Immunoactive products of placenta. III. Suppression of natural killing activity

Placental and trophoblast-enriched cells from iso or allopregnant mice (14 to 17 days of gestation) strongly suppress natural killing by mouse splenocytes. The suppression is not strain restricted and acts at the level of the effector cell. It was not reduced by pretreatment of trophoblast cells with RNA and protein synthesis inhibitors, nor by prostaglandin synthetase inhibitors. However, treatment with trypsin abolished the suppressive activity. Because CTL and ADCC cytotoxicity were also inhibited by trophoblast cells at the effector stage, we postulate that trophoblast cells in vivo are endowed with the ability to inactivate various types of cytotoxic cells in their vicinity that are potentially harmful for the conceptus.

Preferential elimination of NK and CTL functions by anti-D44 monoclonal antibody

Monoclonal antibodies reactive with T cells at various stages of maturation were used in negative selection experiments to study their effects on NK function in the presence of complement. Anti-D47 and anti-A50, respectively, directed against corticothymocytes and mature peripheral E+ cells were without effect. Anti-D66 reactive with an epitope of the T cell E receptor inhibited up to 60% of NK activity. Anti-D44, which primarily recognizes corticothymocytes and 60 to 80% of the E(+)-PBL was found to abrogate NK activity together with alloreactive CTL reactivity but to leave intact most of the MLR and PHA proliferative responses. Therefore D44 appears as a discrete antigen allowing preferential elimination of NK cells and CTL from PBL.

Preferential elimination of NK and CTL functions by anti-D44 monoclonal antibody

Monoclonal antibodies reactive with T cells at various stages of maturation were used in negative selection experiments to study their effects on NK function in the presence of complement. Anti-D47 and anti-A50, respectively, directed against corticothymocytes and mature peripheral E+ cells were without effect. Anti-D66 reactive with an epitope of the T cell E receptor inhibited up to 60% of NK activity. Anti-D44, which primarily recognizes corticothymocytes and 60 to 80% of the E(+)-PBL was found to abrogate NK activity together with alloreactive CTL reactivity but to leave intact most of the MLR and PHA proliferative responses. Therefore D44 appears as a discrete antigen allowing preferential elimination of NK cells and CTL from PBL.

Immunoactive products of placenta. III. Suppression of natural killing activity

Placental and trophoblast-enriched cells from iso or allopregnant mice (14 to 17 days of gestation) strongly suppress natural killing by mouse splenocytes. The suppression is not strain restricted and acts at the level of the effector cell. It was not reduced by pretreatment of trophoblast cells with RNA and protein synthesis inhibitors, nor by prostaglandin synthetase inhibitors. However, treatment with trypsin abolished the suppressive activity. Because CTL and ADCC cytotoxicity were also inhibited by trophoblast cells at the effector stage, we postulate that trophoblast cells in vivo are endowed with the ability to inactivate various types of cytotoxic cells in their vicinity that are potentially harmful for the conceptus.

Helper activity for antibody synthesis encoded by mRNA extracted from human peripheral blood mononuclear cells

Translation products in Xenopus laevis of mRNA from human peripheral blood mononuclear cells were tested for their capacity to replace T cells in the anti-SRBC response of nude spleen cells. When the starting material came from PHA or FCS-stimulated lymphocytes, the translated lymphokines, displaying such a B cell helper activity were found to be encoded by mRNA sedimenting at 6-7S and 13S on a sucrose density gradient. 6-7S mRNA from control, non-stimulated lymphocytes was also able to code for B cell helper activity. Thorough T-cell depletion of mouse responder cell populations left unchanged the activity of 6-7S mRNA products while preventing that of 13S products. The latter were found to contain IL-2, which suggests that their action on B cells was indirect, mediated by T-cell stimulation.

Immunoactive products of murine placenta. II.--Afferent suppression of maternal cell-mediated immunity by supernatants from short-term cultures of murine trophoblast-enriched cell suspensions

Supernatants from short-term cultures of mid-term murine trophoblast cells were assayed for their in vitro regulatory potential. They markedly inhibited cell-mediated lympholysis and mixed lymphocyte reaction in a non-specific, non-restricted fashion. By contrast, the mitogenic response to optimal doses of ConA was unaffected, while the plaque-forming cell response to sheep red blood cells was either unmodified or slightly enhanced. These data suggest that placenta-derived cells secrete factors which selectively impair some cell-mediated immune responses. It is suggested that these factors play an important role in the lack of generation of cytolytic T lymphocytes towards paternal alloantigens expressed on the trophoblast during allopregnancy.

