Biomedical subjects

D L Roelen

Publications and source records attributed to D L Roelen.

28 records · Page 2Linked to original sources

PubMed1996

Semi-allogeneic (F1) versus fully allogeneic blood transfusions: differences in their ability to induce specific immunological unresponsiveness.

The beneficial effect on graft survival achieved by pretransplant blood transfusions is well established. However, the type of major histocompatibility complex (MHC) mismatch between transfusion donor and recipient seems to play a role in determining the outcome. The hypothesis that this sharing of MHC antigens is correlated with the level of sensitization or tolerization was studied in mice by pretreatment with semi-allogeneic (F1) or with fully allogeneic whole blood transfusions. Limiting dilution analysis (LDA) in vitro for donor-specific T helper (Thp) and cytotoxic T lymphocyte precursors (CTLp) performed on splenocytes isolated from transfused recipients 2 or 4 weeks after transfusion showed that the duration and magnitude of the response was reduced after a semi-allogeneic compared to a fully allogeneic transfusion. After a semi-allogeneic transfusion, both Thp and CTLp frequencies had returned to naive levels 4 weeks after transfusion, whereas after infusion of fully allogeneic blood, they remained elevated after 4 weeks. When a fully allogeneic heart was transplanted 2 or 4 weeks after transfusion, a small but significant improvement in graft prolongation (2 weeks, not significant, 4 weeks: p < 0.01) was observed following pretreatment with a semi-allogeneic transfusion (2 weeks: median survival time (MST) 30 days, 4 weeks: MST 29 days) compared to that obtained after fully allogeneic transfusion (2 weeks: MST 23 days, 4 weeks: MST 12 days). The semi-allogeneic transfusions were correlated with a statistically significant prolonged (7 days) persistence of donor-derived MHC class II+ cells in the recipient and with reduced levels of anti-donor MHC class I-specific antibody formation compared to these responses after transfusion with fully allogeneic cells. These results demonstrate that pretreatment with a semi-allogeneic blood transfusion is more tolerizing and less sensitizing than pretreatment with a fully allogeneic blood transfusion. These findings may be explained by the sharing of MHC antigens between recipient and transfusion donor.

Animals↗

PubMed1996

A cell-saving non-radioactive limiting dilution analysis-assay for the combined determination of helper and cytotoxic T lymphocyte precursor frequencies.

We have developed a limiting dilution analysis-assay which makes the determination of both helper and cytotoxic T lymphocyte precursor frequencies possible. The way in which T helper precursor frequencies are determined in this combined assay is essentially the same as the method published previously. Experimental conditions for the combined assay have been optimized to obtain cytotoxic T lymphocyte precursor frequencies that are comparable to those determined in the assay routinely used in our laboratory. For all situations where the amount of available cell material is a limiting factor, it will be an advantage that with the same number of cells needed for a standard cytotoxic T lymphocyte precursor frequency determination, in the combined assay both helper and cytotoxic T lymphocyte precursor frequencies can be determined. This is especially convenient in the case of bone marrow transplantation, where evidence is accumulating that low or negative cytotoxic T lymphocyte and/or T helper precursor frequencies may be a prerequisite for a successful transplantation with a minimal risk of graft-versus-host disease.

Hematopoietic Stem Cells↗

PubMed1995

No evidence of an influence of the noninherited maternal HLA antigens on the alloreactive T cell repertoire in healthy individuals.

In order to test whether a selective T cell nonresponsiveness to noninherited maternal human leukocyte antigens (NIM) exists, we measured the frequencies of alloreactive T cells of healthy individuals to their NIM HLA antigens and to their noninherited paternal (NIP) HLA antigens by limiting dilution assays. Both the frequencies of cytotoxic T cell precursors (CTLp) and IL-2-producing helper T cell precursors (HTLp) were determined. Similar frequencies were observed for NIM class I-reactive CTLp and NIP class I-reactive CTLp. This was the case when frequencies were determined against total NIM and NIP haplotypes but also when CTLp frequencies against individual NIM and NIP antigens were measured. A positive finding of this study was the confirmation of our earlier observation that CTLp frequencies against individual HLA-A antigens are generally lower than CTLp frequencies against HLA-B. This was found both for the maternal and the paternal HLA-A and -B antigens. Similarly, comparable frequencies of IL-2-producing helper T cell precursors directed against NIM HLA class II antigens and NIP HLA class II antigens were found. When breast-feeding in the neonatal period was considered, no differences in the frequencies of CTLp and HTLp were observed between children who had been breast-fed and children who had not. Therefore the present data do not support the hypothesis that confrontation with noninherited maternal HLA in neonatal life leads to down-regulation of alloreactive T cell responses to the mother.

