Functional and biochemical properties of a mouse placental immunoregulatory factor

Microenvironment of the feto–maternal interface protects the semiallogenic fetus through its immunomodulatory activity on dendritic cells

OBJECTIVE

To investigate the immunomodulatory activity of decidual culture supernatant on dendritic cell (DC) functions.

DESIGN

In vivo and in vitro experimental study using mice.

SETTING

Academic research laboratory.

ANIMAL(S)

C57BL/6-mated female Balb/c mice.

INTERVENTION(S)

Culture supernatants of decidual cells obtained from the uteri of allogenic pregnant mice (Balb/c x C57BL/6) were collected. Dendritic cells were purified from Balb/c mice spleens and pulsed with antigen during overnight culture. In some cultures, decidual supernatant was added at 5%, 10%, or 20% final concentration. Endometrial culture supernatant-treated DCs served as a control. Antigen-pulsed DCs were injected into the front footpads of syngeneic mice.

MAIN OUTCOME MEASURE(S)

Lymph nodes of primed mice were removed 5 days after DC injection. Antigen-specific proliferation and interleukin-10 and interferon gamma production by lymphocytes were measured by (3)H-Thymidine incorporation and ELISA, respectively.

RESULT(S)

The results showed that decidual culture supernatant markedly blocked in vivo antigen presentation by DCs and inhibited their capacity to induce interferon gamma (but not interleukin-10) production by primed lymphocytes.

CONCLUSION(S)

It seems that soluble factors produced by decidual cells are important mediators of immunoregulation at the feto-maternal interface, which provide the two fundamental requirements for protection of the semiallogenic fetus, namely immunologic tolerance and predominance of T helper 2 immunity, through modulation of DCs function.

Effect of pregnancy and placental factors on the quality of humoral immune response

Asymmetrical IgG molecules are characterised by the presence of a mannose-rich oligosaccharide group in only one of the two Fab fragments, which impairs the corresponding paratope, causing such molecules to behave as univalent antibodies and therefore as antigen blockers [1-3]. During human and murine pregnancy, an increase has been detected in asymmetrical IgG molecules in serum and those bound to the placenta, which normally releases factors capable of modulating the immune response. It thus seemed of interest to investigate the effect of placental culture supernatants (PCS) on in vivo and in vitro synthesis of rat immunoglobulin IgG1, IgG2a, IgG2b and IgG2C, particularly the ratio of symmetrical and asymmetrical molecules in each isotype. The effect of PCS was determined in vivo by means of passive transfer to virgin females and in vitro by analysing the supernatants of spleen cells cultured in the presence of PCS. The results showed that neither pregnancy status nor PCS were capable of modifying serum levels of IgG2a, IgG2b or IgG2c, whereas the level of IgG1 was reduced. When PCS were added to the spleen cells cultures, an in vitro increase was observed in IgG2a, IgG2b and IgG2c production. The separation of symmetrical from asymmetrical IgG molecules was performed by affinity chromatography in Concanavalin A-Sepharose, as such lectin binds high mannose sugars present only in asymmetrical IgG molecules. It is shown that pregnancy and PCS induce an increase in IgG1 and IgG2 molecules asymmetrically glycosylated, capable of binding to ConA-Sepharose. Therefore, the placenta is capable of releasing factors which can regulate the relative proportion of asymmetrical IgG molecules and induce quantitative and qualitative modifications of the in vitro and in vivo produced antibodies.

Altered modulation of the in vitro antibody synthesis by placental factors from the CBA/J x DBA/2 abortion-prone mating combination

PROBLEM

The in vitro immunomodulating effect of placental culture supernatants (PSs) obtained from two H-2k x H-2d allogeneic crossbreedings, the CBA/J x DBA/2 abortion-prone mating combination, and the reproductively normal pregnancy CBA/J x BALB/c crossbreeding were compared, and the influence of previous deliveries was evaluated. The behavior of placentae obtained from CBA/J females with two previous pregnancies by BALB/c males was also investigated.

METHOD OF STUDY

Supernatants of cultures of murine placentae were added to a mouse immunoglobulin (Ig) G1 hybridoma culture which produced anti-dinitrophenol (anti-DNP) antibodies. The quantity of monoclonal antibody produced, the nature of these antibodies, and the proliferation of the hybridoma cells were studied.

RESULTS

CBA/J x DBA/2 placental factors obtained from multiparous females induced a diminished asymmetric IgG antibody production without varying the quantity of antibody produced. In contrast, PSs obtained from the nonresorption-prone CBA/J x BALB/c mating combination with the same number of previous deliveries enhanced the production of both symmetric and asymmetric anti-DNP molecules and also increased the proportion of asymmetric blocking monoclonal antibodies (mAbs) synthesized by the hybridoma. Both of the PSs analyzed had induced similar inhibition of 3H-thymidine uptake. PSs obtained from the abortion-prone mating combination whose CBA/J females had two previous pregnancies by BALB/c males showed similar immunomodulating effects to those observed using multiparous CBA/J x BALB/c placentae.

