Macrophages in experimental rat lung isografts and allografts: infiltration and proliferation in situ

Function of alveolar macrophages in lung cancer microenvironment

BACKGROUND

Cancer tissues contain a wide variety of immune cells that play critical roles in suppressing or promoting tumor progression. Macrophages are one of the most predominant populations in the tumor microenvironment and are composed of two classes: infiltrating macrophages from the bone marrow and tissue-resident macrophages (TRMs). This review aimed to outline the function of TRMs in the tumor microenvironment, focusing on lung cancer.

REVIEW

Although the functions of infiltrating macrophages and tumor-associated macrophages have been intensively analyzed, a comprehensive understanding of TRM function in cancer is relatively insufficient because it differs depending on the tissue and organ. Alveolar macrophages (AMs), one of the most important TRMs in the lungs, are replenished in situ, independent of hematopoietic stem cells in the bone marrow, and are abundant in lung cancer tissue. Recently, we reported that AMs support cancer cell proliferation and contribute to unfavorable outcomes.

CONCLUSION

In this review, we introduce the functions of AMs in lung cancer and their underlying molecular mechanisms. A thorough understanding of the functions of AMs in lung cancer will lead to improved treatment outcomes.

Disulfiram, an Anti-alcoholic Drug, Targets Macrophages and Attenuates Acute Rejection in Rat Lung Allografts

Macrophages contribute to post-transplant lung rejection. Disulfiram (DSF), an anti-alcoholic drug, has an anti-inflammatory effect and regulates macrophage chemotactic activity. Here, we investigated DSF efficacy in suppressing acute rejection post-lung transplantation. Male Lewis rats (280-300 g) received orthotopic left lung transplants from Fisher 344 rats (minor histocompatibility antigen-mismatched transplantation). DSF (0.75 mg/h) monotherapy or co-solvent only (50% hydroxypropyl-β-cyclodextrin) as control was subcutaneously administered for 7 days (n = 10/group). No post-transplant immunosuppressant was administered. Grades of acute rejection, infiltration of immune cells positive for CD68, CD3, or CD79a, and gene expression of monocyte chemoattractant protein and pro-inflammatory cytokines in the grafts were assessed 7 days post-transplantation. The DSF-treated group had significantly milder lymphocytic bronchiolitis than the control group. The infiltration levels of CD68+ or CD3+ cells to the peribronchial area were significantly lower in the DSF than in the control groups. The normalized expression of chemokine ligand 2 and interleukin-6 mRNA in allografts was lower in the DSF than in the control groups. Validation assay revealed interleukin-6 expression to be significantly lower in the DSF than in the control groups. DSF can alleviate acute rejection post-lung transplantation by reducing macrophage accumulation around peripheral bronchi and suppressing pro-inflammatory cytokine expression.

Activation of Humoral Immunity during the Pathogenesis of Experimental Chronic Lung Allograft Dysfunction

Alloreactive and autoreactive antibodies have been associated with the development of chronic lung allograft dysfunction (CLAD), but their pathogenic role is disputed. Orthotopic left lung transplantation was performed in the Fischer-344 to Lewis rat strain combination followed by the application of ciclosporine for 10 days. Four weeks after transplantation, lipopolysaccharide (LPS) was instilled into the trachea. Lungs were harvested before (postoperative day 28) and after LPS application (postoperative days 29, 33, 40, and 90) for histopathological, immunohistochemical, and Western blot analyses. Recipient serum was collected to investigate circulating antibodies. Lung allografts were more strongly infiltrated by B cells and deposits of immunoglobulin G and M were more prominent in allografts compared to right native lungs or isografts and increased in response to LPS instillation. LPS induced the secretion of autoreactive antibodies into the circulation of allograft and isograft recipients, while alloreactive antibodies were only rarely detected. Infiltration of B cells and accumulation of immunoglobulin, which is observed in allografts treated with LPS but not isografts or native lungs, might contribute to the pathogenesis of experimental CLAD. However, the LPS-induced appearance of circulating autoreactive antibodies does not seem to be related to CLAD, because it is observed in both, isograft and allograft recipients.

