Tissue Factor Activity of Syncytiotrophoblast Plasma Membranes and Tumoral Trophoblast Cells in Culture

During pregnancy, important modifications of hemostasis occur resulting in mothers in hypercoagulability and the role of placental cells such as trophoblast cells has been hypothesized. In this study, we first showed that syncytiotrophoblast plasma membranes, isolated from normal human placenta, expressed a strong tissue factor (TF) activity. We then studied TF activity of two continuous trophoblast cell lines (JEG-3 and BeWo) in comparison to human umbilical vein endothelial cells (HUVEC) and transformed human endothelial cells (ECV-304). TF assays were performed on intact detached confluent cells. Unstimulated JEG-3 and BeWo cells exhibited a very high TF activity which slightly increased after 2 to 4 h TNF-α stimulation. In contrast, HUVEC and ECV-304 had a lower basal TF activity which was mainly inducible by TNF-a, with a maximum effect after 4 to 6 h stimulation. For both cell types, TF activity was decreased to basal value after 16-hour TNF-α stimulation. These results support that trophoblast cells are able to express TF but the involvement of this property in the hemostatic physiological changes observed during pregnancy, remains to be demonstrated.

[Find your way in the jungle of mAbs]

The rapidly increasing number of approved monoclonal antibodies (mAbs) and the huge number of mAbs in clinical development are a matter of concern for who wants to easily identify targets, indications, mechanisms of action and possible adverse effects. The current nomenclature being of limited interest, simple rationales will be presented for helping practitioners in rapidly classify mAbs depending on their structure-pharmacology relationship and in evaluating their potential effects, particularly in transfusion medicine.

Rituximab-induced T cell depletion in patients with rheumatoid arthritis: association with clinical response

OBJECTIVE

Rituximab, a monoclonal antibody specifically targeting CD20, induces B cell depletion and is effective in the treatment of rheumatoid arthritis (RA). This study was undertaken to evaluate whether routine monitoring of lymphocyte subpopulations, especially T cells, may be useful in patients receiving rituximab for RA.

METHODS

We examined data on all RA patients receiving rituximab between July 2007 and November 2012 in our center. Peripheral blood CD3+, CD4+, CD8+, CD3-CD56+, and CD19+ lymphocyte counts before and during the first course of rituximab were measured by flow cytometry. The Mann-Whitney nonparametric test was used to compare lymphocyte subpopulation counts before and during treatment.

RESULTS

Data on 52 patients were examined. Rituximab induced unexpected and substantial depletion of T cells, mainly CD4+ cells, in most patients. The CD4+ cell count decreased by a mean ± SD of 37 ± 33% as compared to baseline at week 12, reaching <200 cells/μl in 3 patients. Importantly, lack of CD4+ cell depletion was associated with no clinical response. Therefore, the mechanism of action of rituximab may depend at least in part on T cells.

CONCLUSION

Rituximab induces substantial T cell depletion, mainly of CD4+ cells, which is associated with the clinical response in RA. Routine monitoring of T cells may be useful in the clinical setting of RA.

Efficiency of immunoglobulin G replacement therapy in common variable immunodeficiency: correlations with clinical phenotype and polymorphism of the neonatal Fc receptor

Treatment of common variable immunodeficiency disorders (CVID) is based on replacement therapy using intravenous (i.v.) or subcutaneous (s.c.) immunoglobulin (Ig)G. Interindividual variation of IgG dose is common. A total of 380 CVID patients on stable IgG replacement from two prospective cohorts were analysed. An 'efficiency' index was defined as the ratio of serum IgG trough level minus IgG residual to the average weekly dose of IgG infusion. A reduced efficiency of IgG was associated independently with the i.v. route (P < 0·001) and with the presence of at least one CVID disease-related phenotype (lymphoproliferation, autoimmune cytopenia or enteropathy) (P < 0·001). High IgG efficiency was noted in patients homozygotes for the variable number tandem repeat (VNTR) 3/3 polymorphism of the neonatal Fc receptor gene [IgG Fc fragment receptor transporter alpha chain (FCGRT)] promoter, and this was particularly significant in patients treated with IVIG (P < 0.01). In a multivariate analysis, FCGRT VNTR 3/3 genotype (P = 0·008) and high serum albumin (P < 0·001) were associated independently with increased efficiency of i.v. Ig.

