End-to-end test for fractionated online adaptive MR-guided radiotherapy using a deformable anthropomorphic pelvis phantom

Objective.In MR-guided radiotherapy (MRgRT) for prostate cancer treatments inter-fractional anatomy changes such as bladder and rectum fillings may be corrected by an online adaption of the treatment plan. To clinically implement such complex treatment procedures, however, specific end-to-end tests are required that are able to validate the overall accuracy of all treatment steps from pre-treatment imaging to dose delivery.Approach.In this study, an end-to-end test of a fractionated and online adapted MRgRT prostate irradiation was performed using the so-called ADAM-PETer phantom. The phantom was adapted to perform 3D polymer gel (PG) dosimetry in the prostate and rectum. Furthermore, thermoluminescence detectors (TLDs) were placed at the center and on the surface of the prostate for additional dose measurements as well as for an external dose renormalization of the PG. For the end-to-end test, a total of five online adapted irradiations were applied in sequence with different bladder and rectum fillings, respectively.Main results.A good agreement of measured and planned dose was found represented by highγ-index passing rates (3%/3mmcriterion) of the PG evaluation of98.9%in the prostate and93.7%in the rectum. TLDs used for PG renormalization at the center of the prostate showed a deviation of-2.3%.Significance.The presented end-to-end test, which allows for 3D dose verification in the prostate and rectum, demonstrates the feasibility and accuracy of fractionated and online-adapted prostate irradiations in presence of inter-fractional anatomy changes. Such tests are of high clinical importance for the commissioning of new image-guided treatment procedures such as online adaptive MRgRT.

PAGAT gel dosimetry for everyone: gel production, measurement and evaluation

Polymer gel (PG) dosimetry is a valuable tool to measure complex dose distributions in 3D with a high spatial resolution. However, due to complex protocols that need to be followed for in-house produced PGs and the high costs of commercially available gels, PG gels are only rarely applied in quality assurance procedures worldwide. In this work, we provide an introduction to perform highly standardized dosimetric PG experiments using PAGAT (PolyAcrylamide Gelatine gel fabricated at ATmospheric conditions) dosimetry gel. PAGAT gel can be produced at atmospheric conditions, at low costs and is evaluated using magnetic resonance imaging (MRI). The conduction of PG experiments is described in great detail including the gel production, treatment planning, irradiation, MRI evaluation and post-processing procedure. Furthermore, a plugin in an open source image processing tool for post-processing is provided free of charge that allows a standardized and reproducible analysis of PG experiments.

Development of phantom materials with independently adjustable CT- and MR-contrast at 0.35, 1.5 and 3 T

Quality assurance in magnetic resonance (MR)-guided radiotherapy lacks anthropomorphic phantoms that represent tissue-equivalent imaging contrast in both computed tomography (CT) and MR imaging. In this study, we developed phantom materials with individually adjustable CT value as well as [Formula: see text]- and [Formula: see text]-relaxation times in MR imaging at three different magnetic field strengths. Additionally, their experimental stopping power ratio (SPR) for carbon ions was compared with predictions based on single- and dual-energy CT. Ni-DTPA doped agarose gels were used for individual adjustment of [Formula: see text] and [Formula: see text] at [Formula: see text] and 3.0 T. The CT value was varied by adding potassium chloride (KCl). By multiple linear regression, equations for the determination of agarose, Ni-DTPA and KCl concentrations for given [Formula: see text] [Formula: see text] and CT values were derived and employed to produce nine specific soft tissue samples. Experimental [Formula: see text] [Formula: see text] and CT values of these soft tissue samples were compared with predictions and additionally, carbon ion SPR obtained by range measurements were compared with predictions based on single- and dual-energy CT. The measured CT value, [Formula: see text] and [Formula: see text] of the produced soft tissue samples agreed very well with predictions based on the derived equations with mean deviations of less than [Formula: see text] While single-energy CT overestimates the measured SPR of the soft tissue samples, the dual-energy CT-based predictions showed a mean SPR deviation of only [Formula: see text] To conclude, anthropomorphic phantom materials with independently adjustable CT values as well as [Formula: see text] and [Formula: see text] relaxation times at three different magnetic field strengths were developed. The derived equations describe the material specific relaxation times and the CT value in dependence on agarose, Ni-DTPA and KCl concentrations as well as the chemical composition of the materials based on given [Formula: see text] and CT value. Dual-energy CT allows accurate prediction of the carbon ion range in these materials.

