Endometrial suppressor cells in beef cattle

Endometrial cells were recovered post mortem from cyclic and pregnant crossbred beef cattle (n = 5 each) on Days 16 to 18 after estrus, and were evaluated for their ability to suppress lymphocyte responses and release suppressor factor into the culture medium. The suppressor factor was assessed for transforming growth factor-beta (TGF-beta) activity. In addition, Percoll was used to fractionate endometrial cells from Angus cows (n = 4) on Days 16 to 18 of pregnancy to determine the density of the suppressor cells. Endometrial cells from cyclic and pregnant cows suppressed lymphocyte proliferative responses and released suppressor factor into the culture medium. The suppressor factor exhibited TGF-beta activity. Suppressor activities tended to be greatest for fractionated cells with densities of 1.01 and 1.095 g/mL. In conclusion, the bovine endometrium contains low- and high-density suppressor cells capable of releasing suppressor factor. The factor seems to be associated with TGF-beta.     

High-density ovine endometrial cells exhibit natural killer activity during early pregnancy

Natural killer (NK)-like activity was assessed for peripheral blood lymphocytes (PBL) and unfractionated and fractionated endometrial cells recovered from ewes during the estrus cycle (Days 12 to 14) and early pregnancy (Days 16 to 18). The PBL and endometrial cells (each designated as effector cells) were cocultured with chromium-51 (51Cr) labeled NK-sensitive K-562 target cells in effector:target cell ratios ranging from 25:1 to 200:1, respectively. Lytic activity (i.e., release of 51Cr into the medium) was assessed at 22 h of culture. A high-density (> or = 1.088 g/mL) population of endometrial cells from the pregnant ewes exhibited NK-like activity, whereas endometrial cells from the cyclic ewes failed to exhibit activity. Lytic activity of these cells was greater (P < 0.05) for pregnant than for cyclic ewes (12.0 and 2.1%, respectively) at the effector:target cell ratio of 100:1, respectively. For both groups of ewes, PBL exhibited NK-like activity. These data indicate that the ovine endometrium contains NK-like cells with lytic activity between Days 16 and 18 of pregnancy.     

Ovine endometrial cells fail to lyse K-562 target cells: a preliminary investigation

The ability of unfractionated and fractionated endometrial cells to lyse K-562 target cells was investigated within ewes during the late luteal phase of the estrous cycle (Days 12 to 14) and pregnancy (Days 16 and 19). In separate experiments, lymphokine activated killer (LAK) cells and endometrial cells, both designated as effector cells, were co-cultured with chromium-51 (51Cr)-labeled K-562 target cells in varying effector: target cell ratios. At 22 h, lytic activity was assessed by the release of 51Cr into the culture medium. The LAK cells exhibited lytic activity in a ratio-dependent manner, whereas the unfractionated and fractionated endometrial cells failed to lyse the target cells. For ratios combined, the rate of cytotoxicity for unfractionated endometrial cells recovered from ewes in the cyclic and pregnant (Days 16 and 19 combined) groups was 13.9 and 5.4%, respectively. Although the findings are preliminary, they indicate that ovine endometrial cells recovered during the late luteal phase and early pregnancy failed to exhibit natural killer activity upon K-562 target cells.     

Temporal patterns of secretion of porcine uterine suppressor and stimulatory macromolecules

Temporal secretory patterns of porcine uterine suppressor (>/=230 kD) and stimulatory (29 kD) macromolecules were evaluated within uterine luminal protein (ULP) secretions recovered during early pregnancy. The ULP was recovered by uterine flushing from four Landrace gilts each on Days 9, 12, 15 and 18 of pregnancy. Unfractionated and fractionated ULP (using Sephacryl S-200) was tested for suppression or stimulation of phytohemagglutinin-induced peripheral blood T-lymphocyte proliferation. For all days of pregnancy, unfractionated ULP suppressed (P<0.002 to 0.0001) lymphocyte proliferative responses, with the greatest (P<0.05) activity observed for ULP collected on Day 9 of pregnancy. Suppressor activity resulted from the >/=230 kD component, in which the activity was greater (P<0.05) for ULP from gilts on Day 9 than Days 12, 15 and 18 of pregnancy. The 29 kD component failed (P>0.05) to stimulate lymphocyte proliferation, although there was a nonsignificant stimulatory trend for 2 of 4 gilts each at Days 12 and 15 of pregnancy. These findings demonstrate a temporal secretory pattern for the >/=230 kD lymphocyte suppressor component, which may be requisite for the immunological survival of the conceptus during early pregnancy. The inconsistent appearance of the lymphocyte stimulatory factor (29 kD component) tends to minimize its biological significance relative to the immunology of pregnancy.     

