Graft-infiltrating T helper cells, CD45RC phenotype, and Th1/Th2-related cytokines in donor-specific transfusion-induced tolerance in adult rats

Specific tolerance to LEW.1W (RT1u) heart allografts can be induced in adult LEW.1A (RT1a) rats by donor-specific blood transfusion (DST). We have previously shown that both rejected and tolerated grafts are heavily infiltrated by T lymphocytes, and that in both cases these T cells are capable of developing similar cytotoxic responses against donor cells in vitro; tolerance is therefore not due to the deletion of alloreactive T cells. At the same time, we found that the accumulation of IL-2 and IFN-gamma mRNA was decreased in tolerated grafts compared with rejected grafts. These results suggested that the induction of allograft tolerance in DST-treated animals could be mediated by anergy or suppression of graft-infiltrating Th1 cells. Although Th1 and Th2 clones have not yet been characterized in the rat, peripheral CD4+ rat T cells can be divided into two populations, based on their expression of the isoform RC of the CD45 molecule. Upon activation, CD45RChigh CD4+ T cells produce IL-2 and IFN-gamma and responsible for the induction of the graft-versus-host reaction, whereas CD45RClow CD4+ T cells produce IL-4 in vitro and provide B cell help. In the present study, we show that heart allografts from both DST-treated and untreated rats were infiltrated by equivalent numbers of leukocytes, of which CD4+ T cells also made up similar percentages. Among these CD4+ T cells, we observed that in allografts from DST-treated recipients the CD45RChigh population on day 5 was very significantly smaller (P = 0.004) than in the untreated group, while CD45RClow populations remained comparable. Moreover, using a new quantitative RT-PCR method, we found a dramatic reduction in the accumulation of IL-2, IFN-gamma, IL-10, IL-4, and IL-13 mRNA in hearts from DST-treated recipients compared with those of untreated recipients during the week following transplantation. These results show that in heart allografts from DST-treated recipients, despite phenotypic changes suggesting Th1 inhibition by Th2 imbalance, T helper function was inhibited as a whole, and that in vivo the phenotype CD4+ CD45RClow does not always correlate with Th2-related cytokine-producing cells.

Leukaemia Inhibitory Factor derived from rat colon carcinoma cells increases host susceptibility to tumour growth

We have tested Leukaemia Inhibitory Factor (LIF) production by 12 rat colon tumour clones isolated from a single cell line that display various degrees of tumorigenicity. A highly significantly relationship was found between levels of soluble LIF produced by the clones and their in vivo tumorigenicity. Such results suggested a role for LIF as a tumour facilitating agent. To test this hypothesis, the highly tumorigenic and LIF producing PROb clone was transfected with the LIF cDNA in antisense orientation in order to decrease LIF production. Conversely, REGb, a low LIF producer that is rejected by syngeneic animals, as well as nude mice, was transfected with the LIF cDNA to increase its production. PROb cells transfected with antisense cDNA were shown to have decreased LIF production along with decreased tumorigenicity. LIF-transfected REGb cells expressing high LIF levels still regressed in syngeneic rats, but could form progressive tumours in nude mice. We did not detect LIF receptors on PROb or REGb cells and their in vitro proliferation was not modified by the addition of exogenous LIF. Therefore, LIF was not an autocrine growth regulator for PROb and REGb cells. Instead, LIF appears to facilitate in vivo tumour growth, without being an immunosuppressive factor sufficient on its own to allow growth of immunogenic cells in fully immunocompetent hosts.

Effects of MHC-encoded TAP1 and TAP2 gene polymorphism and matching on kidney graft rejection

