Dendritic Cells and Antigen Specific T Cell Responses: Effect of Pregnant Mouse Serum

Tolerance to the semi-allogenic fetal graft by the maternal immune system is a medical enigma that has stimulated investigations for a half of century. Several hypotheses have been proposed to explain the tolerance of mother to the fetus. The successful pregnancy is proposed and proved by many scientists to be a Th2 dominant phenomenon. This hypothesis is proved in most aspects of feto-maternal interface, but systemic effects of pregnancy on immune system, are controversial. Dendritic cells (DCs) are the most potent activators of naïve T lymphocytes capable of tolerance induction as well as immunity. These cells can influence Th cell differentiation, by inducing Th1 or Th2 responses as well. Therefore DCs are one of the probable candidates which mediate immune regulation during pregnancy. The aim of this study was to determine if pregnant mouse serum has any effect on DCs’ functional capacity to stimulate antigen specific proliferation of T lymphocytes and their cytokine profile. In this experimental study, mid-gestational sera were obtained from allogenic pregnant Balb/c mice (Balb/c C57BL/6) on days 9-11 of gestation. DCs were purified from Balb/c mice spleens through a three steps method including collagenase digestion of spleen tissues, selection of low-density cells by Nycodenz density gradient medium and plastic adherence. The purity of DCs was determined by flowcytometry, using anti CD11c antibody. DCs were pulsed with Conalbumin as a foreign antigen during overnight culture. In some cultures pregnant mouse sera were added at 2.5% final concentration. Two other groups of DCs were treated with normal mice sera and FBS, respectively. Antigen pulsed DCs were injected in to mice palms. Draining lymph node cells of immunized mice were cultured in presence of Conalbumin after 5 days and their proliferation was measured by 3H-thymidin incorporation method. IFN- and IL-10 production by stimulated T cells was also measured in their culture supernatant using sandwich ELISA. The results were analyzed using non-parametric Mann-Whitney test. Our results showed that normal serum-treated, antigen-pulsed DCs induced a strong proliferative response of T cells and high levels of IFN- and IL-10 production. However, treatment of DCs with pregnant mouse serum markedly blocked their ability to induce antigen-specific lymphocyte proliferation. IFN- and IL-10 productions were also decreased by lymph node cells of mice injected with pregnant serum treated DCs. Our results demonstrate that pregnant mouse serum has suppressive effect on DCs capacity to induce antigen specific proliferation and cytokine secretion by T cells. The suppressive effects of pregnant serum can be induced through HLA-G, IL-10, PGE2, progesterone and several other factors, existing mostly at the feto-maternal interface but because of their overflow can be found in the serum as well. However, determination of the exact mechanism underlying this phenomenon needs more investigation.