Suppression of a pokeweed mitogen-stimulated plaque-forming cell response by a human B lymphocyte-derived aggregated IgG-stimulated suppressor factor: suppressive B cell factor (SBF)

The mechanisms whereby formed immune complexes (IC) or immunoglobulin aggregates can suppress further antibody production were explored by culturing normal human peripheral blood mononuclear leukocytes (PBL) with heat-aggregated IgG (HAIgG) and collecting the culture supernatants at 24 hr. These supernatants were found to suppress a pokeweed mitogen (PWM)-induced rheumatoid factor plaque-forming cell (RF-PFC) response in normal individuals. PWM-induced anti-trinitrophenylated sheep red blood cell (TNP-SRBC) PFC were also inhibited by suppressor supernatants from HAIgG-stimulated PBL, suggesting that the polyclonal PFC response was inhibited by a suppressor factor. The suppressor factor inhibited PWM stimulated RF-PFC throughout the culture period, but suppression was maximal at the peak of the RF-PFC response. Suppressor factor was only effective at the initiation of cultures, suggesting that it inhibited early events in the PWM-stimulated RF-PFC response. Molecular weight determination of the suppressor factor by differential membrane fractionation suggested a m.w. range of 30,000 to 50,000, and chromatography on Sephadex G-100 showed a peak activity at an approximate m.w. of 32,000. Studies suggested the factor was not an interferon. Depletion of T lymphocytes by E rosetting and macrophages/monocytes by G-10 adherence did not affect the generation of suppressor factor. Depletion of T lymphocytes (OKT4, OKT8) and NK cells (Leu-11b) by antibody-dependent, complement-mediated cytotoxicity also did not affect the generation of suppressor factor. Depletion of B lymphocytes with OKB7 resulted in the generation of significantly less suppressor factor. Suppression produced by unstimulated purified B lymphocytes was approximately one-half that seen when B lymphocytes were stimulated with HAIgG. Differential membrane fractionation studies suggested that only HAIgG-stimulated B cell cultures contained peak activity in the 30,000 to 50,000 m.w. fraction. Supernatants from unstimulated purified T cells also generated suppression, which was approximately one-half of that seen with HAIgG-stimulated B cells, but no increase in suppressor activity was seen in T cell cultures after incubation with HAIgG. These studies demonstrate that HAIgG is capable of stimulating B lymphocytes to produce a lymphokine, suppressive B cell factor (SBF), which is capable of suppressing a polyclonal PFC response. SBF may be important in feedback control of human immunoglobulin production.     

Murine pregnancy decidua produces a unique immunosuppressive molecule related to transforming growth factor beta-2

Non-T small lymphocytic suppressor cells in murine allopregnancy release a potent immunosuppressive factor in vitro that is neutralized by rabbit anti-transforming growth factor (TGF)-beta. Previous studies have suggested that the decidual suppressor factor (DSF) is smaller than TGF-beta 1, and in this paper, we show that DSF on HPLC-sieving columns also elutes later than TGF-beta 2. Nevertheless, DSF has the ability to promote anchorage-independent growth of NRK fibroblasts similar to TGF-beta s. Using turkey antibodies specific for TGF-beta 1 or beta 2, we show that DSF is related to TGF-beta 2 rather than TGF-beta 1, and this relationship was confirmed by using a panel of murine mAb to TGF-subtypes. PAGE and Western blotting showed that the TGF-beta 2-reactive molecules in HPLC-purified DSF was slightly smaller than TGF-beta 2 and approximately 20 to 23 kDa. The DSF molecule is therefore closely related to TGF-beta 2 but as released from decidua, differs in size. The TGF-beta 2-related decidual suppressor factor was also obtained from the decidua of synpregnant C.B.-17 severe combined immune deficiency (SCID) and pregnant SCID-BG (C57BL/6 background) mice, confirming the lack of T or B cell dependence of DSF production and the generality of production of a TGF-beta-related suppressor factor by decidua associated with successful pregnancy in mice.     

