RT7-defined alloantigens in rats are part of the leucocyte common antigen family

Irradiation and bone marrow reconstitution affect the functional Ly49 natural killer cell repertoire in rats

Total body irradiation (TBI) is part of the preconditioning regimen for allogeneic bone marrow transplantation (alloBMT) and the procedure is associated with treatment-related toxicity and delayed immune reconstitution. Natural killer (NK) cells develop and acquire functional competence in close interaction with stromal bone marrow cells that are considered relatively radioresistant compared to the hematopoietic compartment. We thus undertook a study to assess the effect of TBI on the reconstitution of class I MHC-specific Ly49 NK cell receptors in a rat model of alloBMT. In rats subjected to TBI alone or followed by MHC-matched BMT, the irradiation conditioning induced a skewing of the Ly49 repertoire. Specifically, the activating Ly49s3^bright subset exhibited increased frequency and receptor density which correlated with augmented alloreactivity relative to untreated control rats. Our results highlight the plasticity of NK cells and indicate that ionizing radiation (IR) affects the stromal compartment and as a consequence the maturation and functional properties of bone marrow-derived NK cells. These changes lasted throughout the 6 months observation period, showing that irradiation induces long term effects on the generation of the NK cell receptor repertoire.

A novel multicolor immunostaining method using ethynyl deoxyuridine for analysis of in situ immunoproliferative response

Immune responses are generally accompanied by antigen presentation and proliferation and differentiation of antigen-specific lymphocytes (immunoproliferation), but analysis of these events in situ on tissue sections is very difficult. We have developed a new method of simultaneous multicolor immunofluorescence staining for immunohistology and flow cytometry using a thymidine analogue, 5-ethynyl-2′-deoxyuridine (EdU). Because of the small size of azide dye using click chemistry and elimination of DNA denaturation steps, EdU staining allowed for immunofluorescence staining of at least four colors including two different markers on a single-cell surface, which is impossible with the standard 5-bromo-2′-deoxyuridine method. By using two rat models, successfully detected parameters were the cluster of differentiation antigens including phenotypic and functional markers of various immune cells, histocompatibility complex antigens, and even some nuclear transcription factors. Proliferating cells could be further sorted and used for RT-PCR analysis. This method thus enables functional in situ time-kinetic analysis of immunoproliferative responses in a distinct domain of the lymphoid organs, which are quantitatively confirmed by flow cytometry.

Immune reconstitution and graft-versus-host reactions in rat models of allogeneic hematopoietic cell transplantation

Allogeneic hematopoietic cell transplantation (alloHCT) extends the lives of thousands of patients who would otherwise succumb to hematopoietic malignancies such as leukemias and lymphomas, aplastic anemia, and disorders of the immune system. In alloHCT, different immune cell types mediate beneficial graft-versus-tumor (GvT) effects, regulate detrimental graft-versus-host disease (GvHD), and are required for protection against infections. Today, the “good” (GvT effector cells and memory cells conferring protection) cannot be easily separated from the “bad” (GvHD-causing cells), and alloHCT remains a hazardous medical modality. The transplantation of hematopoietic stem cells into an immunosuppressed patient creates a delicate environment for the reconstitution of donor blood and immune cells in co-existence with host cells. Immunological reconstitution determines to a large extent the immune status of the allo-transplanted host against infections and the recurrence of cancer, and is critical for long-term protection and survival after clinical alloHCT. Animal models continue to be extremely valuable experimental tools that widen our understanding of, for example, the dynamics of post-transplant hematopoiesis and the complexity of immune reconstitution with multiple ways of interaction between host and donor cells. In this review, we discuss the rat as an experimental model of HCT between allogeneic individuals. We summarize our findings on lymphocyte reconstitution in transplanted rats and illustrate the disease pathology of this particular model. We also introduce the rat skin explant assay, a feasible alternative to in vivo transplantation studies. The skin explant assay can be used to elucidate the biology of graft-versus-host reactions, which are known to have a major impact on immune reconstitution, and to perform genome-wide gene expression studies using controlled combinations of minor and major histocompatibility between the donor and the recipient.

Kinetics of lymphocyte reconstitution after allogeneic bone marrow transplantation: markers of graft-versus-host disease

GVHD causes extensive morbidity and mortality in patients who receive alloHCT. Predictive and reliable markers for GVHD are currently lacking but required to improve the safety and accessibility of alloHCT. We present an experimental rat model of myeloablative total body irradiation and fully mismatched major and minor histoincompatible, T cell-depleted BMT, followed by delayed infusion of donor lymphocytes. This treatment, in contrast to marrow transplantation alone, resulted in severe aGVHD and 100% lethality within 2-6 weeks. We investigated the reconstitution kinetics and phenotypes of donor leukocyte subpopulations as well as the histopathology of selected organs that may correlate with GVHD, with the goal to find potential disease-related markers. We observed histological changes mainly confined to the skin, with degenerative changes in the basal layer. LNs and spleen showed deranged architecture with markedly increased accumulation of lymphocytes, whereas the gut, liver, and lungs appeared normal. Of the lymphocyte markers tested, donor-derived CD62L(+) T cells were markedly decreased in animals suffering from GVHD. Furthermore, we observed peripheral depletion of CD4(+)CD25(hi)FoxP3(+) T(reg), which was in contrast to controls. The relative frequency of these lymphocyte subpopulations in blood may therefore serve as accessible cellular markers of aGVHD. We propose that the animal model presented is instructive for the identification of clinically relevant markers of GVHD, which could improve disease diagnosis and management in alloHCT.

