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Biomedical subjects

W Weimar

Publications and source records attributed to W Weimar.

At least 163 records · Page 9Linked to original sources
PubMed1996

Peripheral monitoring of direct and indirect alloantigen presentation pathways in clinical heart transplant recipients.

It has been reported that the response to alloantigens presented by the direct and indirect pathway may be of differential relevance after human kidney transplantation. Accordingly, we monitored these routes in peripheral blood mononuclear cells (PBMC) of heart transplant patients from before transplantation and up to 2 years thereafter in an attempt to find a correlation with the clinical status of the patients. Both before and after transplantation, comparable proportions of PBMC samples reacted in mixed lymphocyte culture to nondepleted donor spleen cells (direct route), but never to donor cells depleted for antigen-presenting cells (indirect route). In contrast, the latter route could easily be activated by a nominal antigen and persisted after transplantation, although the proportion of PBMC samples responding was significantly suppressed, irrespective of the occurrence of rejection. Consequently, complete removal of antigen-presenting cells from the stimulator population in a mixed lymphocyte culture with PBMC as responder is not a suitable tool for measuring indirect presentation of alloantigens, and therefore not relevant for monitoring the immunological status of heart transplant recipients.

Antigen Presentation↗
PubMed1996

Culture of graft-infiltrating cells from cryopreserved endomyocardial biopsies.

Graft-infiltrating cells can be cultured from fresh endomyocardial biopsies (EMB) taken after heart transplantation to determine their growth patterns, phenotypic composition, and functional characteristics for clinical or scientific purposes. In this study we investigated whether graft-infiltrating cells can also be cultured successfully after cryopreservation of these EMB. Three different cryopreservation methods were used. One method gave successful growth in 100% of the cases (n = 6): The biopsy fragments were preincubated in 10% vol/vol dimethyl sulfoxide during 5 min at 0 degree C, frozen to -70 degrees C at approximately 1 degree C per minute, and subsequently immersed and stored in liquid nitrogen. Thawing was performed rapidly in water at 37 degrees C. In addition, the effect of cryopreservation on cell surface phenotype and donor-specific cytotoxicity of these graft-infiltrating cells was analyzed. When compared to cultures of nonfrozen control biopsies, both qualities remained constant in most cases, although a variation in CD4+/CD8+ cell ratio was observed in 33% of these cultures. However, when nonfrozen fragments of size-matched biopsies were cultured separately, a similar variation in phenotype was noted, indicating that this phenomenon can be attributed to sampling variation and not to the cryopreservation procedure. The present findings suggest that it is no longer required to culture fresh (nonfrozen) post-transplant EMB to propagate graft-infiltrating cells: Culturing can be limited to cryopreserved EMB that are selected retrospectively, depending on actual clinical or scientific interests. Besides greatly facilitating the long-term monitoring of heart transplant recipients, this also means a substantial decrease in cost and work load for laboratories involved in heart transplantation.

Biopsy↗
PubMed1996

Randomized trial of misoprostol in patients with chronic renal transplant rejection.

Chronic vascular rejection is a major cause of long-term graft failure after renal transplantation. We investigated the effect of the addition of misoprostol (200 micrograms four times daily) to standard immunosuppressive therapy on the outcome of chronic rejection in a double-blind, placebo-controlled trial. Patients had to fulfill predefined histological and clinical criteria. After an entry of 40 patients into the study (22 misoprostol, 18 placebo), the inclusion of additional patients was terminated because of a high incidence of withdrawal due to adverse effects. Of the patients who used their study medication for at least 3 months (16 misoprostol, 15 placebo), graft function deteriorated in all but 5 misoprostol-treated and all but 2 placebo-treated patients. There was no difference in dialysis-free survival. Withdrawal because of adverse effects (mainly gastrointestinal complaints) occurred in 3 cases in the placebo group and in 11 cases in the misoprostol group (P < 0.05). In conclusion, we found no evidence for a beneficial effect of misoprostol on the course of chronic renal allograft rejection, while use of the drug was accompanied by a high incidence of side effects.

Adult↗
PubMed1996

Low-density lipoprotein oxidation is increased in kidney transplant recipients.