The products of TAP1 and TAP2 genes, recently mapped within the MHC class II region, are involved in antigen presentation by MHC class I molecules, especially in the transport of endogenous peptides. As for most MHC genes, a polymorphism has been described and the possibility that it could influence the recipient immune response by modulating antigen presentation in kidney transplantation has been tested. The aim of our study was to compare TAP1 and TAP2 gene polymorphism and matching in 53 couples of kidney donors and recipients without any rejection episodes and in 55 other couples who had experienced at least 2 acute cellular rejection episodes; 70 healthy individuals served as controls. Our results showed that allelic variant frequencies of TAP1 alleles (1A to 1C) and TAP2 alleles (2A to 2E), as assessed by amplification refractory mutation system-polymerase chain reaction, were similar among "rejection" and "no rejection" populations. Furthermore, there were no differences of TAP1 and/or TAP2 matching between donors and recipients in the 2 groups. In contrast, we showed that the recipients of the no rejection group were better matched with their corresponding donors for the HLA-DR genes than those of the rejection group. These results suggest that the currently described polymorphism in the limited coding region of TAP1 and TAP2 genes does not influence the incidence of kidney allograft rejection episodes and seems not to be a strong link to the adjacent DR/DQ subregion. Moreover, the observed increase frequency of TAP1B allele in the whole recipient's group as compared with controls (16.2% vs. 7.1% in the healthy individuals; P < 0.02) was not linked to the rejection occurrence but to the presence of glomerulonephritis as initial disease. Our study suggests that, in the clinical conditions tested, neither TAP polymorphism nor TAP matching influences the renal graft outcome.

Prolongation of allogeneic heart graft survival in rats by administration of a peptide (a.a. 75-84) from the alpha 1 helix of the first domain of HLA-B7 01

Allospecific T lymphocytes mediate graft rejection through specific, direct or indirect, recognition of processed determinants of foreign MHC class I molecules. Small synthetic peptides derived from highly conserved sequences of the alpha 1 helix of the first domain of certain MHC class I molecules have been shown to inhibit CTL responses in vitro and to prolong graft survival in rats when combined with subtherapeutic doses of cyclosporine. Here, we report that the survival of LEW.1W heart allografts was significantly prolonged when transplanted into congenic LEW.1A recipients treated only with a peptide corresponding to residues 75-84 of the human HLA-B7-01 molecule (B7.75-84) before transplantation. The experimental value for mean survival time (+/- SD) in untreated recipients was 13 +/- 6 days and in peptide-treated recipients was 42 +/- 27 days (P < 0.002). A total of 64% of treated recipients had a functioning graft at 30 days, while grafts were rejected in all rats belonging to the control group within this time. Within graft-infiltrating leukocytes (GIL) in B7.75-84-treated animals, the proportion of T cells was significantly lower and that of CD5-/TCR alpha beta-/CD16-/CD8+ and MHC class II+ cells concomitantly increased, as compared with nontreated animals. GIL from B7.75-84-treated animals also exhibited a dramatic decrease (approximately 70%) of allospecific and spontaneous (NK) cytotoxic activity, whereas their proliferation and IL-2 production were similar in both experimental groups. The IFN-gamma, IL-2, and IL-10 mRNA levels from GIL from peptide-treated recipients were similar to levels of controls, reflecting a state of activation of GIL. Perforin and granzyme A mRNA, the level of which may be modulated parallel to impaired cytotoxic functions, were at similar levels in both experimental groups. These data demonstrate that B7.75-84 significantly prolongs graft survival in LEW.1A rats when given as a single agent and suggests that a specifically decreased cytotoxic response (allospecific and spontaneous) plays a major role.

Glomerulonephritis recurrences after kidney transplantation

Almost all forms of glomerulonephritis affecting the native kidney may recur in the transplanted kidney. However, in a large majority of patients, recurrent glomerulonephritis has only a minimal impact on graft function and survival; less than 5% of all graft losses are the result of recurrence. Kidney transplantations provide an attractive experimental model for investigating the pathophysiological mechanisms in diseases, such as diabetes, in which the recurrence of glomerulonephritis is frequent, and segmental glomerular sclerosis in which glomerulonephritis is severe.

Increased plasma levels of human interleukin for DA1.a cells/leukemia inhibitory factor in sepsis correlate with shock and poor prognosis

Animal study results have suggested a role in sepsis for human interleukin for DA1.a cells/leukemia inhibitory factor (HILDA/LIF). HILDA/LIF and interleukin-6 (IL-6) levels were prospectively studied by serial ELISAs in 34 septic patients. HILDA/LIF was detected in 11 of 34 patients at plasma levels of 100-37,000 pg/mL. Peak HILDA/LIF levels correlated with increased temperature and creatinine and IL-6 and with decreased arterial CO2 (P < .05). Multivariate analysis showed that shock and decreased arterial CO2 accounted for 75% of peak HILDA/LIF plasma variations (R2 = .753). Fatal outcome was most often associated with detectable HILDA/LIF (> 56 pg/mL) and peak IL-6 plasma levels > 850 pg/mL (sensitivity, 83%; specificity, 87%), but both (at respective levels of > 480 and > 850 pg/mL) were associated with fatal outcome. HILDA/LIF was detected in septic patients exhibiting shock, and its levels correlated with higher mortality and shorter survival.