Partial NK cell tolerance induced by radioresistant host cells in rats transplanted with MHC-mismatched bone marrow

We have studied the effect of radioresistant host cells in inducing tolerance and adaptation of the MHC recognition repertoire of donor-derived NK cells in stem cell allotransplanted (allo-SCT) rats. Sub-lethally irradiated PVG.1AV1 rats (RT1(av1)) were transplanted with bone marrow from fully MHC-mismatched allotype-marked PVG.7B (RT1(c)) rats; MHC-identical PVG (RT1(c)) controls were transplanted in parallel. In the PVG.7B → PVG.1AV1 allogeneic chimeras, NK cells were donor derived and showed partial tolerance toward host cells. Allogeneic chimeras failed to efficiently reject PVG.1AV1 cells by an NK-mediated mechanism in vivo (allogeneic lymphocyte cytotoxicity), and IL-2-cultured NK cells derived from these chimeras showed diminished cytolytic activity against PVG.1AV1 cells in vitro. There were corresponding changes in the phenotype and function of the highly alloreactive Ly49i2(+) NK cells, which are specifically inhibited by a donor MHC class I ligand, RT1-A1(c). The ligand-negative host MHC haplotype apparently induced expression of a second uncharacterized inhibitory MHC receptor responsible for the partial tolerance toward host-derived cells, along with a modest increase in Ly49i2 receptor levels. The host MHC haplotype did not induce a general hyporesponsiveness in Ly49i2(+) NK cells, which showed normal activation responses in a panel of MHC congenic strains. The data suggest that the MHC constitution of radiation-resistant host cells can have permanent, albeit not fully tolerogenic, effects on the development of a functional NK repertoire following allo-SCT.

Monoclonal antibodies to rat leukocyte surface antigens, MHC antigens, and immunoglobulins

The CD nomenclature used for human-leukocyte surface antigens is now being widely applied to naming their homologs in other species. This appendix catalogs those CD antigens that have been clearly defined in the rat. There are also many other antigens defined in the rat, but only those for which good biochemical data are available, such as amino acid sequences, are given here. The most commonly used antibodies are summarized.

A second prophylactic MHC-mismatched bone marrow transplantation protects against rat acute myeloid leukemia (BNML) without lethal graft-versus-host disease

BACKGROUND

We have employed a rat model for human acute myeloid leukemia, a promyelocytic leukemia in the BN rat strain (BNML), to develop new protocols for immunotherapy in combination with allogeneic bone marrow transplantation (alloBMT). The status of mixed chimerism in allotransplanted rats provided an opportunity for immunotherapy using alloreactive donor cells. In addition to T or natural killer (NK) cells, we introduced a second infusion of bone marrow cells as prophylactic donor lymphocyte infusions (DLI) to test whether an effective graft-versus-leukemia (GVL) response could be obtained without clinical graft-versus-host disease (GVHD).

METHODS

BN rats were sublethally irradiated and transplanted with T-cell depleted bone marrow cells from either fully major histocompatibility complex (MHC)-mismatched (PVG) donor rats or MHC-matched (PVG.1N) as controls. Seven days after transplantation, rats were given 500 leukemic cells to mimic minimal residual disease. Additional cellular therapy was given at day +7. The efficiency of DLI was monitored by chimerism analysis in peripheral blood.

RESULTS

Rats receiving infusions of NK cells succumbed to leukemia. T-DLI induced complete donor T-cell chimerism and lethal GVHD. A second alloBMT protected against leukemia. This effect was dependent on an MHC incompatibility between the donor and host and also on the presence of alloreactive T cells in the second bone marrow inoculum, resulting in an increased, mixed donor T-cell chimerism.

CONCLUSION

A second prophylactic transplantation influenced the degree of T-cell chimerism to balance favorably between GVL and GVHD. If applicable to humans, repeated alloBMT may provide a novel approach to leukemia therapy.

T cells are required for the peripheral phase of B-cell maturation

B-lymphocyte maturation is considered to be independent of the thymus. However, there is circumstantial evidence suggesting that it may be impaired in nude animals that lack the thymus. Our study shows that the proportion of immature B-lymphocyte subsets (CD90(high) IgM(high) and CD90(high) IgM(low)) was significantly increased, whereas that of mature B-lymphocyte subsets (CD90- IgM(low) and CD90- IgM(high)) was decreased in the blood and lymph nodes of nude rats. In addition, the expression of major histocompatibility complex class II, intercellular adhesion molecule-1, CD44 and l-selectin was significantly down-regulated both on immature and mature B-lymphocyte subsets. After implantation of thymic tissue under the kidney capsule of nude rats the block in B-lymphocyte maturation was alleviated and the expression of surface molecules was normalized. Comparable effects were seen after the adoptive transfer of T lymphocytes. Thus, we show that in nude rats B cells do not mature properly because of the lack of T-cell help and that T lymphocytes are required for the peripheral phase of B-lymphocyte maturation, as well as for the appropriate expression of surface molecules. This should be considered when treating patients with T-cell deficiencies.