Ectopic expression of recipient CD47 inhibits mouse macrophage-mediated immune rejection against human stem cell transplants

Like conventional transplants, immunosuppression is required to facilitate survival and function of human embryonic stem cell (hESC) derivatives after implantation into xenogeneic recipients. We have previously reported that T cells alone are sufficient to reject allogeneic murine ESC derivatives; and strategies that inhibit T-cell activation, including coreceptor and costimulation blockade, prevent hESC derivatives from being rejected. This study aimed to investigate, in addition to T cells, whether macrophages contribute to transplant rejection of hESC xenografts with nonobese diabetic (NOD)/SCID mice that lack functional T and B cells but have macrophages. We show that acute rejection against hESC-derived endothelial cells (hESC-ECs) was mediated, to some degree, by infiltrating macrophages that phagocytosed them. Transgenic expression of murine CD47 on cell surface of hESC-ECs mitigates macrophage-mediated phagocytosis and improves their survival after transplantation. Our results highlight that innate immune cells, such as macrophages, can reject hESC derivatives, raising concern against the use of NOD/SCID as transplant recipients for testing in vivo function of hESC-derived tissues. Augmenting CD47 signaling promotes survival and function of hESC derivatives after xenogeneic transplantation.-Leung, C. S., Li, J., Xu, F., Wong, A. S. L., Lui, K. O. Ectopic expression of recipient CD47 inhibits mouse macrophage-mediated immune rejection against human stem cell transplants.

Non-neuronal neuropeptide Y and its receptors during acute rejection of rat pulmonary allografts

This study tested the hypothesis that neuropeptide Y (NPY) and NPY receptors 1 (Y1) and 2 (Y2) participate in lung allograft rejection. Inflammation in grafts may include interaction between blood leukocytes and graft endothelial cells and marked accumulation of intravascular blood leukocytes. Fewer leukocytes accumulate in lung than in kidney allografts. Lung transplantion was performed in the Dark Agouti to Lewis rat strain combination. Intravascular and intraalveolar leukocytes were isolated from the grafts, and we evaluated the mRNA expression of NPY, Y1, and Y2 by real-time RT-PCR as well as the peptide expression of NPY by radioimmunoassay and immunohistochemistry. NPY and Y1 were expressed by pulmonary intravascular and intraalveolar leukocytes. Y1 was up-regulated by pulmonary intravascular and intraalveolar leukocytes during allograft rejection while Y2 could not be detected. Higher NPY expression levels in intravascular leukocytes were observed in lung compared to kidney allografts, which were investigated previously. Our findings suggest that an increased leukocytic expression of NPY in lung compared to kidney allografts results in a reduced accumulation of leukocytes in allograft vessels.

Macrophage adaptation in airway inflammatory resolution

Bacterial and viral infections (exacerbations) are particularly problematic in those with underlying respiratory disease, including post-viral infection, asthma, chronic obstructive pulmonary disease and pulmonary fibrosis. Patients experiencing exacerbations tend to be at the more severe end of the disease spectrum and are often difficult to treat. Most of the unmet medical need remains in this patient group. Airway macrophages are one of the first cell populations to encounter airborne pathogens and, in health, exist in a state of reduced responsiveness due to interactions with the respiratory epithelium and specific factors found in the airway lumen. Granulocyte-macrophage colony-stimulating factor, interleukin-10, transforming growth factor-β, surfactant proteins and signalling via the CD200 receptor, for example, all raise the threshold above which airway macrophages can be activated. We highlight that following severe respiratory inflammation, the airspace microenvironment does not automatically re-set to baseline and may leave airway macrophages more restrained than they were at the outset. This excessive restraint is mediated in part by the clearance of apoptotic cells and components of extracellular matrix. This implies that one strategy to combat respiratory exacerbations would be to retune airway macrophage responsiveness to allow earlier bacterial recognition.