Studies on purification of human gamma interferon: chromatographic behavior of accompanying IL2 and B-cell helper activity

Gamma interferon (gamma IFN) was produced in human lymphocyte cultures stimulated by PHA. Titers were in the range of 10,000-30,000 U/ml. Crude gamma IFN was adsorbed on silicic acid, from which the antiviral activity was eluted by a buffer containing a high salt concentration and ethylene glycol. This treatment allowed quantitative recovery of gamma IFN with a specific activity of 5 X 10(5)-1 X 10(6) U/mg of proteins. IL2 and B-cell helper activities were adsorbed and eluted from silicic acid together with the antiviral activity. This finding might be of practical interest for the purification of these lymphokines, particularly IL2. Gamma interferon was further purified on Blue Sepharose to a specific activity of 2 X 10(7) U/mg. The resulting preparations still contained IL2 and B cell helper activities. However, taking advantage of the differences in apparent hydrophobicity and in isoelectric point, we were able to dissociate antiviral activity from lymphokines. Such dissociation should facilitate the study of the biological properties of human natural gamma IFN.

Antibody-dependent cellular cytotoxicity (K) and natural killing (NK) in B-suppressed germ-free nude rats

The influence of the thymus and the possible requirement for surface immunoglobulin expression for the development of K and NK activity were assessed in rats. This species was chosen in preference to mice as they show good levels of K-cell activity. Studies were carried out in athymic (rnu/rnu) rats some of which were treated from birth with rabbit anti-rat IgM antibody to suppress B-cell development. The results indicate that normal levels of both K and NK activity develop in the spleens of 6-8-week-old athymic rats, which do not contain cells expressing surface membrane immunoglobulin. While K and NK cells show characteristics of the lymphoid lineage, neither the thymus nor surface membrane immunoglobulin expression appears to be required for development of normal levels of these cytolytic activities.

Inhibition of in vitro natural killer activity by the third component of complement: role for the C3a fragment

Purified human native third component of complement, C3, was found to inhibit in vitro natural killer (NK) cell cytotoxicity in both mouse and human systems. The effect was dose and time dependent, a 50% inhibition being reached with 190 nM C3 (35 micrograms/ml) added during the NK assay or after a 30-min preincubation of the effector cells with this C3 concentration. C3 was shown to act at the effector-cell population level because pretreatment of the target cells did not modify the NK lysis. The inhibition was not due to general cytotoxicity nor to cell agglutination. Moreover, another in vitro cytotoxicity system (represented by alloreactive cytotoxic lymphocytes) was not affected by purified C3. Structural analysis of the active part of the C3 molecule shows that the C3-induced inhibition is supported by the C3a fragment. Release of carboxyl-terminal arginine residue by carboxypeptidase B, converting C3a into des-Arg77-C3a, did not alter the inhibitory effect displayed by this fragment. These results suggest that C3a may play an important role in the regulation of NK activity.

NK activity in carrageenan-treated mice

NK activity was determined by measuring 51chromium released from Yac-1 target cells incubated with spleen cells from normal or carrageenan (Car)-treated mice. Intraperitoneal administration of a single dose of i-Car (3 mg) provoked splenomegaly in mice. This splenomegaly accompanied during the first days (2-3), a marked increase of NK activity, then a decrease of this activity at day 8-9. It was returned to normal level at day 30. The modulation of NK activity in Car-treated mice is not due to the variation of the number of NK cells, since the frequency of target-binding cells (TBC) was not modified. The increase in NK activity during the first days may be due to the presence of interferon induced by carrageenan. Concomitant injection of an anti-mouse interferon globulin with carrageenan abolished the boosting of NK activity. NK activity of spleen cells from Car-treated mice at day 8 could not be stimulated by interferon in vitro as it could with the normal spleen cells. No decrease of NK activity was observed in Car-treated mice at day 8, when indomethacin was administered. Hence the decrease of this activity in Car-8 mice might be partially due to the alteration of NK effector cells induced by prostaglandins.

Study of the mechanism for in vitro activation of mouse NK cells by interferon

The enhancement of the lytic capacity of mouse splenic 'natural killer' (NK) cells by interferon has been studied in vitro as a model for NK cell differentiation from inactive immediate precursors. We show that the increased cytotoxicity is a function of interferon concentration, and that two stages in the NK cell differentiation pathway can be distinguished. The first, very brief, can be performed at 0 degree C and without protein synthesis and probably corresponds to the fixation of interferon on its cell surface receptors. The second, resulting from the inductive signal given by interferon, proceeds for several hours and requires both RNA and protein synthesis. Our results also indicate that target cells for interferon-induced cytotoxicity are cells with 'null' characteristics, similar to the mature NK cells. Finally, they suggest that no soluble intermediary factor other than interferon is involved in the enhancing of NK cell cytotoxicity.