Mitogen responsiveness and inhibitory activity of mesenteric lymph node cells

Summary Blood-, lymph node-, and tumour-infiltrating lymphocytes (PBL, LNC, and TIL, respectively) from patients with colonic neoplasms were tested for responsiveness to phytohaemagglutinin (PHA). All populations responded, with LNC and PBL showing comparable reactivities while TIL were less reactive as assessed by incorporation of ³H-thymidine. Increased mitogen responsiveness was observed for T cells enriched by SRBC rosette formation or passage through nylon columns. Mitomycin C-treated LNC and TIL inhibited PHA induced ³H-thymidine incorporation of admixed autologous PBL, suggesting the presence of suppressor cells. Suppressor activity resided primarily in the SRBC rosetting population and was dose-dependent, with increasing numbers of LNC giving greater diminution of PHA response. Suppression by LNC was apparent only when they were added to PBL responders within 6 h of the initiation of stimulation assays, in common with the effects of Concanavalin A (Con A)-induced suppressors on PBL phytomitogen responsiveness. Con A-induced and LNC-suppressor activity could be reversed by addition of lymphocyte-conditioned medium (CM) containing T cell growth factor (TCGF; interleukin IL-2). These data provide further evidence that the suppressor phenomena observed in this system are a function of activated T cells present both in drainage lymph nodes and at the tumour site.     

Effect of oestrous cycle and early pregnancy on uterine production and expression of immune regulatory factors in gilts

This study was undertaken to characterize uterine immune factors involved in the establishment of pregnancy in gilts. Thirty crossbred Yorkshire-Landrace gilts of similar age and weight were observed twice a day for oestrous behaviour with intact boars. On the day of first standing oestrus (Day 0) and 12h later, 15 gilts were inseminated with pooled semen from Duroc boars of proven fertility. Pregnant gilts were slaughtered either on Days 10, 15 or 25 of gestation (n=5 per day). The other 15 gilts were not inseminated and were slaughtered on either Days 0, 10 or 15 of the oestrous cycle (n=5 per day). Immediately after slaughter, endometrial tissue samples from the mesometrial side were removed for gene expression using RNase protection assay and in situ hybridization methodologies. The other uterine horn was flushed with 20 ml of PBS to collect the uterine fluid. In pregnant gilts, endometrial interleukin (IL)-6 mRNA expression was higher on Day 15 than on Days 10 and 25 (P<0.01 and P<0.1, respectively). On Day 15, IL-6 expression was also significantly higher (P<0.01) in pregnant gilts than in cyclic gilts. In both pregnant and cyclic gilts, transforming growth factor (TGF)-beta2 in uterine fluid was significantly higher (P<0.0001) on Day 15 than on Day 10. At the gene expression level, TGF-beta2 also increased between Days 10 and 15 in both cyclic and pregnant gilts but differences were not significant. On Day 15, concentrations of interferon-gamma and prostaglandin E(2) (PGE(2)) in uterine fluid were markedly higher (P<0.001) in pregnant gilts than in cyclic gilts, whereas the total amount of TGF-beta2 in uterine fluid and its endometrial expression were approximately 70% higher although this increase was not significant. Finally, tumour-necrosis factor-alpha and granulocyte-macrophage/colony-stimulating factor mRNA expressions were undetectable in all endometrial samples. In conclusion, production and/or expression of uterine TGF-beta2, IL-6 and PGE(2) increased during the embryonic attachment period and are coincidental with embryonic interferon-gamma production.     

Strong suppression by monocytes of T cell mitogenesis in chicken peripheral blood leukocytes