The Metabolic Prospective and Redox Regulation of Macrophage Polarization

Macrophage plasticity is an important feature of these innate immune cells. Macrophage phenotypes are divided into two categories, the classically activated macrophages (CAM, M1 phenotype) and the alternatively activated macrophages (AAM, M2 phenotype). M1 macrophages are commonly associated with the generation of proinflammatory cytokines, whereas M2 macrophages are anti-inflammatory and often associated with tumor progression and fibrosis development. Macrophages produce high levels of reactive oxygen species (ROS). Recent evidence suggests ROS can potentially regulate macrophage phenotype. In addition, macrophages phenotypes are closely related to their metabolic patterns, particularly fatty acid/cholesterol metabolism. In this review, we briefly summarize recent advances in macrophage polarization with special attention to their relevance to specific disease conditions and metabolic regulation of polarization. Understanding these metabolic switches can facilitate the development of targeted therapies for various diseases.

The divergent roles of macrophages in solid organ transplantation

PURPOSE OF REVIEW

This review summarizes the phenotype and function of macrophages in the context of solid organ transplantation and will focus on fundamental insights into their paradoxical pro-inflammatory versus suppressive function. We will also discuss the therapeutic potential of regulatory macrophages in tolerance induction.

RECENT FINDINGS

Macrophages are emerging as an essential element of solid organ transplantation. Macrophages are involved in the pathogenesis of ischemia reperfusion injury, as well as both acute and chronic rejection, exacerbating injury through secretion of inflammatory effectors and by amplifying adaptive immune responses. Notably, not all responses associated with macrophages are deleterious to the graft, and graft protection can in fact be conferred by macrophages. This has been attributed to the presence of macrophages with tissue-repair capabilities, as well as the effects of regulatory macrophages.

SUMMARY

The explosion of new information on the role of macrophages in solid organ transplantation has opened up new avenues of research and the possibility of therapeutic intervention. However, the role of myeloid cells in graft rejection, resolution of rejection and tissue repair remains poorly understood. A better understanding of plasticity and regulation of monocyte polarization is vital for the development of new therapies for the treatment of acute and chronic transplant rejection.

Pulmonary delivery and tissue distribution of aerosolized antisense 2'-O-Methyl RNA containing nanoplexes in the isolated perfused and ventilated rat lung

Pulmonary delivery of drugs, particularly in the treatment of lung cancer, is an attractive strategy for future targeted therapy. In this context, inhalation of nanoplexes might offer a new mode for drug delivery in gene therapy. However, limited data are currently available demonstrating pulmonary delivery, cellular uptake as well as local tolerability in lung tissue. The aim of this study was to elucidate the pulmonary delivery, tissue distribution and local tolerability of aerosolized chitosan-coated poly(lactide-co-glycolide) based nanoplexes containing antisense 2'-O-Methyl RNA (OMR). Therefore, an aerosol of OMR-nanoplexes or OMR alone was administered intra-tracheally using the model of the isolated perfused and ventilated rat lung. Localization of OMR in rat lung tissue was examined by immunohistochemistry. Administration of the OMR-nanoplex formulation resulted in significantly higher cellular OMR uptake of the respiratory epithelium in contrast to the administration of OMR alone, indicating that drug administration via aerosolized nanoplexes is able to target lung tissue. No prominent changes in lung physiology parameters were observed following inhalation, suggesting good local tolerability of OMR-nanoplex formulation.

Treatment with keratinocyte growth factor does not improve lung allograft survival in the rat

PURPOSE

Lung allografts are threatened by primary graft dysfunction, infections, and rejection. Novel therapies protecting pulmonary allografts are badly needed. Keratinocyte growth factor (KGF) protects the lung against a variety of injurious stimuli and exerts anti-inflammatory effects. The aim of the study was to test the potential of recombinant truncated KGF (DeltaN23-KGF, palifermin) to attenuate pulmonary allograft rejection.

MATERIALS AND METHODS

Intratracheal instillation of 5 mg/kg DeltaN23-KGF was performed twice in donor rats on days 3 and 2 before explantation of the lung. In control animals, an equivalent volume of vehicle was instilled. Left lungs were transplanted in the fully allogeneic Dark Agouti to Lewis rat strain combination and in the less stringent Fischer 344 to Wistar Kyoto combination. Allograft recipients were additionally treated with DeltaN23-KGF post-transplantation. Graft outcome, leukocytic infiltration, and major histocompatibility complex (MHC) class II antigen expression was analyzed.

