatory capacity.
Conclusion This study demonstrates for the first time that PGE₂ contributes to the suppressive