Adult↗

PubMed1995

The presence of activated donor HLA class I-reactive T lymphocytes is associated with rejection of corneal grafts.

Although the cornea is considered to be an immunological privileged site, corneal transplantation can result in immunological rejection followed by graft failure, especially in patients with vascularized corneas. Several studies suggest a beneficial effect of matching for the HLA class I antigens on corneal graft survival, although a large study (the Collaborative Corneal Transplantation Study) failed to confirm this. To circumvent an endless discussion on studies either confirming or denying the relevance of HLA matching, we decided to approach this problem in another way. A more direct way to assess the importance of HLA class I antigens in corneal transplantation is to measure whether rejection of an allograft is associated with priming of cytotoxic T lymphocytes recognizing the mismatched HLA antigens of the donor. In the present study, 13 patients with good graft function and 10 with ongoing rejection of their corneal allografts were analyzed for the presence of CTL directed against mismatched donor HLA class I antigens, by limiting dilution assays. CTLs were divided into naive and primed CTLs based on the measurement of their in vitro sensitivity or resistance to anti-CD8 or cyclosporine. Cytotoxic T cell precursor frequencies directed against the mismatched donor HLA class I antigens were similar in nonrejectors and rejectors. However, rejection was strongly associated with the presence of primed, donor-specific CTL, whereas these primed cells were absent in case of good graft function. These data show that HLA antigens of a transplanted cornea are immunogenic and targets for rejection by cytotoxic T cells. Therefore, this study supports the need for HLA-A and -B matching in corneal transplantation in patients with a high probability of rejection.

Antibodies↗

PubMed1994

IgG antibodies against an HLA antigen are associated with activated cytotoxic T cells against this antigen, IgM are not.

Pre-existing alloantibodies against the mismatched HLA-A and HLA-B antigens of the donor, when present in current sera, are believed to be detrimental to kidney graft survival. When these antibodies are present only in historical sera, their immunoglobulin class has reported to be important with respect to the expected graft survival, IgG antibodies being associated with poor graft prognosis and IgM with reasonable graft survival. In the present study, we have tested whether the immunoglobulin class of anti-HLA antibodies is reflected in the activation state of CTLs directed against these HLA antigens as measured by their in vitro resistance or sensitivity to CsA. The results indicate that the presence of IgG anti-HLA antibodies is associated with the presence of activated CTLs (CsA resistant), whereas in the case of IgM antibodies, mainly naive CTLs (CsA sensitive) are found. This observation may explain the different prognoses of historical positive crossmatches due to IgG versus IgM alloantibodies.

Cyclosporine↗

PubMed1994

The relative radioresistance of interleukin-2 production by human peripheral blood lymphocytes: consequences for the development of a new limiting dilution assay for the enumeration of helper T lymphocyte precursor frequencies.

We describe a limiting dilution assay for the enumeration of alloreactive helper T lymphocyte precursor frequencies in human peripheral blood. The proliferation rate of the murine indicator cell line, cytotoxic T lymphoblastic line 2 (CTLL-2) induced by interleukin-2 (IL-2) culture supernatants was determined by staining with the fluorescent DNA dye propidium-iodide. Lymphocytes from healthy individuals as well as from patients with end stage kidney disease and no previous allosensitization exhibited a relative radioresistance of their IL-2 production up to gamma irradiation doses of 40-60 Gy. This differs from previous findings in the literature, showing a total inhibition of the IL-2 production in unsensitized individuals using a gamma irradiation dose of 20 Gy. The consequences of this relative radioresistance are that for a reliable stimulator cell inactivation in assays for the enumeration of helper T lymphocyte precursors gamma irradiation doses of at least 50 (-60) Gy are needed. Increasing the gamma irradiation dose for the inactivation of the stimulator cells can result in a decrease of the antigen presenting capacity of these cells.

Animals↗

PubMed1994

Cytotoxic T lymphocytes against HLA-B antigens are less naive than cytotoxic T lymphocytes against HLA-A antigens.

