Cytokine alteration and speculated immunological pathophysiology in silicosis and asbestos-related diseases

Inflammatory Alteration of Human T Cells Exposed Continuously to Asbestos

Asbestos is a known carcinogen and exposure can lead to lung cancer and malignant mesothelioma. To examine the effects of asbestos fibers on human immune cells, the human T cell leukemia/lymphoma virus (HTLV)-1 immortalized human T cell line MT-2 was employed. Following continuous exposure to asbestos fibers for more than eight months, MT-2 sublines showed acquisition of resistance to asbestos-induced apoptosis with decreased death signals and increased surviving signals. These sublines showed various characteristics that suggested a reduction in anti-tumor immunity. On the other hand, inflammatory changes such as expression of MMP7, CXCR5, CXCL13 and CD44 was found to be markedly higher in sublines continuously exposed to asbestos compared with original MT-2 cells. All of these molecules contribute to lung inflammation, T and B cell interactions and connections between mesothelial cells and T cells. Thus, further investigation focusing on these molecules may shed light on the role of chronic inflammation caused by asbestos exposure and the occurrence of malignant mesothelioma. Finally, regarding peripheral T cells from healthy donors (HD) and asbestos-exposed patients with pleural plaque (PP) or malignant pleural mesothelioma (MPM), following stimulation of CD4+ T cells, T cells from MPM patients showed reduced potential of interferon (IFN)-γ expression. Moreover, levels of interleukin (IL)-6, one of the most important cytokines in chronic inflammation, in cultured supernatants were higher in PP and MPM patients compared with HD. Overall, asbestos-induced chronic inflammation in the lung as well as the pleural cavity may facilitate the onset of asbestos-induced cancers due to alterations in the interactions among fibers, immune cells such as T and B cells and macrophages, and mesothelial and lung epithelial cells. Further investigations regarding chronic inflammation caused by asbestos fibers may assist in identifying molecular targets for preventive and therapeutic strategies related to the effects of asbestos exposure.

The proliferative effects of asbestos-exposed peripheral blood mononuclear cells on mesothelial cells

Malignant mesothelioma (MM) is thought to arise from the direct effect of asbestos on mesothelial cells. However, MM takes a long time to develop following exposure to asbestos, which suggests that the effects of asbestos are complex. The present study examined the effects of asbestos exposure on the cell growth of MeT-5A human mesothelial cells via cytokines produced by immune cells. Peripheral blood mononuclear cells (PBMCs) were stimulated with antibodies against cluster of differentiation (CD)3 and CD28 upon exposure to the asbestos chrysotile A (CA) or crocidolite (CR); the growth of MeT-5A cells in media supplemented with PBMC culture supernatants was subsequently examined. MeT-5A cells exhibited an increase in proliferation when grown in supernatant from the 7-day PBMC culture exposed to CA or CR. Analysis of cytokine production demonstrated increased levels of granulocyte colony-stimulating factor (G-CSF), granulocyte-macrophage colony-stimulating factor (GM-CSF), interleukin (IL)-1α, IL-1β, IL-3, IL-5, IL-13 and IL-17A in supernatants. Individual administration of these cytokines, excluding G-CSF and GM-CSF, led to an increase in cell growth of MeT-5A, whereas this effect was not observed following the combined administration of these cytokines. The results indicate that cytokines secreted by immune cells upon exposure to asbestos cause an increase in the growth activity of mesothelial cells, suggesting that alterations in the production of cytokines by immune cells may contribute to tumorigenesis in individuals exposed to asbestos.

Exposure to negatively charged-particle dominant air-conditions on human lymphocytes in vitro activates immunological responses

Indoor air-conditions may play an important role in human health. Investigation of house conditions that promote health revealed that negatively charged-particle dominant indoor air-conditions (NAC) induced immune stimulation. NAC was established using fine charcoal powder on walls and ceilings and utilizing forced negatively charged particles (approximate diameter: 20 nm) dominant in indoor air-conditions created by applying an electric voltage (72 V) between the backside of the walls and the ground. We reported previously that these conditions induced a slight and significant increase of interleukin-2 during 2.5 h stay, and an increase of natural killer (NK) cell cytotoxicity, when examining human subjects after a two-week night stay under these conditions. In the present study, we investigated whether exposure to NAC in vitro affects immune conditions. Although the concentrations of particles were different, an incubator for cell culture with NAC was set and cellular compositions and functions of various freshly isolated human lymphocytes derived from healthy donors were assayed in the NAC incubator and compared with those of cultures in a standard (STD) incubator. Results showed that NAC cultivation caused an increase of CD25 and PD-1 expressing cells in the CD4 positive fraction, enhancement of NK cell cytotoxicity, production of interferon-y (IFNγ), and slight enhancement of regulatory T cell function. In addition, the formula designated as the "immune-index" clearly differed between STD and NAC culture conditions. Thus, NAC conditions may promote human health through slight activation of the immune system against cancer cells and virus infection as shown by this in vitro study and our previously reported human studies.

