The DNA damage response pathway regulates the expression of the immune checkpoint CD47

CD47 is a cell surface ligand expressed on all nucleated cells. It is a unique immune checkpoint protein acting as "don't eat me" signal to prevent phagocytosis and is constitutively overexpressed in many tumors. However, the underlying mechanism(s) for CD47 overexpression is not clear. Here, we show that irradiation (IR) as well as various other genotoxic agents induce elevated expression of CD47. This upregulation correlates with the extent of residual double-strand breaks (DSBs) as determined by γH2AX staining. Interestingly, cells lacking mre-11, a component of the MRE11-RAD50-NBS1 (MRN) complex that plays a central role in DSB repair, or cells treated with the mre-11 inhibitor, mirin, fail to elevate the expression of CD47 upon DNA damage. On the other hand, both p53 and NF-κB pathways or cell-cycle arrest do not play a role in CD47 upregualtion upon DNA damage. We further show that CD47 expression is upregulated in livers harvested from mice treated with the DNA-damage inducing agent Diethylnitrosamine (DEN) and in cisplatin-treated mesothelioma tumors. Hence, our results indicate that CD47 is upregulated following DNA damage in a mre-11-dependent manner. Chronic DNA damage response in cancer cells might contribute to constitutive elevated expression of CD47 and promote immune evasion.

Gut microbiota shape 'inflamm-ageing' cytokines and account for age-dependent decline in DNA damage repair

OBJECTIVE

Failing to properly repair damaged DNA drives the ageing process. Furthermore, age-related inflammation contributes to the manifestation of ageing. Recently, we demonstrated that the efficiency of repair of diethylnitrosamine (DEN)-induced double-strand breaks (DSBs) rapidly declines with age. We therefore hypothesised that with age, the decline in DNA damage repair stems from age-related inflammation.

DESIGN

We used DEN-induced DNA damage in mouse livers and compared the efficiency of their resolution in different ages and following various permutations aimed at manipulating the liver age-related inflammation.

RESULTS

We found that age-related deregulation of innate immunity was linked to altered gut microbiota. Consequently, antibiotic treatment, MyD88 ablation or germ-free mice had reduced cytokine expression and improved DSBs rejoining in 6-month-old mice. In contrast, feeding young mice with a high-fat diet enhanced inflammation and facilitated the decline in DSBs repair. This latter effect was reversed by antibiotic treatment. Kupffer cell replenishment or their inactivation with gadolinium chloride reduced proinflammatory cytokine expression and reversed the decline in DSBs repair. The addition of proinflammatory cytokines ablated DSBs rejoining mediated by macrophage-derived heparin-binding epidermal growth factor-like growth factor.

CONCLUSIONS

Taken together, our results reveal a previously unrecognised link between commensal bacteria-induced inflammation that results in age-dependent decline in DNA damage repair. Importantly, the present study support the notion of a cell non-autonomous mechanism for age-related decline in DNA damage repair that is based on the presence of 'inflamm-ageing' cytokines in the tissue microenvironment, rather than an intrinsic cellular deficiency in the DNA repair machinery.

Immunological Properties of Human Embryonic Stem Cell-Derived Retinal Pigment Epithelial Cells

Age-related macular degeneration is caused by dysfunction and loss of retinal pigment epithelium (RPE) cells, and their transplantation may rescue visual functions and delay disease progression. Human embryonic stem cells (hESCs) may be an unlimited source of RPE cells for allotransplantation. We analyzed the immunomodulatory properties of hESC-derived RPE (hESC-RPE) cells, and showed that they inhibited T cell responses. Co-culture experiments showed that RPE cells inhibited interfon-γ secretion and proliferation of activated T cells. Furthermore, hESC-RPE cells enhanced T cell apoptosis and secretion of the anti-inflammatory cytokine interleukin-10 (IL-10). In addition, RPE cells altered the expression of T cell activation markers, CD69 and CD25. RPE cells transplanted into RCS rats without immunosuppression survived, provided retinal rescue, and enhanced IL-10 blood levels. Our data suggest that hESC-RPE cells have immunosuppressive properties. Further studies will determine if these properties are sufficient to alleviate the need for immunosuppression therapy after their clinical allotransplantation.

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T cells proliferation and IFN-γ secretion are inhibited by hESC-RPE cells

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T cells apoptosis and secretion of IL-10 are enhanced by hESC-RPE cells

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RPE cells survive, provide retinal rescue, and enhance IL-10 blood levels in vivo

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These findings are relevant to immunosuppressive regimens for RPE cell therapies

Early age decline in DNA repair capacity in the liver: in depth profile of differential gene expression

Aging is associated with progressive decline in cell function and with increased damage to macromolecular components. DNA damage, in the form of double-strand breaks (DSBs), increases with age and in turn, contributes to the aging process and age-related diseases. DNA strand breaks triggers a set of highly orchestrated signaling events known as the DNA damage response (DDR), which coordinates DNA repair. However, whether the accumulation of DNA damage with age is a result of decreased repair capacity, remains to be determined. In our study we showed that with age there is a decline in the resolution of foci containing γH2AX and pKAP-1 in diethylnitrosamine (DEN)-treated mouse livers, already evident at a remarkably early age of 6-months. Considerable age-dependent differences in global gene expression profiles in mice livers after exposure to DEN, further affirmed these age related differences in the response to DNA damage. Functional analysis identified p53 as the most overrepresented pathway that is specifically enhanced and prolonged in 6-month-old mice. Collectively, our results demonstrated an early decline in DNA damage repair that precedes ‘old age’, suggesting this may be a driving force contributing to the aging process rather than a phenotypic consequence of old age.

Fn14•TRAIL effectively inhibits hepatocellular carcinoma growth

Background

New strategies for the treatment of hepatocellular carcinoma (HCC) are needed, given that currently available chemotherapeutics are inefficient. Since tumor growth reflects the net balance between pro-proliferative and death signaling, agents shifting the equilibrium toward the latter are of considerable interest. The TWEAK:Fn14 signaling axis promotes tumor cell proliferation and tumor angiogenesis, while TRAIL:TRAIL-receptor (TRAIL-R) interactions selectively induce apoptosis in malignant cells. Fn14•TRAIL, a fusion protein bridging these two pathways, has the potential to inhibit tumor growth, by interfering with TWEAK:Fn14 signaling, while at the same time enforcing TRAIL:TRAIL-R-mediated apoptosis. Consequently, Fn14•TRAIL's capacity to inhibit HCC growth was tested.