In healthy individuals, like in highly sensitized patients, CTL precursors (CTLp) frequencies against HLA-A antigens were found to be significantly lower than CTLp frequencies against HLA-B antigens. In the present study, we tested whether not only quantitative but also qualitative differences exist between CTLs against HLA-A antigens versus HLA-B antigens. Experiments performed in the presence of antibodies against CD8 showed that CTLp directed against HLA-B antigens were significantly less inhibited by anti-CD8 compared with CTLp against HLA-A. The low anti-CD8 inhibition of the CTLp directed against HLA-B antigens may be explained by a higher affinity of the CTLp for HLA-B antigens on the target cells. CTLp directed against HLA-B antigens were also found to be less sensitive to CsA, which suggests that their high affinity is due to previous priming. A clinical relevance of these findings is suggested by the observation that matching for HLA-B antigens is of greater importance for kidney graft survival than matching for HLA-A.

Graft Rejection↗

PubMed1993

Differential inhibition of primed alloreactive CTLs in vitro by clinically used concentrations of cyclosporine and FK506.

Previous studies in highly sensitized patients waiting for a renal transplant showed a lack of correlation between the formation of alloantibodies and the alloantigen specific cytotoxic T cell precursor frequency. The frequencies of CTLp against HLA class I antigens, toward which patients had formed antibodies (not acceptable mismatches, NAM), were similar to those against HLA antigens, toward which no antibodies were present (acceptable mismatches, AM). In more recent studies we tested whether the immunological triggering leading to antibody formation might have resulted in a different population of cytotoxic T cells. Limiting dilution assays performed in the absence or presence of antibodies against CD8 showed that CTL directed against NAM were significantly less inhibited by anti-CD8 compared with those directed against AM. Those "primed" CTL could also be distinguished from the more "naive" CTL on the basis of their resistance to cyclosporine. In contrast to CsA, therapeutic concentrations of FK506 were able to inhibit both "naive" and "primed" CTLs. The clinical relevance of these data is currently being investigated.

Cyclosporine↗

PubMed1993

The detection of cytotoxic T cells with high-affinity receptors for donor antigens in the transplanted heart as a prognostic factor for graft rejection.

Alloreactive T lymphocytes are the initiators and effectors of acute rejection of organ transplants, and T cells with high-affinity receptors for antigen might be especially implicated in this process. It has been shown that the cytotoxic capacity of CTL with low affinity for alloantigens can be inhibited with CD8 mAb, while high-affinity CTL are not affected. To investigate whether the presence of such high-affinity cells in human heart transplants may be predictive for acute rejection, we analyzed their frequency in cultures derived from endomyocardial biopsies in 19 patients, 9 of whom had never experienced acute rejection and 10 who had had one or more rejection episodes. IN the rejectors, already before histological signs of rejection (myocyte damage) had developed, significantly higher donor-reactive CTL frequencies were found compared with the nonrejectors (medians of 10,586 vs 1,169 reactive cells per 10(6) tested cells, P = 0.002). After CD8 inhibition, the difference between rejectors and nonrejectors was even more pronounced (P < 0.001). In patients with rejection, the number of CD8-resistant, high-affinity CTL was higher than 1000 per million cells in all cases, while in patients who had never experienced rejection this number was less than 1000. As these CTL characteristics are already present before the first histological signs of rejection have developed, this might be used as a prognostic factors.

Antibodies, Monoclonal↗

PubMed1989

Renal responsiveness to synthetic human parathyroid hormone 1-38 in healthy subjects.

Renal responsiveness to synthetic human parathyroid hormone (HPTH) 1-38 was examined in seven healthy volunteers. Each subject received three different doses (35 micrograms, 17.5 micrograms, 8.75 micrograms) as bolus intravenous injections. Rapid, transient, dose-dependent decreases in diastolic blood pressure and increases in heart rate were observed, as reported previously in animal studies, suggesting an acute vasodilatory effect of the hormone. The extracellular cyclic AMP responses were brisk and dose-dependent in the group as a whole as well as in the individual subjects. In contrast, the phosphaturic responses, though statistically significant with all three doses, were of a lesser magnitude and showed an individual variability. Nearly maximal decreases in TmP/GFR were found even after the lowest dose with minimal increases in cyclic AMP in some subjects. The injections of HPTH 1-38 also induced a dose-dependent natriuresis which was accompanied by an increase in excreted calcium. It seems that under these experimental conditions the sodium-dependent renal calcium transport cannot be compensated by the effects of the hormone on the distal tubule. HPTH 1-38 can be safely and predictably used for the assessment of renal responsiveness to PTH in routine clinical practice.

Adult↗