Protection of rat endothelial cells from primate complement-mediated lysis by expression of human CD59 and/or decay-accelerating factor

The present study analyzed the ability of human decay-accelerating factor (DAF) and CD59 to protect rat endothelial cell (EC) clones from human and primate complement-mediated lysis. By flow cytometry and Scatchard analysis, we show that human DAF and/or CD59 cDNAs under the transcriptional control of elongation factor 1-alpha promoter were expressed at levels similar to or higher than that of a human EC line. Human DAF and CD59 were released from the surface of transfected rat cells by phosphatidylinositol phospholipase C, demonstrating that the two molecules were linked to the cell membrane by means of a glycolipid anchor. The functional activity of the two human C regulatory proteins expressed on rat EC lines was studied using an in vitro assay of C-dependent cytotoxic in which rat EC were incubated with human or nonhuman primate sera as sources of xenogeneic natural antibodies and C. We demonstrate that human and monkey xenogeneic natural antibodies bind to rat cells and induce lysis by a C-dependent mechanism involving mainly the C direct activation pathway. Our data indicate that human DAF and CD59, expressed either alone or in combination, abrogated all EC cytotoxicity, even in the presence of 50% human serum. This protective phenotype was correlated with decreased membrane attack complex (CD59 and/or DAF transfectants) and C3 deposition (DAF transfectants) on EC surface. Antibodies against the transfected molecules abolished the protection against C-mediated lysis.

The biology of allograft rejection

Organ transplantation is the treatment of choice for patients with several end-stage renal diseases. Despite improvements in immunosuppression and posttransplantation management of patients, allograft rejection remains a problem. In this review, we focus on the recent advances in molecular biology that have provided new opportunities to explore questions regarding the mechanisms of allograft rejection. We have concentrated on antigen presentation and the role of the direct and indirect pathway in allorecognition; effector mechanisms; adhesion molecules and lymphocyte homing; and the role of cytokines in regulating the different steps of rejection.

Rat interleukin-2 immunoglobulin M fusion proteins are cytotoxic in vitro for cells expressing the IL-2 receptor and can abolish cell-mediated immunity in vivo

A hybrid cDNA coding for a fusion protein between rat interleukin 2 (IL-2) and a truncated heavy chain from rat immunoglobulin M (IgM) was constructed. The rat IL-2 and rat IgM CH2-3-4 hybrid gene was subcloned into a vector (PKCR6) for expression of the fusion molecule in Chinese hamster ovary (CHO) cells. Cells transfected with the hybrid cDNA secrete multimeric forms of the fusion protein (IL-2-Mu). Size analysis of the construct revealed that the majority (95%) of the secreted proteins have a high mw (> 500 kDa). The IL-2-Mu construct bind specifically to cells bearing the IL-2 receptors (IL-2R) with a binding affinity around 5 nM. The specific binding to IL-2R leads to T cell proliferation or, if rabbit complement is added, to T cell lysis. Multimeric forms (> 500 kDa) of the fusion protein mediate complement-dependent lysis but trigger only weak proliferation when compared with the low-mw forms (< 500 kDa). In contrast, the latter only efficiently mediate T cell proliferation without inducing complement-dependent lysis. After intravenous administration of CHO supernatant containing IL-2-Mu, or purified IL-2-Mu proteins into rats, the fusion proteins disappeared from the circulation with a t1/2 of 1 hr. The circulating IL-2-Mu constructs in the rat serum retained their capacity to induce complement-dependent lysis of IL-2R-bearing T cells in vitro. Furthermore, the IL-2-Mu construct was able to suppress the delayed-type hypersensitivity (DTH) reaction (an IL-2R, T helper cell-dependent event) in mice. A weak immune response (antirat IL-2-Mu antibodies) was observed when rats received multiple daily injections of the construct.