Results

Fn14•TRAIL induced robust apoptosis of multiple HCC cell lines, while sparing non-malignant hepatocyte cell lines. Differential susceptibility to this agent did not correlate with expression levels of TRAIL, TRAIL-R, TWEAK and Fn14 by these lines. Fn14•TRAIL was more potent than soluble TRAIL, soluble Fn14, or a combination of the two. The requirement of both of Fn14•TRAIL's molecular domains for function was established using blocking antibodies directed against each of them. Subcutaneous injection of Fn14•TRAIL abrogated HCC growth in a xenograft model, and was well tolerated by the mice.

Conclusions

In this study, Fn14•TRAIL, a multifunctional fusion protein originally designed to treat autoimmunity, was shown to inhibit the growth of HCC, both invitro and invivo. The demonstration of this fusion protein’s potent anti-tumor activity suggests that simultaneous targeting of two signaling axes by a single fusion can serve as a basis for highly effective anti-cancer therapies.

Novel CD47: SIRPα dependent mechanism for the activation of STAT3 in antigen-presenting cell

Cell surface CD47 interacts with its receptor, signal-regulatory-protein α (SIRPα) that is expressed predominantly on macrophages, to inhibit phagocytosis of normal, healthy cells. This “don’t eat me” signal is mediated through tyrosine phosphorylation of SIRPα at the cytoplasmic ITIM motifs and the recruitment of the phosphatase, SHP-1. We previously revealed a novel mechanism for the activation of the STAT3 pathway and the regulation of human APC maturation and function that is based on cell:cell interaction. In this study, we present evidence supporting the notion that CD47:SIRPα serves as a cell surface receptor: ligand pair involved in this contact-dependent STAT3 activation and regulation of APC maturation. We show that upon co-culturing APC with various primary and tumor cell lines STAT3 phosphorylation and IL-10 expression are induced, and such regulation could be suppressed by specific CD47 siRNAs and shRNAs. Significantly, >50% reduction in CD47 expression abolished the contact-dependent inhibition of T cell activation. Furthermore, co-immunoprecipitation experiments revealed a physical association between SIRPα and STAT3. Thus, we suggest that in addition to signaling through the ITIM-SHP-1 complex that transmit an anti-phagocytotic, CD47:SIRPα also triggers STAT3 signaling that is linked to an immature APC phenotype and peripheral tolerance under steady state and pathological conditions.

Cells exposed to sublethal oxidative stress selectively attract monocytes/macrophages via scavenger receptors and MyD88-mediated signaling

The innate immune system responds to endogenous molecules released during cellular stress or those that have undergone modifications normally absent in healthy tissue. These structures are detected by pattern-recognition receptors, alerting the immune system to "danger." In this study, we looked for early signals that direct immune cells to cells undergoing stress before irreversible damage takes place. To avoid detecting signals emanating from apoptotic or necrotic cells we exposed fibroblasts to sublethal oxidative stress. Our results indicate that both nonenzymatic chemical reactions and aldehyde dehydrogenase-2-mediated enzymatic activity released signals from fibroblasts that selectively attracted CD14(+) monocytes but not T, NK, and NKT cells or granulocytes. Splenocytes from MyD88(-/-) mice did not migrate, and treatment with an inhibitory peptide that blocks MyD88 dimerization abrogated human monocyte migration. Monocyte migration was accompanied by downmodulation of CD14 expression and by the phosphorylation of IL-1R-associated kinase 1, a well-known MyD88-dependent signaling molecule. The scavenger receptor inhibitors, dextran sulfate and fucoidan, attenuated monocyte migration toward stressed cells and IL-1R-associated kinase 1 phosphorylation. Surprisingly, although monocyte migration was MyD88 dependent, it was not accompanied by inflammatory cytokine secretion. Taken together, these results establish a novel link between scavenger receptors and MyD88 that together function as sensors of oxidation-associated molecular patterns and induce monocyte motility. Furthermore, the data indicate that MyD88 independently regulates monocyte activation and motility.

CD40·FasL and CTLA-4·FasL fusion proteins induce apoptosis in malignant cell lines by dual signaling

Evolution of apoptosis resistance in both lymphoma and leukemia cells is well documented, and induction of apoptosis in malignant cells is a major goal of cancer therapy. Up-regulation of anti-apoptotic signals is one of the mechanisms whereby resistance to apoptosis emerges. We have previously described the fusion proteins CD40·FasL and CTLA-4·FasL, which are formed from two functional membrane proteins and induce apoptosis of activated T cells. The present study explores the potential use of CD40·FasL and CTLA-4·FasL for the killing of malignant cells of lymphatic origin. Using malignant B and T cell lines that differ in surface expression of costimulatory molecules, we found that CTLA-4·FasL induces effective apoptosis of cells expressing CD95 and activates caspases 3, 8, and 9. Only B7-expressing B cells responded to CTLA-4·FasL with rapid abrogation of cFLIP expression. CD40·FasL effectively killed only the T cells that express high levels of CD40L in addition to CD95. In these cells, CD40·FasL significantly diminished cFLIP expression. Importantly, each of the fusion proteins is more potent than its respective components parts, alone or in combination. Thus, the proteins with their two functional ends deliver a pro-apoptotic signal and, in parallel, inhibit an anti-apoptotic signal, thus optimizing the wanted, death-inducing effect. Therefore, these proteins emerge as promising agents to be used for targeted and specific tumor cell killing.

Inhibition of effector function but not T cell activation and increase in FoxP3 expression in T cells differentiated in the presence of PP14

Background

T-helper polarization of naïve T cells is determined by a complex mechanism that involves many factors, eventually leading to activation of Th1, Th2, or Th17 responses or alternatively the generation of regulatory T cells. Placental Protein 14 (PP14) is a 28 kDa glycoprotein highly secreted in early pregnancy that is able to desensitize T cell receptor (TCR) signaling and modulate T cell activation.

Methodology/Principal Findings

Prolonged antigen-specific stimulation of T cells in the presence of PP14 resulted in an impaired secretion of IFN-γ, IL-5 and IL-17 upon restimulation, although the cells proliferated and expressed activation markers. Furthermore, the generation of regulatory CD4⁺CD25^highFoxp3⁺ T cells was induced in the presence of PP14, in both antigen-specific as well as polyclonal stimulation. In accordance with previous reports, we found that the induction of FoxP3 expression by PP14 is accompanied by down regulation of the PI3K-mTOR signaling pathway.

Conclusions/Significance

These data suggest that PP14 arrests T cells in a unique activated state that is not accompanied with the acquisition of effector function, together with promoting the generation of regulatory T cells. Taken together, our results may elucidate the role of PP14 in supporting immune tolerance in pregnancy by reducing T cell effector functions along with augmenting Treg differentiation.