Peripheral blood leukocytes (PBL) isolated from chicken blood by flotation on Ficoll-Hypaque (FH) have much lower proliferative responses to Con A and PHA than PBL isolated by slow-speed (SS) centrifuging at 60 X G. FH preparations contain all categories of blood cells except erythrocytes, whereas SS are almost devoid of nonlymphoid cells. FH responses approach SS levels after filtration through Sephadex G-10, which removes almost all monocytes detectable by neutral red and nonspecific esterase methods, while only partially depleting granulocytes and thrombocytes. Thus, the low responses of FH are probably associated with suppressor activity of monocytes in these preparations, numbering 6 to 8% of mononuclear cells. G-10 filtration decreases responses of SS preparations, indicating that the few (less than 0.1%) monocytes in SS function mainly as helper cells. In co-cultures, irradiated FH cells (FHX) but not SSX produce as much as 90% suppression of SS or FH responses. Suppression by FHX is totally inhibited by heat killing (56 degrees C for 45 min) or monocyte inactivation by preincubation with Trypan blue, and is removed by G-10 filtration, although not completely. Adherent cells isolated from unirradiated FH on Cytodex beads (ADC-CY) produce up to 99% suppression in co-culture with SS or nonadherent cells derived from FH. Soluble suppressor factors can be detected in conditioned media from supernatants of Con A-stimulated cocultures containing suppressor monocytes, but their suppressor activity is partially opposed by stimulatory factors, possibly interleukin 2, also present in supernatants. It is concluded that in FH preparations and therefore in blood, but not in SS, monocytes that have not been activated exert strong suppressor activity on mitogen-induced T cell proliferation. Occasional chickens of one inbred line, RPRL 72, had exceptionally high suppressor activity of monocytes, as shown by very low FH responses and very high suppressor effects of FHX well outside the normal range of variation found in this line or in line RPRL 63. This abnormal suppressor activity may have resulted from activation of suppressor monocytes as a response to subclinical infection.     

LPS activation of bone marrow natural suppressor cells.

Lipopolysaccharide (LPS) from Salmonella typhosa was injected into C57B1/6 mice and the effect on bone marrow (BM) natural suppressor (NS) cell activity was examined. It was shown that injection of LPS, as low as 0.01 microgram/g body weight, could enhance BM NS activity. The enhanced activity was apparent 24 hr postinjection, and returned to normal by Day 5. It was necessary to show that the enhanced suppression displayed characteristics of NS cells. The suppressor cell is Thy negative and can be found in low density Percoll fractions. Suppression was dependent upon interferon-gamma and could be augmented by lymphokines that were contained in the supernatant of TH2 helper cell. The data suggest that BM NS activity may be influenced in vivo during gram-negative sepsis.     

Delineation of suppressor and helper activity within the OKT4-defined T lymphocyte subset in human newborns

Lymphocytes taken from the cord blood of newborns have active suppressor activity. Using in vitro PWM-stimulated cocultures, unfractionated T cells from newborns potently suppressed the expected immunoglobulin G (IgG) synthesis of their mothers' peripheral blood lymphocytes (PBL). Using positive and negative selection techniques, we characterized the active suppressor cell as expressing the OKT4+T8- phenotype. This cord blood lymphocyte subset suppressed maternal IgG synthesis after depletion of maternal suppressor cells, implicating the ability of newborn T cells to suppress directly rather than by inducing adult suppressor activity. Sublethal amounts (1500 rad) of gamma-irradiation fully abrogated the suppressor activity of cord blood T lymphocytes. Radioresistant cord T cells provided T cell help. Irradiation of cord OKT4+ and OKT8+ populations and their subsequent culture with maternal B cells determined that helper activity was a radioresistant subpopulation of the OKT4+ subset. These results indicate significant differences in the functional properties of T cell subsets from adults and newborns. Population studies determined that cord blood lymphocytes had a greater proportion of OKT4+ cells and lower proportion of OKT8+ cells than PBL from unrelated adults. The mothers tested had similar proportions of OKT4+ cells as their babies, and these levels are significantly higher than those of unrelated adults.     

Differential temporal and spatial expression of mRNA encoding extracellular matrix components in decidua during the peri-implantation period.