Oxidative modification of low-density lipoproteins (LDL) plays an important role in the pathogenesis of atherosclerosis. In addition, there is evidence that chronic vascular allograft rejection may be mediated by oxidised LDL. Plasma lipoprotein concentrations and parameters of LDL oxidation were determined in 19 kidney transplant recipients and 19 healthy controls. Plasma triglycerides and total cholesterol was significantly higher in patients than in the controls. The mean LDL diameter was smaller in patients than in the controls (23.6 +/- 0.71 nm vs 27.78 +/- 1.16 nm, P < 0.002). Furthermore, the lag time of copper-induced in vitro LDL oxidation was shorter in patients than in the controls (101 +/- 23 min vs 148 +/- 81 min, P = 0.02). The titre and concentration of both IgG and IgM autoantibodies against malondialdehyde-modified LDL (MDA-LDL) were higher in the patients. We conclude that there is in vitro and in vivo evidence of increased LDL oxidation in renal transplant recipients. This might facilitate the progression of atherosclerosis and enhance the process of chronic vascular rejection.

Adult↗
PubMed1996

Phenotypic analysis of lymphocytes infiltrating human cardiac allografts during acute rejection and the development of graft vascular disease.

Acute rejection (AR) and graft vascular disease (GDV) are processes mediated, at least in part, by cellular processes. Therefore, we cultured graft-infiltrating lymphocytes (GIL) from endomyocardial biopsies (EMB) taken during the first year after transplantation, determined their phenotypic composition, and correlated it to AR and GVD. We observed more often GIL growth from EMB with AR than from non-rejection EMB (P = 0.02), but no difference was found between patients with and without GVD 1 year after transplantation. CD4+ cells were always more numerous than CD8+ cells, and no difference in phenotypic composition was found between AR and non-rejection EMB nor between EMB derived from patients with or without signs of GVD. In conclusion, AR is correlated with cell growth of EMB, but the development of GVD is not associated with AR, GIL growth from EMB, or their phenotypic composition.

Acute Disease↗
PubMed1996

Patterns in donor-specific mRNA and protein production of Th1 and Th2 cytokines by graft-infiltrating lymphocytes and PBMC after heart transplantation.

We used RT-PCR and ELISA to study the kinetics of IL-2 (Th1) and IL-4 (Th2) both on mRNA and protein level from "naive" PBMC and "primed" graft-infiltrating lymphocytes (GIL) obtained from a heart transplant recipient. For this purpose, these cells were stimulated for 1-48 h with donor and control third-party antigens. Only stimulation of GIL with donor-specific antigen resulted in early detectable IL-2 and IL-4 mRNA and protein levels. Maximal relative IL-2 mRNA levels were significantly higher than maximal relative IL-4 mRNA levels (100-fold) in both GIL and PBMC after donor-specific stimulation. This was accompanied by a maximum protein production of 908 pg/ml IL-2 and 19 pg/ml IL-4 by GIL, and of 82 pg/ml IL-2 and undetectable IL-4 production by PBMC. These results suggest that, after stimulation donor-specific "primed" GIL, and not "naive" PBMC, rapidly produce abundant levels of IL-2 (Th1) and IL-4 (Th2) at both the transcriptional and protein level.

Cells, Cultured↗
PubMed1996

Evidence that cyclosporin A prevents clinical cardiac allograft rejection by blocking both direct and indirect antigen presentation pathways.

Monitoring for the responses to alloantigens presented either by the direct or the indirect presentation pathway have been reported to be of clinical value after kidney transplantation. Amongst others, the level of these responses may be dependent on the immunosuppressive treatment. We studied both presentation routes in peripheral blood mononuclear cells (PBMC) of cardiac transplant patients, who experienced episodes of rejection, and related them to the in vivo cyclosporin A (CsA) levels in plasma. PBMC of the recipients were stimulated with irradiated donor cells to determine the direct presentation pathway. As a method for the activation of the immune response via the indirect pathway, PBMC were stimulated with tetanus toxoid. Both immune responses increased when CsA levels inadvertently decreased to inadequate concentrations and histological rejection was diagnosed. After clinical heart transplantation, CsA may prevent rejection by blocking both the direct and the indirect antigen presentation pathway.

Antigen Presentation↗
PubMed1996

Donor-specific cellular immune response against human cardiac valve allografts.

We studied the presence of donor-specific T lymphocytes in explanted human cardiac valve allografts in vivo. From five of seven explants we propagated lymphocyte cultures in an interleukin-2 conditioned medium. Phenotyping revealed the presence of T-cell receptors in more than 95% of the lymphocytes obtained in each culture. Donor-specific cytotoxicity was demonstrated in three patients with known HLA status of the donor. Cytotoxicity was directed against only HLA class I in one patient, and against class I and/or class II in the others. These results indicate that donor-specific cellular reactivity can be induced by transplantation of human cardiac valve allografts.