CONCLUSIONS

We propose that the placenta produces soluble factors that participate in the regulation of antibody synthesis by the mother during gestation. Such a placental immunomodulating effect appears to be altered in the CBA/J x DBA/2 abortion-prone mating combination and could be corrected by previous pregnancies by BALB/c males. These observations suggest that placental factors would be relevant to the protection of the fetus and might play an important role in the immune equilibrium between mother and fetus. Asymmetric antibody production as a Th2 responsiveness was also discussed.

Incidence of rat-soluble placental factors on IgE and IgG2a synthesis

PROBLEM

The in vivo effect of soluble factors present in placental culture supernatants (PCSs) on the synthesis of rat immunoglobulin E (IgE) and IgG2a isotypes was investigated.

METHOD OF STUDY

Batches of Wistar SPF rats immunized with a 10-microgram dose of ovalbumin and Al(OH)3 were used: group I, consisted of virgin rats; group II, virgin females injected simultaneously with PCSs; and group III, pregnant females. As controls, nonimmunized batches were included. Serum samples were collected at days 0 (basal) and 10 after antigen challenge, determining levels of total and specific antiovalbumin of both IgE and IgG2a by enzyme-linked immunoadsorbent assay (ELISA).

RESULTS

In vivo and at least at the doses administered, PCSs exert an inhibitory effect on the synthesis of specific and total anti-ovalbumin IgE during the course of immune response to such challenge. However, PCSs did not modify serum values of total and specific IgG2a.

CONCLUSIONS

These results suggest that PCSs exert selective influence on the synthesis of diverse immunoglobulin isotypes during immune response, through the balance of cytokines synthesized by placental cells.

Preliminary characterization of an immunosuppressive inducer factor secreted by the JEG-3 choriocarcinoma cell line: in vitro and in vivo studies

PROBLEM

The direct immunosuppressive and suppressive inducing capacities of supernatants from human trophoblastic choriocarcinoma cell lines (HCS) are well investigated in several former studies. The responsible factor is not yet determined.

METHOD OF STUDY

We first confirmed those data and we purified a 3-5-kDa suppressor-inducer factor from HCS by using high performance liquid chromatography (HPLC) on both DEAE and gel filtration columns, followed by ultrafiltration. We then tested the activities of such isolated fractions on in vitro immune responses from human cells and in vivo by its effects in a murine local graft-versus-host (GVH) assay (popliteal lymph node assay, PLN).

RESULTS

A single fraction induces both "direct suppression" in vitro as well as in vitro suppressor cell activation/development in human peripheral blood lymphocyte cultures as assessed by suppression of cells cultured in such a fraction containing culture medium of the mixed lymphocyte reaction. Furthermore the very same fraction suppresses in vivo murine allogeneic immune responses as assessed by a local GVH reaction (PLN assay).

CONCLUSIONS

We have isolated a suppressive fraction, whose activities suggest that it might be of interest not only in reproductive immunology, but also in transplantation systems.

Influence of mouse placental factors on in vitro antibody synthesis

Placental culture supernatants (PS) obtained from various mouse crossbreedings were added to mouse IgG1 hybridoma cultures producing anti-DNP antibodies. The quantity of monoclonal antibody (mAb) produced, the nature of these antibodies and the proliferation of the hybridoma cells were studied. It was observed that the supernatants increased or diminished the production of mAb, depending on the genetic origin of the placentae. This effect was the same using placentae from primiparous or multiparous females and it was not due to modifications of the cellular proliferation of the hybridoma, as shown by 3H-thymidine uptake. It was also found that placental supernatants induced an increase in the proportion of asymmetric, blocking antibodies synthesized by the hybridoma. This effect was detected with supernatants from both allogeneic or syngeneic crossbreedings, but only when placentae were obtained from multiparous females. These observations indicate that placentae produce at least two soluble factors that participate in the regulation of antibody synthesis and suggest that these factors play an important role in the immune equilibrium between mother and fetus.

A mouse placental immunoregulatory factor different from transforming growth factor beta

Of the growth-promoting factors, transforming growth factor beta (TGF-beta) has been most clearly shown to act as a potent regulator of inflammation and immunity. It is highly suppressive for T and B lymphocyte proliferation, cytotoxic T lymphocyte generation, and lymphokine-activated killer cell development, as well as natural killer cell activity. Moreover, there is accumulating evidence that TGF-beta also may contribute to impaired immune surveillance of tumor development. In previous work, we isolated and described a 40 kD glycoprotein extracted from mouse placenta. This placental factor (PF) is also a potent immune modulator in vivo: it is highly inhibitory of secondary antibody responses as well as cellular responses, such as local graft-versus-host reactions. Because placenta has been shown to be a major source of TGF-beta and several reports have indicated an important role for TGF-beta in the immunosuppressive mechanisms taking place during the course of mammalian gestation, we have looked for the presence of TGF-beta in our placental factor preparations. Our results clearly indicate that they do not contain TGF-beta or TGF-beta-like molecules by the following criteria: (1) no inhibition of Mv-1 Lu cell proliferation at any dose tested; (2) no band detected by immunoblotting using different polyclonal reagents specific for TGF-beta 1; and (3) no activity retained on or eluted from an affinity column made of immobilized monoclonal antibody against TGF-beta 2. Aliquots of the same preparations retained their full immune inhibitory capacity in vivo throughout the various assays.(ABSTRACT TRUNCATED AT 250 WORDS)