Multipotent stem cells from adult olfactory mucosa

Multipotent stem cells are thought to be responsible for the generation of new neurons in the adult brain. Neurogenesis also occurs in an accessible part of the nervous system, the olfactory mucosa. We show here that cells from human olfactory mucosa generate neurospheres that are multipotent in vitro and when transplanted into the chicken embryo. Cloned neurosphere cells show this multipotency. Multipotency was evident without prior culture in vitro: cells dissociated from adult rat olfactory mucosa generate leukocytes when transplanted into bone marrow-irradiated hosts, and cells dissociated from adult mouse olfactory epithelium generated numerous cell types when transplanted into the chicken embryo. It is unlikely that these results can be attributed to hematopoietic precursor contamination or cell fusion. These results demonstrate the existence of a multipotent stem-like cell in the olfactory mucosa useful for autologous transplantation therapies and for cellular studies of disease.

Naive, Effector, and Memory T Lymphocytes Efficiently Scan Dendritic Cells In Vivo: Contact Frequency in T Cell Zones of Secondary Lymphoid Organs Does Not Depend on LFA-1 Expression and Facilitates Survival of Effector T Cells

Contact between T cells and dendritic cells (DCs) is required for their subsequent interaction leading to the induction of adaptive immune responses. Quantitative data regarding the contact frequencies of T cell subsets in different lymphoid organs and species are lacking. Therefore, naive, effector, and memory CD4 T cells were injected into rats in absence of the cognate Ag, and 0.5-96 h later, spleen, lymph nodes, and Peyer's patches were removed. Cryosections were analyzed for contact between donor T cells and endogenous DCs in the T cell zone, and donor cell proliferation. More than 60% of injected naive CD4 T cells were in contact with endogenous DCs at all time points and in all organs analyzed. Surprisingly, we were unable to detect any differences between naive, effector, and memory CD4 T cells despite different expression levels of surface molecules. In addition, contact frequency was similar for T cells in lymphoid organs of rats, mice, and humans; it was unaffected by the absence of LFA-1 (CD11a/CD18), and sustained effector T cells in an activated state. Thus, the architecture of the T cell zone rather than expression patterns of surface molecules determines the contact efficiency between T cells and DCs in vivo.

Macrophages in spleen and liver direct the migration pattern of rat neutrophils during inflammation

OBJECTIVE

The exact fate of polymorphonuclear neutrophilic granulocytes (PMN; neutrophils) after their mobilization from the bone marrow is not known. It is believed that they, after a relatively short lifespan (1-3 d), become apoptotic and phagocytosed by macrophages. We have recently shown that transfused neutrophils sequestrate not only in lungs, liver and spleen, but also to a large extent in the bone marrow, possibly because of uptake by macrophages. Hence, we studied if inactivation of macrophages would alter the pattern of neutrophil migration.

METHODS

We used transfused congenic or syngeneic neutrophils in rats with or without sterile peritonitis, induced by a casein preparation (Bacto-Tryptone). To perturb macrophage function, we either killed them with liposome-encapsulated clodronate or overloaded them with inert phagocytosable particles. Transfused neutrophils were tracked with flow cytometric or radiometric methods.

RESULTS

Not more than a small portion of the neutrophils migrated to the inflamed peritoneal cavity under any circumstance. Their ecotaxis to liver and spleen was reduced in rats with liver and spleen macrophages either congested with polystyrene particles or depleted by clodronate. The bone marrow uptake and blood retention of transfused neutrophils were increased in macrophage-depleted rats 18 h after transfusion. In rats depleted of liver macrophages only, the sequestration in the liver was reduced, without detectably changed uptake in bone marrow and spleen.

CONCLUSION

Macrophages are instrumental to the neutrophil migration stream in the organism, and their function in this regard is robust and not easily decreased by inert phagocytosable particles or a killing agent.

Marrow frequency of rat long-term repopulating cells: evidence that marrow hematopoietic stem cell concentration may be inversely proportional to species body weight

As measured by the long-term repopulating cell (LTRC) assay, only a few hematopoietic stem cells (HSCs) or perhaps a single HSC are required to totally repopulate the lymphohematopoietic tissues of lethally irradiated mice, cats, and humans, raising the question as to why large mammals require more marrow cells to either rescue them from lethal irradiation or establish a long-term hematopoietic graft than do small mammals. An explanation might be that HSC marrow frequency across species is not constant, but decreases as species body weight increases. This hypothesis was tested by comparing the LTRC marrow concentration of mice to that of rats. Specifically, histocompatible AKR/J Thy 1.1 marrow was transferred to 7-Gy irradiated C3H/HeN, Thy 1.2 mice, and histocompatible Norway Black marrow (NBr), RT 7.2 marrow was transferred to 7-Gy irradiated RT 7.1 Lewis rats. The recipients were scored for successful grafts 6 to 20 weeks later. By limiting dilution analysis, a value of 1 LTRC/47 700 marrow cells was calculated for mice, but only 1 LTRC/502,000 marrow cells was calculated for rats. Viewed in the context of marrow grafting in larger mammals, these results suggest that species with greater body mass have lower marrow HSC frequency.