Changes in the temporal and spatial patterns of expression of mRNA encoding uterine extracellular matrix (ECM) proteins were determined during the peri-implantation period. Northern blot hybridization of cDNAs corresponding to laminin (LM) B1, LM B2, entactin, fibronectin, collagen (CL) type IV alpha 1, and CL IV alpha 2 was performed on RNA extracted from either whole mouse uteri or endometrial explants between Day 4, i.e., the day of implantation, and Day 7 of pregnancy, when the decidual response is well established. These analyses revealed a dramatic increase in LM B2, CL IV alpha 1, and CL IV alpha 2 mRNA expression by Day 7 of pregnancy. Relative levels of the mRNA encoding other ECM components, including LM B1, were not altered when compared to changes in the relative level of expression of glyceraldehyde-3-phosphate dehydrogenase mRNA. The differential expression of the B chains of LM appeared to be limited to the stromal cells of the endometrium. In situ hybridization of uterine sections with cRNA probes corresponding to LM B1, LM B2, and CL IV alpha 1 demonstrated that LM B1 was expressed temporally in high amounts in the primary decidual zones (PDZ) and persisted throughout PDZ degeneration. LM B2 mRNA was expressed in both primary and secondary decidual zones and persisted through Day 8 of pregnancy. CL IV alpha 1 mRNA expression mimicked that of LM B2. Oviduct ligation on Day 2 of pregnancy was used to prevent embryo transport to one uterine horn, whereas decidualization and embryo implantation were permitted in the contralateral horn. This experiment demonstrated that the increases in uterine ECM mRNA expression were not due solely to the changing hormonal milieu of the uterus. ECM components, including CL IV, have been shown to bind growth factors such as transforming growth factor-beta (TGF-beta) in an insoluble but biologically active form. The remarkable similarity between the pattern of CL IV and LM B2 expression and previously reported TGF-beta deposition (Tamada et al., Mol Endocrinol 1990; 4:965-972) prompted examination of the effects of this growth factor on blastocyst development in vitro. TGF-beta 1 was tested for its ability to alter embryo outgrowth on LM-coated tissue culture surfaces; however, significant differences in the rate or extent of outgrowth in the presence of TGF-beta were not detected.(ABSTRACT TRUNCATED AT 250 WORDS)     

Suppressor T cell activation by human leukocyte interferon

Murine fibroblast interferon (IFN beta) activates murine suppressor T lymphocytes in vitro, which suppress plaque-forming cell responses by spleen cells. Suppression of human in vitro immune responses by IFN was investigated to determine whether human IFN also activates suppressor T cells. Human leukocyte IFN (IFN alpha) suppressed pokeweed mitogen-induced polyclonal immunoglobulin production by human peripheral blood mononuclear cells (PBMC) by 80 to 90% at doses of 200 to 350 U/ml. Responses by IFN alpha-treated PBMC were suppressed in a dose-dependent manner; control cultures had maximal responses on day 7. PBMC incubated with 10,000 U/ml of IFN alpha contained activated suppressor cells that decreased pokeweed mitogen-stimulated, polyclonal immunoglobulin production by autologous cells by 70 to 80%. Suppression mediated by these cells was prevented by catalase, ascorbic acid, and 2-mercaptoethanol (2-ME). In murine systems, these reagents interfere with expression of suppressor T cell activity by preventing activation of soluble immune response suppressor. Selection procedures with monoclonal antibodies identified the suppressor cell as an OKT8+ (suppressor/cytotoxic) T lymphocyte. Selected OKT8+ cells required less IFN alpha (1000 U/ml) for activation and were effective in smaller numbers than unfractionated activated PBMC. IFN alpha-activated suppressor cells also inhibited proliferation in mixed lymphocyte and mitogen-stimulated PBMC cultures; again, catalase and 2-ME blocked suppression. These results indicate that IFN alpha activates suppressor T cells in human PBMC cultures; the ability of catalase, 2-ME, and ascorbic acid to block suppression suggests that these suppressor T cells have certain similarities to IFN beta or to concanavalin A-activated murine suppressor T cells.     

Suppression of pokeweed mitogen-stimulated immunoglobulin production in patients with rheumatoid arthritis after treatment with total lymphoid irradiation

Patients with intractable rheumatoid arthritis (RA) were treated with total lymphoid irradiation (TLI, 2000 rad). We previously reported long-lasting clinical improvement in this group associated with a persistent decrease in circulating Leu-3 (helper subset) T cells and marked impairment of in vitro lymphocyte function. In the present experiments, we studied the mechanisms underlying the decrease in pokeweed mitogen stimulated immunoglobulin (Ig) secretion observed after TLI. Peripheral blood mononuclear cells (PBL) from TLI-treated patients produced 10-fold less Ig (both IgM and IgG) in response to pokeweed mitogen than before radiotherapy. This decrease in Ig production was associated with the presence of suppressor cells in co-culture studies. By using responder cells obtained from normal individuals (allogeneic system), PBL from eight of 12 patients after TLI suppressed Ig synthesis by more than 50%. In contrast, PBL from the same patients before TLI failed to suppress Ig synthesis. Suppression by post-TLI PBL was also demonstrated in an autologous system by using responder cells cryopreserved before TLI. Again, only cells obtained after TLI were suppressive in four of seven patients. PBL with suppressive activity contained suppressor T cells, and the latter cells bore the Leu-2 surface antigen. In 50% of the patients studied, suppressor cells were also found in the non-T fraction and were adherent to plastic. Interestingly, the Leu-2+ cells from TLI-treated patients were no more potent on a cell per cell basis than purified Leu-2+ cells obtained before TLI. Additional experiments suggested that the suppression mediated by T cells after TLI is related to the increased ratio of Leu-2 to Leu-3 cells observed after radiotherapy.     