Association of Fcγ receptor IIIA variant with a subset of anti-topoisomerase I-positive patients in systemic sclerosis: a descriptive pilot study

Hypothesizing a pathophysiological role of anti-topoisomerase I antibodies (anti-topo I) through autoantibody-dependent cell-mediated cytotoxicity (ADCC) and cytotoxic effectors expressing receptors for the Fc portion of IgG in systemic sclerosis (SSc), 267 SSc patients (56 with anti-topo I and 102 with anti-centromere antibodies (ACA)) were genotyped for the functional FCGR3A-V158F polymorphism. A descriptive analysis of patients according to their clinical and immunological status and FCGR3A-158 V/F genotypes was performed using multiple correspondence analysis. This descriptive analysis revealed an association between the FCGR3A-158 VV genotype and the presence of anti-topo I. By contrast, no relationship was found between FCGR3A polymorphism and the presence of ACA. SSc patients with anti-topo I appear to be more frequently homozygous for the high-affinity FcγRIIIA-coding allele, suggesting that some autoantibodies may be pathogenic through ADCC.

Pre-treatment lymphopenia as a prognostic biomarker in colorectal cancer patients receiving chemotherapy

BACKGROUND

Lymphopenia is a predictor of the efficacy and hematological toxicity of chemotherapy in various advanced cancers. There is little data about this relationship in colorectal cancer. In this retrospective study, the influence of pretreatment lymphopenia on hematological toxicity and the efficacy of chemotherapy was investigated in colorectal cancer patients.

PATIENTS AND METHODS

In total, 260 patients were included in the study. Correlations between pre-treatment lymphopenia (lymphocyte count < 1,000/μl) and the occurrence of hematological toxicity and efficacy of first-line palliative chemotherapy were investigated.

RESULTS

Lymphopenia was found in 49/260 (19%) patients. Ten of these patients with lymphopenia (20.4%) experienced severe hematological toxicity compared with 17 of the remaining 211 (8%) patients (P = 0.01). Lymphopenia was identified as an independent factor for hematological toxicity. Among patients who received palliative chemotherapy, the objective response rate was significantly lower in lymphopenic patients than in the other patients (12.5% vs. 40.2%; P = 0.004). Lymphopenia was strongly associated with shorter progression-free survival (median 4 vs. 7 months; P = 0.033) and shorter overall survival (median 16 vs. 24 months, P = 0.024). Multivariate analysis revealed that lymphopenia had an independent effect on survival.

CONCLUSIONS

Our findings show that lymphopenia is an independent predictive factor for both hematological toxicity and efficacy of chemotherapy in colorectal cancer. Pre-treatment lymphocyte count may represent a simple and new predictive biomarker of chemotherapy effects in colorectal cancer patients.

Intralesional therapy with anti-CD20 monoclonal antibody rituximab: local and systemic efficacy in primary cutaneous B-cell lymphoma

Rituximab (MabThera, Roche) is a chimeric monoclonal antibody directed against the CD20 antigen. Its efficacy and safety were first demonstrated in the treatment of systemic B-cell lymphomas. We report the use of intralesional injections of rituximab into some but not all cutaneous lesions in a patient with multiple primary cutaneous follicular centre B-cell lymphoma. This treatment resulted in tumour regression, even of the lesions that had not been injected. We therefore hypothesize that there is systemic diffusion of rituximab from injected sites despite the low doses injected locally, or the induction of a specific antitumour immune response acting systemically.

Relationship between calcineurin inhibition and plasma endothelin concentrations in cyclosporine-A-treated kidney transplant patients

OBJECTIVE

The inter-individual variability of cyclosporine (CsA) pharmacokinetics is well known. However, there is obviously also an inter-individual pharmacodynamic variability, which might be explored by the measurement of biomarkers of CsA effects.

METHODS

In 11 renal transplant patients, blood CsA concentrations, calcineurin inhibition in peripheral blood mononuclear cells and endothelin plasma concentrations were measured over a 4-h period after CsA intake.