Side-gated, enhancement mode, InAs nanowire double quantum dot devices-toward controlling transverse electric fields in spin-transport measurements

A double quantum dot system with a definitive transverse electric field in the plane of the sample is defined by combining a facile side-gating technique with enhancement mode InAs nanowires. Positive bias on the plunger gates enhance quantum dot segments along the nanowire, negative bias on barrier gates deplete regions, and situating gates biased at opposite polarities on opposing sides of the nanowire allows an electric field to be engineered. With sufficiently biased barrier regions stable bias triangle features are observed in the weak interdot coupling regime. The singlet-triplet energy splitting Δ _ST in Pauli spin-blockaded features is studied as a function of an external magnetic field applied perpendicular to the sample plane. We interpret an apparent absence of mixing between singlet and triplet states as an indication that the spin-orbit field is oriented out of the sample plane due to the induced electric field. Finally, we discuss the potential of combining advanced gating architectures with enhancement mode nanowires to control the orientation of the spin-orbit field-a prospect that could enable multiple, nanowire-based spin-qubits to be operated on a single chip with a fixed-angle external magnetic field applied.

Feasibility of polymer gel-based measurements of radiation isocenter accuracy in magnetic fields

For conventional irradiation devices, the radiation isocenter accuracy is determined by star shot measurements on films. In magnetic resonance (MR)-guided radiotherapy devices, the results of this test may be altered by the magnetic field and the need to align the radiation and imaging isocenter may require a modification of measurement procedures. Polymer dosimetry gels (PG) may offer a way to perform both, the radiation and imaging isocenter test, however, first it has to be shown that PG reveal results comparable to the conventionally applied films. Therefore, star shot measurements were performed at a linear accelerator using PG as well as radiochromic films. PG were evaluated using MR imaging and the isocircle radius and the distance between the isocircle center and the room isocenter were determined. Two different types of experiments were performed: i) a standard star-shot isocenter test and (ii) a star shot, where the detectors were placed between the pole shoes of an experimental electro magnet operated either at 0 T or 1 T. For the standard star shot, PG evaluation was independent of the time delay after irradiation (1 h, 24 h, 48 h and 216 h) and the results were comparable to those of film measurements. Within the electro magnet, the isocircle radius increased from 0.39  ±  0.01 mm to 1.37  ±  0.01 mm for the film and from 0.44  ±  0.02 mm to 0.97  ±  0.02 mm for the PG-measurements, respectively. The isocenter distance was essentially dependent on the alignment of the magnet to the isocenter and was between 0.12  ±  0.02 mm and 0.82  ±  0.02 mm. The study demonstrates that evaluation of the PG directly after irradiation is feasible, if only geometrical parameters are of interest. This allows using PG for star shot measurements to evaluate the radiation isocenter accuracy with comparable accuracy as with radiochromic films.

Analysis of receptor oligomerization by FRAP microscopy

Here we describe an approach to investigate di- or oligomerization of transmembrane receptors in living cells with fluorescence recovery after photobleaching (FRAP). We immobilized a defined fraction of receptors with antibodies and then measured lateral mobility of the nonimmobilized fraction by FRAP. We validated this approach with CD86 and CD28 as monomeric and dimeric reference proteins, respectively. Di- or oligomerization of G protein-coupled receptors is strongly debated. We studied human beta-adrenergic receptors as prototypical G protein-coupled receptors and found that beta(1)-AR shows transient interactions whereas beta(2)-AR can form stable oligomers. We propose that this FRAP method can be widely applied to study di- or oligomerization of cell-surface proteins.