Silica exposure and altered regulation of autoimmunity

Silica particles and asbestos fibers, which are known as typical causatives of pneumoconiosis, induce lung fibrosis. Moreover, silicosis patients often complicate with autoimmune diseases, and asbestos-exposed patients suffer from malignant diseases such as pleural mesothelioma and lung cancer. We have been conducting experimental studies to investigate altered regulation of self-tolerance caused by silica exposure, including analyses using specimens such as plasma and immunocompetent cells obtained from silicosis patients, as a means of examining the supposition that silica exposure induces molecular and cellular biological alterations of immune cells. These approaches have resulted in the detection of several specific autoantibodies, alterations of CD95/Fas and its related molecules, and evidence of chronic activation of responder T cells and regulatory T cells following silica exposure. In this review, we present details of our investigations as an introduction to scientific approaches examining the immunological effects of environmental and occupational substances.

Peritoneal mesothelioma: current status and future directions

Peritoneal mesothelioma is a rare malignancy where life expectancy with systemic chemotherapy remains poor. Most patients with this disease are diagnosed late with extensive peritoneal disease burden leading to nausea, pain, and abdominal distention as a result of ascites and a partial bowel obstruction. A newly proposed staging system comprising elements of the tumor burden measured by the peritoneal cancer index, abdominal nodal status, and extra-abdominal metastases has been demonstrated to reliably stratify patient outcomes based on staging subgroups after cytoreductive surgery and hyperthermic intraperitoneal chemotherapy. This new staging system may form the basis of selecting patients for radical surgery and improve survival outcomes.

[Regarding the special feature of "the frontline of nanoparticle research": progress of the Study Group on Fibrous and Particulate Substances (SGFPS)]

Among the symposia organized by various study groups in the Japanese Society of Hygiene (JSH), the Study Group on Fibrous and Particulate Substances (SGFPS) presented a symposium entitled "The frontline of nanoparticle research" chaired by Professor Takemi Otsuki (Kawasaki Medical School, Japan) and Dr. Seishiro Hirano (National Institute for Environmental Studies, Japan) on 26 March, 2012, as a part of the program of the 82nd Annual Meeting of JSH in Kyoto, Japan. Special features consist of three presentations given at the above-mentioned symposium. In this article, we introduce the progress of the Study Group on Fibrous and Particulate Substances (SGFPS) from the initial symposium entitled "Asbestos: Science and Society" held at the 76th Annual Meeting of JSH at Ube, Japan to the last above-mentioned symposium in Kyoto. The health-related issues caused by exposure to fibrous materials such as asbestos and also particulated substances such as nanoparticles will be lasting in the future and researchers including our study group have to make their best efforts to resolve these problems and to reduce health impairments due to exposure to environmental fibrous and particulated substances.

Resistance to asbestos-induced apoptosis with continuous exposure to crocidolite on a human T cell

We have been investigating the immunological effects of asbestos. The establishment of a low-dose and continuously exposed human T cell line, HTLV-1 immortalized MT-2, to chrysotile (CB) revealed reduction of CXCR3 chemokine receptor and production of IFN-γ that caused a decline of tumor immunity. These effects were coupled with upregulation of IL-10, TGF-β, and BCL-2 in asbestos-exposed patients. To observe the immunological effects of crocidolite (CR) on human T cells, a trial to establish a low-dose and continuously exposed model was conducted and compared with a previously reported CB-exposed model (MT-2CB). Transient exposure of MT-2 original cells to CB or CR induced a similar level of apoptosis and growth inhibition. The establishment of a continuously exposed subline to CR (MT-2CR) revealed resistance against CR-induced apoptosis and upregulation of the BCL-2/BAX ratio similar to that recorded for MT-2CB. Both sublines showed reduced production of IFN-γ, TNF-α, and IL-6 with increased IL-10. cDNA microarray with network/pathway analyses focusing on transcription factors revealed that many similar factors related to cell proliferation were involved following continuous exposure to asbestos in both MT-2CB and MT-2CR. These results indicate that both CB and CR fibers affect human T cells with similar degrees even though the carcinogenic activity of these substances differs due to their chemical and physical forms. Trials to identify early detection markers for asbestos exposure or the occurrence of asbestos-inducing malignancies using these findings may lead to the development of clinical tools for asbestos-related diseases and chemoprevention that modifies the reduced tumor immunity.