The fate of effector T cells in vivo is determined during activation and differs for CD4+ and CD8+ cells

Effector T cells generated in the mesenteric lymph nodes (mLN) are known to accumulate in mLN and the tissue drained by them after circulating in the blood. Their accumulation is due less to preferential entry into mLN but more to preferential proliferation within mLN. The factors regulating the proliferation of effector T cells in vivo are unclear, and it is unknown whether they are different for CD4(+) and CD8(+) effector T cells. Rat T cells from mLN or peripheral lymph nodes (pLN) were stimulated polyclonally via the TCR and CD28 and injected i.v. into congenic recipients. Using three-color flow cytometry and immunohistochemistry, they were identified in mLN, pLN, and blood over time, and proliferation was determined by measuring bromodeoxyuridine incorporation. Only effector mLN T cells showed a significantly increased proliferation rate after entry into mLN compared with that in pLN (2.4 +/- 1.8% vs 0.8 +/- 0.4%). Proliferation among the injected cells was higher when they had contact with dendritic cells within mLN (9.0 +/- 4.3%) than when they did not (4.1 +/- 2.1%). Furthermore, effector mLN T cells which were observed 56 days after injection maintained the capacity for preferential proliferation within mLN. Interestingly, CD4(+) effector mLN T cells proliferated at a higher rate (4.8 +/- 0.7%), remaining in mLN, whereas CD8(+) effector mLN T cells proliferated at a lower rate (3.3 +/- 1.0%) and were able to leave the mLN into the blood. Elucidating the factors regulating the proliferation of effector T cells in vivo will help to modify their distribution for therapeutic purposes.

In vivo depletion of hematopoietic stem cells in the rat by an anti-CD45 (RT7) antibody

Anti-CD45 monoclonal antibodies (mAbs) are potentially powerful tools for the depletion of mature leukocytes. As their application for immunotherapy also depends on their effects on bone marrow (BM) progeny, the in vivo effects of an anti-CD45 mAb (anti-RT7(a) mAb) on BM precursor cells were analyzed in a rat model. Anti-RT7(a) mAb treatment was performed in LEW.1W (RT1(u) RT7(a)) rats with the use of different dosages. In addition, major histocompatibility complex (MHC)-congenic BM transplantation making use of a diallelic polymorphism (RT7(a)/RT7(b)) of rat CD45 was applied. Following injection of anti-RT7(a) mAb into normal LEW.1W rats, T cells were profoundly depleted in blood, lymph nodes, and spleen, whereas B cells were coated only by the antibody. Single injection of anti-RT7(a) mAb in a high dose induced a lethal aplastic syndrome with severe thrombocytopenia. Rescue of antibody-treated animals with BM from congenic LEW.1W-7B rats (RT1(u) RT7(b)) and transplantation of BM from LEW.1W rats pretreated with anti-RT7(a) mAb into sublethally irradiated LEW.1W-7B recipients revealed a profound effect of the mAb on progeny of myeloid and T-cell lineage. Following repeated antibody treatment of stable mixed chimeras (RT7(b)/RT7(a)), very few RT7(a)-positive B cells were still detectable after 6 months and their number declined during the subsequent year. These observations show that this anti-RT7(a) mAb effectively depletes mature T cells as well as BM precursor cells of myeloid, T-cell, and thrombocytic lineage after in vivo application. In contrast, mature B cells are not depleted, but precursors also appear to be eliminated. Overall, the findings suggest that the anti-RT7(a) mAb efficiently depletes early rat hematopoietic stem cells.

Susceptibility to cyclosporin A-induced autoimmunity: strain differences in relation to autoregulatory T cells

Cyclosporin A-induced autoimmunity (CsA-AI), also called autoimmune syngeneic graft-vs-host disease, is a thymus dependent, T cell mediated rodent animal model of disease and is considered to be an experimental model for human scleroderma. Since adoptive transfer of CsA-AI by effector T cells can be prevented by autoregulatory T cells, there may also be a role for dominant tolerance in the resistance of certain rat strains to develop clinical manifest CsA-AI. LEW rats have been reported to be susceptible, whereas BN rats are resistant to CsA-AI. In the present study we first demonstrate that PVG, but not DA rats, are susceptible to CsA-AI and that disease characteristics in PVG rats are comparable to LEW rats in terms of pathogenesis and T cell kinetics, although of more rapid onset and greater severity. Next, we examined whether the relative presence of autoregulatory T-helper cells, i.e. CD25+ and/or CD45RClow CD4 T cells, is increased in resistant BN and DA rats. The results obtained reveal that the genetically determined CD45RChigh/CD45RClow ratio, but not the percentage CD25+ cells, within the CD4 T cell compartment of naïve rats is correlated with resistance to CsA-AI in these rat strains. We conclude that the relative presence of autoregulatory T cells with a CD45RClow T-helper cell phenotype may be a critical determinant in susceptibility to CsA-AI.

New tools to trace populations of inflammatory cells in the CNS

Cells of the central nervous system (CNS) and immune system communicate regularly. There is a constant surveillance of the intact, healthy CNS by activated T-cells, and massive infiltration of the CNS by immune cells under pathological conditions such as neurodegeneration or neuroinflammation. Labeling CNS-infiltrating T-cells is an essential tool to identify the signals and mechanisms, which mediate the interaction between immune cells and cells of the CNS. In this article, we will present an overview describing currently used cellular markers and demonstrate how these markers have contributed to our current knowledge of CNS inflammation and immune surveillance.

Long-term donor chimerism after MHC (RT1) mismatched bone marrow transplantation in the rat: the role of host alloreactive NK cells

We have investigated the role of major histocompatibility complex (MHC) (RT1) disparities in the engraftment of bone marrow (BM) cells after whole body irradiation of rats. Mononuclear BM cells from PVG.RT7.2 (RT1c) rats were injected i.v. into sublethally (10Gy) whole body irradiated PVG (RT1c) rats and RT1 congenic and recombinant PVG rats. Repopulation of the BM, spleen, and blood with donor cells was assessed by FACS analysis of cells labelled with the fluorescein isothiocyanate (FITC)-labelled HIS41 monoclonal antibody (MoAb) against the RT7.2 marker. In RT1 matched (PVG.RT7.2 --> PVG) and RT1-mismatched combinations (PVG.RT7.2 --> PVG.1AV1), where radioresistant host natural killer (NK) cells could not recognize the BM inoculum as foreign, a donor chimerism close to 100% was observed after 6-8 weeks. However, in rat strain combinations where host NK cells could recognize an RT1 mismatch, almost no donor cells survived, and the rats were repopulated with leukocytes of host origin. In intra-MHC recombinant rat strains the element determining rejection or acceptance of the allograft mapped to the RT1-B/D-C/E/M region in PVG.R8 and PVG.R23 rats, in accordance with the patterns of NK alloreactivity in these strain combinations. NK cells may therefore be a primary obstacle to successful allogeneic BM engraftment in this model.