Novel chiral isoxazole derivatives: Synthesis and pharmacological characterization at human β-adrenergic receptor subtypes

Isoxazole derivative (+/-)-4 and the three pairs of stereoisomeric 3-bromo-isoxazolyl amino alcohols (S,R)-(-)-7a/(R,R)-(+)-7b, (S,R)-(-)-8a/(R,R)-(+)-8b, and (S,R)-(-)-9a/(R,R)-(+)-9b were synthesized and assayed for their affinity and efficacy at human beta(1)-, beta(2)-, and beta(3)-adrenergic receptors (beta-ARs) in membranes from Chinese hamster ovary (CHO) cells stably transfected with the respective receptor subtype. Whereas derivative (+/-)-4 did not bind at all three beta-ARs, stereoisomers (S,R)-7a-(S,R)-9a behaved as high-affinity ligands at beta(1)- and, particularly, at beta(2)-ARs (K(i) 2.82-66.7 nM). The K(i) values of isomers (R,R)-7b-(R,R)-9b at beta(1)- and beta(2)-subtypes were about 30-100 times higher than those of their (S,R)-7a-9a counterparts, indicating a sizable stereochemical effect. The affinity at beta(3)-ARs was negligible for all the investigated compounds. When submitted to a functional assay, the three stereoisomeric pairs showed a comparable pattern of efficacy at all three beta-AR subtypes. The highest value of efficacy (75-90%) was observed at beta(2)-ARs, whereas all compounds behaved as partial agonists (30-60%) at the beta(3)-subtype. The lowest degree of efficacy (15-35%) was found at beta(1)-ARs. The affinity/efficacy profile of the derivatives under study has been compared with that of the two model compounds, Broxaterol [(+/-)-1] and BRL 37344 [(+/-)-6].

Gs activation is time-limiting in initiating receptor-mediated signaling

To analyze individual steps of G(S)-linked signaling in intact cells, we used fluorescence resonance energy transfer (FRET)-based assays for receptor-G protein interaction, G protein activation, and cAMP effector activation. To do so, we developed a FRET-based sensor to directly monitor G(S) activation in living cells. This was done by coexpressing a Galpha(s) mutant, in which a yellow fluorescent protein was inserted, together with cyan fluorescent protein-tagged Gbetagamma subunits and appropriate receptors in HEK293 cells. Together with assays for receptor activation and receptor-G protein interaction, it is possible to characterize large parts of the G(S) signaling cascade. When A(2A)-adenosine or beta(1)-adrenergic receptors are coexpressed with G(S) in HEK293T cells, the receptor-G(S) interaction was on the same time scale as A(2A) receptor activation with a time constant of <50 ms. G(S) activation was markedly slower and around 450 ms with similar kinetics following activation of A(2A)- or beta(1)-receptors. Taken together, our kinetic measurements demonstrate that the rate of G(S) activation limits initiation of G(S)-coupled receptor signaling.

Mildew-resistant mutants induced in North American two- and six-rowed malting barley cultivars

Mildew-resistant mutants were induced with sodium azide in three North American malting barley cultivars, two in the six-rowed Ursula (URS1 and URS2), one in the six-rowed Gertrud (GER1), and one in the two-rowed Prudentia (PRU1). Two of the mutants, URS1 and PRU1, showed complete resistance and were shown to have two new alleles at the mlo locus; these were designated, respectively, mlo31 and mlo32. Mutant URS2, showing partial resistance, was inherited as a dominant gene, but was not an allele at the Mla locus. The mean yield of each mutant was higher than that of its parental line, but yield levels varied across environments, although this was independent of the severity of the mildew attack. Other reasons, for example, the severity of the necrotic lesions in the mutants, may account for yield variations. The malting quality of the GER1 mutant proved similar to that of Gertrud, but both URS1 and URS2 showed lower malt extract than Ursula. This lower extract might be due to the smaller grain size of the mutants that could, in turn, result from necrotic lesions in the leaves, as implied by the effects on grain yield.

Superoxide potently induces ceramide formation in glomerular endothelial cells

Recent evidence suggests that the sphingolipid-derived second messenger ceramide and oxidative stress are intimately involved in apoptosis induction. Here we report that exposure of microcapillary glomerular endothelial cells to superoxide-generating substances, including hypoxanthine/xanthine oxidase and the redox cyclers DMNQ and menadione results in a dose-dependent and delayed increase in the lipid signaling molecule ceramide. Long-term incubation of endothelial cells for 2-30 h with either DMNQ or hypoxanthine/xanthine oxidase leads to a continuous increase in ceramide levels. In contrast, short-term stimulation for 1 min up to 1 h had no effect on ceramide formation. The DMNQ-induced delayed ceramide formation is dose-dependently inhibited by reduced glutathione, whereas oxidized glutathione was without effect. Furthermore, N-acetylcysteine completely blocks DMNQ-induced ceramide formation. All superoxide-generating substances were found to dose-dependently trigger endothelial cell apoptosis. In addition, glutathione and N-acetylcysteine also prevented superoxide-induced apoptosis and implied that ceramide represents an important mediator of superoxide-triggered cell responses like apoptosis.