Increased frequency of circulating invariant natural killer T cells in malignant pleural mesothelioma patients

Invariant natural killer T (iNKT) cells are a distinct subset of human T cells, which expresses an invariant T cell receptor Vα24 Jα18 and recognizes glycolipid antigens in the context of CD1d molecules. iNKT cells exert pivotal regulatory roles in many immune responses, including antitumor immune responses. Alterations in iNKT cell frequency, phenotype, and activation state have been reported in cancer patients. No data are available on the iNKT cells in malignant pleural mesothelioma (MPM), a rare, but very aggressive, malignancy of the pleura with a very poor prognosis. Here, we studied the frequency, phenotype, and cytokine profile of circulating iNKT cells in MPM patients, and correlated results with tumor histological types (epithelioid, sarcomatoid, biphasic) and clinical stages (I-III). We found that the iNKT cell frequency was significantly increased in MPM patients with epithelioid and sarcomatoid types in comparison with healthy volunteers (HV); only three biphasic mesotheliomas were available in this study, thus no conclusions can be drawn for this MPM type. The increased frequency significantly correlates with the clinical stage of tumor with the highest value at the stage III in both epithelioid and sarcomatoid subtypes. According to the histological types, we measured changes in the frequencies of CD4⁺ CD8⁺ (DP) and CD4⁻CD8⁻ (DN), but not in the cytokine profiles (IFN-γ/IL-4 expression). These results demonstrate that the frequency of iNKT cells is increased in MPM patients and that this increase correlates with MPM type and stage.

Asbestos-induced cellular and molecular alteration of immunocompetent cells and their relationship with chronic inflammation and carcinogenesis

Asbestos causes lung fibrosis known as asbestosis as well as cancers such as malignant mesothelioma and lung cancer. Asbestos is a mineral silicate containing iron, magnesium, and calcium with a core of SiO₂. The immunological effect of silica, SiO₂, involves the dysregulation of autoimmunity because of the complications of autoimmune diseases found in silicosis. Asbestos can therefore cause alteration of immunocompetent cells to result in a decline of tumor immunity. Additionally, due to its physical characteristics, asbestos fibers remain in the lung, regional lymph nodes, and the pleural cavity, particularly at the opening sites of lymphatic vessels. Asbestos can induce chronic inflammation in these areas due to the production of reactive oxygen/nitrogen species. As a consequence, immunocompetent cells can have their cellular and molecular features altered by chronic and recurrent encounters with asbestos fibers, and there may be modification by the surrounding inflammation, all of which eventually lead to decreased tumor immunity. In this paper, the brief results of our investigation regarding reduction of tumor immunity of immunocompetent cells exposed to asbestos in vitro are discussed, as are our findings concerned with an investigation of chronic inflammation and analyses of peripheral blood samples derived from patients with pleural plaque and mesothelioma that have been exposed to asbestos.

Asbestos induces reduction of tumor immunity

Asbestos-related cancers such as malignant mesothelioma and lung cancer are an important issue in the world. There are many conflicts concerning economical considerations and medical evidence for these cancers and much confusion regarding details of the pathological mechanisms of asbestos-induced cancers. For example, there is uncertainty concerning the degree of danger of the iron-absent chrysotile compared with iron-containing crocidolite and amosite. However, regarding bad prognosis of mesothelioma, medical approaches to ensure the recognition of the biological effects of asbestos and the pathological mechanisms of asbestos-induced carcinogenesis, as well as clinical trials to detect the early stage of mesothelioma, should result in better preventions and the cure of these malignancies. We have been investigating the immunological effects of asbestos in relation to the reduction of tumor immunity. In this paper, cellular and molecular approaches to clarify the immunological effects of asbestos are described, and all the findings indicate that the reduction of tumor immunity is caused by asbestos exposure and involvement in asbestos-induced cancers. These investigations may not only allow the clear recognition of the biological effects of asbestos, but also present a novel procedure for early detection of previous asbestos exposure and the presence of mesothelioma as well as the chemoprevention of asbestos-related cancers.