RESULTS

Mean plasma endothelin concentrations were higher than those of healthy subjects (3.66+/-0.46 pg ml(-1) versus 3.15+/-0.40 pg ml(-1), P<0.01) but were not related to CsA dose or blood concentrations. There was a linear relationship between calcineurin inhibition at t (0) and mean endothelin concentrations (r (2)=0.51, P<0.05). Patients with gingival hypertrophy had higher mean endothelin concentrations than patients without this complication (4.0 pg ml(-1) versus 3.4 pg ml(-1), P<0.01), although CsA doses and concentrations were not different between these two groups.

CONCLUSION

We observed a correlation between calcineurin inhibition and endothelin concentrations. Endothelin plasma concentrations is a biomarker of CsA effect, which may provide more information than CsA blood concentrations.

Association between polymorphism in IgG Fc receptor IIIa coding gene and biological response to infliximab in Crohn's disease

AIM

To test the hypothesis of an association between polymorphism in FCGR3A (the gene coding for FcgammaRIIIa, which is expressed on macrophages and natural killer cells, is involved in antibody-dependent cell-mediated cytotoxicity and has recently been associated with a positive response to rituximab, a recombinant immunoglobulin G1 antibody used in non-Hodgkin's lymphomas) and response to infliximab in Crohn's disease.

METHODS

FCGR3A-158 polymorphism was determined using an allele-specific polymerase chain reaction assay in 200 Crohn's disease patients who had received infliximab for either refractory luminal (n = 142) or fistulizing (n = 58) Crohn's disease. Clinical and biological responses (according to C-reactive protein levels) were assessed in 200 and 145 patients, respectively.

RESULTS

There were 82.9% clinical responders in V/V patients vs. 72.7% in V/F and F/F patients (N.S.). Globally, the decrease in C-reactive protein was significantly higher in V/V patients than in F carriers (P = 0.0078). A biological response was observed in 100% of V/V patients, compared with 69.8% of F carriers (P = 0.0002; relative risk, 1.43; 95% confidence interval, 1.27-1.61). In the sub-group of patients with elevated C-reactive protein before treatment, the multivariate analysis selected the use of immunosuppressive drugs and FCGR3A genotype as independent factors influencing the clinical response to infliximab (P = 0.003).

CONCLUSION

Crohn's disease patients with FCGR3A-158 V/V genotype have a better biological and, possibly, clinical response to infliximab.

Association between the SDF1-3'A allele and high levels of CD34(+) progenitor cells mobilized into peripheral blood in humans

Some patients unexpectedly fail to mobilize sufficient numbers of haematopoietic progenitor cells (HPCs) into the peripheral blood for autologous transplantation. Considering the important role of the chemokine stromal cell-derived factor 1 (SDF-1) in HPC homing, we investigated a possible relationship between SDF1 gene polymorphism and HPC mobilization capacity in 63 patients with malignancy. Some 67% of the good mobilizers (> or = 50 CD34(+) cells/microl) and only 36% of the intermediate/poor mobilizers were SDF1-3'A allele carriers (P = 0.032). In multivariate analysis, the presence of the SDF1-3'A allele was the only factor predictive of good CD34(+) cell mobilization (P = 0.025). This is the first report showing the involvement of genetic factors for HPC mobilization in humans and suggests a significant role for SDF-1 in this process.

Development of an ex vivo model of pig kidney perfused with human lymphocytes. Analysis of xenogeneic cellular reactions

BACKGROUND

Because of the explosive nature and the extremely rapid process of hyperacute rejection (HAR), significant infiltration of the xenograft by immunocompetent cells is not observed, and the role and the mechanism of action of cell-mediated rejection in discordant xenografts are therefore still under discussion.

METHOD

We developed an experimental approach using pig kidneys perfused with human peripheral blood lymphocytes (PBL) in which the immunologic barrier of hyperacute rejection was excluded and which mimics the in vivo situation.

RESULTS

PBL retention in the kidney was evaluated at 20-minute intervals for 3 hours. Retention increased from 30% to 80% with the time of perfusion and was specific because significantly fewer syngeneic lymphocytes were retained. Phenotype analysis of recovered PBL showed a significant decrease in natural killer (NK) cells. Immunohistochemical studies revealed the presence of NK cells and T lymphocytes in the glomerular and interstitial tubular structures of the kidney. Functional studies showed a progressive cessation of diuresis and augmentation of renal vascular resistance when the kidney was perfused with PBL. Electron microscopy examinations of kidney sections perfused with PBL showed swollen endothelial zones, suggesting alterations to and damage of the endothelium.