Adult↗
PubMed1996

Increased low density lipoprotein oxidation in stable kidney transplant recipients.

We studied factors that may add to the high risk of atherosclerosis in kidney transplant recipients. Plasma lipoprotein concentrations and parameters of low density lipoprotein (LDL) oxidation were determined in 19 clinically stable kidney recipients and 19 healthy controls. Plasma triglycerides and total cholesterol were increased in the patients. High density lipoprotein-cholesterol (HDL-c) was in the normal range. The mean LDL diameter was smaller in patients than in controls (236.5 +/- 7.3 A vs. 247.8 +/- 11.6 A, P < 0.002), which was due to a higher frequency of the LDL subclass pattern B in the patients than in controls (58% vs. 28%). The lag time of copper-induced in vitro LDL oxidation was shorter in patients than in controls (101 +/- 23 min vs. 148 +/- 81 min, P = 0.02). The titer and concentration of autoantibodies against malondialdehyde-modified (MDA-LDL) determined by ELISA were higher in the patients than in the controls. This difference was found in both IgG (titer + 9%, concentration + 75%; P < 0.05) and IgM (titer + 35%, concentration + 102%; P < 0.001). Based on these results, we propose that there is in vitro and in vivo evidence of enhanced LDL oxidation in patients post-renal transplantation. This might represent one cause for the clinical finding of advanced atherosclerosis in these patients.

Adult↗
PubMed1996

Inverted V delta 1/V delta 2 ratio within the T cell receptor (TCR)-gamma delta T cell population in peripheral blood of heart transplant recipients.

We investigated the levels of TCR-gamma delta T cells and their subpopulations V delta 1 and V delta 2 in the peripheral blood lymphocytes (PBL) of 28 heart transplant (HTx) patients. Patients (n = 10) receiving cyclosporin A (CsA) for treatment of a nephrotic syndrome (NS) and 10 healthy individuals served as controls. There was no difference in levels of TCR-gamma delta T cells between the different groups. However, an elevated proportion of V delta 1+ gamma delta T cells was found in the PBL of HTx patients, especially when these cells were present in their graft-infiltrating lymphocyte (GIL) cultures. V delta 1+ gamma delta T cells of HTx patients showed normal expression of CD45RO and lacked the activation markers CD25 and HLA-DR. After expanding in IL-2-containing medium, PBL cultures of HTx patients more often were dominated by V delta 1 cells than PBL cultures of controls, in which V delta 2 cells were predominantly grown. The aberrant composition of the TCR-gamma delta population in HTx patients was not a result of immunosuppressive medication, since the proportion V delta 1+ gamma delta T cells was normal in the PBL of the NS patients receiving a similar dose of CsA. It is postulated that long-term antigenic stimulation by the graft, at low level, might be responsible for the altered composition of the gamma delta pool in the HTx patients. Since no donor HLA-specific gamma delta T cells have been detected, other ligands, such as heat shock proteins, may be involved.

Adolescent↗
PubMed1996

Cyclosporin A impairs the nocturnal blood pressure fall in renal transplant recipients.

In renal transplant recipients, hypertension and a diminished nocturnal blood pressure fall are frequently found. To investigate whether this diminished nocturnal blood pressure fall is related to the use of cyclosporin A or to other factors, such as the use of glucocorticoids, we measured 24-hour ambulatory blood pressure in 18 renal transplant recipients both before and 16 weeks after conversion from cyclosporin A to azathioprine. Renal blood flow and glomerular filtration rate were estimated from 131I-hippurate and 125I-iothalamate clearances, respectively, and plasma concentrations of renin, atrial natriuretic peptide, norepinephrine, prostaglandin E2, and thromboxane B2 were determined. During cyclosporin A treatment, mean 24-hour blood pressure was 117 +/- 3 mm Hg, and the nocturnal fall in blood pressure was 4 +/- 9 mm Hg. A nondipping diurnal blood pressure pattern was present in 13 patients. After conversion to azathioprine, mean 24-hour blood pressure decreased to 109 +/- 3 mm Hg (P < .001), the nocturnal fall increased to 9 +/- 6 mm Hg, and the number of patients with a nondipping diurnal blood pressure pattern decreased to 9. The nocturnal fall in heart rate (17 +/- 10 beats per minute) during cyclosporin A did not change after conversion. Body weight and plasma concentrations of norepinephrine and renin did not change. Plasma concentrations of prostaglandin E2 and thromboxane B2 decreased after conversion, as did plasma atrial natriuretic peptide. Renal blood flow and glomerular filtration rate increased after conversion. In conclusion, cyclosporin A appears to be involved in the disturbance of the circadian blood pressure rhythm in renal transplant recipients. Although the precise mechanism is unclear. the elevated plasma atrial natriuretic peptide and slightly suppressed plasma renin concentrations suggest that intravascular volume expansion may contribute to the observed hemodynamic alterations.