[Archives of "comprehensive approach on asbestos-related diseases" supported by the "special coordination funds for promoting science and technology (H18-1-3-3-1)"-- overview of group research project, care and specimen registration, cellular characteristics of mesothelioma and immunological effects of asbestos]

The research project entitled "Comprehensive approach on asbestos-related diseases" supported by the "Special Coordination Funds for Promoting Science and Technology (H18-1-3-3-1)" began in 2006 and was completed at the end of the Japanese fiscal year of 2010. This project included four parts; (1) malignant mesothelioma (MM) cases and specimen registration, (2) development of procedures for the early diagnosis of MM, (3) commencement of clinical investigations including multimodal approaches, and (4) basic research comprising three components; (i) cellular and molecular characterization of mesothelioma cells, (ii) immunological effects of asbestos, and (iii) elucidation of asbestos-induced carcinogenesis using animal models. In this special issue of the Japanese Journal of Hygiene, we briefly introduce the achievements of our project. The second and third parts and the third component of the fourth part are described in other manuscripts written by Professors Fukuoka, Hasegawa, and Toyokuni. In this manuscript, we introduce a brief summary of the first part "MM cases and specimen registration", the first component of the fourth part "Cellular and molecular characterization of mesothelioma cells" and the second component of the fourth part "Immunological effects of asbestos". In addition, a previous special issue presented by the Study Group of Fibrous and Particulate Substances (SGFPS) (chaired by Professor Otsuki, Kawasaki Medical School, Japan) for the Japanese Society of Hygiene and published in Environmental Health and Preventive Medicine Volume 13, 2008, included reviews of the aforementioned first component of the fourth part of the project. Taken together, our project led medical investigations regarding asbestos and MM progress and contributed towards the care and examination of patients with asbestos-related diseases during these five years. Further investigations are required to facilitate the development of preventive measures and the cure of asbestos-related diseases, particularly in Japan, where asbestos-related diseases are predicted to increase in the next 10 to 20 years.

Lung function in asbestos-exposed workers, a systematic review and meta-analysis

BACKGROUND

A continuing controversy exists about whether, asbestos exposure is associated with significant lung function impairments when major radiological abnormalities are lacking. We conducted a systematic review and meta-analysis in order to assess whether asbestos exposure is related to impairment of lung function parameters independently of the radiological findings.

METHODS

MEDLINE was searched from its inception up to April 2010. We included studies that assessed lung function parameters in asbestos exposed workers and stratified subjects according to radiological findings. Estimates of VC, FEV1 and FEV1/VC with their dispersion measures were extracted and pooled.

RESULTS

Our meta-analysis with data from 9,921 workers exposed to asbestos demonstrates a statistically significant reduction in VC, FEV1 and FEV1/VC, even in those workers without radiological changes. Less severe lung function impairments are detected if the diagnoses are based on (high resolution) computed tomography rather than the less sensitive X-ray images. The degree of lung function impairment was partly related to the proportion of smokers included in the studies.

CONCLUSIONS

Asbestos exposure is related to restrictive and obstructive lung function impairment. Even in the absence of radiological evidence of parenchymal or pleural diseases there is a trend for functional impairment.

Up-regulation of T lymphocyte and antibody production by inflammatory cytokines released by macrophage exposure to multi-walled carbon nanotubes

Our data demonstrate that multi-walled carbon nanotubes (MWCNTs) are internalized by macrophages, subsequently activating them to produce interleukin (IL)-12 (IL-12). This cytokine induced the proliferative response of T lymphocytes to a nonspecific mitogen and to ovalbumin (OVA). This increase in the proliferative response was accompanied by an increase in the expression of pro-inflammatory cytokines, such as interferon-gamma (IFNγ), tumor necrosis factor-alpha (TNFα) and IL-6, in mice inoculated with MWCNTs, whether or not they had been immunized with OVA. A decrease in the expression of transforming growth factor-beta (TGFβ) was observed in the mice treated with MWCNTs, whereas the suppression of the expression of both TGFβ and IL-10 was observed in mice that had been both treated and immunized. The activation of the T lymphocyte response by the pro-inflammatory cytokines leads to an increase in antibody production to OVA, suggesting the important immunostimulatory effect of carbon nanotubes.

