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

Trametinib Attenuates Delayed Rejection and Preserves Thymic Function in Rat Lung Transplantation

Delayed immunological rejection after human lung transplantation causes chronic lung allograft dysfunction, which is associated with high mortality. Delayed rejection may be attributable to indirect alloantigen presentation by host antigen-presenting cells; however, its pathophysiology is not fully understood. The mitogen-activated protein kinase pathway is activated in T cells upon stimulation, and we previously showed that the MEK inhibitor, trametinib, suppresses graft-versus-host disease after murine bone marrow transplantation. We investigated whether trametinib suppresses graft rejection after two types of rat lung transplantation and analyzed its immunological mode of action. Major histocompatibility complex-mismatched transplantation from brown Norway rats into Lewis rats and minor histocompatibility antigen-mismatched transplantation from Fischer 344 rats into Lewis rats were performed. Cyclosporine (CsA) and/or trametinib were administered alone or consecutively. Acute and delayed rejection, lymphocyte infiltration, and pulmonary function were evaluated. Administration of trametinib after CsA suppressed delayed rejection, reduced inflammatory cell infiltration and fibrosis within the graft, and preserved pulmonary functions at Day 28. Trametinib suppressed functional differentiation of T and B cells in the periphery but preserved thymic T cell differentiation. Donor B cells within the graft disappeared by Day 14, indicating that delayed graft rejection at Day 28 was mainly due to indirect presentation by host antigen-presenting cells. Finally, trametinib administration without CsA preconditioning suppressed rejection after minor histocompatibility antigen-mismatched transplantation. Trametinib attenuates delayed rejection upon major histocompatibility complex-mismatched transplantation by suppressing indirect presentation and is a promising candidate to treat chronic lung allograft dysfunction in humans.

Significantly enhanced lung metastasis and reduced organ NK cell functions in diet-induced obese rats

BACKGROUND

Obesity was identified as a major risk factor for malignant diseases, but underlying mechanisms remain unclear. Natural killer (NK) cells, a pivotal aspect of innate immunity, are capable of identifying and killing virally infected and tumor cells. Previous studies have shown altered NK cell functions in obesity, and the current study aimed to investigate the relationship between altered NK cell functions and increased cancer risk in obesity.

METHODS

To induce obesity male F344-rats received a high-fat diet (34% fat) or a control diet (4% fat). Thereafter, syngeneic mammary adenocarcinoma cells (MADB106) or a vehicle were intravenously (i.v.) injected. 15 min after injection, half of each group of rats were killed, lungs removed and immunohistochemically stained. Numbers of NK cells, MADB106 cells and NK cell-tumor cell interactions were quantified. Twenty-one days after tumor-cell injection the other half group of rats was killed and lung metastases were counted and relative mRNA concentrations of different NK cell receptors were determined.

RESULTS

After short-term MADB106-challenge, DIO fed animals showed significantly decreased NK cell numbers in the blood and NK cell-tumor cell interactions in the lung as compared to their control littermates. Twenty-one days after MADB106 injection, the lungs of the DIO fed rats showed significantly more lung metastases compared to control animals, accompanied by reduced relative mRNA concentrations of the activating NK cell receptor NKG2D.

CONCLUSIONS

We conclude that induction of obesity in F344-rats leads to reduced lung NK cell function against tumor cells and results in significantly enhanced lung metastasis as compared to lean animals. It can be hypothesized that obesity-induced altered NK cell functions play an important role in cancer growth and metastasis.

Innate immunity in cystic fibrosis lung disease

Chronic lung disease determines the morbidity and mortality of cystic fibrosis (CF) patients. The pulmonary immune response in CF is characterized by an early and non-resolving activation of the innate immune system, which is dysregulated at several levels. Here we provide a comprehensive overview of innate immunity in CF lung disease, involving (i) epithelial dysfunction, (ii) pathogen sensing, (iii) leukocyte recruitment, (iv) phagocyte impairment, (v) mechanisms linking innate and adaptive immunity and (iv) the potential clinical relevance. Dissecting the complex network of innate immune regulation and associated pro-inflammatory cascades in CF lung disease may pave the way for novel immune-targeted therapies in CF and other chronic infective lung diseases.