Bone marrow aplasia induced by passenger leukocytes from heart allografts

OBJECTIVE

Organ allografts contain passenger leukocytes that are transferred to the recipient with the transplantation, but their functional relevance to the recipient's immune system is still controversial.

MATERIALS AND METHODS

To clarify the functional capacity of passenger leukocytes, we attempted to enhance their effect in rat heart allograft recipients by selective depletion of recipient leukocytes using a monoclonal antibody (mAb) against a recipient-specific allotype of CD45 (RT7(a)).

RESULTS

Although antibody treatment of the recipient alone led to profound lymphopenia and reversible myelosuppression, additional transplantation of an major histocompatibility complex-incompatible heart graft from an RT7(b) donor led to lethal aplastic anemia in the recipients. This lethal effect was completely abrogated by postoperative anti-CD3 treatment of the recipient and was partially abrogated or delayed by depletion of passenger leukocytes through additional anti-RT7(b) antibody treatment of the recipient or gamma-irradiation of the graft.

CONCLUSIONS

The results suggest a role for both donor and recipient-type T cells for the induction of aplastic anemia in this model. The study shows that, under defined conditions, allogeneic passenger leukocytes in a heart graft can have a profound effect on the recipient's immune system and bone marrow.

The functional relevance of passenger leukocytes and microchimerism for heart allograft acceptance in the rat

With an organ transplant, hematopoietic donor cells are transferred to the recipient. To study the relevance of the resulting microchimerism for allograft acceptance, we analyzed a rat model of cyclosporine-induced tolerance for strongly incompatible heart allografts. Using a monoclonal antibody that detects a donor-specific CD45 allotype (RT7a), we selectively depleted donor leukocytes at different times after transplantation (days 0 or 18). Depletion was similarly effective at both times. However, only depletion on day 0 prevented tolerance induction and was associated with severe acute or chronic graft rejection. This indicates that passenger leukocytes have an essential immunomodulatory effect on the induction phase of allograft acceptance.

Naive and Memory T Lymphocytes Migrate in Comparable Numbers Through Normal Rat Liver: Activated T Cells Accumulate in the Periportal Field

Although the liver is known to contain a significant number of lymphocytes, migration of these through the compartments of the liver, parenchyma and periportal field, has not been studied. The periportal field, in particular, is affected in several immunological disorders of the liver. Populations of labeled naive, activated, and memory T cells were injected into congenic rats. The recipient livers and draining lymph nodes were removed at various time points, and cryostat sections were analyzed for the presence of donor cells using quantitative immunohistology. Donor cell proliferation and apoptosis were examined in vivo by BrdU (5 μM 5-bromo-2-deoxyuridine) incorporation and the TUNEL technique, respectively. Early after injection (0.5–1 h), naive, activated, and memory T cells were localized to the parenchyma and periportal field in comparable numbers. With time, all T cell subsets left the parenchyma but remained or, in the case of activated T cells, significantly accumulated in the periportal field. Furthermore, 12% of activated donor T cells proliferated in vivo within the periportal field, and 0.5% showed evidence of apoptosis. Taken together, not only activated and memory, but also naive T cells continuously migrate through the liver, showing a preference for the periportal field, and activated T cells mainly proliferate there. This may explain why many immunological liver diseases predominantly affect the periportal field.

Production of human allotype-specific anti-CD45 monoclonal antibodies

The aim of this work was to raise allotype specific monoclonal antibodies to human CD45, with the long-term objective of producing a reagent which could be used to prolong graft survival in renal transplantation through removal of passenger leukocytes from the graft. At present there are no anti-CD45 monoclonal antibodies able to distinguish between host and donor leukocytes. An in vitro immunisation technique has been developed through which donated human leukocytes are sensitised to CD45 prior to fusion with a myeloma cell line. IgM was produced by all the anti-CD45-positive clones. Flow cytometric analysis using these antibodies showed their ability to differentiate between blood from individual donors, indicating the existence of allotypic forms of human CD45, in conformity with the findings in rats and pigs. Therefore, a reagent which could be used in renal transplantation is a technical possibility.

Activated T cells enter rat lymph nodes and Peyer's patches via high endothelial venules: survival by tissue-specific proliferation and preferential exit of CD8+ T cell progeny

Activated T cells reach the lymph nodes via afferent lymphatics but it is unknown to what extent they also enter them directly via high endothelial venules (HEV). Little is known about the mechanism mediating the proliferation of activated T cells within lymphoid tissues in vivo or the subsequent fate of the progeny. Therefore, we stimulated rat T cells via TCR and CD28 in vitro and after injection identified them in the blood and the HEV of lymphoid organs at several time points. In addition, the proliferation of these cells was studied after entering different lymphoid organs. Our results show that, firstly, activated T cells continuously enter lymph nodes and Peyer's patches directly via HEV. Second, they proliferate within lymphoid organs, the rate significantly depending on the microenvironment. Third, mainly CD8+ progeny are able to leave the tissues and re-enter the blood. Thus, the distribution of activated T cells circulating through the body can be regulated during entry, but also within the tissue by influencing their proliferation and subsequent release.