Glycosylation: An intrinsic sign of "danger"

The "danger" model of immunity posits that the immune system is triggered by endogenous danger signals, rather than exogenous non-self signals per se. It has been proposed that danger signals may consist of both intracellular "pre-packed" molecules released from damaged cells and stress-induced proteins. Here we focus on glycosylation aberrancies as a unifying concept for danger signaling. According to this proposition glycosylation patterns reliably reflect cellular phenotypic state and appearance of altered carbohydrate structures may constitute a pivotal phenotypic alteration that alarms the immune system to danger and initiates immunity. Viewed from this vantage point, healthy cells avert immune recognition by virtue of their normal terminal glycosylation patterns. By contrast, abnormal cells display and release glycoproteins and glycolipids with aberrant terminal glycosylation trees, which in turn immunologically flag these cells. Diverse carbohydrate-binding receptors are expressed on immune cells and are used to detect these phenotypic changes. Thus, in addition to the "pre-packed" and stress-induced signals this glycosylation-based signal represents an endogenous signal reliably reflecting the cell phenotypic status, enabling the immune system to monitor the tissue/cell's physical condition and to respond accordingly.

Human embryonic stem cells suppress T cell responses via arginase I-dependent mechanism

Human embryonic stem cells (hESCs) can proliferate extensively in culture and give rise to progeny of the three germ layers. Several reports suggested that mouse and hESCs may attenuate immune responses. In this study, we focused on the mechanism by which hESCs inhibit T cell responses. Using coculture experiments, we demonstrate that hESCs inhibit cytokine secretion and T cell proliferation in response to potent T cell activators. Furthermore, we show that hESCs downmodulate the TCR-associated CD3-zeta chain. These effects are maintained when hESCs are replaced by their conditioned media and can be restored by the addition of L-arginine to hESC-conditioned media or by treatment of hESCs with a specific arginase inhibitor. Moreover, we show arginase-I expression and activity in hESCs. We further demonstrate that mouse ESCs (mESCs) similarly inhibit T cell activation via arginase I, suggesting an evolutionary conserved mechanism of T cell suppression by ESCs. In addition, we demonstrate that arginase I expression is not limited to ESCs in culture, but can also be detected in the inner cell mass and the trophectoderm of preimplantation mouse embryos and hESC-derived trophectoderm cells. Finally, T cells infiltrating ESC-derived teratomas have significantly lower levels of CD3-zeta chain. Collectively, the data indicate a role for ESC-arginase I activity in the attenuation of T cell activation.

The induction of APC with a distinct tolerogenic phenotype via contact-dependent STAT3 activation

BACKGROUND

Activation of the signal transducer and activator of transcription 3 (STAT3) within antigen presenting cells (APCs) is linked to abnormal APCs differentiation and function. We have previously shown that STAT3 is activated within APC by a novel contact-dependent mechanism, which plays a key role in mediating the immunomodulatory effects of hMSC. In order to better understand the underlying mechanisms that control APC maturation in a contact dependent manner, we extended our observation to tumor cells. Tumors were shown to secrete a variety of tumor-derived factors that activate STAT3 within infiltrating APCs. We now tested whether tumor cells can activate STAT3 within APC using the contact-dependent mechanism, in addition to soluble factors, and compared these two STAT3 activating pathways.

PRINCIPAL FINDINGS

We demonstrate that in addition to tumor-derived secreted factors tumor cells activate STAT3 by a mechanism that is based on cell-cell interaction. We further demonstrate that these two STAT3 activating mechanisms differ in their JAK usage and their susceptibility to JSI-124 inhibition thereby representing two distinct pathways. Significantly, although both pathways activate STAT3, they modulate DCs maturation in a different manner that results in disparate phenotypic outcomes. Whereas the soluble-dependent pathway results in an immature phenotype, the contact-dependent pathway results in an apparently mature phenotype. Albeit their mature-like phenotype these latter cells express the tolerogenic markers ILT3 and ILT4 and possess T cell inhibitory activity.

SIGNIFICANCE

This data suggests that, in at least certain cellular microenvironments, cell:cell interactions represent a novel way to activate STAT3 signaling, uncouple APC activation events and consequently regulate immunity and tolerance. Significantly, we have now demonstrated that this contact-dependent signaling pathway differs from that mediated by soluble factors and cytokines, inducing disparate phenotypic outcome, suggesting these two mechanisms have different and possibly complementary biological functions.

Toll-like receptor 3 signaling attenuates liver regeneration

The current model for liver regeneration suggests that cell damage triggers Toll-like receptor (TLR) signaling via MyD88, leading to the induction of nuclear factor kappaB (NF-kappaB) and secretion of inflammatory cytokines that in turn prime liver regeneration. TLR3 is unique among TLRs in that it signals through TRIF (TIR domain-containing adaptor-inducing interferon-beta), not through MyD88, and may lead to activation of either the inflammatory or apoptotic pathway. The inflammatory pathway leads to NF-kappaB activation, whereas the apoptotic pathway, believed to be mediated by Rip3, leads to caspase-8 activation. In this study, we explored the role of TLR3 in liver regeneration by comparing the response to 70% partial hepatectomy of TLR3(wt) and TLR3(-/-) mice. We found that following partial hepatectomy, TLR3(-/-) mice demonstrated earlier hepatocyte proliferation. Furthermore, within the first hours, we observed a dramatic TLR3-dependent NF-kappaB activation and an increase in Rip3 levels in hepatocytes, accompanied by caspase-8 activation but without an apoptotic outcome.

CONCLUSION

TLR3 plays an inhibitory role in the priming of liver regeneration, thus reinforcing the role of the innate immune system in balancing tissue regeneration.

Bi-functional fusion proteins: Induction of effective apoptosis of malignant cell lines by dual signaling (41.14)

One mechanism involved in evolution of death resistant malignant cells is upregulation of anti-apoptotic signals. CTLA-4FasL, that integrates the capacities to bind to B7 and to Fas receptor (CD95), induces effective apoptosis of activated T cells by activating the caspases in parallel to decreasing the expression of the anti-apoptoic protein cFLIP. Aims: Explore the ability of CTLA-4FasL and CD40FasL (binds to CD40L and CD95) to induce apoptosis of malignant B and T cell lines, and test whether they decrease cFLIP in conjunction with caspases activation. Results: CTLA-4FasL induced effective apoptosis of malignant T and B cell lines that express CD95 (tested by annexin/PI). Activation of caspase 3, 8 and 9 was verified by western blots. Only B7 expressing B cells responded to CTLA-4FasL presence with rapid abrogation of cFLIP expression. CD40FasL also induced apoptosis of T and B cell lines, and was most toxic to T cell line that expressed high levels of CD40L in addition to CD95. These CD40L expressing cells decrease cFLIP in response to CD40FasL. CTLA-4FasL and CD404FasL were more potent than either of their components, alone or in combination. Conclusion: Both fusion proteins activate Fas receptor, but maximal potency is seen when target malignant cells express a binding site for the second domain of the fusion proteins (B7 or CD40L). This potency is probably related to inhibition of anti-apoptotic signals.