CONCLUSIONS

This system provides a valuable model for the study of early discordant xenogeneic cellular rejection and demonstrates the predominance of xenograft infiltration by NK cells.

[Anti-pig xenogeneic response by human CD4+ T-lymphocytes]

When considering the hypothesis of xenotransplantation, and if it becomes possible to control hyperacute and delayed vascular rejection, the recognition of porcine graft by human T CD4+ lymphocytes could still constitute a very important barrier. The direct recognition of porcine MHC class II molecules (SLA-DR and SLA-DQ) by human TCR has been demonstrated in vitro. It is accompanied by a proliferative lymphocytic response, as co-stimulatory molecules are able to interact across the species barrier. In vivo, this type of recognition only applies to porcine cells with antigen-presenting functions, mainly the graft dendritic cells which emigrate into the recipient lymphoid organs. The other recognition pathway is indirect, whereby the recipient dendritic cells capture porcine xenoantigens in the graft, then process and present them to the lymphocytes in the lymphoid organs. This indirect pathway can be shown in vitro by utilizing porcine MHC class II-negative endothelial cells. In this model, human purified T CD4+ lymphocyte proliferation is tightly dependent on the presence of human antigen-presenting cells and their HLA class II molecules. As the xenogenic peptides all differ from self peptides, the indirect T-cell response will be very strong and probably difficult to control.

Trophoblast cell line resistance to NK lysis mainly involves an HLA class I-independent mechanism

The lack of classical HLA molecules on trophoblast prevents allorecognition by maternal T lymphocytes, but poses the problem of susceptibility to NK lysis. Expression of the nonclassical class I molecule, HLA-G, on cytotrophoblast may provide the protective effect. However, the class I-negative syncytiotrophoblast escapes NK lysis by maternal PBL. In addition, while HLA-G-expressing transfectants of LCL.721.221 cells are protected from lymphokine-activated killer lysis, extravillous cytotrophoblast cells and HLA-G-expressing choriocarcinoma cells (CC) are not. The aim of this work was therefore to clarify the role of HLA class I expression on trophoblast cell resistance to NK lysis and on their susceptibility to lymphokine-activated killer lysis. Our results showed that both JAR (HLA class I-negative) and JEG-3 (HLA-G- and HLA-Cw4-positive) cells were resistant to NK lysis by PBL and were equally lysed by IL-2-stimulated PBL isolated from a given donor. In agreement, down-regulating HLA class I expression on JEG-3 cells by acid treatment, masking these molecules or the putative HLA-G (or HLA-E) receptor CD94/NKG2 and the CD158a/p58.1 NKR with mAbs, and inducing self class I molecule expression on JAR cells did not affect NK or LAK lysis of CC. These results demonstrate that the resistance of CC to NK lysis mainly involves an HLA class I-independent mechanism(s). In addition, we show that the expression of a classical class I target molecule (HLA-B7) on JAR cells is insufficient to induce lysis by allospecific polyclonal CTL.

Human allogeneic lymphocytes trigger endothelial cell tissue factor expression by a tumor necrosis factor-dependent pathway

Lymphocyte adhesion to endothelial cells and the extravascular deposition of fibrin are 2 important processes during pathologic situations such as allograft rejection. Tissue factor (TF) expression was therefore measured on human umbilical vein endothelial cells (HUVECs) after coculture with allogeneic lymphocytes (PBLs) by a factor Xa generation assay. When cocultured with PBLs, HUVECs expressed strong procoagulant activity related to the TF/factor VII-dependent pathway, which was enhanced when endothelial cells were treated with interferon-gamma (IFN-gamma). The highest TF activity was measured when 10(5) lymphocytes were incubated with 10(4) HUVECs (ratio 10: 1) for 4 hours, a time-dependent course similar to that obtained with tumor necrosis factor-alpha (TNF-alpha), and direct contact between the 2 cell types was necessary. PBL-induced TF activity was inhibited by cycloheximide or actinomycin D, indicating active protein synthesis that was confirmed by the increase in TF mRNA detected by reverse transcription-polymerase chain reaction. It was then demonstrated that 1 of the primary signaling pathways leading to endothelial cell TF expression was a rapid initial interaction between membrane TNF expressed on PBLs and the 75-kd TNF receptor, with subsequent involvement of platelet-activating factor and P-selectin. Finally, we showed that the transduction of external signals involving the activation of protein kinase C and protein tyrosine kinases also contributed to the regulation of TF expression.