Conceptus-mediated integrity of endometrial epithelial cells and maintenance of relaxin synthesis in pregnant rabbits: effects of unilateral oviduct ligation

A previous study indicated rabbit endometrial relaxin synthesis is stimulated by blastocyst (Lee VH, Fields PA, Biol Reprod 1990; 40:737-745). To evaluate this hypothesis, unilateral oviduct ligations were placed (A) at the oviduct isthmus on Day 1 post-copulation and (B), in a separate group of rabbits, at the infundibulum before copulation. Blastocysts migrate into and implant in the uterine horn contralateral to the ligated oviduct only (conceptus-bearing uterus). The uterine horn ipsilateral to the ligated oviduct will be referred to as the non-conceptus-bearing uterus. Uteri and ovaries were removed on Days 4-28 of pregnancy and were evaluated for relaxin using guinea pig anti-porcine relaxin serum and avidin-biotin light microscopy immunohistochemistry. Results were identical for both models. Blastocysts first attach to the antimesometrial uterine surface by Day 7 post-copulation. Implantation on the mesometrial surface occurs on Days 8-11. Relaxin was observed in antimesometrial endometrial glands of both conceptus and non-conceptus-bearing uteri on Days 4-7 of pregnancy. Beyond Day 7, relaxin was observed in antimesometrial and mesometrial endometrial glandular and luminal epithelial cells at implantation sites of the conceptus-bearing uterus only. Relaxin was not found between implantation sites. Endometrial epithelial cells of the non-conceptus-bearing uterus were regressing by Day 9. These data indicate a conceptus-mediated maintenance of endometrial epithelial cells. Furthermore, the data suggest a paracrine maintenance of epithelial cell integrity and relaxin synthesis since these parameters are preserved only in the conceptus-bearing uterus. Cell-cell communication between conceptus and endometrium appears to be specific since endometrium between implantation sites does not contain relaxin. Uterine tissue from pseudopregnant rabbits (Days 1-16) was evaluated. Relaxin was observed in the antimesometrial glands on Day 7 only. Like the endometrium in the ligation model, endometrial epithelial cells of the pseudopregnant rabbit uterus were regressing by Day 9. These results indicate that pregnancy is not required for, but may enhance, relaxin synthesis. In addition, endometrial epithelial cells regress in the absence of pregnancy. Regression of endometrial epithelial cells on Day 9 suggests that maternal recognition of pregnancy occurs during the preimplantation period (Days 4-8).     

Natural killer-like cells in the sheep: functional characterization and regulation by pregnancy-associated proteins

Natural killer (NK) cells represent an important component of the innate immune system. In ruminants there are few reports regarding presence or characterization of NK cells. Although absence of expression of major histocompatibility complex proteins on ovine trophoblast makes it potentially a target for NK cells, little is known about regulation of NK cells by products of pregnancy in sheep. Objectives of the present study were to determine whether cells with characteristics of NK cells exist in preparations of ovine peripheral blood lymphocytes (PBL) and endometrial epithelial cells (EEC) and to determine regulation of such cells by two pregnancy-associated molecules with immunoregulatory properties (ovine uterine serpin [OvUS] and interferon-tau [IFN-tau]). Ovine PBL and EEC lysed a putative NK target cell, the BHV-1 infected D17 cell, and lysis by both types of cells was neutralized by antibody against a molecule called function-associated molecule (FAM) expressed on NK cells of several species. Moreover, inhibitors that interfere with perforin-mediated lysis blocked NK-like activity of PBL. The NK-like lytic activity of PBL and EEC was inhibited by OvUS, whereas ovine and bovine IFN-tau significantly enhanced NK-like activity of PBL. In conclusion, NK-like activity present in preparations of ovine PBL and EEC is mediated by FAM(+) cells, is dependent on processes that involve perforin processing, and is regulated by OvUS and IFN-tau. Inhibition of NK-like activity of PBL and EEC by OvUS is consistent with a role for OvUS in protecting the conceptus from maternal cytotoxic lymphocytes. Stimulation of lysis by IFN-tau implies the existence of other inhibitory mechanisms during early pregnancy to prevent NK cell-mediated destruction of the conceptus.     