Migration of dendritic cells to the draining lymph node after allogeneic or congeneic rat skin transplantation

BACKGROUND

After transplantation, donor dendritic cells (DC) migrating to the draining lymph node of the recipient are thought to play an important role in the initiation of graft rejection. In this study, we compared the in vivo migration of DC after allogeneic skin transplantation with that after congeneic skin transplantation.

METHODS

A rat model was used with the PVG-RT7b rats as donor animals. These rats have leukocytes bearing an epitope of the leukocyte common antigen that can be recognized by the monoclonal antibody His 41. The cells of the allogeneic (ACI) and congeneic (PVG) recipient animals do not express this marker.

RESULTS

In both recipient rat strains, graft-derived His 41+ DC could be detected in the T cell areas of the draining lymph nodes after skin transplantation. However, the number of migrated His 41+ cells present was lower in the allogeneic recipients. Similar results were obtained when skin DC isolated from the PVG-RT7b rats were injected subcutaneously into the hind footpads of allogeneic and congeneic recipients. Although the numbers of migrated His 41+ DC present were lower, the lymph nodes of the allogeneic recipients were much more enlarged and the grafts were rejected which did not occur in the congeneic recipients.

CONCLUSIONS

The presence of donor-derived DC in the graft draining lymph nodes underlines the importance of the direct route of allo-activation. The lower numbers of migrated His 41+ DC in lymph nodes of allogeneic recipients may be the result of killing of the cells after presentation of the allo-antigens to the recipient T cells.

CD4+ T cells from 2,4,6-trinitrobenzene sulfonic acid (TNBS)-induced colitis rodents migrate to the recipient's colon upon transfer; down-regulation by CD8+ T cells

CD4+ T cells play an important role in the aetiology of inflammatory bowel disease (IBD), but it is not clear which factor(s) cause activation of these cells. The aim of this study was to examine the effects of adoptive transfer of splenic (CD4+) T cells from TNBS/ethanol-sensitized donor rats to naive recipients and the migration pattern of transferred T cells. For the transfer experiments, colitis was induced in rats by colonic administration of TNBS/ethanol. Seventeen days later, either total splenic T cells or CD4+, or CD8+ T cells were transferred to naive recipients. At days 1, 2 and 3 after transfer, the recipients were killed and the migration pattern of the transferred T cells was studied, as well as inflammatory cells in several organs, including the colon. To determine cytokine profiles of the T cells, colitis was induced in mice. Therefore, different combinations of 2,4-dinitrobenzene sulfonic acid (DNBS) in ethanol or saline, or ethanol alone were intrarectally administered. At day 9 after induction of colitis, mice were killed and cytokine profiles in the colon were studied by reverse transcriptase-polymerase chain reaction (RT-PCR) and immunohistochemistry. The results show that CD4+ T cells from donor rats with TNBS/ethanol-induced colitis migrate in particular to the colon upon transfer to naive recipients, and that this process is down-regulated by CD8+ T cells. This migration is probably caused by T cell recognition of the colonic bacterial flora and initiates an inflammatory reaction in the recipient's colon, characterized by an increase of the recipient's own T cells, macrophages, and neutrophils. In the mice experiments we showed that a second administration of DNBS/ethanol or ethanol alone, which presumably causes bacterial translocation, results in increased numbers of T cells into the colon, accompanied by an increase in Th1 cytokines. These data suggest that Th1 cells recognize the colonic bacterial flora.

The lung as a source and a target organ for T- and B-lymphocytes

In lung transplantation, a substantial number of donor leukocytes are transferred from the donor to the recipient by the graft. Using a rat model, it was analyzed in this study to what extent leukocytes leave the lung, to which phenotype they belong, and to which organs they migrate. The model used was the orthotopic transplantation of the left lung of LEW.7B(RT7b) rats into LEW(RT7a) recipients. Lung allografts are not rejected in this strain combination, which differs only in the RT7 system, a genetic polymorphism of CD45. Using the RT7b marker (monoclonal antibody His41), the distribution of donor leukocytes passively transferred with the graft was studied by immunohistology 2 wk after transplantation. At this time, 2.9 +/- 0.1% (n = 6) of the peripheral blood leukocytes in the recipients were derived from the donor lung. The donor cell population detected in the blood consisted of T cells (59 +/- 4%), B cells (5.1 +/- 0.2%) and a surprisingly high fraction of natural killer (NK) cells (36 +/- 3%). No monocytes or granulocytes were found. In lymph nodes, spleen and thymus donor-derived T- and B-cells could be shown in typical T- and B-areas, respectively. Donor-derived leukocytes were found in the liver and the skin. In the tissue and the bronchoalveolar lavage (BAL) of the host lung, predominantly T cells were found. Furthermore, in the donor tissue and BAL more than 70% of T- and B-cells were host type, demonstrating that the donor lung had been repopulated to a great extent by host lymphocytes. This supports the relevance of BAL as a diagnostic tool in lung diseases. Thus, the lung is an immunologically important site, releasing lymphocytes which migrate to other organs and also attracting many lymphocytes from the circulation.

