Veronika Grau

Accumulating monocytes in the vasculature of rat renal allografts: phenotype, cytokine, inducible no synthase, and tissue factor mRNA expression.

Background. Necrotic patches and hemorrhagic lesions develop in the renal tissue between day 4 and day 5 after transplantation of fully allogeneic DA rat kidneys to LEW recipients.These lesions are at least in part due to destruction and obstruction of blood vessels. Damage of graft endothelial cells and blood coagulation are likely to be mediated by intravascular graft leukocytes. However, this cell population has not been thoroughly characterized before. Methods. We perfused untreated control kidneys, renal isografts, and allografts on day 4 after transplantation with phosphate-buffered saline/ethylenediaminetetraacetic acid to harvest leukocytes from both the blood stream as well as from the marginal intravascular pool. The mRNA expression of typical products of activated monocytes was analyzed in reverse-transcriptase polymerase chain reaction experiments. Graft monocytes were purified and their immunophenotype was investigated by flow cytometry. Results. Allograft rejection led to a 10-fold increase in the number of intravascular graft leukocytes compared to isografts. A mean number of about 100×106 leukocytes was harvested from a single allogeneic kidney, about 73% of these cells were monocytes and most of them displayed an activated phenotype. Compared to isografts, intravascular allograft leukocytes displayed an increased expression of tumor necrosis factor-&agr;, inducible NO synthase and tissue factor. Conclusions. Our study shows that large numbers of activated monocytes accumulate inside allograft vessels. As they express genes the products of which might damage the allograft by inducing cell death or thrombosis, we speculate that they directly participate in allograft destruction.

Monocytes in the rat: Phenotype and function during acute allograft rejection

Summary: Cells of the monocyte/macrophage system originate from the bone marrow, reach the organs via the blood, immigrate through post‐capillary venules and further differentiate into organ‐specific tissue macrophages. In rats and other species, activated monocytes/macrophages aggravate autoimmune reactions, rejection of non‐vascularized allografts and chronic allograft rejection. It is very likely that they also contribute to acute allograft destruction. So far it has been impossible to distinguish the function of monocytes from that of macrophages, because cell phenotypes and their alterations upon activation are ill‐defined. We have thus begun to characterize the ex vivo phenotype and function of rat monocytes in the normal state and during renal allograft rejection. Monocytes are recovered from both the central and the marginal blood pool by perfusing either the recipients circulation or the allograft vasculature. Rat monocytes have a unique surface phenotype. During allograft rejection or after infusion of interferon‐γ they up‐regulate class II MHC molecules, CD161 (NKR‐P1A), CD62L and CD8, while CD4 and CD43 are down‐modulated. Activated perfusate monocytes exert increased in vitro cytotoxicity against tumour targets, which differs from that of NK cells. We speculate that activated monocytes contribute to kidney allograft destruction by directly damaging endothelial cells or by promoting intravascular coagulation.

Rat monocytes up-regulate NKR-P1A and down-modulate CD4 and CD43 during activation in vivo: monocyte subpopulations in normal and IFN-gamma-treated rats.

LEW rats were treated intravenously with recombinant rat interferon‐γ (IFN‐γ) for 3 days to achieve intravascular accumulation, proliferation, and activation of monocytes. Monocytes, defined by their expression of the ED1, ED9, and Ox41 antigens, were recovered from the vasculature by perfusion with PBS/EDTA, subsequently depleted of erythrocytes and granulocytes by Percoll density gradient centrifugation, and analyzed by flow cytometry and immunocytology. In untreated and control‐infused specified pathogen‐free (SPF) rats, lymphocytes and monocytes formed overlapping cell populations with respect to size and internal granularity. At least two intravascular monocyte subsets, probably central and marginating cells, were distinguished by their size and differential expression of CD43, CD4, CD11a, CD18, and L‐selectin. It is interesting to note that a fraction of the monocytes in normal and control‐infused animals carried the NKR‐P1A molecule. IFN‐γ treatment provoked a duplication of monocyte size and granularity. Both the number of positive monocytes and the level of expression of NKR‐P1A strongly increased after IFN‐γ infusion, whereas CD43 (leukosialin) and CD4 were impressively down‐regulated. NKR‐P1A+ L‐selectin+CD43low CD4‐ monocytes also occur in the vasculature of rats during immune reactions in vivo. We speculate that these cells are involved in organ damage and that their number is controlled by activation‐induced cell death within the vessels. J. Leukoc. Biol. 62: 741–752; 1997.

IL-24 is Expressed by Rat and Human Macrophages

Recently, a number of interleukin-10 (IL-10) homologues, among them IL-24 formerly known as melanocyte differentiation factor-7 (mda-7), has been described. Since IL-10 is released by macrophages and plays an important role in the resolution of inflammatory processes, we hypothesized that IL-24 might also be expressed in cells of the monocyte/macrophage lineage. We analyzed IL-24 expression on the mRNA and protein level in stimulated rat and human macrophages. In rat alveolar macrophages and NR8383 cells, IL-24 mRNA induction was observed following stimulation with LPS and IL-4 whereas TNF-alpha failed. Intracellular IL-24 protein was detected in unstimulated and IL-4 stimulated NR8383 cells. Also human blood monocytes showed a strong up-regulation of IL-24 mRNA following preparation which was enhanced by LPS and lowered by IL-10. Furthermore, infection of human monocytes with influenza A virus A/PR/8 caused an induction of IL-24 mRNA expression. In conclusion, our data show that IL-24 expression is induced in stimulated and infected rat and human macrophages, however, more insights into the functions of IL-24 are necessary to define its physiological relevance.

