Immunoactive products of human placenta. II. Direct inhibition of non-MHC restricted cytolytic activity of human CD3 alpha-beta but not CD3 gamma-delta expressing T cell clones

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.

A placenta-derived suppressor factor with a T-cell bias

PROBLEM

Functional and mechanistic aspects of immunosuppression by murine placental supernatants (MPS) were investigated.

METHOD OF STUDY

MPS and a low molecular weight fraction of the supernatant (MPSf) were tested for suppressive action on T-cell reactivity in vitro and in vivo, on B-cell responses and on T-cell activation events.

RESULTS

MPS and MPSf suppress mitogen-induced proliferation and mixed lymphocyte reactions of human and murine lymphocytes, antigen-induced proliferation of T cells in vitro and in vivo, proliferation of CD8+ lymphocytes, proliferation induced by cross-linking of surface CD3 and the in vivo response of mice to allogeneic stimuli. MPSf affects cell cycling of activated T cells and blocks interleukin (IL)-2 production. MPSf does not affect antibody production or the induction of MHC class II expression on B cells.

CONCLUSIONS

MPSf is a potent inhibitor of T-cell responses in vitro and in vivo, with no demonstrable effect on B-cell function.

Modulation of the immune response by progesterone-induced lymphocyte factors

Rat spleen and peripheral blood lymphocytes express progesterone receptors whose concentration is increased greatly during the early phase of pregnancy. After stimulation of progesterone the expression of receptors was augmented 2-3 times. When cells were cultured in the presence of progesterone they released a soluble factor that inhibited cellular immunoreactions (MLR, CRC) and cellular proliferation as measured by thymidine incorporation by spleen-cell culture. This factor also inhibited the synthesis of anti-DNP antibodies by a mouse hybridoma and diminished the proportion of cells in phase S. However, the percentage of asymmetric molecules produced by the hybridoma remained unaltered. These results support the hypothesis that soluble factors released by rat lymphocytes modulate the immune response of the mother and participate in the mechanism that protects the fetus against antipaternal antibodies.

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.

Effect of rat placental culture supernatants on cellular and humoral immune responses

PROBLEM

To evaluate the effect of rat placental culture supernatants (PS) on spontaneous, mitogen- and alloantigen-induced lymphoproliferation, antibody synthesis regulation, and symmetric/asymmetric antibody ratio.

METHOD OF STUDY

The effect of PS was determined: (a) on cell proliferation of murine hybridoma cells and on spontaneous or ConA-induced proliferation of murine and rat splenocytes by thymidine incorporation; (b) on rat or mouse cell-mediated cytotoxicity (CMC) by 51Cr release; and (c) on antibody synthesis by enzyme-linked immunoadsorbent assay (ELISA).

RESULTS

With 20% PS, hybridoma cell inhibition was 37% and that of splenocytes up to 60%, whereas it was 75 and 43%, respectively, in the presence of ConA. Despite marked cell death, hybridoma proliferation index increased significantly. There was a drop in total antidinitrophenylated (DNP) immunoglobulin G1 (IgG1) antibody production and an increase in asymmetric antibody percentage, correlating with placental supernatant concentration.

CONCLUSIONS

Rat placental culture supernatants inhibit cell proliferation in all cases, diminish total antibody production, and increase the percentage of asymmetric antibodies by the hybridoma, and they increase antibody production by rat splenocytes.

Maternal anti-placental cell-mediated reactivity and spontaneous abortions

PROBLEM

Does Th1/Th2 balance determine pregnancy outcome, and if so, what determines Th1/Th2 balance in pregnancy?

METHOD

Review and synthesis of existing data.

RESULTS

A bias toward Th1 is strongly correlated with pregnancy failure in mice and humans. Pregnancy usually shifts the balance toward Th2 and placental factors/progesterone and progesterone-stimulated CD8+ T cell production of suppressor factor; TGFbeta2 and IL4/10 may be responsible. The bias toward a Th1 response may result from intracellular parasitic infection and other as yet undefined factors.

CONCLUSION

The Th1/Th2 balance thesis appears to be valid.

Immunoactive products of placenta. VI. Induction of transient murine T cell anergy by a low-molecular-weight compound obtained from supernatants of human placental cultures

A low-molecular-weight material present in human placental supernatant (lymphocyte proliferation inhibiting factor, LPIF, or filtrate) can induce tolerance/hyporesponsiveness in vivo. We already knew from previous experiments that this material acted only on preactivated or malignant T cells, and even the malignant cells could be rescued from its action if cells were washed quickly after contact. To understand the mechanisms of its action, we have set up systems of specific stimulation. The material inhibits anti-Vbeta-specific stimulation. In a mixed lymphocyte reaction if responder cell populations from a first MLR performed in the presence of LPIF are harvested, extensively washed to discard suppressor molecules, and restimulated by related or third-party lymphocytes in an H2-incompatible combination, the response to a third-party stimulator (a primary one) is unaffected by prior exposure to the material, which nevertheless renders the population unresponsive to restimulation by the original MHC-stimulating haplotype. Cells triggered by anti-Vbeta6 antibodies in the presence of LPIF are unable to undergo restimulation by the very same anti-Vbeta6 MoAb, while they conserve their capacity to proliferate in a primary fashion in response to the unrelated anti-Vbeta8 MoAb. When analyzed by FACS using anti-Vbeta FITC-conjugated MoAbs, cells that are unresponsive or blocked in their proliferation by the action of the filtrate after anti-Vbeta stimulation are still live and unexpectedly transiently hyperexpress the TcR. These findings confirm the requirement for T cell stimulation for suppression to be enacted and demonstrate that such is exerted by anergy rather than by clonal deletion, at least in vitro.