Malignant and non-malignant lung tissue areas are differentially populated by natural killer cells and regulatory T cells in non-small cell lung cancer

Even though the lung represents a special immune compartment with the capacity of a high inflammatory response, ineffective anti-tumour immunity is common in lung-associated malignancies. We asked whether a differential composition of the immune cell infiltrate in malignant (MLTAs) and non-malignant lung tissue areas (N-MLTAs) exists and might potentially contribute to this effect. We performed a comparative analysis of immune cells residing in MLTAs and N-MLTAs of non-small cell lung cancer (NSCLC) patients. To this end, we used immunophenotyping and functional analyses on directly isolated immune cells and tissue arrays on archived paraffin-embedded specimens. A strong T cell infiltration was prominent in both tissue compartments whereas CD4(+)CD25(+)CD127(-) T regulatory cells were present in MLTAs only. Nonetheless, concurrent functional ex vivo T cell analyses revealed no significant difference between T cells of MLTA and N-MLTA, suggesting that tumour-infiltrating T cells were not functionally impaired. Interestingly, T cell infiltration was less pronounced in specimens with a high neutrophilic infiltrate. NK cell infiltration was strikingly heterogenous between MLTA and N-MLTA. While NK cells were almost absent in the malignant tissue regions, non-malignant counterparts were selectively populated by NK cells and those NK cells showed strong cytotoxic activity ex vivo. We report that malignant and non-malignant tissue areas in NSCLC are selectively infiltrated by certain immune cell types with NK cells being displaced from the tumour tissue. These phenomena have important implications for tumour immunology of NSCLC and should be considered for the development of future immunologic intervention therapies.

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.

Natural killer cell-mediated rejection of experimental human lung cancer by genetic overexpression of major histocompatibility complex class I chain-related gene A

Studies have highlighted molecular and cell biological mechanisms of the NKG2D-NKG2D ligand system in the activation of natural killer (NK) cell and T cell functions. In this study we explore the potential of genetic overexpression of human major histocompatibility complex class I chain-related gene A (MICA), a powerful NKG2D ligand, for the induction of NK cell-mediated antitumor immunity in a humanized murine model of non-small cell lung cancer. Using tissue microarray technology we detected expression of MICA in only 30% of the samples from patients with lung cancer. Staining was always weak and focal, indicating that expression of MICA is detectable but limited in human lung cancer. Genetic overexpression of MICA by means of adenoviral transduction or transfection of expression plasmids was feasible in cell lines in vitro, primary human cancer tissue ex vivo, and in experimental human cancers in vivo. The presence of MICA on the surface of largely NK cell-resistant human lung cancer cells reestablished NK cell susceptibility and provoked NK cell-mediated antitumor immunity by murine and human NK cells in two different experimental therapy models. In this study we analyze the interaction of human NK cells with MICA-positive human cancer cells in an in vivo setting. Our data demonstrate that MICA overexpression can function as NK cell-mediated immunotherapy in experimental lung cancer.

Lymphocyte migration into different lung compartments during an antigen induced inflammation: is the spleen a major reservoir of these lymphocytes?

The hypothesis was tested whether lymphocytes of immunized and pulmonary challenged LEW rats adhere in higher numbers to the lung vascular bed than control lymphocytes and whether these immigrating cells come from the spleen. The kinetic of a primary immune response to sheep red blood cells (SRBC) was characterized in different lung compartments such as the vascular marginal pool, the interstitium and the bronchoalveolar space. The adherence of genetically labeled splenocytes from SRBC-immunized and challenged rats and from non-challenged rats was investigated in challenged lungs using the ex vivo system of the isolated buffer-perfused lung (IPL). Furthermore, immunized animals were splenectomized and challenged with SRBC. It was found that lymphocytes were increased with a maximum in the lung interstitium on day 3 and in the bronchoalveolar lavage fluid (BALF) on day 4. The adhesion to the pulmonary vascular endothelium of splenic T cells from SRBC-immunized rats in the IPL was not significantly increased compared to those from control animals. A significant transmigration from the vasculature into the BALF was not found. On day 4 after challenge the cell numbers in the lung compartments of the splenectomized animals were comparable to controls. The spleen alone has no significant role as a source of lymphocytes in lung inflammation. Therefore, the pulmonary immune response seems to be triggered mainly by the local environment and not by the accompanying systemic immune reaction.