Enhancement of mouse natural killer cell activity by type II interferon

It is likely that interferons are key molecules in the physiological regulation of natural killing (NK) activity. This assumption is based on the strong enhancing effect exerted by type I interferon on NK cells. The aim of this study was to examine whether type II interferon, released upon activation of T lymphocytes by a mitogen, had the same enhancing effect. Crude PHA-induced interferon was purified on affinity chromatography columns (Blue Sepharose), and the eluted fractions were tested in parallel for antiviral activity and for in vitro boosting effect on spleen cell natural cytotoxicity. We found that both activities were unseparable. Acid pretreatment of purified type II interferon, as well as addition of anti-type II interferon serum, greatly decreased the enhancement of the spleen cell cytotoxic response. Responder cells to type II interferon are NK cells (surface Ig-negative, Thy-1-negative, devoided of acid Fc receptors) as assessed by classical spleen cell fractionation procedures based on cell surface markers. Comparison between the dose-response curves obtained with type I and type II interferons suggest that both interferon preparations stimulate NK activity in a comparable manner. We could conclude that interferon molecules (type I as well as type II) display a positive immunoregulatory function on NK cells.

Immunity to a 3-methylcholanthrene-induced fibrosarcoma in the C57BL/6 mouse: in vivo analysis by the adoptive tumor neutralization test

Analyses of the adoptive tumor neutralization test (modified Winn test) in C57BL/6 mice made immune to a 3-methylcholantheene-induced fibrosarcoma showed that the reaction was mediated by a thymus-derived lymphocyte, it was tumor-specific, and the resistance of the immunized donor mouse to the challenge was strongly correlated with the protection of the recipient mouse. Proliferation of immune cells and close contact between tumor cells and immune T-cells were required. The hypothesis of a participation of the recipient in the reaction was considered because of the lack of adoptive protection of pangenic nude mice.

Cytostatic effect of spleen cells of cyclophosphamide-treated mice on tumor cells

Spleen cells of mice receiving an i.p. injection of a sublethal dose of cyclophosphamide (CY) have the ability to inhibit tumor growth in vitro. This effect is dose dependent and is maximal at the peak of the spleen regeneration which follows the phase of atrophy due to CY toxicity. This cytostasis is neither tumor-specific nor strain-restricted and the cells responsible for this inhibition of tumor cell multiplication have the characteristics of macrophages: they lack the Thy 1-2 antigenic marker, appear in CY treated nude mice, stick on plastic vessels, and are retained by adherence columns (nylon wool or Sephadex G10); their activity is greatly reduced when a specific macrohpage toxic reagent such as carrageenan is added to the cultures. The effector cells are similar to those which are able to suppress the response of normal splenocytes to T and B mitogens, and which appear in the same conditions of induction, after CY injection.

Induction of suppressor cells in mice by cyclophosphamide

The injection of a single sublethal dose of cyclophosphamide (CY) into adult C3H/He mice induced splenic atrophy followed by considerable hypertrophy. During the phase of splenomegaly, the in vitro reactivity of spleen cells to the mitogens phytohaemagglutin and lipopolysaccharide was drastically decreased. Furthermore, the spleen cell population from CY-treated mice contained suppressor cells capable of inhibiting the in vitro reactivity of normal lymphocytes to these mitogens. After the removal of adherent cells, the suppressive activity was completely absent from the remaining fraction. The suppressive activity was also abolished after treatment of spleen cells with anti-immunoglobulin antiserum plus complement (C). After treatment with anti-Thy 1-2 antiserum plus C, the suppressive activity was not modified. Nude mice, B mice, young and old NZB mice, also developed suppressor cells with similar functional characteristics when treated with CY. However, in Nude mice the suppressor cells were not adherent and did not bear surface Ig. After fractionation of spleen cells by velocity sedimentation, the suppressive activity was detected in the fastest fraction with a velocity over 5 mm/h.

