Effect of IL-15 addition on asbestos-induced suppression of human cytotoxic T lymphocyte induction.

BACKGROUND: Asbestos fibers possess tumorigenicity and are thought to cause mesothelioma. We have previously reported that exposure to asbestos fibers causes a reduction in antitumor immunity. Asbestos exposure in the mixed lymphocyte reaction (MLR) showed suppressed induction of cytotoxic T lymphocytes (CTLs), accompanied by a decrease in proliferation of CD8+ T cells. Recently, we reported that asbestos-induced suppression of CTL induction is not due to insufficient levels of interleukin-2 (IL-2). In this study, we continue to investigate the mechanism responsible for the effect of asbestos fibers on the differentiation of CTLs and focus on interleukin-15 (IL-15) which is known to be a regulator of T lymphocyte proliferation. METHODS: For MLR, human peripheral blood mononuclear cells (PBMCs) were cultured with irradiated allogenic PBMCs upon exposure to chrysotile B asbestos at 5 µg/ml for 7 days. After 2 days of culture, IL-15 was added at 1 ng/ml. After 7 days of MLR, PBMCs were collected and analyzed for phenotypic and functional markers of CD8+ T cells with fluorescence-labeled anti-CD3, anti-CD8, anti-CD45RA, anti-CD45RO, anti-CD25, and anti-granzyme B antibodies using flow cytometry. To examine the effect of IL-15 on the expression level of intracellular granzyme B in proliferating and non-proliferating CD8+ lymphocytes, PBMCs were stained using carboxyfluorescein diacetate succinimidyl ester (CFSE) and then washed and used for the MLR. RESULTS: IL-15 addition partially reversed the decrease in CD3+CD8+ cell numbers and facilitated complete recovery of granzyme B+ cell percentages. IL-15 completely reversed the asbestos-induced decrease in percentage of granzyme B+ cells in both non-proliferating CFSE-positive and proliferating CFSE-negative CD8+ cells. The asbestos-induced decrease in the percentage of CD25+ and CD45RO+ cells in CD8+ lymphocytes was not reversed by IL-15. CONCLUSION: These findings indicate that CTLs induced upon exposure to asbestos possess dysfunctional machinery that can be partly compensated by IL-15 supplementation, and that IL-15 is more effective in the recovery of proliferation and granzyme B levels from asbestos-induced suppression of CTL induction compared with IL-2.

The Effects of Asbestos Fibers on Human T Cells.

Asbestos exposure causes malignant tumors such as lung cancer and malignant mesothelioma. The effects of asbestos fibers on immunocompetent cells, however, have not been well studied. Asbestos physically comprises a fibrous substance, which differs from silica particles which are a particulate substance, although chemically it is a mineral silicate. Since silicosis patients previously exposed to silica particles often suffer from lung and autoimmune diseases, it is clear that silica exposure impairs immune tolerance. Similarly, asbestos may alter the immune system in asbestos-exposed individuals. Given that malignant tumors can result following exposure to asbestos, the attenuation of anti-tumor immunity in cases of asbestos exposure is an important area of investigation. We observed the effect of asbestos fibers on T lymphocytes, such as CD8+ cytotoxic T lymphocytes (CTLs), CD4+ helper T (Th), and regulatory T (Treg) cells, and showed that anti-tumor immunity was attenuated, as demonstrated in a system that stimulates fresh cells isolated from peripheral blood in vitro and a system that is continuously exposed to a cell line. In this manuscript, we introduce the experiments and results of studies on CTLs, as well as Th and Treg cells, and discuss how future changes in immunocompetent cells induced by asbestos fibers can be clinically linked.

Effect of asbestos exposure on differentiation and function of cytotoxic T lymphocytes.