Intratracheal macrophage-activating lipopeptide-2 reduces metastasis in the rat lung

Primary surgery of tumors bears the risk of metastasis to organs such as the lungs. In order to prevent such metastatic processes, in the present study, local intratracheal instillation of macrophage-activating lipopeptide-2 (MALP-2) as a bacterial-derived immunomodulator of cellular host defense responses was performed, and the effects on tumor cell clearance as well as tumor colonization were investigated in the lungs of Fischer 344 (F344) rats. Compared with vehicle controls, local administration of MALP-2 parallel to intravenous inoculation of MADB106 mammary adenocarcinoma tumor cells resulted in a significant reduction of lung colony numbers, whereas MALP-2 application 1 or 3 d afterwards was not effective. Quantification of leukocyte subsets in the lung tissue by immunohistochemistry revealed a significant increase of the number of monocytes in situ, as well as an increased co-localization of Natural Killer (NK) cells with tumor cells. Synthetic MALP-2 is easily available, with virtually no limitation to the amount of compound, and easily applicable by inhalation. Therefore, as local immunostimulative effects of the bacterial antigen MALP-2 have successfully been demonstrated, its use as an immunotherapeutic agent is worth further investigation.

Cloning and molecular characterization of the rat CB2 cannabinoid receptor

The rat peripheral cannabinoid receptor (rCB2) was cloned from a Sprague-Dawley rat spleen cDNA library and when translated, encodes a protein of 410 amino acids. Alignment of rCB2 with mouse (mCB2) and human (hCB2) peripheral cannabinoid receptors reveals a high degree of homology except in the carboxy terminus where rCB2 is 50 and 63 residues longer than hCB2 and mCB2, respectively. PCR screening and sequencing of rat genomic DNA showed that rCB2 is encoded by three exons interrupted by two introns, one of which is polymorphic and contains a 209 base pair B2 (SINE) element. By Northern hybridization and ribonuclease protection assay (RPA), rCB2 mRNA was detected in rat spleen, testis, thymus and lung but not in rat brain, heart, kidney or liver. Like hCB2 and mCB2 receptors, rCB2 activates mitogen-activated protein kinase when it is stably expressed in Chinese Hamster Ovary (CHO) cells. The importance of the carboxy terminus in regulating CB2 receptor desensitization and internalization is well-established. Thus, the profound differences identified in this region of the CB2 receptor between species mandates caution when extrapolating experimental results from non-human models to the effects of chronic CB2 receptor stimulation in humans.

Kinetics of the early recruitment of leukocyte subsets at the sites of tumor cells in the lungs: natural killer (NK) cells rapidly attract monocytes but not lymphocytes in the surveillance of micrometastasis