Nitric oxide stimulates chronic ceramide formation in glomerular endothelial cells

Exposure of glomerular endothelial cells for 24 h to compounds releasing NO, including spermine-NO, MAHMA-NO, and S-nitroso-glutathione, results in a dose-dependent and delayed (after 24 h) increase in the lipid signaling molecule ceramide. This NO-induced stimulation occurs in a cGMP-independent fashion since the membrane-permeant cGMP analogue dibutyryl cGMP has no effect on chronic ceramide production. Short-term incubation of endothelial cells for 20 min reveals that NO and dibutyryl cGMP fail to stimulate an acute ceramide increase, whereas TNF-alpha, a well-known activator of sphingomyelinases, is able to acutely increase ceramide formation. Interestingly, N-oleoylethanolamine, an acidic ceramidase inhibitor, potentiates NO-induced chronic ceramide production, indicating that ceramide generation rather than ceramide metabolism is modulated by NO. Furthermore, NO-induced delayed ceramide formation is partially inhibited by the thiol-specific inhibitor iodoacetamide and the radical scavenger alpha-tocopherol, suggesting a regulatory role of thiol-containing enzymes and the involvement of a redox-sensitive mechanism. In addition, NO causes an increased DNA fragmentation in glomerular endothelial cells which is further enhanced by N-oleoylethanolamine and can be mimicked by exogenous ceramide. In summary, these results imply that ceramide represents an important mediator of NO-triggered chronic cell responses like apoptosis. Inhibition of ceramide synthesis may provide a new therapeutic approach to the treatment of pathological conditions involving increased NO formation.

Generation of neutralizing human monoclonal antibodies against parvovirus B19 proteins

Infections caused by human parvovirus B19 are known to be controlled mainly by neutralizing antibodies. To analyze the immune reaction against parvovirus B19 proteins, four cell lines secreting human immunoglobulin G monoclonal antibodies (MAbs) were generated from two healthy donors and one human immunodeficiency virus type 1-seropositive individual with high serum titers against parvovirus. One MAb is specific for nonstructural protein NS1 (MAb 1424), two MAbs are specific for the unique region of minor capsid protein VP1 (MAbs 1418-1 and 1418-16), and one MAb is directed to major capsid protein VP2 (MAb 860-55D). Two MAbs, 1418-1 and 1418-16, which were generated from the same individual have identity in the cDNA sequences encoding the variable domains, with the exception of four base pairs resulting in only one amino acid change in the light chain. The NS1- and VP1-specific MAbs interact with linear epitopes, whereas the recognized epitope in VP2 is conformational. The MAbs specific for the structural proteins display strong virus-neutralizing activity. The VP1- and VP2-specific MAbs have the capacity to neutralize 50% of infectious parvovirus B19 in vitro at 0.08 and 0.73 microgram/ml, respectively, demonstrating the importance of such antibodies in the clearance of B19 viremia. The NS1-specific MAb mediated weak neutralizing activity and required 47.7 micrograms/ml for 50% neutralization. The human MAbs with potent neutralizing activity could be used for immunotherapy of chronically B19 virus-infected individuals and acutely infected pregnant women. Furthermore, the knowledge gained regarding epitopes which induce strongly neutralizing antibodies may be important for vaccine development.