Asbestos exposure is known to cause malignant mesothelioma, which is associated with poor prognosis. We focused on and examined the effect of asbestos exposure on the differentiation and function of cytotoxic T lymphocytes (CTLs). CTLs have the ability to specifically attack tumor cells after being differentiated from naïve CD8+ T cells following antigen stimulation. Exposure to chrysotile B asbestos suppressed the differentiation of CTLs during the mixed lymphocyte reaction (MLR) and was associated with a decrease in proliferation of CD8+ T cells. Additionally, in an effort to investigate the mechanism associated with suppressed CTL differentiation upon exposure to asbestos, we focused on IL-2, a cytokine involved in T cell proliferation. Our findings indicated that insufficient levels of IL-2 are not the main cause for the suppressed induction of CTLs by asbestos exposure, although they suggest potential improvement in the suppressed CTL function. Furthermore, the functional properties of peripheral blood CD8+ lymphocytes from asbestos-exposed individuals with pleural plaque (PP) and patients with malignant mesothelioma (MM) were examined. MM patients showed lower perforin levels in CD8+ lymphocytes following stimulation compared with PP-positive individuals. The production capacity of IFN-γ in the MM group tended to be lower compared with healthy volunteers or PP-positive individuals. In an effort to determine whether chronic and direct asbestos exposure affected the function of CD8+ T cells, cultured human CD8+ T cells were employed as an in vitro model and subjected to long-term exposure to chrysotile (CH) asbestos. This resulted in decreased levels of intracellular perforin and secreted IFN-γ. Those findings underlie the possibility that impaired CD8+ lymphocyte function is caused by asbestos exposure, which fail to suppress the development of MM. Our studies therefore reveal novel effects of asbestos exposure on CTLs, which might contribute towards the development and implementation of an effective strategy for the prevention and cure of malignant mesothelioma.

Role of Nephronectin in Pathophysiology of Silicosis.

Silicosis is a typical form of pneumoconiosis and is characterized as a type of lung fibrosis. Silica particles are captured and recognized upon by alveolar macrophages via the macrophage receptor with collagenous structure (MARCO) scavenger receptor, and thereafter the inflammasome is activated. Thereafter, various chemokines/cytokines play their roles to eventually form fibrosis. Additionally, silica particles chronically activate T helper cells which sets the background for the formation of silicosis-associated autoimmune disturbances. The occurrence and progression of lung fibrosis, the extracellular matrix-related molecules such as integrins and their ligands including fibronectin, vitronectin, laminin, and collagens, all play important roles. Here, the roles of these molecules in silicosis-related lung fibrosis are reviewed from the literature. Additionally, the measurement of serum nephronectin (Npnt), a new member of the integrin family of ligands, is discussed, together with investigations attempting to delineate the role of Npnt in silica-induced lung fibrosis. Serum Npnt was found to be higher in silicosis patients compared to healthy volunteers and seems to play a role in the progression of fibrosis with other cytokines. Therefore, serum Npnt levels may be employed as a suitable marker to monitor the progression of fibrosis in silicosis patients.

Decrease in Serum Amyloid a Protein Levels Following Three-month Stays in Negatively Charged Particle-dominant Indoor Air Conditions.

OBJECTIVE: The changes in serum adipokines and cytokines related to oxidative stress were examined during 3 months 'Off to On' and 'On to Off' periods using negatively charged particle-dominant indoor air conditions (NCPDIAC). METHODS: Seven volunteers participated in the study, which included 'OFF to 3 months ON' periods (ON trials) for a total of 16 times, and 'ON to 3 months OFF' (OFF trials) periods for a total of 13 times. RESULTS: With the exception of one case, serum amyloid A (SAA) levels decreased significantly during the ON trials. CONCLUSION: Considering that SAA is an acute phase reactive protein such as C reactive protein (CRP), this observed decrease might indicate the prevention of cardiovascular and atherosclerotic changes, since an increase in high-sensitive CRP is associated with the subsequent detection of these events.

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.

Search for biomarkers of asbestos exposure and asbestos-induced cancers in investigations of the immunological effects of asbestos.

The immunological effects of asbestos exposure on various lymphocytes such as the regulatory T cell (Treg), responder CD4+ T helper cell (Tresp), CD8+ cytotoxic T lymphocytes (CTL), and natural killer (NK) cells were investigated. Results show that asbestos exposure impairs antitumor immunity through enhancement of regulatory T cell function and volume, reduction of CXCR3 chemokine receptor in responder CD4+ T helper cells, and impairment of the killing activities of CD8+ cytotoxic T lymphocytes (CTL) and NK cells. These findings were used to explore biological markers associated with asbestos exposure and asbestos-induced cancers and suggested the usefulness of serum/plasma IL-10 and TGF-ß, surface CXCR3 expression in Tresp, the secreting potential of IFN-γ in Tresp, intracellular perforin level in CTL, and surface expression NKp46 in NK cells. Although other unexplored cytokines in serum/plasma and molecules in these immunological cells, including Th17, should be investigated by experimental procedures in addition to a comprehensive analysis of screening methods, biomarkers based on immunological alterations may be helpful in clinical situations to screen the high-risk population exposed to asbestos and susceptible to asbestos-related cancers such as mesothelioma.

Biological Effects of Cloth Containing Specific Ore Powder in Patients with Pollen Allergy.