Contact-dependent induction of regulatory antigen-presenting cells by human mesenchymal stem cells is mediated via STAT3 signaling

OBJECTIVE

Mesenchymal stem cells (MSCs) are multipotent cells that are capable of differentiating into multilineages of the mesenchyme. MSCs were shown to have immune-modulating properties in vitro and were successfully used in vivo for controlling graft-versus-host disease, skin rejection, and modulation of inflammation. Our previous study suggested that human MSCs (hMSCs) block antigen-presenting cell (APC) maturation in a contact-dependent manner as well as induce the expression of the anti-inflammatory cytokine, interleukin-10 (IL-10). However, the molecular mechanisms that block initiation of immune responses by MSCs remains to be investigated.

METHODS

A coculture system of hMSCs and APCs was used to study Signal Transducer and Activators of Transcription-3 (STAT3) activation using nonradioactive STAT3 transcription factor assay, flow cytometric immunostaining, and Western blotting.

RESULTS

We show that the transcription factor STAT3 is constitutively activated in hMSCs, and upon coculturing with APCs, there is a significant increase in its activity in both cell types. This increase in STAT3 activity is independent of soluble factor(s) and requires cell-cell contact. Importantly, blocking STAT3 signaling in the APCs by specific inhibitors resulted in reduced IL-10 expression and reversal of hMSC-mediated inhibition of proinflammatory cytokines.

CONCLUSION

These findings suggest that APC's STAT3 plays a key role in mediating the immunomodulatory effects of hMSCs. Moreover, the induction of STAT3 signaling by hMSCs is mediated by a novel mechanism involving cell-cell interaction rather than the classical mechanism of induction by cytokines.

TLR3 signaling in a hepatoma cell line is skewed towards apoptosis

Toll-like receptors (TLRs) recognize pathogen-associated molecular patterns (PAMPS) leading to the activation of the innate immune response and subsequently to the shaping of the adaptive immune response. Of the known human TLRs, TLR3, 7, 8, and 9 were shown to recognize nucleic acid ligands. TLR3 signaling is induced by double-stranded (ds)RNA, a molecular signature of viruses, and is mediated by the TRIF (TIR domain-containing adaptor-inducing IFNbeta) adaptor molecule. Thus, TLR3 plays an important role in the host response to viral infections. The liver is constantly exposed to a large variety of foreign substances, including pathogens such as HBV (hepatitis B virus) and HCV (hepatitis C virus), which frequently establish persistent liver infections. In this work, we investigated the expression and signaling pathway of TLR3 in different hepatoma cell lines. We show that hepatocyte lineage cells express relatively low levels of TLR3 mRNA. TLR3 signaling in HEK293 cells (human embryonic kidney cells) activated NF-kappaB and IRF3 (interferon regulatory factor 3) and induced IFNbeta (interferon beta) promoter expression, which are known to lead to pro-inflammatory cytokine secretion. In Huh7 cells, there was only a short-term IRF3 activation, and a very low level of IFNbeta expression. In HepG2 cells on the other hand, while no induction of pro-inflammatory factors was observed, signaling by TLR3 was skewed towards the induction of apoptosis. These results indicate preferential induction of the apoptotic pathway over the cytokine induction pathway by TLR3 signaling in hepatocellular carcinoma cells with potential implications for therapeutic strategies.

CD40{middle dot}FasL inhibits human T cells: evidence for an auto-inhibitory loop-back mechanism

A chimeric CD40.FasL (CD40-CD95L) protein was designed with the combined capacities to bind to two surface receptors on activated T cells, CD40 ligand (CD40L; CD154) and Fas receptor (CD95). CD40.FasL, once tethered to the cell surface via one of its ends, can transmit a signal via its other end. In principle, simultaneous triggering from both ends is possible, and thus there is the intriguing potential for 'auto-inhibition' if such dual triggering occurs on the same cell itself. Several lines of evidence support this mechanism: (i) CD40.FasL is cytotoxic to Fas receptor-positive cell lines of different cell lineages, (ii) CD40.FasL's function is potentiated when there is enforced expression of CD40L on target cells, (iii) CD40.FasL inhibition does not require intercellular contact, as demonstrated by soft agar clone formation and cell dilution analysis and (iv) introduction of exogenous CD40 into the system interferes with CD40.FasL inhibition. Taken together, these data are consistent with a 'loop-back' inhibitory mechanism within individual activated (CD40L and Fas receptor expressing) T cells causing suicide of these T cells. Significantly, this type of fusion protein provides a unique way to confine immunoinhibition to activated T cells.

CTLA-4.FasL inhibits allogeneic responses in vivo

CTLA-4.Fas ligand (CTLA-4.FasL), a paradigmatic 'trans signal converter protein (TSCP)', can attach to APC (via CTLA-4 binding to B7) and direct intercellular inhibitory signals to responding T cells (via FasL binding to Fas receptor), converting an activating APC-to-T cell signal into an inhibitory one. Our previous studies established that CTLA-4.FasL inhibits human primary mixed lymphocyte reactions (MLR) and induces alloantigen-specific hyporesponsiveness ex vivo. The present study extends this to an in vivo context. Using splenocytes from MHC-mismatched C57BL/6 and Balb/c mice, we demonstrated that his(6)CTLA-4.FasL, effectively inhibits murine MLR. Moving in vivo, we demonstrated that subcutaneously administered his(6)CTLA-4.FasL modulates the in vivo response of infused allogeneic splenocytes. his(6)CTLA-4.FasL reduces the number of cells in each cell division, and increases the percentage of dead cells in each division. These findings are consistent with an antigen-induced cell death of the alloreactive cells, and bolsters recombinant TCSP promise as a therapeutic for transplantation diseases.

alpha2,6-Sialylation promotes binding of placental protein 14 via its Ca2+-dependent lectin activity: insights into differential effects on CD45RO and CD45RA T cells

Placental protein 14 (PP14; glycodelin) is a pregnancy-associated immunoregulatory protein that is known to inhibit T cells via T-cell receptor desensitization. The recent demonstration of PP14 as lectin has provided insight into how it may mediate its CD45 glycoprotein-dependent T-cell inhibition. In this study, we have investigated PP14's lectin-binding properties in detail. Significantly, PP14 reacts with N-acetyllactosamine (LacNAc) as was also found for members of the galectin family, such as the potent immunoregulatory protein, galectin-1. However, in contrast to galectin-1, PP14's binding is significantly enhanced by alpha2,6-sialylation and also by the presence of cations. This was demonstrated by preferential binding to fetuin as compared with its desialylated variant asialofetuin (ASF) and by using free alpha2,6- versus alpha2,3-sialylated forms of LacNAc in competitive inhibition and direct solid-phase binding assays. Interestingly, from immunological point of view, PP14 also binds differentially to CD45 isoforms known to differ in their degree of sialylation. PP14 preferentially inhibits CD45RA+, as compared with CD45RO+ T cells, and preferentially co-capped this variant CD45 on the T-cell surface. Finally, we demonstrate that PP14 promotes CD45 dimerization and clustering, a phenomenon that may regulate CD45 activity.