Adult↗
PubMed1996

Donor-derived human leukocyte antigen class I proteins in the serum of heart transplant recipients.

BACKGROUND: Human leukocyte antigen class I proteins are expressed on most cell types in all organ allografts but are constitutively secreted only by certain organs, for example, the liver. We hypothesized that detectable levels of donor-derived human leukocyte antigen proteins would be released from transplanted cardiac allografts only when the allograft was immunologically stimulated, that is, during rejection and perhaps during viral infection. If so, then the release of donor human leukocyte antigen might be a noninvasive monitor of these events. METHODS: We used an enzyme-linked immunosorbent assay to detect donor-derived human leukocyte antigen-A2 in the serum of 21 human leukocyte antigen-A2 negative recipients of human leukocyte antigen-A2-positive heart transplants. The level of donor human leukocyte antigen-A2 during the first 100 days after transplantation was correlated with the clinical status of the patient. RESULTS: We found little or no donor human leukocyte antigen in the serum of heart transplant recipients whose postoperative clinical course was unremarkable for infection or rejection. We did find donor-derived human leukocyte antigen in the serum of heart transplant recipients transiently in the week immediately after transplantation, continuously from patients in whom chronic rejection was developing, during cytomegalovirus infection, and during some, but not all, acute rejection episodes as determined by endomyocardial biopsy. CONCLUSIONS: These findings are consistent with the hypothesis that the donor human leukocyte antigen serum level reflects vascular diseases, rather than myocardial disease in the transplanted heart. Therefore, the serum level of donor human leukocyte antigen cannot be used as a monitor of cellular infiltration and myocyte damage as currently assessed by endomyocardial biopsy but may be an early indicator of the development of vascular disease such as chronic rejection.

Biopsy↗
PubMed1996

The intragraft cytokine mRNA pattern reflects the efficacy of steroid antirejection therapy.

BACKGROUND: We studied the effect of antirejection therapy on intragraft cytokine mRNA expression. METHODS: Therapy consisted of three doses of 1 gm of intravenous methylprednisolone. We determined its effect on intragraft mRNA expression of immunoregulatory (interleukin-2, interleukin-4) and inflammatory cytokines (interleukin-1 beta, interleukin-6, tumor necrosis factor-alpha), and the high-affinity interleukin-2 receptor (p55 chain) in endomyocardial biopsy specimens from cardiac allograft recipients. RESULTS: By reverse-transcriptase polymerase chain reaction methods, we detected mRNA transcription for interleukin-2 in 56% of the pretreatment endomyocardial biopsy specimens (n = 16), for interleukin-4 in 31%, and for interleukin-6 in 56% of the specimens, and interleukin-2 receptor, interleukin-1 beta, interleukin-6, tumor necrosis factor-alpha were constitutively expressed. Individual cytokine mRNA profiles were not helpful in differentiating between rejections that proved to be methylprednisolone resistant (n = 9) or methylprednisolone sensitive (n = 7). After successful antirejection therapy, the overall intragraft mRNA expression was downregulated. None of the posttreatment endomyocardial biopsy specimens taken from six patients with methylprednisolone-sensitive rejections expressed the interleukin-2 gene, in contrast to 88% of the endomyocardial biopsy specimens obtained from eight patients with methylprednisolone-resistant rejections (p = 0.005). Moreover, intragraft interleukin-4 and interleukin-6 mRNA transcripts were hardly detectable (both 17%) in methylprednisolone-reversible rejections, but in ongoing rejections interleukin-4 mRNA expression was found in 62% (p = 0.14), and interleukin-6 was found in 88% of the endomyocardial biopsy specimens (p = 0.03). Semiquantitative analysis showed that the intragraft interleukin-2 receptor, interleukin-1 beta, and tumor necrosis factor-alpha mRNA levels were lower in posttreatment endomyocardial biopsy specimens from methylprednisolone-reversible rejections than in endomyocardial biopsy specimens from methylprednisolone-irreversible rejections (p = 0.03). CONCLUSIONS: Our data suggest that the efficacy of antirejection therapy with methylprednisolone is reflected in intragraft cytokine mRNA profiles.

Adolescent↗