OBJECTIVE: The custom-homebuilding company, Cosmic Garden Co. Ltd., located in Okayama City, Japan was established in 1997 and uses specific natural ore powder (SNOP) in wall materials and surveys customers in order to improve allergic symptoms. METHODS: To investigate the biological effects of SNOP, patients with a pollen allergy were recruited to stay in a room surrounded by cloth containing SNOP (CCSNOP), and their symptoms and various biological parameters were compared with those of individuals staying in a room surrounded by control non-woven cloth (NWC). Each stay lasted 60 min. Before and immediately after the stay, a questionnaire regarding allergic symptoms, as well as POMS (Profile of Mood Status) and blood sampling, was performed. Post-stay minus pre-stay values were calculated and compared between CCSNOP and NWC groups. RESULTS: Results indicated that some symptoms, such as nasal obstruction and lacrimation, improved, and POMS evaluation showed that patients were calmer following a stay in CCSNOP. Relative eosinophils, non-specific Ig E, epidermal growth factor, monocyte chemotactic protein-1, and tumor necrosis factor-α increased following a stay in CCSNOP. CONCLUSION: This ore powder improved allergic symptoms, and long-term monitoring involving 1 to 2 months may be necessary to fully explore the biological and physical effects of SNOP on allergic patients.

Environmental factors and human health: fibrous and particulate substance-induced immunological disorders and construction of a health-promoting living environment.

Among the various scientific fields covered in the area of hygiene such as environmental medicine, epidemiology, public health and preventive medicine, we are investigating the immunological effects of fibrous and particulate substances in the environment and work surroundings, such as asbestos fibers and silica particles. In addition to these studies, we have attempted to construct health-promoting living conditions. Thus, in this review we will summarize our investigations regarding the (1) immunological effects of asbestos fibers, (2) immunological effects of silica particles, and (3) construction of a health-promoting living environment. This review article summarizes the 2014 Japanese Society for Hygiene (JSH) Award Lecture of the 85th Annual Meeting of the JSH entitled "Environmental health effects: immunological effects of fibrous and particulate matter and establishment of health-promoting environments" presented by the first author of this manuscript, Prof. Otsuki, Department of Hygiene, Kawasaki Medical School, Kurashiki, Japan, the recipient of the 2014 JSH award. The results of our experiments can be summarized as follows: (1) asbestos fibers reduce anti-tumor immunity, (2) silica particles chronically activate responder and regulatory T cells causing an unbalance of these two populations of T helper cells, which may contribute to the development of autoimmune disorders frequently complicating silicosis, and (3) living conditions to enhance natural killer cell activity were developed, which may promote the prevention of cancers and diminish symptoms of virus infections.

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.

Quantitation and human monocyte cytotoxicity of the polymerization agent 1-hydroxycyclohexyl phenyl ketone (Irgacure 184) from three brands of aqueous injection solution.

In this study, levels of the photoinitiator 1-hydroxycyclohexyl phenyl ketone (1-HCHPK) in aqueous injection solutions were analyzed by GC-MS. In our previous studies, photoinitiators such as 2-methyl-4'-(methylthio)-2-morpholinopropiophenone (MTMP) were detected in intravenous (i.v.) injection bag solution, and they were found to be cytotoxic to human monocytes. Therefore, we hypothesized that 1-HCHPK might display similarly cytotoxicity. The purpose of this study was to quantitate the amount of contaminants from plastic containers such as those used for peripheral parenteral nutrition and to determine the cytotoxicity of such extracts on human monocytes. The sample extraction procedure for GC-MS analysis involved a liquid-phase extraction. The solvent was evaporated under a stream of nitrogen at 50°C to yield a residue, which was dissolved in n-hexane and injected into a GC-MS. Normal human peripheral blood mononuclear cells (PBMC), isolated from the buffy coat by centrifugation, were suspended in RPMI 1640 medium supplemented with 10% (v/v) heat-inactivated fetal calf serum. In the 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide (MTT) cell viability assay, cells (1×10(4)) were treated with 1-HCHPK for 24 h or 48 h at 37°C. From the GC-MS analysis, 6.13-8.32 µg/mL of 1-HCHPK was found in 20 mL vials of water for injection solution. In the MTT assay, 1-HCHPK decreased cell viability for both the 24 h and 48 h incubation periods. In conclusion, our findings suggest that 1-HCHPK could promote adverse events in patients. Future studies will clarify the possible health risks of photoinitiator accumulation in human cells.