Early host defense mechanisms play a critical role for the outcome of metastatic disease but most of the initial steps of such responses against tumor cells are still unknown. Here, the specificity and kinetics of leukocyte subsets in response to intravenous inoculation of vital dye labeled Fischer 344 rat syngeneic MADB106 tumor cells were monitored in lungs in situ by immunohistochemistry and image analysis over a time-period of 6 hr. In comparison with sham injections, tumor cell inoculation induces a dynamic sequence of rapidly increasing granulocyte (+40% at 5 min), NK and T cell (+60% at 15 min) as well as monocyte (+100% at 30 min) numbers in lung tissue. Already within the first minutes frequent colocalizations of granulocytes and NK cells with tumor targets were found in situ. Within the first hour NK cells selectively kill tumor targets, because depletion of NK cells in vivo drastically increases both the number of MADB106 cells retained in lungs and the emerging numbers of lung tumor colonies. In addition, the tumor-cell-induced increase of monocytes strictly depends on the presence of NK cells because NK-depletion completely abrogates the time specific response of monocytes. Under NK depleted conditions the tumor-induced recruitment of CD4(+) T cells is more pronounced suggesting a compensatory mechanism. In contrast, B cell numbers progressively decrease within hours after cell inoculation. These findings demonstrate that NK and T cells mediate the initial steps in the surveillance of lung metastasis. NK cells rapidly kill tumor cells and subsequently recruit monocytes in vivo.

Lymphocytes in the bronchoalveolar space reenter the lung tissue by means of the alveolar epithelium, migrate to regional lymph nodes, and subsequently rejoin the systemic immune system

Lymphocytes in the bronchoalveolar space are routinely obtained and examined in lung diseases such as asthma or sarcoidosis. In a pig model, labeled lymphocytes were found in regional lymph nodes after intrabronchial instillation, indicating that reentry of lymphocytes from the bronchoalveolar space into the body is possible. In the present study, the route and kinetics of the reentry of bronchoalveolar lymphocytes were investigated in a congenic rat model using immunohistochemistry on cryostat and semithin sections and confocal laser scanning microscopy. As early as 15 min after intratracheal instillation lymphocytes were found to leave the bronchoalveolar space by transmigration through alveolar but not bronchial epithelium and were observed in interstitial alveolar tissue. At 6 hr after intratracheal instillation, T and B lymphocytes appeared in the draining lymph nodes of the lung with an increase after 24 and 48 hr. The kinetic pattern clearly differed in nondraining lymph nodes and other organs. After 6 hr, only single cells were found in nondraining lymph nodes, spleen, and blood with a slight increase after 24 hr, and only occasionally were single cells seen in the liver, thymus, or Peyer's patches 24 and 48 hr after instillation. In conclusion, T and B lymphocytes can leave the alveolar space by reentry into the lung tissue through alveolar epithelium. They reach regional lymph nodes by means of lymphatic vessels and are then distributed all over the body to rejoin the systemic immune system. Coming into contact with environmental antigens, these lymphocytes could perform an important function in the lung immune system and might be a target for inhalative therapy.

Naive and memory T cells migrate in comparable numbers through the normal rat lung: only effector T cells accumulate and proliferate in the lamina propria of the bronchi

T cells reach the lung via the pulmonary and bronchial arteries that supply the alveolar and bronchial regions. Although these regions are differentially affected by T cell-mediated diseases, the migration of T-cell subsets in these two regions has not been studied. Naive, memory, and effector T cells were injected into congenic rats and traced in sections of normal lung. All three T-cell subsets were found in large numbers in the alveolar region and exited again quickly. Only effector T cells accumulated in the lamina propria of the bronchi. Further, 72 h after injection 6% of the effector T cells still proliferated in the lung, whereas apoptotic effector T cells were only observed 1 h after injection (0.2%). Thus, not only effector and memory but also naive T cells continuously migrated through the lung. The preferential accumulation of effector T cells in the bronchial lamina propria may explain why some diseases preferentially affect the bronchial region.