Bacterial pro-transglutaminase from Streptoverticillium mobaraense--purification, characterisation and sequence of the zymogen

The zymogen of bacterial transglutaminase was found during cultivation of Streptoverticillium mobaraense (DSMZ strain) using rabbit antibodies raised against the active enzyme. Ion-exchange chromatography at pH 5.0 yielded a highly purified pro-enzyme. Structure information was obtained by means of Edman degradation and analysis of PCR amplified nucleotide fragments. The data revealed an excess of negatively charged amino acids in the pro-region resulting in a decreased isoelectric point of the zymogen. Additionally, the new sequence gave rise to some modifications to the previously published hypothetical structure of prepro-transglutaminase derived from genomic DNA [Washizu, K., Ando, K., Koikeda, S., Hirose, S., Matsuura, A., Takagi, H., Motoki, M. & Takeuchi, K. (1994) Biosci. Biotechnol. Biochem. 58, 82-87]. Inactive transglutaminase, which carries an activation peptide of 45 amino acids, has a calculated molecular mass of 42445 Da. Its pro-region provides for both suppression of activity and increased thermostability. Furthermore, it could be shown that the micro-organism produces a protease which cleaves pro-transglutaminase at the C-side of Pro45. Rapid transformation of the mature enzyme also occurs by addition of other proteases. During conversion, 43 and 41 amino acid peptides are released by bovine trypsin and dispase from Bacillus polymyxa, respectively. The detection of endogenous substrates in the murein layer makes discussion of the physiological role of bacterial transglutaminases necessary.

Iodine-123 salmon calcitonin, an imaging agent for calcitonin receptors: synthesis, biodistribution, metabolism and dosimetry in humans

Calcitonin is used to reduce high serum calcium levels in patients with malignancy, and as therapy for osteoporosis and Paget's disease. Receptors for the peptide have been identified in some human cancer cells including those of lung, breast, bone, prostate, and medullary carcinoma of the thyroid, suggesting that an imaging agent for the receptors might be useful in nuclear oncology. A modified chloramine-T method was used to label a pharmaceutical form of salmon calcitonin (SCT) with iodine-123. Labelling can be performed within 5 min including purification, resulting in >95% radiochemical purity and 70% yield. Digestion analysis shows labelling with two iodine atoms on the tyrosine residue. A Chinese hamster ovary cell-based assay showed that the receptor binding and activation were not impaired by the labelling. Biodistribution in mice was similar to that of commercially available mono-iodinated 125I-labelled SCT, kidney being the principal target organ. Evaluation in three patients previously diagnosed as having Paget's disease (injected with 37 MBq [123I]diiodotyrosyl22-SCT, containing less than 4 IU hormone, imaged dynamically up to 0.5 h and at intervals up to 24 h) shows early uptake in liver, kidney and sites of known Paget's disease but not in normal bone, and later uptake in thyroid and stomach. Blood clearance was fitted to a biexponential with half-lives of 3.4-7.4 min and 3-34 h. Radiation dosimetry was estimated using MIRDOSE 3. The highest doses (mean mGy/MBq) were to thyroid (6.8x10(-1)) and kidney (6.0x10(-2)), with a whole-body dose 3.0x10(-2). High performance liquid chromatography analysis revealed that urinary radioactivity was mostly in the form of iodide and diiodotyrosine within minutes of injection, indicating rapid in vivo breakdown. In summary, [123I]diiodotyrosyl22-SCT binds to calcitonin receptors and can image sites of Paget's disease but its imaging potential is not optimal because of rapid breakdown and clearance from target tissues, and an alternative radiolabelling approach is required.

The role of the regional lymph node in the response to secondarily vascularized grafts

Studies using neonatal hearts grafted into the foot pads of adult rats have shown significant differences in the tempo of rejection in various RT1-incompatible combinations of donor and recipient rats. The model allows simultaneous study of events in the graft and in the regional node draining the graft. Removal of the regional node in the inductive stages of the immune response resulted in highly significant prolongation of graft survival. This effect was not due to lymphatic interruption per se or to clonal deletion. The effect was independent of the presence of the primary graft. Second grafts implanted in animals from which both the original graft and its regional node had been removed showed prolonged survival. Once survival of the original graft, from which the node was removed, was established, survival of second grafts bearing the same antigens was also prolonged, although third-party grafts were rejected in first set time. The data suggest that the microenvironment and anatomical connections of the lymph node that first receives antigen, or the cells that have contacted antigen in the graft, or both, play a vital role in an orderly sequence of cellular interaction and migration that culminates in graft rejection. Interruption of this sequence by node removal appears to divert the alloimmune response toward specific enhancement of the graft.