Splenic modifications induced by cyclophosphamide in C3H/He, nude, and "B" mice

The spleen cell population of adult C3H/He mice injected with a single sublethal dose of cyclophosphamide (CY) has been analyzed. An initial phase of spleen atrophy is followed by a considerable hypertrophy, and a progressive return to normal. During the phase of spleen atrophy, both B and T cell compartments are depleted, as estimated by the percentages of cells killed by anti-Thy 1-2 and anti-Ig antisera plus complement. During the stage of regeneration, the percentage of Ig + cells increases rapidly, and at the peak of splenomegaly, the percentage of Ig + cells is high whereas almost no Thy 1-2 + cells are detectable. Progresively, the spleen cell content returns to the original values. In thymo-deprived mice (nude mice and B mice) the percentage of null cells increases during the stage of regeneration, and B mice develop a large number of Ig +-bearing cells. Histologic examination shows that follicles (B-dependent areas) disappear 1 to 2 days before periarteriolar sheaths (T-dependent areas). At the peak of splenomegaly the architecture of the spleen is destroyed, and the interstitial tissue is composed of a dense and uniform layer of lymphoid cells. Progressively, the architecture returns to normal. In nude mice, the disappearance of follicles, and the appearance of a homogenous layer of lymphocytes has been observed. When analyzed for their pattern of electrophoretic mobilities (E.M.), spleen cells from untreated mice reveal two peaks of E.M. 0.80 and 1.15 micron x s-1 x V-1 x cm-1. After CY treatment, during the step of splenic hypertrophy, these two peaks disappear, and a single peak of intermediate mobility appears. In T-deprived mice, a single peak of the same mobility is detected at this stage. The nature and origin of cells which appear during the phase of regeneration are unclear, but their appearance in T-deprived mice argues against thymo dependence. These spleen cells have the ability to suppress the response of normal spleen lymphocytes to T and B cell mitogens.

Suppression of the humoral immune response by plasmacytomas: mediation by adherent mononuclear cells

Mice bearing plasmacytomas have a severely impaired ability to mount a primary immune response; T cells from these mice, however, appear by both in vivo and in vitro criteria to function normally. This unusual pattern of immunodeficiency appears to be mediated by a regulatory cell found in the spleens and peritoneal cavities but not in the lymph nodes or thymuses of mice bearing plasmacytomas. The number of cells with suppressor activity in the spleens of plasmacytoma-bearing mice is directly proportional to the size of the subcutaneous tumor borne by the host. These cells are capable of suppressing antibody production in in vitro cultures of normal spleen cells but have no demonstrable effect on the ability of normal spleen cells to proliferate in vitro in response to phytohemagglutinin or 8-Br-guanosine-3', 5'-monophosphate (T and B cell mitogens, respectively). Characterization of the suppressor cell population on the basis of its cell surface properties, its radioresistance, its morphology, and its ability to adhere to various solid matrices suggest that these cells are adherent mononuclear cells. These data support the concept that plasma cell tumors indirectly induce an impairment in the humoral immune response of their hosts by stimulating the expression of regulatory functions in a population of splenic and peritoneal macrophages.

[Suppressive cells induced by cyclophosphamide in the spleen of C3H mice]

The spleen cell population of C3H/He mice injected with a single sublethal dose of cyclophosphamide (CY) was analysed. An initial atrophy was followed by a considerable hypertrophy and a progressive return to normal. During the phase of spleen atrophy, both B and T cell compartments were depleted. During regeneration, the percentage of Ig+ cells increased rapidly, and at the peak of splenomegaly, the percentage of Ig+ cells was high while no Thy1-2+ cells were detectable. The peculiar points of histology were disappearance of normal T and B compartments, substituted by a layer of lymphoid cells. During the phase of splenectomegaly, the in vitro reactivity of spleen cells to the mitogens PHA and LPS was drastically decreased. Furthermore, the spleen cell population from CY treated mice contained suppressor cells, capable of inhibiting the in vitro reactivity of normal lymphocytes to these mitogens and the multiplication of tumour cells in culture. These cells were adherent, Ig+, Thy1-2- cells. They developed in CY treated T deprived mice. After velocity sedimentation the suppressive activity was detected in the 6 mm/h fraction.

Evidence for splenic suppressor cells in C3H/He, T-cell-deprived C3H/He, and nude mice bearing a 3-methylcholanthrene-induced fibrosarcoma

Suppressor cells were demonstrated in the spleens of C3H/He mice carrying 3-methylcholantrene-induced fibrosarcomas. These cells inhibited the in vitro reactivity of normal lymphocytes to T- and B-cell mitogens. They disappeared within a few days after the tumor was surgically removed. Pretreatment of spleen cells (ScC) from tumor-bearing (TB) mice with either iron and a nagnet, antiserum against Thy 1.2 antigen plus complement, or antiserum against immunoglobulin plus complement demonstrated that the suppressor cells were adherent, non-T-cells bearing immunoglobulin at their surfaces. The suppressive effect could still be demonstrated by addition of SpC from TB mice 24 or 48 hours after phytohemagglutinin stimulation of normal SpC, SpC from TB C3H/He mice inhibited mitogen-induced stimulation of both C3H/He and DBA/2 lymphocytes. In T-cell-deprived TB C3H/He mice, suppressor cells were also observed and had the same characteristics as those in non-T-cell-deprived mice. In nude mice, however, although suppressor cells were active, they were not adherent and did not bear immunoglobulin at their surfaces. The existence of these suppressor cells may be one reason why the immune system of TB animals is unable to reject the tumor.