Human T lymphocyte proliferative response to resting porcine endothelial cells results from an HLA-restricted, IL-10-sensitive, indirect presentation pathway but also depends on endothelial-specific costimulatory factors

To investigate the mechanisms of cellular rejection in pig-to-human xenotransplantation, the proliferation of different human purified lymphocyte subpopulations in response to swine leukocyte Ag class II-negative porcine aortic endothelial cells (PAEC) was measured in the presence or absence of human autologous adherent cells (huAPC). CD8+ lymphocytes proliferated moderately in the absence of huAPC, and the immune response was slightly increased when huAPC were added. CD56+ lymphocytes failed to proliferate in response to PAEC whether huAPC were present or not. CD4+ lymphocytes alone did not proliferate in response to PAEC, but a strong proliferative response was observed in the presence of metabolically active huAPC. This response was totally abolished by mAbs directed against HLA class II molecules or by pretreatment of huAPC by human IL-10. Even in the presence of huAPC, CD4+ lymphocytes failed to respond to fixed PAEC or to PAEC-lysates, suggesting that PAEC must be viable to support lymphocyte proliferation. Finally, none of the nonendothelial porcine adherent cells tested was able to induce human lymphocyte proliferation, despite the fact that they also provided a large set of xenogeneic peptides. Our results show that the indirect presentation pathway of xenoantigens by huAPC to CD4+ lymphocytes is crucial in the response to porcine endothelial cells, and that IL-10 could be of therapeutic interest to prevent human lymphocyte activation by this pathway. Furthermore, we demonstrated that stimulatory signals specifically provided by endothelial cells are also necessary for this huAPC-restricted proliferative response.

Docosahexaenoic and eicosapentaenoic acids inhibit in vitro human endothelial cell production of interleukin-6

The interaction between lymphocytes, cytokines, and endothelial cells (EC) is a key step in the inflammatory process. Interleukin-6 (IL-6) a pleiotropic cytokine in its effects, seems to be an early indicator of acute systemic inflammation. In this study, we have examined the effects of polyunsaturated fatty acids (PUFAs) on the production of IL-6 by human unstimulated EC or EC stimulated with TNF-alpha (100 U/ml); IL-4 (100 U/ml); LPS (1 ug/ml); or allogeneic peripheral blood lymphocytes (PBL). Twenty-four hour culture supernatants of immunoreactive IL-6 were measured by Sandwich ELISA. We have shown that the production of IL-6 was potentiated when EC were stimulated with TNF-alpha; IL-4; LPS; or monocyte-depleted PBL in comparison to unstimulated EC. The addition of n-3 PUFAs in culture medium (100 ug/ml DHA or EPA) significantly reduces the production of IL-6 by unstimulated EC; or stimulated with TNF-alpha; IL-4 pg/ml); LPS or depleted PBL respectively for DHA and EPA, whereas the n-6 PUFAs (Arachidonic acid), even used at the highest concentration, was ineffective. This inhibitory effect is PUFA dose dependent but is more potent with EPA than DHA. Regardless of the mode of action, since IL-6 is known to be involved in hematopoiesis, in the regulation of the immune response and in the inflammatory reaction, these results suggest that n-3 PUFAs may play a role in suppressing inflammation. Further studies are needed to elucidate the mechanism involved and the choice between the two fatty acids for clinical and therapeutic purposes.