Decreased CXCR3 expression in CD4+ T cells exposed to asbestos or derived from asbestos-exposed patients

Asbestos causes malignant tumors such as lung cancer and malignant mesothelioma (MM). To determine whether asbestos exposure causes reduction of antitumor immunity, we established an in vitro T-cell line model of low-dose and continuous exposure to asbestos using an human adult T-cell leukemia virus-1 immortalized human polyclonal T-cell line, MT-2, and revealed that MT-2 cells exposed continuously to asbestos showed resistance to asbestos-induced apoptosis. In addition, the cells presented reduction of surface CXCR3 chemokine receptor expression and IFN-γ production. In this study, to confirm that these findings are suitable for clinical translation, surface CXCR3 and IFN-γ expression were analyzed using freshly isolated human CD4(+) T cells derived from healthy donors and patients with pleural plaque (PP) or MM. The results revealed that CXCR3 and IFN-γ expression in the ex vivo model were reduced in some cases. Additionally, CXCR3 expression in CD4(+) T cells from PPs and MMs was significantly reduced compared with that from healthy donors, and CD4(+) T cells from patients with MMs exhibited a marked reduction in IFN-γ mRNA levels after stimulation in vitro. Moreover, CD4(+)CXCR3(+) T cells in lymphocytes from MMs showed a tendency for an inverse correlation with its ligand CXCL10/IP10 in plasma. These findings show reduction of antitumor immune function in asbestos-exposed patients and indicate that CXCR3, IFN-γ, and CXCL10/IP10 may be candidates to detect and monitor disease status.

Dysregulation of the immune system caused by silica and asbestos

Silica and asbestos cause pneumoconioses known as silicosis and asbestosis, respectively, that are each characterized by progressive pulmonary fibrosis. While local effects of inhaled silica particles alter the function of alveolar macrophages and sequential cellular and molecular biological events, general systemic immunological effects may also evolve. One well-known health outcome associated with silica exposure/silicosis is an increase in the incidence of autoimmune disorders. In addition, while exposure to silica--in the crystalline form--has also been seen to be associated with the development of lung cancers, it remains unclear as to whether or not silicosis is a necessary condition for the elevation of silica-associated lung cancer risks. Since asbestos is a mineral silicate, it would be expected to also possess generalized immunotoxicological effects similar to those associated with silica particles. However, asbestos-exposed patients are far better known than silicotic patients for development of malignant diseases such as lung cancer and mesothelioma, and less so for the development of autoimmune disorders. With both asbestos and crystalline silica, one important dysregulatory outcome that needs to be considered is an alteration in tumor immunity that allows for silica- or asbestos- (or asbestos-associated agent)-induced tumors to survive and thrive in situ. In this review, the immunotoxicological effects of both silica and asbestos are presented and contrasted in terms of their abilities to induce immune system dysregulation that then are manifest by the onset of autoimmunity or by alterations in host-tumor immunity.

[Immunological effects of silica/asbestos]

Silica and asbestos cause pneumoconioses known as silicosis and asbestosis, respectively, that are each characterized by progressive pulmonary fibrosis. On the other hand, silicosis patients often suffer from a type of immunological dysregulation that gives rise to autoimmunity. These epidemiological findings suggest that silica may affect the immune system in humans. In addition, as asbestos itself is a mineral silicate, it may possess generalized immunotoxicological effects similar to those associated with silica particles. Because asbestos-exposed patients are well-known to often develop malignant diseases such as lung cancer and mesothelioma, one silica-like dysregulatory outcome that needs to be considered (apart from autoimmunity) is an alteration in host tumor immunity. In this review, the immunotoxicological effects of both silica and asbestos are presented and discussed in terms of immune system dysregulation as manifested by the onset of autoimmunity or alterations in host tumor immunity.

Adrenal failure caused by a retroperitoneal malignant mesothelioma

A 62-year-old man presented with clinical signs of acute abdominal pain and adrenal insufficiency. Computerized tomographic scans revealed bilateral adrenal tumors and the left adrenal tumor was surgically resected. The patient was found to have retroperitoneal mesothelioma presenting as bilateral metastatic adrenal tumors, which were well controlled by systemic chemotherapy with CDDP and 5-FU. This case appears to be the first reported case in the literature of adrenal failure due to bilateral adrenal infiltration caused by retroperitoneal malignant mesothelioma.