Activation of human CD4+CD45RA+ T cells by chrysotile asbestos in vitro

Genome-wide profiling reveals novel microRNAs in hand-spinning-specific chrysotile exposure

Aim: We aimed to explore miRNA expression profiles in hand-spinning chrysotile exposed workers and their potential influencing factors. Methods: miRNA array technique was applied to screen differentially expressed miRNAs between plasma samples from three exposed workers and three controls. Then, seven selected miRNAs were validated in 143 workers and 100 controls, and the potential influencing factors were revealed by multiple linear regression. Finally, the expression levels of those seven miRNAs were evaluated in human mesothelial cells (Met-5A) that were exposed to chrysotile at 5 μg·cm-2 for 8, 24 and 48 h, respectively. Results & conclusion: Hand-spinning chrysotile exposure can result in differential expression of miRNAs. Several of those miRNAs have positive correlations with asbestos exposure.

Nonpulmonary outcomes of asbestos exposure

The adverse pulmonary effects of asbestos are well accepted in scientific circles. However, the extrapulmonary consequences of asbestos exposure are not as clearly defined. In this review the potential for asbestos to produce diseases of the peritoneum, immune, gastrointestinal (GIT), and reproductive systems are explored as evidenced in published, peer-reviewed literature. Several hundred epidemiological, in vivo, and in vitro publications analyzing the extrapulmonary effects of asbestos were used as sources to arrive at the conclusions and to establish areas needing further study. In order to be considered, each study had to monitor extrapulmonary outcomes following exposure to asbestos. The literature supports a strong association between asbestos exposure and peritoneal neoplasms. Correlations between asbestos exposure and immune-related disease are less conclusive; nevertheless, it was concluded from the combined autoimmune studies that there is a possibility for a higher-than-expected risk of systemic autoimmune disease among asbestos-exposed populations. In general, the GIT effects of asbestos exposure appear to be minimal, with the most likely outcome being development of stomach cancer. However, IARC recently concluded the evidence to support asbestos-induced stomach cancer to be "limited." The strongest evidence for reproductive disease due to asbestos is in regard to ovarian cancer. Unfortunately, effects on fertility and the developing fetus are under-studied. The possibility of other asbestos-induced health effects does exist. These include brain-related tumors, blood disorders due to the mutagenic and hemolytic properties of asbestos, and peritoneal fibrosis. It is clear from the literature that the adverse properties of asbestos are not confined to the pulmonary system.

Expression of the T cell receptor Vbeta repertoire in a human T cell resistant to asbestos-induced apoptosis and peripheral blood T cells from patients with silica and asbestos-related diseases

To explore the effects of asbestos and silica on the human immune system, an experimental model of low-dose and long-term exposure was established using a human HTLV-1-immortalized polyclonal T cell line, MT-2 (MT-2Org). MT-2 cells were continuously exposed to asbestos at a concentration (10 microg/ml) which does not induce complete cell death during short-term exposure. After acquiring resistance to CB-induced apoptosis (designated MT-2Rst), an immunological comparison was made between the MT-2Org and MT-2Rst lines in terms of T cell receptor-Vbeta (TcR-Vbeta) expression. MT-2Rst cells showed excess expression of various TcR-Vbeta, although TcR-Vbeta-overpresenting cells were characterized as undergoing apoptosis due to first contact with CB. Patients with asbestos-related diseases (ARD), such as asbestosis and malignant mesothelioma, were compared with silicosis (SIL) patients as a disease control and with healthy donors (HD). SIL and ARD not only differed in their causative materials, silica and asbestos as mineral silicates, but also in terms of complications; autoimmune disorders in SIL and tumors in ARD. ARD patients showed a restricted overpresentation of TcR-Vbeta without clonal expansion, whereas SIL patients revealed significant overpresentation of TcR-Vbeta 7.2. These experimental and clinical analyses indicate the superantigenic and dysregulation of autoimmunity-inducing effects of asbestos and silica, respectively.