Removal of primate xenoreactive natural antibodies by extracorporeal perfusion of pig kidneys and livers

Organ perfusion is one of the possible strategies to attenuate rejection of discordant xenografts by reducing the levels of the recipient's xenoreactive natural antibodies (XNA). Its efficacy in terms of XNA removal was studied in models of primate blood or plasma perfusion through porcine kidneys or livers, with special attention to haematological consequences and potential side-effects. We first perfused the blood of rhesus monkeys through pig kidneys and livers, and demonstrated that the perfusion of a pig liver resulted in higher XNA adsorption (72 +/- 13%) than the perfusion of a pig kidney (51 +/- 25%). However, when we normalized for the weight of the perfused organs and for levels of natural antibodies in individual monkeys, livers adsorbed less antibody (1.4 +/- 0.9 U antibody/g) than kidneys (7.2 +/- 7 U antibody/g). Histological signs of rejection were observed in perfused kidneys, but not in perfused livers. A major drawback of the perfusion of blood through livers was a considerable decrease in the primates' haemoglobin and platelet levels. To avoid this, we developed a plasma liver perfusion device. This method allowed a significant improvement in the haemodynamic state of primates and was particularly effective in preventing anaemia. Moreover, plasma liver perfusion was as effective as blood liver perfusion to remove natural antibodies and, resulted in a marked decrease in their functional activity as assessed by complement-dependent cytotoxicity (CDC) and antibody-dependent cell-mediated cytotoxicity (ADCC). The level of other plasma proteins was not significantly affected, apart from a dilution effect. After xenoperfusion a strong antibody response was evidenced by ELISA, CDC and ADCC between days 7 and 14 and then decreased progressively. We conclude that the separation of blood to allow the perfusion of plasma through a pig organ is safer than the perfusion of unseparated blood and is associated with efficient natural antibody removal. However, organ perfusion is limited by a rebound in antibody levels after a few days, and thus will have to be associated with anti-B cell immunosuppressive therapy for long-term or repeated applications.

[Role of the endothelium in leukocyte trafficking]

Vascular endothelium controls leukocyte recirculation and recruitment, receiving messages from underlying tissues and transforming them into informations quickly read by the passaging leukocytes. These messages induce adhesive interactions between leukocytes and endothelium via adhesion molecules. Multiple receptor-ligand pairs function in 4 steps: initial tethering and rolling of leukocytes; leukocyte triggering by chemotactic factors; arrest and strong adhesion to endothelium; and ultimately transendothelial migration (diapedesis).

Human NK cell-mediated direct and IgG-dependent cytotoxicity against xenogeneic porcine endothelial cells

Once hyperacute rejection has been prevented, the pig-to-human xenograft might be exposed to vascular cell-mediated rejection directed against vascular structures. In order to evaluate the relative importance of direct and antibody-dependent anti-endothelial cell-mediated cytotoxicity in different individuals, freshly isolated human blood leukocytes were incubated with confluent porcine aortic endothelial cells (PAEC) in a 4 h Cr-release cytotoxicity assay. Peripheral blood mononuclear cells (PBMC) and lymphocytes (PBL) of all subjects tested (but not monocytes or neutrophils) directly killed PAEC, with wide interindividual variations (from 2.8% to 32%). The addition of heat-inactivated autologous serum to PBMC and PBL (but not to myeloid cells) always enhanced cytotoxicity. This antibody-dependent cell-mediated cytotoxicity (ADCC) was also observed in the presence of adult pooled serum and cord blood pooled serum and was eliminated after adsorption of adult pooled serum to insoluble protein A, demonstrating that IgG is the only class of immunoglobulin involved in this phenomenon. Moreover, blocking Fc gamma RIII with an anti-CD16 mAb eliminated ADCC without affecting direct cytotoxicity. When the ADCC exerted by the PBL of all subjects was assessed with the same preparation of purified IgG, wide interindividual variations were again observed. Surprisingly, there was no correlation between direct cytotoxicity and ADCC although, as depletion experiments demonstrated, both were due to CD16+ natural killer (NK) cells. These results argue that CD16+ NK cells could play an important role in early vascular rejection of porcine discordant xenografts, by both a direct and an IgG xenoreactive natural antibody-dependent cell-mediated cytotoxicity.