RESULTS

In both rat strain combinations, DeltaN23-KGF treatment did not improve pulmonary allograft outcome. Graft infiltration by macrophages and T lymphocytes remained unchanged. In addition, we demonstrated that MHC class II antigens were more abundant in KGF-treated allografts compared to control-treated grafts, which probably results in an increased alloreactivity.

CONCLUSION

In conclusion, intratracheal DeltaN23-KGF treatment is not effective to prevent acute pulmonary allograft rejection.

Acute rejection of experimental lung allografts: Characterization of intravascular mononuclear leukocytes

Leukocytes interacting with endothelia of lung allografts probably play a seminal role in acute rejection, but have not been characterized before. Transplantation was performed in the Lewis to Lewis and in the Dark Agouti to Lewis rat strain combinations. DNA replication was detected in T-cells on day 2 after pulse-labelling in vivo with 5-bromo-2'-deoxyuridine (BrdU). On day 5, leukocytes were isolated by intensive perfusion the graft, subject to flow cytometry and to quantitative RT-PCR. About 34 million leukocytes accumulated in allograft vessels, but only 10 and 6 million cells in isografts and control lungs, respectively. During rejection, IFN-gamma, IL-1beta and IL-10 mRNA expression increased, IL-12 mRNA decreased, whereas IL-2, IL-6, TNF-alpha, and TGF-beta mRNA did not change. The phenotype of graft monocytes was partially activated and intravascular T-cells proliferated. In conclusion, during rejection, monocytes with unusual properties accumulate and T-lymphocytes are activated in lung allograft blood vessels.

Immunohistochemical detection of nicotinic acetylcholine receptor subunits α9 and α10 in rat lung isografts and allografts

The success of clinical lung transplantation is poor in comparison to other solid organ transplants and novel therapeutic approaches are badly needed. In the view of the recent discovery of anti-inflammatory pathways mediated via nicotinic acetylcholine receptors, we investigated changes in this system in pulmonary isografts and allografts by immunohistochemistry. Lung transplantation was performed in the isogeneic Lewis to Lewis rat strain combination. For allogeneic transplantation Dark Agouti rats were used as donors. Nicotinic alpha9 and alpha10 acetylcholine receptor subunits were detected on alveolar macrophages as well as in the lung parenchyma of native and transplanted lungs. The expression of both receptor subunits was up-regulated in the parenchyma of day 4 allografts. These allografts were characterized by accumulations of alveolar macrophages strongly expressing the alpha9 and the alpha10 receptor subunit. Therapeutic application of nicotinic agonists might down-modulate pro-inflammatory functions of alveolar macrophages and protect pulmonary transplants.

Donor B cells in splenic follicles of experimental pulmonary allograft recipients

BACKGROUND

After transplantation, passenger leukocytes move to lymphoid organs of the recipient. These cells appear to initiate allograft rejection, but they also might be involved in tolerance induction.

MATERIALS AND METHODS

Orthotopic left lung transplantation was performed in the Dark Agouti to Lewis rat strain combination with no immunosuppression. Recipient spleens were removed at intervals of 24 h until day 6 after transplantation. For comparison, spleens from renal allograft recipients were analysed. Donor-derived major histocompatibility complex (MHC) class II antigens were detected by monoclonal antibody OX76. In double-staining experiments with antibodies specific for leukocyte subpopulations, their localisation and identity was analysed.

RESULTS

OX76-positive leukocytes were already detected in recipient spleens on day 1 post-transplantation. They increased in number until day 3 and decreased in number thereafter. Most of them were localised in splenic follicles and expressed the B cell variant of CD45R and IgG. Cell surface antigens typical for other leukocyte subpopulations were not detected. In the spleens of renal allograft recipients, only few donor-derived cells were seen.

CONCLUSION

After lung transplantation, numerous MHC class II-positive B cells migrate to the splenic follicles of the recipient. These cells might, in part, be responsible for immunologic differences observed between renal and pulmonary allografts.