Human mesenchymal stem cells alter antigen-presenting cell maturation and induce T-cell unresponsiveness

Infusion of either embryonic or mesenchymal stem cells prolongs the survival of organ transplants derived from stem cell donors and prevents graft-versus-host-disease (GVHD). An in-depth mechanistic understanding of this tolerization phenomenon could lead to novel cell-based therapies for transplantation. Here we demonstrate that while human mesenchymal stem cells (hMSCs) can promote superantigen-induced activation of purified T cells, addition of antigen-presenting cells (APCs; either monocytes or dendritic cells) to the cultures inhibits the T-cell responses. This contact- and dose-dependent inhibition is accompanied by secretion of large quantities of interleukin (IL)-10 and aberrant APC maturation, which can be partially overridden by the addition of factors that promote APC maturation (ie, lipopolysaccharide [LPS] or anti-CD40 monoclonal antibody [mAb]). Thus, our data support an immunoregulatory mechanism wherein hMSCs inhibit T cells indirectly by contact-dependent induction of regulatory APCs with T-cell-suppressive properties. Our data may reveal a physiologic phenomenon whereby the development of a distinct APC population is regulated by the tissue's cellular microenvironment.

Differential Regulation of Th1/Th2 Cytokine Responses by Placental Protein 14

The potency of TCR signaling during primary CD4+ T cell activation influences initial cytokine expression patterns and subsequent polarization toward either Th1 or Th2 subsets. In this study, we demonstrate that the T cell inhibitor placental protein 14 (PP14; glycodelin) preferentially inhibits Th1 cytokine responses and chemokine expression when present during ex vivo priming of CD4+ T cells. PP14 synergizes with exogenously added IL-4 in skewing T cell responses. Significantly, PP14 impairs the down-regulation of GATA-3 transcriptional regulator expression that normally accompanies T cell activation, which is a prerequisite for Th1 development. Taken together, these data document for the first time the ability of PP14 to skew Th responses.

CTLA-4. FasL induces alloantigen-specific hyporesponsiveness

The APC:T cell interface can be effectively targeted with immunotherapeutic proteins. We previously described a unique trans signal converter protein, CTLA-4. Fas ligand (FasL), that has the inherent capacities to tether the T cell inhibitor FasL (CD95 ligand) to the surfaces of B7 (CD80 and CD86)-positive APC (via CTLA-4:B7 interaction), and in so doing, to simultaneously interfere with B7-to-CD28 T cell activation signals. Given the continuing need for agents capable of inducing allograft tolerance without generalized immunosuppression, we have explored in depth the functional activity of CTLA-4. FasL in human allogeneic MLR. CTLA-4. FasL inhibits 1 degrees MLR and induces specific hyporesponsiveness in 2 degrees MLR, with both effects only partially reversible with exogenous IL-2. Moreover, the presence of exogenous IL-2 during the 1 degrees MLR does not affect the induction of hyporesponsiveness upon restimulation. Furthermore, CTLA-4. FasL enables partial activation of allostimulated T cells, reduces the fraction of actively dividing cells, and increases the percentage of dead cells among dividing T cells. Taken together, these findings suggest that CTLA-4. FasL-mediated inhibition of secondary alloantigenic responses involves both anergy induction and clonal deletion. Thus, CTLA-4. FasL, a paradigmatic trans signal converter protein, manifests unique functional properties and emerges as a potentially useful immunotherapeutic for modulating alloresponsiveness.

Negative regulation of T cell activation by placental protein 14 is mediated by the tyrosine phosphatase receptor CD45

CD45 is the major protein tyrosine phosphatase receptor on T cell surfaces that functions as both a positive and a negative regulator of T cell receptor (TCR) signaling. Although CD45 is required for the activation of TCR-associated Src family kinases, it also dephosphorylates phosphoproteins involved in the TCR-signaling cascade. This study links CD45 to the inhibitory activity of placental protein 14 (PP14), a major soluble protein of pregnancy that is now known to be a direct modulator of T cells and to function by desensitizing TCR signaling. PP14 and CD45 co-capped with each other, pointing to a physical linkage between the two. Interestingly, however, the binding of PP14 to T cell surfaces was not restricted to CD45 alone, with evidence showing that PP14 binds to other surface molecules in a carbohydrate-dependent fashion. Notwithstanding the broader molecular binding potential of PP14, its interaction with CD45 appeared to have special functional significance. Using transfected derivatives of the HPB. ALL mutant T cell line that differ in CD45 expression, we established that the inhibitory effects of PP14 are dependent upon the expression of intact CD45 on T cell surfaces. Based upon these findings, we propose a new immunoregulatory model for PP14, wherein one of its surface molecular targets, CD45, mediates its T cell inhibitory activity, accounting for the intriguing capacity of PP14 to elevate TCR activation thresholds and thereby down-regulate T cell activation.

Placental protein 14 regulates selective B cell responses

Placental protein 14 (PP14) is a glycoprotein of the lipocalin family that acts as a negative regulator in T cell receptor-mediated activation. In this study, we investigated PP14s potential role in regulating B cell activation. While PP14-inhibited B cell proliferation, IgM secretion and the surface expression of MHC class II, the expression of other surface molecules, such as CD69 and CD86, were unaffected. These observed effects were independent of the anti-IgM concentration used for stimulation, regardless of the presence of either T cells or IL-4, and persisted when B cells were stimulated by stimuli, which circumvent early events during B cell Ag receptor (BCR) activation, namely, protein kinase C activators in combination with Ca(2+) ionophore. Interestingly, we demonstrated that PP14s inhibitory characteristics are reminiscence of that achieved by independent ligation of CD19 using anti-CD19 mAb. Together with our previously reported effects on T cells, these findings identify PP14 as a soluble regulatory factor capable of interacting with both T and B cells in a carbohydrate-dependent manner and as a result it can affect both cellular and humoral immune responses.