Removal of terminal alpha-galactosyl residues from xenogeneic porcine endothelial cells. Decrease in complement-mediated cytotoxicity but persistence of IgG1-mediated antibody-dependent cell-mediated cytotoxicity

To determine the role of the terminal alpha-galactosyl residue in the endothelial damage mediated by human xenoreactive natural antibodies (IgM and IgG), we treated porcine endothelial cells in culture with green coffee bean alpha-galactosidase. A practically complete removal of terminal alpha-Gal residues (as evaluated by flow cytometry with Bandeiraea simplicifolia isolectin B4) and concomitant exposure of N-acetyllactosamine were obtained without altering cell viability. A dramatic decrease in IgM and IgG binding (from a pool of human sera) was observed, confirming the key role of the alpha-galactosyl residues. The enzyme treatment did not induce any nonspecific immunoglobulin binding sites, but led to the exposure of new epitopes for a minor fraction of IgM. The main residual IgM and IgG binding could be due to xenoantigens other than the alpha-galactosyl residues. When alpha-galactosidase-treated endothelial cells were used as targets in cytotoxicity experiments, they were less susceptible than untreated cells to complement-mediated cytotoxicity induced by fresh human serum. In contrast, they did not acquire resistance to human IgG-dependent cellular cytotoxicity, despite the decrease in IgG binding. Because it is known that antibody-dependent cytotoxicity mediated by CD16+ NK cells is dependent on IgG1 and IgG3, and not on IgG2 or IgG4, which was confirmed by blocking experiments, we studied the binding of all four subclasses to intact and alpha-galactosidase-treated endothelial cells. Two major subclasses, IgG1 and IgG2, bound to untreated endothelial cells, whereas IgG3 binding was low and IgG4 binding was negligible. A decrease in IgG1, IgG2, and IgG3 binding was observed upon alpha-galactosidase treatment, indicating that antibodies belonging to these three subclasses recognize alpha-galactosyl residues. The decrease in IgG2 binding was more pronounced than the decrease in IgG1 binding. Collectively, these data indicate that IgG1 xenoreactive natural antibodies, including those which are not directed at the alpha-galactosyl residues, could play a major role in the early delayed vascular rejection of pig xenografts.

A simplified and low-cost one-stage chromogenic assay for tissue factor dependent procoagulant activity of endothelial cells

We developed a sensitive tissue factor (TF) chromogenic assay on a limited number of endothelial cells (EC), performed in microtiter plates, and which uses a normal pooled human plasma instead of purified concentrates as a source of coagulation factors. Primary cultures of human umbilical vein EC (HUVEC), both unstimulated and stimulated by lipopolysaccharide (LPS) were incubated with 50 microliters of of diluted normal human plasma (NHP) and 50 microliters of Factor Xa-specific chromogenic substrate (CBS 31-39, Stago, France). Hirudin was added at 4 U/ml to the plasma/CBS 31-39 mixture to inhibit thrombin generation. Optical densities were read at 405 nm and corresponding amounts of generated factor Xa were expressed in mU Xa/well using a standard curve established with purified human Factor Xa. The following parameters were then defined: the number of EC to plate (10(4) EC/well of a 96-well plate), the plasma-test dilution (1:20), the concentration of CBS 31-39 (0.50 mM) and the incubation time of reagents with EC (2 hours). The procoagulant activity (PCA) measured was only dependent on TF since it was no longer detectable either when FVII-deficient plasma was tested instead of normal human plasma or when PCA assays were performed in the presence of a blocking anti-human TF monoclonal antibody. This method allowed detection of a TF-dependent PCA on as few as 1000 EC per well. In addition, TF expression equal to 50% of maximal values was measured with LPS concentrations as low as 1 ng/ml, supporting the high sensitivity of the assay.

Evidence of noninvolvement of swine MHC class II in the in vitro proliferative response of human lymphocytes to porcine endothelial cells

Successful pig-to-human xenotransplantation may expose swine endothelium to the human immune system. Since endothelial MHC class II expression is crucial in the genesis of an allogeneic lymphocyte response, the involvement of porcine MHC (SLA) class II molecules in the induction of human lymphocyte proliferation was studied. When cocultured with a confluent monolayer of irradiated porcine aortic endothelial cells (PAEC), human peripheral blood mononuclear cells (PBMC) incorporated tritiated thymidine. Monocyte depletion strongly reduced the magnitude of the lymphocyte proliferative response. Resting cultured PAEC were SLA class II-negative and an induction of these molecules during the xenogeneic mixed lymphocyte endothelial cell culture (XMLEC) was not observed. Moreover, the addition of an antibody directed against the SLA-DR molecule was without effect. Lymphocyte proliferation was also studied in response to SLA class II-positive stimulating cells--either human TNF-alpha-stimulated PAEC or porcine splenocytes. Induction of SLA class II molecules on PAEC had no effect on the human PBMC proliferative response. Moreover, human PBMC did not proliferate in response to porcine splenocytes. These results suggest (1) that SLA class II molecules are not involved in the induction of the human lymphocyte proliferative response and (2) that the endothelial nature of the stimulating cells plays a key role in this proliferation.