Increased production of matrix metalloproteinase-7 (MMP-7) by asbestos exposure enhances tissue migration of human regulatory T-like cells.

The effects of asbestos on immunocompetent cells have been investigated. In particular, attention was paid to regulatory T cell function, which was observed using the HTLV-1 immortalized human polyclonal T cell line MT-2. Exposure to asbestos (approximately more than 25 µg/mL for 1-3 day) induced apoptosis, and we observed an increase in regulatory T cell function and acceleration of the cell cycle with continuous exposure to low concentrations of asbestos (5-10 µg/mL for more than eight months). Furthermore, cDNA microarray analysis in this study revealed that expression of matrix metalloproteinase-7 (MMP-7) was markedly higher in exposed sublines compared to original MT-2 cells. It was determined that MMP-7 had no effect on Treg function, as determined by examination of sublines and by addition of recombinant MMP-7 and neutralizing antibodies or inhibitors of MMP-7. However, when examining melting of the extracellular matrix (an MMP-7-mediated event) or the extent to which the MT-2 parent strain or long-term exposed subline cells pass through a fibronectin-coated filter, more filter passes were observed for the subline. These results suggest that the effect of asbestos fibers on Treg cells results in excessive migration of the tumor microenvironment through hypersecretion of MMP-7 together with an increase in suppressive function and enhancement of cell cycle progression. Therefore, one possible way to prevent the development of asbestos-induced cancer is to reduce the function (including MMP-7 production) or amount of Treg cells by physiologically active substances or food ingredients. Alternatively, it may be possible to invoke immune checkpoint treatments when carcinogenesis occurs.

Enhanced expression of nicotinamide nucleotide transhydrogenase (NNT) and its role in a human T cell line continuously exposed to asbestos.

The effects of asbestos fibers on human immune cells have not been well documented. We have developed a continuously exposed cell line model using the human T-lymphotropic virus 1 (HTLV-1)-immortalized human T cell line MT-2. Sublines continuously exposed to chrysotile (CH) or crocidolite (CR) showed acquired resistance to asbestos-induced apoptosis following transient and high-dose re-exposure with fibers. These sublines in addition to other immune cells such as natural killer cells or cytotoxic T lymphocytes exposed to asbestos showed a reduction in anti-tumor immunity. In this study, the expression of genes and molecules related to antioxidative stress was examined. Furthermore, complexes related to oxidative phosphorylation were investigated since the production of reactive oxygen species (ROS) is important when considering the effects of asbestos in carcinogenesis and the mechanisms involved in resistance to asbestos-induced apoptosis. In sublines continuously exposed to CH or CR, the expression of thioredoxin decreased. Interestingly, nicotinamide nucleotide transhydrogenase (NNT) expression was markedly enhanced. Thus, knockdown of NNT was then performed. Although the knockdown clones did not show any changes in proliferation or occurrence of apoptosis, these clones showed recovery of ROS production with returning NADPH/NADP+ ratio that increased with decreased production of ROS in continuously exposed sublines. These results indicated that NNT is a key factor in preventing ROS-induced cytotoxicity in T cells continuously exposed to asbestos. Considering that these sublines showed a reduction in anti-tumor immunity, modification of NNT may contribute to recovery of the anti-tumor effects in asbestos-exposed T cells.

Structure-based design of gRNA for Cas13.

Cas13 endonuclease activity depends on the RNA local secondary structure with strong preference for single-stranded (SS) regions. Hence, it becomes indispensable to identify the SS regions for effective Cas13 mediated RNA knockdown. We herein present rational gRNA design by integrating experimental structure-seq data and predicted structural models. Utilizing structure-seq data for XIST transcript, we observed that gRNAs targeting the SS regions significantly induce transcript knockdown and cleavage than those targeting double-stranded (DS) regions. Further, we identified the "central seed region" in the gRNA that upon targeting the SS regions efficiently facilitates Cas13 mediated cleavage. In our following pursuits, we considered the scenario wherein experimental structure-seq data is not available, hence we used SS18-SSX2 fusion transcript indicated in synovial sarcomas and computationally predicted its structure. We observed that gRNAs targeting the SS regions predicted from the structure, efficiently induced necrosis compared to gRNAs that target the DS regions. In conclusion, for the effective RNA knockdown, the Cas13 mediated targeting strategy presented herein emphasizes the designing of gRNAs specifically targeting SS regions by utilizing structural information. Further, this strategy, in turn, can be anticipated to narrow the search space for gRNA design (by exclusively targeting SS regions) especially when lncRNAs are the targets.