A temporal and spatial summation model for T-cell activation: signal integration and antigen decoding

Commitment of T cells to cytokine production and proliferation requires sustained (up to several hours) T-cell receptor (TCR) signaling that is achieved through serial engagement. This article proposes a kinetic model, adopted from neurons, which is based on the local temporal summation of successive signals. This model offers an explanation for how signals originating from serially triggered TCRs are accumulated and integrated over the period required for T-cell activation, given that each TCR-evoked signal is rapidly lost. The principal innovation of this model is the suggestion that signaling intermediates produced by serially triggered TCRs are not simply sustained but are incrementally built up. Several phenomena related to T-cell behavior and self-nonself discrimination are discussed.

Serial triggering of T cell receptors results in incremental accumulation of signaling intermediates

Triggering of the T cell receptor (TCR) leads to the production of intracellular intermediates with half-life of a few minutes. Signaling kinetics of events originating from serial TCR triggering and its relation to antigen dose was investigated. In this study we documented incremental accumulation of short-lived intermediates of the extracellular signal-regulated kinase (ERK) family, produced during successive TCR triggering. The rate and extent of the intermediate accumulation are essentially determined by the level of TCR engagement and are augmented by costimulation. ERK-1 and ERK-2 exhibit different rates of accumulation following serial receptor triggering. The data indicate that the quantitative kinetic differences in downstream signaling pathways induce qualitatively distinct biological outcomes. Although CD69, interleukin-2, and interferon-gamma (IFN-gamma) were primarily produced by high antigen doses that supported high MAPK phosphorylation, maximal interleukin-5 expression is induced by low and intermediate stimulus doses that do not support significant accumulation of activated ERK. We further demonstrated that the rate of phosphorylated ERK accumulation correlates with the duration of delay between T cell stimulation and the onset of IFN-gamma response, with stronger stimuli giving a more rapid IFN-gamma response. This delay might reflect the time required for the accumulation of signaling intermediates up to a threshold level that is necessary for activation. Thus, the data suggest that signaling events originating from serially triggered TCR are not simply sustained but are gradually accumulated and are integrated in a corresponding response.

Focal localization of placental protein 14 toward sites of TCR engagement

TCR signal transduction is amplified by the dynamic accumulation of accessory molecules at APC-T cell contact sites, along with the simultaneous exclusion from these sites of negative regulators, such as certain tyrosine phosphatases and large glycosylated proteins. However, given the general nature of the cytoskeleton-driven clustering mechanism underlying molecular segregation events at the APC-T cell interaction site, the possibility exists that negative regulators might similarly be segregated at these sites. Using fluorescence microscopy, we have demonstrated that placental protein 14 (PP14), a direct T cell inhibitor, focuses toward APC-T cell contact sites in conjunction with conjugate formation. We have further established that the function of PP14 is dependent upon its localization to the sites of TCR triggering, where it negatively regulates T cell activation. Thus, PP14 provides an example of a soluble negative T cell regulator whose inhibitory activity is linked to modulation of the APC-T cell contact site, thereby hindering early events triggered by the TCR.

A rheostatic mechanism for T-cell inhibition based on elevation of activation thresholds

The activation of discrete T-cell responses depends on the triggering of individualized threshold numbers of T-cell receptors (TCRs). The results of this study indicate that the lipocalin placental protein 14 (PP14), a T-cell inhibitor produced by cells of the reproductive and hematopoietic systems, mediates its anti-inflammatory activity by elevating the T-cell activation threshold, thereby rendering T cells less sensitive to stimulation. Significantly, the data demonstrate hierarchical sensitivity of selected cytokine responses to PP14-mediated inhibition, with the hierarchy reflecting their respective activation thresholds. These findings suggest a novel paradigm for immunoinhibition wherein negative regulators can finely tune, rather than inactivate, T-cell responses, and thereby skew the cytokine output of immunologic responses.

alpha2-macroglobulin modulates the immunoregulatory function of the lipocalin placental protein 14

Human placental protein 14 (PP14; also known as glycodelin and progesterone-associated endometrial protein) is an immunosuppressive protein of the lipocalin structural superfamily. Mechanisms regulating serum PP14's immunosuppressive activity remain to be elucidated. In the present study, an interaction between PP14 and a major serum protein carrier, alpha(2)-macroglobulin (alpha(2)M), was documented for the first time. Using native gel electrophoresis, we showed that PP14, as well as its alternative splice variant PP14.2, binds to both alpha(2)M and methylamine-activated (MA)-alpha(2)M. Cross-competition studies demonstrated that the variants compete for binding to alpha(2)M. PP14 bound to alpha(2)M and MA-alpha(2)M with K(d) values of 167+/-70 and 221+/-56 nM (means+/-S.D.) respectively, as determined by surface plasmon resonance. Significantly, the addition of alpha(2)M or MA-alpha(2)M to a T-cell proliferation assay strongly potentiated the inhibitory capacity of PP14. On the basis of these findings, alpha(2)M emerges as the first serum protein that can physically associate with, and thereby regulate, PP14. Moreover, this represents the first documented interaction between the protein carrier alpha(2)M and a lipocalin protein.

Placental protein 14 functions as a direct T-cell inhibitor

Human placental protein 14 (PP14, also referred to as glycodelin and progesterone-associated endometrial protein) inhibits phytohemagglutinin (PHA)-stimulated T-cell proliferation and monokine secretion within PBMC populations. However, the mechanisms underlying these and other PP14 immunoinhibitory activities remain unclear. In the present study, we asked whether PP14's T-cell inhibitory effect is a direct one or, alternatively, an indirect consequence of accessory cell (AC) perturbation. Using either immunopurified PP14 or first-trimester amniotic fluid (AF) as a rich source of PP14, we documented inhibition of the proliferation of highly purified peripheral blood T-cells when stimulated with anti-CD3 mAbs or PHA in the presence of paraformaldehyde-fixed AC. Significantly, PP14 inhibited T-cell proliferation and IL-2 secretion induced by immobilized anti-CD3 and anti-CD28 mAbs in the absence of AC. PP14 depletion (via immunoprecipitation) abrogated AF's T-cell inhibitory activity, indicating that the PP14 within the amniotic fluid is required for this immunoregulatory effect. These findings establish that PP14 can inhibit T-cell proliferation in the absence of AC and thus add PP14 to the relatively restricted set of immunoinhibitory proteins that are known to target T-cells directly. Additional data demonstrate that PP14's inhibitory effect can be overridden by stimuli which circumvent early events during T-cell receptor (TCR) activation, namely, protein kinase C activators in combination with Ca2+ ionophores. These latter results suggest that PP14 inhibits early events in the TCR signaling pathway.