Expression of Fas antigen and Fas ligand in bronchoalveolar lavage from silicosis patients

OBJECTIVE

To understand the role of apoptosis through Fas/Fas ligand (FasL) interaction in the pathogenesis of silicosis, we examined the expression of Fas antigen, FasL and apoptosis in bronchoalveolar lavage fluid lymphocytes obtained from patients with silicosis.

MATERIALS AND METHODS

Ten patients with silicosis, and 10 healthy controls were studied. Non-adherent cells were separated and analysed by cytometry for the expression of Fas antigen, FasL, and the co-expression of Fas/FasL. By double staining, we studied the FasL expression on CD4, CD8, CD56 and CD45RO-positive cells. DNA fragmentation was investigated by the terminal deoxy(d) UTP nick end labelling (TUNEL) method.

RESULTS

We have found Fas and FasL expression in silicosis patients to be significantly higher than those in healthy controls. Interestingly, 6-18% of lymphocytes from silicosis patients co-expressed Fas and FasL. In silicosis patients, FasL was highly expressed on CD4+, CD56+ and CD45RO+ bronchoalveolar lavage cells. Fas antigen expressing cells showed DNA fragmentation characteristic for apoptosis.

CONCLUSION

FasL was significantly expressed on cytotoxic effector and memory cells. The Fas/FasL system is implicated in the inflammatory process observed in silicosis patients.

Soluble Fas mRNA is dominantly expressed in cases with silicosis

Although it is well known that cases with silicosis exhibit various immunological abnormalities, the mechanisms involved in the occurrence of immuno-dysfunction or dysregulation induced by silica compounds have not yet been determined. Fas is a well-known cell surface molecule that is involved in the apoptosis pathway that belongs to the tumour necrosis factor-receptor family. Soluble Fas (sFas) is produced as an alternatively spliced product of the Fas gene and protects cells from apoptosis due to antagonization of the binding between membrane form of the Fas gene (mFas) and the Fas ligand. To determine the role of the Fas/Fas ligand system in silica-induced immunological abnormalities, we investigated Fas and Fas-ligand message expression levels using the multiplex reverse transcription-polymerase chain reaction (RT-PCR) method with peripheral blood mononuclear cells from silicosis cases with no clinical symptoms of autoimmune diseases. Although the relative expression levels of the Fas or Fas-ligand genes were not remarkably altered in these cases, we observed the sFas message was dominantly expressed compared with mFas expression. These results suggest that self-recognizing clones in cases with silicosis survive for decades, escaping the exclusion mechanisms induced by apoptosis. Then they cause the appearance of autoantibodies and the acquisition of autoimmune diseases sequentially.

Elevated soluble Fas/APO-1 (CD95) levels in silicosis patients without clinical symptoms of autoimmune diseases or malignant tumours

Soluble Fas (sFas) is produced as translation products of alternative mRNA splicing, and antagonizes the membranous Fas molecule in Fas/Fas ligand interactions. We investigated the serum sFas levels in 64 Japanese silicosis patients with no clinical symptoms of autoimmune diseases or malignant tumours, using ELISA for sFas. The serum sFas levels in the silicosis patients were significantly higher than those in healthy volunteers. Elevated serum sFas levels were also detected in patients with systemic lupus erythematosus but, unexpectedly, no difference was observed in sFas levels between progressive systemic sclerosis patients and healthy volunteers. On the other hand, there was no significant difference in the expression of Fas on peripheral blood lymphocytes between the patients with silicosis and age-matched healthy volunteers. These observations provided the first evidence that serum sFas levels are elevated in silicosis patients without clinical symptoms of autoimmune diseases or malignant tumours. It remains to be clarified whether patients with elevated sFas levels have a tendency to develop autoimmune diseases later, or whether some other distinct factor(s) is necessary to initiate the progression of autoimmune diseases.