Suppressor cells in transplantation tolerance. II. Identification and probable mode of action of chimeric suppressor T cells

In order to differentiate between donor (chimeric F1) cells and host cells as being responsible for suppression in transplantation tolerance (TT), cells from tolerant donors were first subject to negative selection through F1 hybrid intermediate host animals. This revealed that the suppressor cells was neither completely removed from the lymph nor recoverable from the lymphoid tissues of the filter rat when highly suppressive inocula were used, suggesting that suppression did not directly depend on cells with receptors for alloantigens. The phenotype of donor and host cells in the recirculating pool was studied with fluorescent antisera and showed that both host cells and chimeric F1 cells were in the thoracic duct lymph of tolerant rats and were capable of recirculation. T and B lymphocytes of both types were present but the IgG-positive, presumptive memory B cells were highly enriched in those rapidly recirculating cells, obtained by filtration of tolerant inocula through irradiated intermediate hosts. These cells were also highly enriched for suppressor function. Methods which selectively depleted either the chimeric T cells or the B cells were applied to tolerant inocula and on adoptive transfer of these inocula, suppression was eliminated only when chimeric T cells were eliminated. This strict dependence of suppression of F1 hybrid T cells is interpreted as evidence that these cells probably suppress directly, via an anti-idiotypic mechanism, the alloreactive cells bearing idiotype-positive major histocompatibility complex receptors.

Suppressor cells in transplantation tolerance. I. Analysis of the suppressor status of neonatally and adoptively tolerized rats

The lymphocytes from neonatally tolerant rats which adoptively transfer tolerance to sublethally irradiated recipients do so by specifically suppressing the regeneration of alloreactivity which normally occurs after irradiation. Although tolerant cells will only partially suppress normal alloreactive cells when the two are mixed in near equivalent numbers, experiments in which the interval between injection of tolerant and normal cells into irradiated recipients was gradually extended, indicated that total suppression of normally alloreactive cells was achieved after 8 weeks of prior residence of tolerant cells in the adoptive host. Further evidence that tolerant cells would only suppress if present in excess of normal cells was obtained by reducing the tolerant cell population in tolerant donor rats by whole body irradiation. These animals then lost their ability to suppress normal alloreactive cells administered to them. The immune status of adoptively tolerized animals did not mimic that of the donors of the tolerant cells. Even where full tolerance, as measured by skin graft survival, failure to synthesize alloantibodies, and capacity to further transfer skin graft tolerance to secondary recipients, was evident the lymphocytes of these animals showed considerable graft-versus-host (GVH) reactivity. The persistence of tolerance through repeated adoptive transfers was correlated with the persistence of donor (chimeric) cells and the indicator skin graft on adoptive recipients only amplified tolerance expression where the inocula of tolerant cells given was weakly suppressive. Finally, removal of the minor population of chimeric cells from tolerant inocula using cytotoxic alloantisera abolished the capacity to transfer tolerance. These results imply an active role for chimeric cells which is best understood as an immune response involving proliferation driven by the idiotypes of the alloreceptors on host cells.

Adoptive immunotherapy of leukemia in the rat, without graft-VS-host complications

PVG rats bearing a transplantable T cell leukemia were treated with large inocula of lymphoid cells from AUG rats sensitized either against the leukemia or against PVG lymphocytes. AUG and PVG bear identical Ag-B antigens but differ at minor loci, including the Pta loci, which code for differentiation antigens expressed only on peripheral T lymphocytes. Treatment with AUG cells immune to either the PVG leukemia or normal PVG cells resulted in prolonged survival of leukemic rats, a profound but ephemeral leukopenia and prolonged disappearance of leukemic cells from lymphoid tissue. All treated animals, however, eventually died with large, discrete deposits of leukemic cells in both hard and soft tissues. Despite the deliberate mismatching of host and donor cells for minor transplanation antigens, no evidence of GVH symptoms was observed in treated rats. This was interpreted as a result of directing the adoptive immune response to antigens of restricted distribution, i.e., on leukocytes and not on somatic cells.