Differential effects of chondroitin sulfates A and B on monocyte and B-cell activation: evidence for B-cell activation via a CD44-dependent pathway

At inflammatory sites, proteoglycans are both secreted by activated mononuclear leukocytes and released as a consequence of extracellular matrix degradation. Chondroitin 4-sulfate proteoglycans constitute the predominant ones produced by activated human monocytes/macrophages. In this study, we show that two chondroitin 4-sulfate forms, CSA and CSB, can activate distinct peripheral blood mononuclear cell types. Whereas CSA activates monocytes (to secrete monokines), CSB activates B-cells (to proliferate). In contrast, the chondroitin 6-sulfate CSC and heparin do not exert these functional effects. We further show that CD44 monoclonal antibodies block CSB-induced B-cell proliferation. These findings point to glycosaminoglycans, and specifically chondroitin 4-sulfates, as a novel class of immunological mediators at inflammatory sites. Furthermore, the data link CD44 to B-cell activation, paralleling the established roles of CD44 in T-cell and monocyte activation.

Normal and atypical butyrylcholinesterases in placental development, function, and malfunction

1. In utero exposure to poisons and drugs (e.g., anticholinesterases, cocaine) is frequently associated with spontaneous absorption and placental malfunction. The major protein interacting with these compounds is butyrylcholinesterase (BuChE), which attenuates the effects of such xenobiotics by their hydrolysis or sequestration. Therefore, we studied BuChE expression during placental development. 2. RT-PCR revealed both BuChEmRNA and acetylcholinesterase (AChE) mRNA throughout gestation. However, cytochemical staining detected primarily BuChE activity in first-trimester placenta but AChE activity in term placenta. 3. As the atypical variant of BuChE has a narrower specificity for substrates and inhibitors than the normal enzyme, we investigated its interactions with alpha-solanine and cocaine, and sought a correlation between the occurrence of this variant and placental malfunction. 4. Atypical BuChE of serum or recombinant origin presented > 10-fold weaker affinities than normal BuChE for cocaine and alpha-solanine. However, BuChE in the serum of the heterozygote and a homozygous normal were similar in their drug affinities. Therefore, heterozygous serum or placenta can protect the fetus from drug or poison exposure, unlike homozygous atypical serum or placenta. 5. Genotype analyses revealed that heterozygous carriers of atypical BuChE were threefold less frequent among 49 patients with placental malfunction than among 76 controls of the entire Israeli population. These observations exclude heterozygote carriers of atypical BuChE from being at high risk for placental malfunction under exposure to anticholinesterases.

Characterization of the imprinted IPW gene: allelic expression in normal and tumorigenic human tissues

IPW (Imprinted gene in the Prader-Willi syndrome region) is a recently identified paternally expressed gene. Previous work has demonstrated IPW expression in the human fetus and adult, with monoallelic expression in adult lymphoblasts and fibroblasts, and in fetal tissues. To further examine the expression of IPW, a series of experiments were carried out using RT-PCR to measure IPW expression in placentae and various fetal and tumor tissues. Biallelic expression of IPW was found in testicular germ cell tumor and bladder cancer cells, suggesting loss of imprinting in the latter case. Both H19 and Insulin-like growth Factor 2 (IGF2), two additional imprinted genes, also showed biallelic expression in those same tumors that demonstrated IPW biallelic expression. Of note, the naturally occurring parthenogenetic-derived mature teratoma unexpectedly expressed large amounts of IPW. Lastly, the pluripotent embryonal cancer cell line Tera-2 expressed IPW at the same level before and after differentiation induced by retinoic acid, suggesting that this gene functions in a 'housekeeping' capacity throughout cell growth. This was in contradistinction to H19 and IGF2, both of which showed significant transcriptional upregulation after Tera-2 cell differentiation.

H19 expression and tumorigenicity of choriocarcinoma derived cell lines

Certain embryonal tumors demonstrate a loss of heterozygosity at the parentally imprinted region of chromosome 11p15.5. It has been hypothesized that this implicates a tumor suppressor gene at this locus. The human H19 gene maps to 11p15.5, is expressed in fetal tissues including the placenta and is paternally imprinted. Here we show that the abundance of H19 transcripts in cells of two choriocarcinoma derived cell lines (JAr and JEG-3) differs greatly. While JAr cells express high levels of H19 RNA, the expression of H19 in JEG-3 cells is much lower than that of normal trophoblasts. Cells of these two cell lines were subcutaneously injected into nude mice with subsequent tumor formation. A fivefold increase in the H19 RNA level was measured in tumors derived from JEG-3 cell lines as compared to these cells before injection. However this increase in H19 RNA did not alter the clonogenicity in soft agar nor the growth rate of the cells derived from these tumors as compared to the original JEG-3 cells. Nevertheless, the cells retaining the elevated level of H19 transcripts were more tumorigenic than the original cells. We propose that there is a selection of cells expressing high levels of H19 from the total JEG-3 cell population during the microevolution of tumor formation. These observations, together with our previous publications on H19 expression in human cancers, do not support the notion of a tumor suppressor role for the H19 gene.

The interaction between cytotrophoblasts and their derived tumor cells

Previous experiments demonstrated that human cytotrophoblasts and cells of the choriocarcinoma cell line JAr interact in vitro. As a result of this interaction there is an increased synthesis of CG and hPL, probably as a result of the increased CG and hPL synthesis by the cytotrophoblasts. In the present investigation we studied this interaction in greater detail and found that both cytotrophoblasts and JAr cells undergo changes in their biological properties as a result of this interaction. JAr cells and cytotrophoblasts cocultured for 72 hr were fractionated according to their size by centrifugal elutriation. The number of cells in the fraction which contain the largest cells was very significantly increased as a result of the coculture. This increase was due to an increase in the number of cells of both cell types. This fraction was the most active one in the synthesis of CG and hPL. The synthesis of DNA by the JAr nuclei in this fraction of the cocultured cells was almost completely inhibited but in the parallel fraction of the JAr cells cultivated alone the level of DNA synthesis was equal to that of all other JAr cell fractions. Heterokaryons are formed in the coculture. In these heterokaryons a factor which inhibits DNA synthesis in the cytotrophoblasts may inhibit DNA synthesis in JAr nuclei and at least be partly responsible for the inhibition of DNA synthesis observed.