Treatment of relapsing experimental autoimmune encephalomyelitis with largely MHC-matched allogeneic bone marrow transplantation

BUF rats suffering from severe relapsing experimental autoimmune encephalomyelitis (R-EAE), a model for multiple sclerosis, were treated with intensive cytoreductive therapy and grafting of allogeneic bone marrow (BM). BN.1B rats were used as EAE-resistant, largely MHC-matched donors, resembling human BMT from HLA-identical siblings. The treatment induces complete remission and low recurrence rates of R-EAE. Evidence is provided that the efficacy of the treatment depends on a high degree of lymphoablation: a minority of rats had host-type residual activated T lymphocytes in the CNS after treatment. Furthermore, complete replacement of host-type BM by donor-type hemopoietic cells is essential, as higher relapse rates were observed in animals with incomplete reconstitution by donor cells than in completely reconstituted rats. Overall, our results indicate that patients with severe MS might benefit from treatment with HLA-matched allogeneic BM.

A non-expressed transgene as a cell marker for the investigation of cellular traffic after splenic autotransplantation

The investigation of cellular interactions during the regeneration of splenic transplants depends upon distinguishing host cells from graft derived cells. As a cell marker which, in contrast to many other marker systems, does not affect histocompatibility, the non-expressed transgene mMT-HGHRH-1 was introduced by mating into NMRI inbred mice to generate the transgenic mouse line BSM. By transplanting non-transgenic NMRI splenic tissue into transgenic BSM hosts, host derived cells could be identified in the transplants by in situ hybridization after regeneration. In a reciprocal approach, implant derived cells were detected in a transgenic transplant after 3 weeks of regeneration in a non-transgenic host. Relative amounts of transgenic cells in transplant cross-sections were estimated from the signal intensity of autoradiographs by densitometry and computer analysis. This approach could be broadly applied in studies of transplantation systems.

Both activated and nonactivated leukocytes from the periphery continuously enter the thymic medulla of adult rats: phenotypes, sources and magnitude of traffic

Although the thymus is primarily noted for the export of T cells to the periphery, a small influx of cells has also been observed. It is still a matter of debate whether entry into the thymus depends on prior activation. The phenotypes, sources and degree of immigration are largely unknown. We monitored by quantitative immunohistochemistry the entry of cells from the periphery into the rat thymus in three experimental models. We injected i.v. recirculating, small, nonactivated CD4+ T cell subsets, often referred to as naive (CD45RC+) and memory or antigen-experienced (CD45RC-) cells, purified from thoracic duct lymph of allotype-marked donors, allotype-marked leukocytes released from spleen or lung transplants, or leukocytes labeled in the periphery for 12 weeks during the S-phase of the cell cycle by oral application of 5-bromo-2-deoxyuridine (BrdUrd). Early after i.v. injection (0.5 h), significantly more antigen-experienced (CD45RC-) CD4+ T cells entered the thymus, and by 24 h four times as many cells from the CD45RC- subset as from the CD45RC+ subset had entered the thymus and localized to the medulla. None of the thymic entrants expressed the interleukin (IL)-2 receptor. Following spleen transplantation approximately 40% of donor cells entering the thymic medulla were T cells and approximately 55% were B cells. In contrast, from a lung transplant, approximately 85% of peripheral immigrants were T cells and approximately 10% were B cells. After both procedures, a small number of NK cells and monocytes/macrophages were found among the immigrants (< 5%). Rats were fed BrdUrd continuously for 12 weeks, a procedure which labeled approximately 30% of peripheral lymphocytes but not cortical thymocytes. BrdUrd-labeled cells were localized almost exclusively to the thymic medulla and represented approximately 10% of medullary cells. Of the thymic immigrants approximately 50% were T cells, approximately 30% were B cells (including approximately 15% IgD+ cells), approximately 15% were NK cells and the remainder (approximately 5%) were monocytes/macrophages. Only a quarter of BrdUrd-labeled cells expressed the IL-2 receptor. The thymus is continuously infiltrated by both activated and nonactivated leukocytes from the periphery, including T cells, B cells, NK cells and monocytes. These immigrants are supplied by lymphoid and nonlymphoid organs in a characteristic subset composition. Their entry is facilitated by prior antigen experience or activation. Thus, the participation of the thymic medulla in general leukocyte traffic suggests a mechanism by which the T cell repertoire could potentially be modulated by the peripheral tissues.

Sequestration patterns of transfused rat neutrophilic granulocytes under normal and inflammatory conditions

The fate of polymorphonuclear neutrophilic granulocytes (PMN) after their mobilization from the bone marrow of healthy individuals is not clearly understood. It has been suggested that there is a continuous utilization of these cells in widespread, subclinical inflammatory foci, where they are ultimately degraded. The goal of the present experiments was to determine whether an alternative ecotaxis ("homing") exists, namely sequestration and degradation of PMN by mononuclear phagocytes exposed to the bloodstream in the liver, spleen and bone marrow. Blood PMN were collected from donor rats, labelled with 51 Cr, and injected i.v. into 2 syngeneic rats, one of them having an induced sterile peritonitis. After various time intervals up to 18 h, the rats were killed and exsanguinated. As expected, we found cell-bound radioactivity in liver, spleen, and bone marrow. The bone marrow uptake of PMN appeared to be much lower in the inflammation rats than in the normal controls. These findings were confirmed in PMN transfer experiments using PVG rats congenic for the RT7 alloantigenic system. Here, transfused blood leukocytes were traced with fluorescent, monoclonal HIS41 antibodies and flow cytometry. A possible corticosteroid effect on the bone marrow sequestration could not be substantiated. Uptake and degradation of PMN takes place in organs containing phagocytes exposed to the bloodstream. Sequestration of PMN in the bone marrow is apparently down-regulated in inflammatory states, perhaps increasing the PMN availability to inflamed tissue.