Effects of transforming growth factor beta on the functions of natural killer cells: depressed cytolytic activity and blunting of interferon responsiveness

Type beta transforming growth factor (TGF-beta) is a unique polypeptide that has been isolated from a number of different tissues and can induce the phenotypic transformation of non-neoplastic fibroblasts as measured by the stimulation of their growth in soft agar. Recently, TGF-beta has been demonstrated to exert profound inhibitory effects on T and B lymphocyte proliferation. In this study, the effects of TGF-beta on natural killer (NK) cell function were investigated. After 20 hr of culture in the presence of TGF-beta, the NK activity of peripheral blood lymphocytes (PBL) was significantly reduced compared with PBL cultured in medium alone. Similarly, TGF-beta produced a significant depression in the cytolytic activity of highly enriched large granular lymphocytes (LGL). This effect of TGF-beta appeared to be mediated directly on the effector cells, because cultivation of the K562 target cells in TGF-beta did not affect target cell susceptibility to lysis. Binding studies with 125I-TGF-beta indicated that LGL possess approximately 1400 high-affinity (Kd = 1PM) receptors/cell, which represents a considerably higher affinity receptor for TGF-beta than that found on fibroblasts. Culturing of PBL and LGL in TGF-beta resulted in a marked blunting of the boosting of NK cytolysis by interferon-alpha but not by interleukin 2, which suggested that TGF-beta may down-regulate interferon-alpha receptors on NK cells. These results, indicate that in addition to inhibitory effects on T and B cells, TGF-beta also inhibits NK cell function. Although the in vivo role of TGF-beta is presently undefined, it may be an important immunoregulatory protein that has a negative influence on lymphocyte activation.     

Active suppression of host-vs-graft reaction in pregnant mice. VI. Soluble suppressor activity obtained from decidua of allopregnant mice blocks the response to IL 2

The mammalian fetus expresses a variety of antigens against which the maternal immune system can react and which in an allogeneic mating bears paternal transplantation antigens. Although these antigens may be expressed on the fetal trophoblast cells that contact maternal uterine decidua, the "fetal allograft" is not usually rejected. Previous studies have demonstrated the presence of nonspecific non-thymus-derived suppressor cells in the lymph nodes draining the uterus and in decidua of laboratory mice undergoing first allogeneic pregnancy. These suppressor cells appeared to be small lymphocyte cells that inhibit the generation of cytotoxic T lymphocytes (CTL) in vitro and in vivo and elaborate a nonspecific non-MHC-restricted soluble suppressor activity when cultured for 48 hours at 37 degrees C in vitro. We now report that soluble suppressor activity obtained from the decidua (DS) of allopregnant C3H/HeJ mice inhibits both the primary and secondary (memory) CTL response in vitro but does not inhibit lysis of target cells by preformed CTL. DS did not suppress the proliferation of YAC lymphoma cells, P-815 cells, or a C3H placental trophoblastoma line. Suppressor activity was obtained from anti-thy-1.2 + complement-resistant cells in the decidua, could also be obtained from the decidua of allopregnant CD1 nu/nu mice, and was associated with a single peak of activity of approximately 100,000 daltons on Sephacryl 200 chromatography. Suppression could not be overcome by adding either crude or HPLC-purified IL 2 to the mixed lymphocyte cultures in vitro, and both crude and column-purified suppressor factor inhibited the IL 2-dependent proliferation of H-Y cells (a cloned T cell line with NK activity). Furthermore, DS inhibited the IL 2-dependent generation of cytotoxic effector cells in vitro in the absence of allogeneic stimulator cells. Thus, a soluble suppressor factor obtained from non-T cells present in the decidua of successfully allopregnant mice could block the response to IL 2 and inhibit the generation of both specific and nonspecific cytotoxic effector cells. The significance of this inhibition with respect to survival of the "fetal allograft" is discussed.