Local proliferation contributes to lymphocyte numbers in normal lungs

Lymphocytes in the bronchoalveolar lavage fluid (BAL) are increased in many lung diseases, which might be an indicator for protective reactions or pathology. Higher lymphocyte numbers at distinct organ sites may be due to a number of reasons such as increased entry, increased proliferation, reduced apoptosis or reduced exit. It is not known whether lymphocyte numbers are influenced by local proliferation in the healthy lung. Therefore, the proliferation of lymphocytes was studied in vivo in different lung compartments of healthy rats: the marginal vascular pool, the interstitial pool and the bronchoalveolar pool. Bromodeoxyuridine (BrdU) was used as an S-phase proliferation marker. The cells were obtained 1 h and 24 h after i.v. injection of BrdU. The labeled cells and their phenotypes were determined by immunocytochemistry, since it was not possible to use flow cytometry because of the low numbers. In the lung compartments 0.7-1.5% of all nucleated cells were found to be BrdU+, whereas 24 h later this increased to 3.2-5.7%. The frequency of BrdU+ T cells was significantly higher in the lung compartments compared to the blood, with the maximum in the marginal vascular pool. Local proliferation of lymphocytes involved mainly CD8+ T cells. Thus, local proliferation plays a role in the number and composition of lymphocytes in the healthy normal lung.

Blockade of leucocyte function-associated antigen-1 (LFA-1) decreases lymphocyte trapping in the normal pulmonary vasculature: studies in the isolated buffer-perfused rat lung

Adhesion molecules regulate the migration of lymphocytes in lymphoid and non-lymphoid organs. In the lung, little is known about lymphocyte sticking and migration through the pulmonary vascular endothelium in physiological or pathological situations. Therefore the isolated buffer-perfused rat lung was used to investigate the mobilization of lymphocytes out of the normal lung into the venous effluent and to the bronchoalveolar space. The lymphocyte subset composition was characterized in the venous effluent, the lung tissue and the bronchoalveolar lavage (BAL) using immunocytology. Lymphocytes continuously left the normal lung at a total of 5.0 +/- 0.7 x 106 cells within the first hour of perfusion. The injection of 200 x 106 lymphocytes via the pulmonary trunk increased the venous release of lymphocytes by 170%. To investigate the effect of LFA-1 and CD44 on the adhesion of lymphocytes to the pulmonary endothelium, lymphocytes preincubated with an anti-LFA-1 MoAb, which blocks the interaction of LFA-1 and intercellular adhesion molecule-1 (ICAM-1), or lymphocytes preincubated with an anti-CD44 MoAb, were injected. The injection of LFA-1-blocked lymphocytes led to an increase by 70% of injected cells recovered in the perfusate within the first hour, whereas anti-CD44 treatment of injected lymphocytes had no effect. The LFA-1-blocked lymphocytes showed higher numbers of T and B cells in the effluent. Thus, the present experiments demonstrate that LFA-1 influences the trapping of lymphocytes in the vasculature of the healthy rat lung.

Stereological quantification of carboxyfluorescein-labeled rat lung metastasis: a new method for the assessment of natural killer cell activity and tumor adhesion in vivo and in situ

The function of natural killer (NK) cells is often studied by assessing in vitro levels of NK cell mediated lysis of target cells, or by assessing in vivo levels of lung tumor cell retention or metastatic colonization of intravenously injected tumor cells. However, these methods do not permit direct quantification and visualization of NK cells and their targets in vivo and in situ. Here, a new approach is described to visualize effector-to-target interactions as well as to estimate total numbers of targets in the lung, in vivo and in situ. MADB106 tumor cells were vitally labeled using carboxyfluorescein (CFSE) and intravenously (i.v.) injected into Fischer 344 rats (10(6) cells/rat). This mammary adenocarcinoma derived cell line is syngeneic to the inbred Fischer 344 rat and highly sensitive to NK cell activity in vivo. Effector-to-target interactions were visualized by immunostaining. Using the optical fractionator method, total numbers of CFSE-labeled MADB106 tumor cells were estimated in the left lung of the animals 5 min after tumor inoculation. To further demonstrate the usefulness of this approach in reflecting in vivo processes, rats were inoculated with MADB106 cells and simultaneously with a single i.v. bolus of either 1 microg/kg adrenaline or saline. Both lungs were removed 5 min later. Adrenaline caused a significant 80% reduction in the total number of lung CFSE-labeled MADB106 tumor cells, suggesting a rapid modulation of metastasis by stress hormones. This new approach facilitates the monitoring of effector-to-target interactions and the quantification of immune cell function or tumor adhesion in vivo and in situ.