Monocytes in the rat.

We review our methods for definition and phenotypical characterisation of normal and activated rat monocytes. To obtain a comprehensive sample of all blood monocytes including cells from the marginal pool of the blood stream, we extensively perfuse the extrapulmonary circulation with cold PBS/EDTA. Normal rat monocytes are isolated from untreated specified pathogen-free male LEW rats. In vivo activated monocytes are investigated after three days of infusion of recombinant IFN-gamma or during acute renal allograft rejection. Rat monocytes are defined by reactivity with mAbs ED1 and ED9, detecting a lysosomal membrane antigen and a member of the signal-regulatory protein family, respectively, as well as by expression of CD11b. Concomitantly rat monocytes are characterized by the absence of CD5, the absence of the B cell form of CD45R, and the absence of reactivity with mAb RP-1. The majority of the monocytes from untreated LEW rats are CD4+, CD11a(high), CD18high, CD43high, CD62-L-, CD161-, and MHC class II-. Upon stimulation of the immune system in vivo, a second monocyte population increases in number. These cells have a larger diameter and an increased granularity. They are CD4-, CD11a(int), CD18int, CD43low, CD62-L+, CD161int, and MHC class II+. Although some reagents are not yet available (e.g. antibodies against rat CD14 and CD16), rat monocytes can be defined and their state of activation can be characterized. The functionally important population of monocytes, which have already marginated, is accessible by perfusion and relatively high monocyte numbers are isolated per rat. As specified pathogen-free rats are available and numerous experimental systems involving acute or chronic inflammation have been established in rats, differentially activated monocytes may be investigated. The rat is thus a suitable experimental animal for basic research on monocytes.

Transplantation of both kidneys from one donor rat

We have developed a technique for harvesting and transplanting two kidneys from one donor rat. Our method involves end-to-end anastomosis of the renal artery and the renal vein. Because of the short distance between the caudal vena cava and the right kidney, renal transplantation is not feasible on the right side of the recipient. The right donor kidney was therefore transplanted to the left side. Graft morphology was assessed on paraffin sections. We observed no differences between conventionally transplanted kidneys (n = 116) and right kidneys transplanted according to the method described (n = 40). In conclusion, our technique is simple, saves time and reduces the number of donor rats.

Long Term iNOS Expression in Thoracic Lymph Nodes of Silicotic Rats

Beside the lung, thoracic lymph nodes are most affected during silicosis. The mechanisms leading to enlargement of the lymph nodes and partial activation of lymph node cells are still unclear. The present study demonstrates an increase in iNOS mRNA expression in the lung draining lymph nodes of rats at 1, 2, and 8 months following silica exposure. Histopathological analysis revealed that iNOS protein was exclusively expressed by macrophages located within the granulomatous areas of the enlarged lymph nodes. In contrast, no differences in mRNA expression and number of iNOS-positive cells were found in the lungs of silica-exposed and non-exposed rats. In vitro experiments showed that silica particles alone did not induce NO release in primary alveolar macrophages (AMs) or the alveolar macrophage cell line NR8383. However, the addition of interferon (IFN)-gamma led to a significant nitric oxide production by primary AMs. NR8383 cells responded only when a combination of IFN-gamma and silica particles was applied. These results indicate that the macrophage activator IFN-gamma, which has already been shown to be expressed at elevated levels by lymphocytes of the silicotic lymph nodes, may be responsible for the long-lasting iNOS expression in thoracic lymph nodes. Our observations support the hypothesis that the mutual activation of lymphocytes and macrophages is a central process in the development of chronic silicosis.

Induction of epidermal fatty acid binding protein in intravascular monocytes of renal allografts1

During acute rejection of rat renal allografts, numerous activated monocytes accumulate in the vasculature of the graft. These monocytes seem to be involved in allograft destruction. Proinflammatory and effector functions of monocytes and macrophages can be down-regulated by peroxisome proliferators, which are probably transported in the cytoplasm by fatty acid binding proteins (FABPs). We performed renal transplantation in rats in the Dark Agouti-to-Lewis strain combination. Intravascular graft leukocytes were harvested 4 days posttransplantation. Epidermal (E)-FABP mRNA and protein expression were investigated by reverse-transcriptase polymerase chain reaction and immunoblotting, respectively. E-FABP-expressing cells were identified by immunofluorescence. After allogeneic transplantation, intravascular graft leukocytes expressed E-FABP mRNA and protein. In isografts, significantly lower expression levels were observed. E-FABP protein was detected in monocytes expressing ED1 and in &agr;&bgr;-T-cell receptor positive T lymphocytes. E-FABP might regulate monocyte activation and may represent a promising target for a therapeutic intervention in allograft rejection.

Cytotoxicity of normal and activated rat monocytes analyzed by flow cytometry.

The cytotoxic potential of activated monocytes might play an important role during severe systemic immune reactions and thus needs further elucidation. As established cytotoxicity tests are not suitable for this purpose, we developed a flow cytometry–based method.

Time course of chemokine expression in acutely rejecting rat kidneys

DURING acute rejection of rat renal allografts, the kidneys are heavily infiltrated by macrophages and T lymphocytes. Other leukocytes are quantitatively less important. Allograft infiltration is visible in perivascular regions on the first day posttransplantation, spreads to the renal interstitium and reaches its maximum on day 4. The number of allograft macrophages remains stable on days 5 to 6 after transplantation, and the number of T lymphocytes decreases during this time. The mechanisms leading to graft infiltration are not fully understood. Chemokines, a family of chemotactic cytokines, are probably involved.