Presence of leukaemia inhibitory factor and interleukin 6 in porcine uterine secretions prior to conceptus attachment

Leukaemia inhibitory factor (LIF) plays an important role in embryo development and implantation. We detected peak LIF activity in porcine uterine luminal fluids (ULF) at day 12 of gestation and during day 7 and 13 of the oestrous cycle. A radio-receptor competition assay showed the presence of a molecule in ULF specifically binding to human LIF receptor (LIF-R). LIF activity was partially neutralized by anti-human LIF antibody. Interleukin-6 (IL-6) activity was detected in ULF throughout the oestrous cycle and pre-implantation period. An anti-murine alpha chain (gp80) of IL-6 receptor (IL-6R) specifically neutralized this activity. LIF and IL-6 mRNA were only detected in day 11 endometrium. The presence of LIF or IL-6 in the uterine cavity has not been previously reported. Our results extend LIF production by endometrium during the oestrous cycle and pre-implantation period to another mammalian species other than mouse.

Decreased anti-donor major histocompatibility complex class I and increased class II alloantibody response in allograft tolerance in adult rats

Permanent tolerance to allografts can be induced in adult rats by donor-specific transfusions (DST) prior to transplantation. We have previously reported, in a model of heart allograft, the presence of a heavy leukocyte infiltrate, in the allograft which displayed a strong allospecific cytotoxicity when tested in vitro against donor cells, and a strong accumulation of mRNA for granzyme A and perforin in vivo. In contrast, there was a major decrease in the accumulation of mRNA for interleukin-2 and interferon-gamma. These results suggested that the DST-induced tolerance was associated with a decrease in type-1 T helper (Th1) cell function. The major role of preformed antibodies in xeno and allorejection is clearly established. Nevertheless, the consequences of alloantibody production in acute rejection and tolerance induction remains to be elucidated. We here analyze the alloantibody response in rejecting and DST-treated recipients. We show that, after transplantation, tolerant recipients, in contrast to rejecting ones, mount a low IgM alloresponse that switches to low IgG production. Detailed analysis of IgG alloantibodies in DST-treated recipients revealed that their production decrease was not equally distributed. Whereas rejecting animals mounted a strong anti-class I and II IgG alloantibody response, DST-treated recipients produced anti-class II and low titers of anti-class I IgG alloantibodies. Furthermore, among IgG subclasses, tolerant recipients predominantly produced IgG2a, a profile which, in the rat, is compatible with a Th2-controlled response. Finally, the passive transfer of immune serum from rejecting animals to DST-treated recipients could abrogate the tolerance. We suggest that the absence of anti-class I alloantibodies combined with preserved and/or increased anti-class II production plays a major role in graft tolerance in this model. These results reinforced the role of alloantibodies in rejection and in induction of tolerance.

Human natural antibodies to porcine platelets

The specificity of human natural antibodies directed against blood cells from pigs was investigated by ELISA and immunoblotting. Both IgG and IgM were identified as xenoantibodies reacting with pig platelets adsorbed to microplates. The antibodies could be absorbed on platelets as well as on RBC, suggesting that the corresponding antigens are expressed on the surface of a variety of cells. Galactose (20 mM) and melibiose (10 mM) partially inhibited (approximately 50%) the binding of antibodies to platelets, whereas lactose and cellobiose (300 mM) did not. On immunoblots, platelet glycoproteins of 115, 125, 135, 180, and 210 kDa were specifically revealed with human sera diluted 1/20. In contrast with the results obtained by ELISA, xenoantibodies reactive with blotted glycoproteins were of the IgM class and the binding was not significantly inhibited by galactose or melibiose. "Anti-Gal" antibodies, purified from human sera by affinity chromatography on a melibiose-Sepharose immunoabsorbent, represented only a minor portion of the antibodies reactive with porcine platelets. Purified anti-Gal antibodies bound to the 115- and 135-kDa components, whereas the antibodies in the nonretained fraction revealed the 125-kDa molecule. As deduced from these data, human serum contains natural antibodies of both IgG and IgM classes directed to several porcine antigens. Gal-reactive structures were identified on the 115- and 135-kDa platelet glycoproteins, which might be homologous to their counterpart on endothelial cells. Also, the present work suggests that a majority of the natural antibodies reacted with other unidentified structures.