Tissue factor activity of syncytiotrophoblast plasma membranes and tumoral trophoblast cells in culture

During pregnancy, important modifications of hemostasis occur resulting in mothers in hypercoagulability and the role of placental cells such as trophoblast cells has been hypothesized. In this study, we first showed that syncytiotrophoblast plasma membranes, isolated from normal human placenta, expressed a strong tissue factor (TF) activity. We then studied TF activity of two continuous trophoblast cell lines (JEG-3 and BeWo) in comparison to human umbilical vein endothelial cells (HUVEC) and transformed human endothelial cells (ECV-304). TF assays were performed on intact detached confluent cells. Unstimulated JEG-3 and BeWo cells exhibited a very high TF activity which slightly increased after 2 to 4 h TNF-alpha stimulation. In contrast, HUVEC and ECV-304 had a lower basal TF activity which was mainly inducible by TNF-alpha, with a maximum effect after 4 to 6 h stimulation. For both cell types, TF activity was decreased to basal value after 16-hour TNF-alpha stimulation. These results support that trophoblast cells are able to express TF but the involvement of this property in the hemostatic physiological changes observed during pregnancy, remains to be demonstrated.

Adhesive properties of choriocarcinoma cells toward lymphocytes activated or not by interleukin-2

Choriocarcinoma cells (CC) in vitro are resistant to NK lysis but sensitive to lysis by blood or decidual effectors activated by interleukin-2 (IL-2). Because lytic activity requires a step of adhesion, the adhesive properties of the choriocarcinoma cells BeWo, JEG-3, and JAR were examined functionally toward peripheral blood lymphocytes. The adhesion of lymphocytes to choriocarcinoma cells was very low and did not increase after stimulating lymphocytes with IL-2. As demonstrated by cytofluorimetry analysis, choriocarcinoma cells and cytotrophoblast cells prepared from term placenta expressed intercellular adhesion molecule-1 (ICAM-1), whereas only CC expressed CD56. Tumor necrosis factor-alpha or interferon-gamma increased the expression of ICAM-1 on choriocarcinoma cells without modifying the adhesion of lymphocytes to choriocarcinoma cells. These results suggest that resistance of choriocarcinoma cells to lysis by cytotoxic effectors could partially be attributed to the low level of lymphocyte adhesion to these cells.

IFN-gamma treatment of rodents infected with erythrocytic stages of Plasmodium chabaudi: differential effects according to the immunological status

Recombinant rat interferon-gamma (rrIFN-gamma) was tested for its antimalarial activity in three different models of Plasmodium chabaudi-blood stage malaria. Doses ranging from 1 x 10(4) to 1 x 10(5) U of rrIFN-gamma were used in each model. In BALB/c mice (lethal infection), prophylactic treatment with daily intraperitoneal (i.p.) injections reduced parasitemia and delayed mortality. In contrast, subcutaneous administration of rrIFN-gamma was inefficient, as was curative schedule of i.p. administration. Euthymic Fischer rats, which develop an acute and resolutive infection, were partly protected by i.p. prophylactic administration of rrIFN-gamma. Parasitemia was reduced without being lengthened, resulting in a marked decrease in parasite burden. Subcutaneous administration was less efficient whereas curative schedule was not. Athymic (nude) Fischer rats which present a longlasting and stable infection were treated with prophylactic and curative schedules of i.p. administration of rrIFN-gamma. In each case, rrIFN-gamma-treated nude rats, as control nude rats, were unable to resolve their chronic infection. The conditions required to obtain a beneficial effect are thus restrictive for a therapeutic use in humans. Moreover, these results show that, despite the fact that IFN-gamma is considered as a major component of the immune response, this cytokine alone is not sufficient to induce the totality of the effector mechanisms necessary to cure malarial infections.