Migration of dendritic cells into the draining lymph nodes of the lung after intratracheal instillation

The migration of dendritic cell (DC)-enriched populations and alveolar macrophage (AM) populations isolated from PVG RT7.2 rats was studied after local administration to recipient PVG RT7.1 rats. The monoclonal antibody His41, which is directed against the common leukocyte antigen of the RT7.2 rat, was used to detect migrated cells. Injection of the splenic DC and AM subcutaneously into the footpads resulted in migration of both cell types to the popliteal lymph nodes after 24 h. DC located predominantly in the T cell-dependent areas, whereas AM located more in the medulla and medullary cords and spread throughout the outer cortex area. After intratracheal instillation of splenic DC, these cells were found predominantly in T cell-dependent areas of the draining lymph nodes of the lung after 24 h. In contrast, AM did not migrate to the draining lymph nodes after intratracheal instillation. Combined with those from earlier studies, these data show that DC present in the alveolar lumen may pick up airborne antigen and migrate to the draining lymph nodes of the lung, where they can induce primary T cell responses.

Evidence that the T cell repertoire of normal rats contains cells with the potential to cause diabetes. Characterization of the CD4+ T cell subset that inhibits this autoimmune potential

Diabetes was induced in a normal nonautoimmune rat strain by rendering the animals relatively T cell deficient using a protocol of adult thymectomy and sublethal gamma irradiation. All male rats and 70% of females developed an acute syndrome with severe loss of weight and hyperglycemia. Diabetes in these lymphopoenic rats was associated with extensive insulitis involving CD4+ and CD8+ T cells and macrophages. The CD8+ T cells were essential for the development of diabetes but not insulitis. The autoimmune diabetes and insulitis were completely prevented by the injection of a particular CD4+ T cell subset, isolated from healthy syngeneic donors, of the phenotype CD45RClow T cell receptor alpha/beta+ RT6+ Thy-1- OX-40-. Cells of this protective phenotype, which make up about 5% of thoracic duct lymphocytes, were found to provide help for secondary antibody responses and produce interleukin 2 (IL-2) and IL-4, but no interferon gamma, on in vitro activation. These data provide evidence for the presence of autoreactive T cells in the normal immune system of the rat and reveal that in the intact animal these cells are prevented from expressing their autoreactive potential by other T cells.

Glucocorticoids induce the expression of CD8 alpha chains on concanavalin A-activated rat CD4+ T cells: induction is inhibited by rat recombinant interleukin 4

Rat T lymphocytes, activated in vitro with concanavalin A (Con A), were shown by flow cytofluorographic analysis to contain a population of cells that simultaneously expressed CD4 and the alpha chain of CD8. The inclusion of the glucocorticoid hormone dexamethasone in the culture medium greatly increased both the frequency of these double-positive cells and the level of CD8 alpha chain expression. The level of expression of CD4 was not affected, and the cells that expressed CD8 antigen only also remained unchanged in surface phenotype. Detailed studies demonstrated unequivocally that the CD4+ CD8 alpha + cells were not artifacts produced by the random association of single-positive cells in the flow cytofluorograph, but arose from precursors that were single-positive CD4+ cells before activation. Furthermore, Con A activation of purified CD4+ T cells, in the presence of T cell-depleted accessory cells, showed that CD8+ T cells played no role in the induction process. However, the induction of CD8 alpha chain expression on CD4+ T cells and the enhancement of this expression by dexamethasone were almost completely inhibited by rat recombinant interleukin 4 (IL-4). Detection of mRNA for rat CD8 alpha chain by Northern blot closely paralleled the cell surface expression of CD8 alpha antigen, indicating that dexamethasone and IL-4 had opposing effects on mRNA levels. In contrast, IL-4 and dexamethasone both induced CD8 alpha chain expression on a rat CD4+ T cell clone when this was activated by specific antigen, and, although the effect with IL-4 was relatively weak, it did not antagonize the effect of the glucocorticoid. The possible significance of these results is briefly discussed.

The extent of clonal structure in different lymphoid organs

To gain insight into the clonal organization of lymphoid organs, we studied the distribution in situ of donor-derived cells in near-physiological chimeras. We introduced RT7b fetal liver cells into nonirradiated congenic RT7a neonatal rats. The chimerism 6-20 wk after injection ranged from 0.3 to 20%. The numbers of cell clones simultaneously contributing to cell generation in a particular histological feature were deduced from the variance in donor cell distribution. In bone marrow and thymus, donor-derived lymphoid cells were found scattered among host cells, indicating a high mobility of cells. In bone marrow, donor cells were evenly distributed over the entire marrow, even at low chimerism. This indicates that leukopoiesis is maintained by the proliferation of many clones. In the thymus, the various lobules showed different quantities of donor-derived lymphoid cells. Mathematical analysis of these differences indicated that 17-18 cell division cycles occur in the cortex. In spleen, the distribution of donor-derived cells over the germinal centers indicated that 5 d after antigenic stimulation, germinal centers develop oligoclonally. The main conclusions of this work are that (a) bone marrow and thymus are highly polyclonal; (b) 17-18 divisions occur between prothymocyte and mature T cell; and (c) lymphoid cells disperse rapidly while proliferating and differentiating.