Immunoactive products of placenta. V. Immunoregulatory properties of a low molecular weight compound obtained from human placental cultures

PROBLEM

We have previously shown that supernatants from short-term cultures of human placental explants (HPS) are immunosuppressive in vitro as well as in vivo. They contain a low M.W. factor endowed with immunoregulatories activities (Filtrate of such with a 5 kDa cut off). In this paper, we wanted to assess whether this low M.W. material accounts for most, if not all, of the immunosuppressive properties of crude HPS and begin to investigate its mode of action.

RESULTS

The filtrate is active across species barrier and inhibits human and murine PHA driven lymphocyte proliferation, Mixed Lymphocyte Reaction, and Natural Killer activity as did crude HPS. It does not affect CTL lytic function at effector stage. Its cross species activity allowed us to study its effects in vivo. It corrects resorbtions in the CBA x DBA/2 murine spontaneous abortion model, and suppresses local and general GVH reactions in a model (A cells into irradiated A x B Fls) relevant to a clinical use e.g., bone marrow transplantation. To ensure that such survival of the recipients was due to donor cells in the latter, surviving experimental animals were analysed by FACS for repopulating lymphocytes phenotype, which was indeed of donor origin. To elucidate the mechanism(s) of action of the active HPS moiety, we first tested various malignant cell lines for the minimal incubation time required for maximal lymphocyte inhibition. In the same vein, we verified that lymphocytes stimulated by PHA and simultaneously treated with filtrate were unresponsive to a second PHA challenge. The effects of the material was reversible if cells were washed out of it early enough before otherwise entering a cycle leading ultimately to cell death in vitro. Finally, we tested several second messenger pathways, none of which were modified.

CONCLUSION

These data suggest that the filtrate contains an entity that represents the main, if not all, the immunosuppressive molecules present in HPS. In addition, they suggest that the material acts only on activated T cells and requires to be present early in the replication activation cycle. Altogether, the in vitro data strongly suggest that the material is acting by inducing clonal deletion in activated (T) cells.

Immunosuppression by hydatidiform mole trophoblast is neutralized by monoclonal antibodies to beta-interferon

PROBLEM

In sheep and cattle, trophoblast-derived interferons serve as signals for the maternal recognition of pregnancy and may regulate the immunologic relationship between the fetus and mother.

METHOD

In this study, soluble extracts prepared from human hydatidiform mole decidua (DE) and trophoblast (HME) were screened for immunosuppressive activity using an interleukin (IL)-2-dependent T-cell line (CTLL2). Antibody neutralization studies were performed with monoclonal antibodies to alpha- and beta-interferon (IFN).

RESULTS

HME suppressed (P < 0.05) IL-2-stimulated (2 IU/well) CTLL2 proliferation at doses ranging from 500 (52 +/- 2% of control) to 100 (74 +/- 5%) micrograms/ml concentrations. DE also suppressed (P < or = 0.05) CTLL2 proliferation in a dose-related fashion from 500 (20 +/- 6% of control) to 100 (71 +/- 8%) micrograms/ml doses. Preincubation with the alpha- and beta-IFN antibody preparations had no effect on CTLL2 suppression by the DE sample. In contrast, the beta-IFN antibody partially neutralized the suppressive activity of HME at each of the dilutions tested. The monoclonal antibody to alpha-IFN failed to neutralize HME suppression at any of the doses tested.

CONCLUSIONS

These results suggest that hydatidiform mole trophoblast produces a beta-IFN-like macromolecule that may abrogate maternal rejection responses that are harmful to the developing fetal allograft.

Modulation of prolactin secretion in human myometrium by cytokines

Prolactin (PRL) secretion and PRL mRNA expression in human myometrial explant cultures was inhibited by the addition of human placental conditioned medium (HPCM). After 3 days treatment with 5% HPCM PRL secretion was reduced to 24% of control values (P < 0.001). The effect persisted even after removal of progesterone, which suppresses myometrial PRL production, from the HPCM. In search for additional regulatory substances present in the uteroplacental unit, we tested a number of growth factors and cytokines known to affect pituitary PRL secretion. Treatment with endothelin-3 (ET-3) at a dose of 10(-6) M was found to increase PRL release by 20% over 3 days (P < 0.05) whereas interleukin-6 (IL-6) showed no effect on PRL levels. Epidermal growth factor, vasoactive intestinal peptide and interferon-alpha (IFN-alpha) were inhibitory. Interleukin-4 (IL-4) was the most potent inhibitor of PRL expression in myometrial tissue, causing a reduction of secreted PRL to less than 50% of controls after 3 days at a dose of > or = 5 ng/ml (P < 0.001) and a concomitant reduction of PRL mRNA levels. These results demonstrate a modulation of PRL expression in the myometrium by locally present factors.

A lectin-binding soluble factor released by CD8+CD57+ lymphocytes from AIDS patients inhibits T cell cytotoxicity

CD8+CD57+ T cells, expanded in peripheral blood lymphocytes of AIDS patients, inhibit the effector phase of HLA-specific cytotoxic T lymphocytes, natural killer and lymphocyte-activated killer cells in a 4-h chromium-release assay. This inhibitory activity present in supernatants of purified sorted CD8+CD57+ cells is mediated by a non-antigen-specific inhibitory factor which is distinct from prostaglandin E2, T cell growth factor (TGF)-beta, latent-TGF-beta, tumor necrosis factor (TNF)-alpha and TNF-beta. Partial biochemical characterization demonstrates that the CD8+CD57+ inhibitory activity (a) is heat, trypsin and acid resistant, (b) binds to concanavalin A columns, indicating its glycosylation state and (c) is mediated by a 20-30-kDa soluble molecule.