Activated peripheral blood mononuclear cells induce p44/42 mitogen-activated protein kinase phosphorylation in trophoblast-like JAR cells

Bi-directional calcium signaling between adjacent leukocytes and trophoblast-like cells

PROBLEM

Trophoblasts are believed to play an important role in mitigating immunological responses against the fetus. To better understand the nature of trophoblast-leukocyte interactions, we have studied signal transduction during intercellular interactions.

METHOD OF STUDY

Using a highly sensitive microfluorometric ratioing method and Ca²(+) -sensitive dyes, we measured Ca²(+) signals in trophoblast-like cell lines (JEG-3 and JAR) or in leukocytes (neutrophils and monocytes) during intercellular contact.

RESULTS

Trophoblast cell lines exhibit Ca²(+) signals during leukocyte contact. In contrast, leukocytes cannot elicit Ca²(+) signals in non-opsonized tumour cells, suggesting that Ca²(+) signaling is not a general feature of cell-cell encounters. Similarly, leukocytes demonstrate Ca²(+) signals during contact with trophoblast cell lines. Ca²(+) signals were confirmed using three dyes and with the Ca²(+) buffer BAPTA.

CONCLUSION

We suggest that leukocyte-to-trophoblast interactions lead to mutual Ca²(+) signaling events in both cell types, which may contribute to immunoregulation at the materno-fetal interface.

Soluble factors from LPS- and PHA-activated PBMC induce MAPK, Stat1 and Stat3 phosphorylation in primary cultures of human term placental trophoblasts: implications for infection and prematurity

Infection of the maternal vaginal tract is one of the single most important antecedents of premature labor. We have hypothesized that the abundant local synthesis of pro-inflammatory cytokines that occurs during infection may disrupt the delicate "immunological cross-talk" that must occur between maternal and fetal tissues in order to carry pregnancy to term. These experiments were undertaken as part of a larger study directed at testing that hypothesis. We prepared primary cultures of human trophoblasts from term placentas. Cell cultures were stimulated with conditioned medium from resting, PHA or LPS-activated peripheral blood mononuclear cells (PBMC). Medium with LPS or PHA at the same concentration as that used to stimulate the PBMC was used as an additional control. Lysates were subjected to western blotting for activated forms of the mitogen-activated protein kinases (MAPK), Stat1, and Stat3. Western blotting showed phosphorylation of the Jun kinase (JNK), p38, and Erk1/Erk2 MAPK in trophoblasts incubated with conditioned medium from LPS or PHA-activated PBMC but not from medium from resting PBMC, or with PHA or LPS alone. Phosphorylation could be detected as early as 5 min and was still observable by 10 min, the latest time point tested. Similarly, Stat1 and Stat3 phosphorylation was observed within 10 min of exposure to conditioned medium and was still observable 10 min after exposure. Immunohistochemistry also demonstrated nuclear translocation of both Stat1 and Stat3 after stimulation of trophoblasts with medium from activated PBMC. These findings are compatible with the hypothesis that immunologic balance at the maternal-fetal interface is maintained by ongoing "cross-talk" between the fetus (and fetally-derived tissues) and the maternal immune system. Infection of the maternal vaginal tract may disrupt this delicate immunologic balance, initiating inflammatory events that ultimately result in preterm labor.

Immune cells contribute to systemic cross-talk between the embryo and mother during early pregnancy in cooperation with the endocrine system

In early pregnancy, human chorionic gonadotropin (HCG) stimulates the corpus luteum to produce progesterone that in turn maintains human embryo implantation in the uterus. This inevitable communication through blood circulation can be called 'systemic cross-talk between the embryo and mother'. Despite considerable evidence suggesting that the human corpus luteum cannot be maintained by HCG alone, no other responsible soluble factors have been proposed. We found that peripheral blood mononuclear cells (PBMC) derived from pregnant women promoted progesterone production by human luteal cells and propose that both hormones and immune cells participate in this systemic cross-talk. This systemic cross-talk by immune cells is believed to operate in embryo implantation. Splenocytes derived from pregnant mice promoted endometrial differentiation and embryo implantation in vivo. Human PBMC derived from women early in pregnancy promoted invasion of murine embryos in vitro. In addition, recombinant HCG increased the effects of human PBMC on murine embryo invasion. Human chorionic gonadotropin also increased chemokine production by human PBMC through a lectin-glycan interaction, which is a primitive pathway in the immune system. Furthermore, chemokines were shown to induce human trophoblast invasion. These findings suggest that the immune system positively contributes to systemic cross-talk between the embryo and mother in cooperation with the endocrine system. (Reprod Med Biol 2006; 5: 19-29).

Gene expression arrays reveal a rapid return to normal homeostasis in immunologically-challenged trophoblast-like JAR cells

The immunologic adaptations of pregnancy have come under increasing scrutiny in the past 15 years. Existing experimental evidence clearly demonstrates that placental trophoblasts play an important role in regulating immunologic/inflammatory responses at the maternal-fetal interface. We used a well-developed gene expression array to examine in greater detail the physiologic response of trophoblast-like choriocarcinoma cells to a model immunologic 'challenge.' We co-cultured PHA-activated or resting peripheral blood mononuclear cells (PBMC) with the human choriocarcinoma cell line JAR for time periods ranging from 2 to 18 h. Messenger RNA expression in the JAR cells was then assessed using a 21,329-gene microarray and novel biostatistical analyses that we have previously published. Patterns of differential gene expression were assessed using a commercial pathway analysis software program. Differences in gene expression between JAR cells cultured with activated PBMC (experimental samples) and JAR cells cultured with resting PBMC (control samples) were seen only at the 2h time point. That is, multiple genes were transcribed in JAR cells in response to activated PBMC, but expression levels of the genes had all returned to baseline by 6h. Molecular modeling demonstrated that the differentially expressed genes were largely associated with cell growth and differentiation. This model was confirmed by noting a two-fold increase in CD10/neutral endopeptidase expression (a marker for cell differentiation) in JAR cells incubated with media from activated PBMC compared with JAR cells incubated with resting PBMC. These findings support the hypothesis that there is a delicate immunologic milieu at the maternal-fetal interface that must be maintained. Immunologic/inflammatory challenge at the maternal-fetal interface is compensated by cellular mechanisms that work to reduce inflammation and rapidly restore immunologic balance.