ABL and BCR genes are not imprinted in androgenetic and gynogenetic human tissues

In the translocation leading to the formation of the Philadelphia chromosome, the hallmark of chronic myeloid leukemia (CML), the translocated chromosome 9 (ABL), is of paternal descent whereas chromosome 22 (BCR) is of maternal origin (1). To study possible imprinting of the human ABL and BCR genes, we used human tissues exclusively endowed with their maternally (benign teratoma) or paternally (complete hydatidiform mole) inherited chromosomes. Using the sensitive PCR technique followed by northern blotting, we demonstrate here that ABL and BCR are expressed to a similar extent in androgenetic and gynogenetic human tissues, thus suggesting that ABL and BCR genes are not imprinted in these human tissues.

Ultrastructural characteristics of cytotrophoblast cells during stages of differentiation

Isolated cytotrophoblast cells from term human placenta were separated into eleven fractions according to cell size, by centrifugal elutriation. Each fraction isolated was examined by electron microscopy to elucidate ultrastructural features consistent with differences in stages of cellular differentiation. As a rule, increasing cell size correlated with evidence of progressive intracellular differentiation. This was represented by the appearance of specialization structures in later fractions, and by changes in the density of organelles and other cellular constituents. Progressive development and maturation of the rough endoplasmic reticulum was also evident. These data are the first to demonstrate successful subfractionation of the heterogeneous cytotrophoblast cell population into distinct groups, each representing different levels of cellular differentiation. These morphologic features of differentiation correlate closely with established biochemical parameters associated with various stages of intermediate cytotrophoblast cell differentiation.

Parallel regulation of parentally imprinted H19 and insulin-like growth factor-II genes in cultured human fetal adrenal cells

Adjacent, parentally imprinted, insulin-like growth factor-II (IGF-II) and H19 genes are highly expressed during embryogenesis and are important for fetal growth. Human fetal adrenals express abundantly both IGF-II and H19 genes. To clarify the significance and regulation of the H19 gene, we studied its expression in fetal adrenals. In situ hybridization experiments showed H19 RNA expression throughout the fetal adrenal cortex, with slightly higher expression in the outer definitive (adult) than in the inner fetal zone. In primary cultures of fetal adrenal cells, ACTH and other activators of the protein kinase-A signal transduction pathway increased both H19 and IGF-II RNA accumulation 1.7- to 10-fold. Staurosporine, a protein kinase-C inhibitor, increased H19 and IGF-II RNA to the same extent as did ACTH. The protein kinase-C activator 12-O-tetradecanoyl phorbol-13-acetate and cytokines, tumor necrosis factor-alpha and interferon-gamma, inhibited H19 and IGF-II RNA accumulation. Transforming growth factor-beta 1 caused a decrease in levels of H19 and IGF-II RNA, whereas the IGFs caused a slight increase. Our data show parallel multifactorial regulation of H19 and IGF-II RNAs in human fetal adrenal cells. This suggests common regulatory mechanisms for these adjacent genes.

Relaxation of imprinting in trophoblastic disease

Genomic imprinting--the uniparental-dependent transmittance of a genetic trait--has been accepted in recent years as a major mechanism in mammalian genetics. We studied the expression of the H19 gene, a parentally imprinted (maternally expressed) gene, by in situ hybridization in human placenta and trophoblastic disease. Expression was found to be abundant, in a decreasing order, in the intermediate trophoblast (villous and interstitial), the cytotrophoblast, and the syncytiotrophoblast. The villous stroma was also prominently labeled. Partial hydatidiform mole showed a similar pattern of expression as normal placenta. As expected, complete hydatidiform mole, whose genome consists of two haploid sets of paternal origin, was not labeled in the villous stroma and surrounding trophoblastic layer. However, some of the large mononuclear cells in the proliferating groups sprouting from the villous surface were strongly labeled. Prominent expression of H19 was found in placental site trophoblastic tumor and gestational choriocarcinoma. The phenomenon of emergence of expression of alleles subject to repression according to their gamete of origin is termed relaxation of imprinting, and is considered to be relevant to tumorigenesis. We suggest that the expression of the maternally expressed H19 gene in the androgenetic tissue of complete hydatidiform mole represents relaxation of imprinting and may be associated with its malignant potential.

Use of a novel system for defining a gene imprinting region

Gene imprinting involves the expression of a single allele, depending on its parental origin. In this report, we describe the use of a novel system, implementing human tissues exclusively endowed with either maternally or paternally inherited chromosomes, to better define a known gene imprinting region. Specific RNA transcripts for Placental Ribonuclease Inhibitor (PRI) and Cathepsin D were analysed by northern blotting for expression in complete hydatidiform mole, mature teratoma, and normal placenta. These genes are in close proximity to the reciprocally imprinted H19 and IGF-2 genes found on chromosome 11p15.5. Since all the tissues studied expressed Cathepsin D and PRI, these are not, by definition, imprinted, but as yet we cannot define the borders of the imprinting area on chromosome 11p15.5.

Genetic imprinting in human evolution: the decisive role of maternal lineage

The modern study of human evolution must take into account physical anthropology, which examines phenotypic expression, and molecular evolution, which examines genotypic change. Recent independent investigations have shown that the process of genetic imprinting, defined as parental-dependent transmission of genetic traits, plays a pivotal role in human evolution. We draw on data from various scientific disciplines to support the hypothesis that maternal lineage via preferential genetic contribution, plays a decisive role in this regard. This concept is of more than theoretical interest, in that, current human disease states can be better understood and studied in the context of loss of genetically-defined evolutionary advantage.

Intermediate cells during cytotrophoblast differentiation in vitro

Differentiation of the human placental trophoblast cell involves a multistep process, with the generation of several distinct types of intermediate cytotrophoblast cells. Using a short term in vitro cell culture system and centrifugal elutriation, we studied the isolation and morphological and biochemical differentiation of these separated intermediate cell populations. Freshly isolated cell fractions, incubated for 24 h, are heterogeneous in their differentiation stages as determined by the secretion of the proteins chorionic gonadotropin alpha and beta, human placental lactogen, and pregnancy specific beta 1-glycoprotein. Maintenance in cell culture allows for the further differentiation of these intermediate cells and for syncytium formation. With the use of sequential trypsinizations, our data also suggest the parallel differentiation of cytotrophoblast cells into two distinct subsets: one which, through differentiation, gets committed to syncytium formation, and the other, which remains mononuclear despite high degrees of biochemical differentiation. These latter cells retain the capacity for syncytium formation when reintroduced into appropriate culture conditions. These findings refine the use of the term "intermediate cell" by previous investigators. We suggest that our in vitro system defines normal intermediate stages of trophoblast differentiation, and also serves as a model to simulate adverse conditions of syncytial degeneration or injury.