The cellular basis of allograft rejection in vivo. II. The nature of memory cells mediating second set heart graft rejection

An adoptive transfer system was used to study the cellular basis of memory in animals immunized by grafting with major histocompatibility complex incompatible tissue. Memory was characterised by a large (greater than 100 fold) increase in the potency of lymphocytes to precure graft rejection. This increase in potency endured for at least 1 yr after sensitization. The memory cells were shown to be Ig-- small lymphocytes which were long lived and which did not recirculate from blood to lymph in normal recipients although they did home to lymphoid tissue from which they could be recovered several months later. The thymus was not required either for the generation of memory cells or their maintenance. Cells carrying memory for alloantibody synthesis did recirculate normally but alloantibody synthesis was shown not to be required for rejection.

The cellular basis of allograft rejection in vivo. I. The cellular requirements for first-set rejection of heart grafts

The nature of the cells required for first-set graft rejection in vivo was examined by using an adoptive transfer system to restore heart-graft rejection in irradiated rats. Highly purified inocula of peripheral T lymphocytes were shown to quantitatively account for the restorative ability of adoptively transferred cells. These T cells were shown to be long-lived small lymphocytes which are not recently derived from the thymus during adult life. They belong to the pool of T cells which constantly recirculate from blood to lymph as shown by their rapid appearance in the lymph of iradiated syngeneic rats after intravenous injection. Neither B lymphocytes nor antibodies in the circulation or in the graft itself are required for first-set graft rejection.

Recirculating, suppressor T cells in transplantation tolerance

An adoptive transfer system was used to examine the capacity of cellular inocula from rats fully tolerant of Ag-B antigens to transfer tolerance to irradiated recipients. Permanent tolerance in these irradiated recipients involved specific suppression of the regenerating immune response. Cells obtained from tissues rich in recirculating lymphocytes were the most effective suppressors. Highly purified inocula of T cells from tolerant donors were potent suppressors in irradiated hosts, but were not capable of direct suppression of peripheral antigen-sensitive T cells.. The role of the thymus in maintaining the complement of recirculating suppressor T cells in tolerant animals was examined after adult thymectomy. Thymectomized tolerant rats did not reject their tolerated grafts, and the longevity of the suppression in tolerant rats was confirmed by showing that adoptive transfer of cells from thymectomized tolerant donors was effective in suppressing irradiated recipients up to 180 days after thymectomy. Cellular inocula from these donors appeared to lose their suppressor function marginally faster than they lost effector function (as measured by their capacity to mediate rejection of third party control grafts). Thymectomy made tolerant rats more vulnerable to the termination of tolerance by challenge with normal cells. Transplantation tolerance is maintained in adult rats by long-lived rapidly recirculating suppressor T cells. The target for the suppressor action of these cells is probably the precursor of alloantigen-sensitive lymphocytes, and the effect of suppression may be deletion or inactivation of the relevant clone of these cells.

The effect of antigenic strength and immunisation on the popliteal lymph node allograft response

The kinetics of the popliteal lymph node response to an allograft of lymphoid cells injected into the foot pad were examined after challenge with strong (Ag-B) and weak (non Ag-B) transplantation antigens. The response to weak antigens was characterised by a lag period of 2 days. The response to strong antigens was more rapid in onset. Active immunisation against weak antigens accelerated the response so that it came to resemble the immediate response to strong antigens. Active immunisation against strong antigens depressed the response. This depression was reproduced by giving passive antiserum to normal recipients. Passive antiserum produced by immunisation against weak antigens was also suppressive. Adoptive transfer of immune lymphoid cells reproduced the effects seen with passive transfer of antiserum. These findings indicate that clonal expansion of antigen-sensitive cells is characteristic of immunity to weak and not to strong antigens and that antibody is produced in both situations and has a similar suppressive effect on the cell-mediated response in addition to its direct effect on the graft.

T cell leukaemia in the rat: the pathophysiology

A new transplantable lymphocytic leukaemia of the inbred Hooded Oxford strain of rat is described. Fewer than 10 cells will transfer to syngeneic recipients. Leukaemic cells bear the surface markers of thymus-derived (T) cells and recirculate from blood to lymph. In contrast to the usual thymic lymphomas of rodents the pathophysiology of the disease bears a close resemblance to human acute lymphoblastic leukaemia.