Factors affecting the choice of suicide method in Okayama: a database analysis from a forensic perspective.

The annual number of suicides in Japan increased sharply in 1998, and since that time it has consistently exceeded 30,000 per year. In this study, we analyze a database of personal and background characteristics of 824 cases (605 men, 219 women) who completed suicide in Okayama Prefecture in 2002 and 2003. The data were obtained with cooperation from the police. Using the methodologies in a previous European study as a model, we classified the suicide methods into 8 categories. To examine the generational and regional differences in the choice of methods, we stratified the sample into 4 age groups (< or =24, 25 approximately 44, 45 approximately 64, and > or =65) and 2 regional groups (Okayama/Kurashiki vs. other areas). Our results on gender differences in 7 of the suicide methods were mostly similar to the European data. However, our data showed a remarkably higher proportionate male-to-female mortality ratio for poisoning by other substances (ICD-10, X65-X69 codes) (1.83, 1.15-2.92). In terms of generational differences in the choice of suicide methods, the Mantel-Haenszel test of homogeneity was significant for most of the categories in our study, suggesting an impact of age on how people commit suicide. There were no remarkable regional differences in our sample. An epidemic curve for suicides via carbon monoxide poisoning using charcoal briquets revealed a trend of time clustering not observed in the other 6 means. The database constructed and used in this study contains richer information than conventional death statistics and is expected to provide helpful knowledge and insights for future epidemiological studies.

Didgeridoo Health Promotion Method Improves Mood, Mental Stress, and Stability of Autonomic Nervous System.

A potential method of health promotion using the traditional wooden brass instrument the didgeridoo was examined, especially in terms of mood, stress, and autonomic nerve stabilization. Twenty Japanese healthy subjects undertook 10 lessons of the Didgeridoo Health Promotion Method (DHPM) and a moods questionnaire, blood pressure, salivary amylase (sAmy) as a stress marker, pulse rate and autonomic balance expressed by Ln[low frequency (LF)/High frequency (HF) were examined twice before the entire lessons and once before and after each lesson. The subjects had improved total mood disturbance (TMD: overall mood disorder degree) as measured by the Japanese version of the Profile of Mood States 2nd Edition (POMS2) as a result of taking the lessons. The pulse of the subjects decreased after the lessons, which correlated with a reduction in sAmy. Additionally, it was found that sAmy decreased after the lessons with increasing age of the subject, subjects with higher TMD before the lessons, or subjects with higher sAmy values before the lessons. With autonomic balance measured by Ln[LF/HF], subjects who had parasympathetic dominance as a result of the lesson were significantly more frequent. Additionally, it has been shown that Ln[LF/HF] decreased over 10 weeks, and it is also clear that the effect is sustained. Health promotion is an important concern for societies as a whole. In this study, it became clear that the DHPM affected mood, stress, and autonomic stability. Future studies should focus on monitoring the effects of continuing the lessons for a longer period of time. Additionally, physical effects such as strength of respiratory muscles should be examined. DHPM may be employed in the work place to promote the mental health of workers as well as in regional neighborhood associations/communities.

Postmortem increase of flecainide level in cardiac blood.

We encountered a case of fatal congestive heart failure that occurred under the influence of flecainide. In this case, an extreme postmortem increase in the flecainide level was identified in cardiac blood. The patient had been administered 400 mg/day of flecainide for seven days before death. Antemortem plasma obtained 13 h before death showed a flecainide concentration of 2.5 mg/L and a pH of 7.4. In comparison, centrifuged supernatants of postmortem right and left cardiac blood contained flecainide concentrations of 13.8 and 44.2 mg/L, respectively, with pH of 5.5 in both samples. This increase in blood flecainide concentration was attributed to postmortem redistribution, as about 18 h had passed between the last intake of flecainide and death.

Decrease in Intracellular Perforin Levels and IFN-γ Production in Human CD8+ T Cell Line following Long-Term Exposure to Asbestos Fibers.

Although the tumorigenicity of asbestos, which is thought to cause mesothelioma, has been clarified, its effect on antitumor immunity requires further investigation. We previously reported a decrease in the percentage of perforin+ cells of stimulated CD8+ lymphocytes derived from patients with malignant mesothelioma. Therefore, we examined the effects of long-term exposure to asbestos on CD8+ T cell functions by comparing long-term cultures of the human CD8+ T cell line EBT-8 with and without exposure to chrysotile (CH) asbestos as an in vitro model. Exposure to CH asbestos at 5 µg/ml or 30 µg/ml did not result in a decrease in intracellular granzyme B in EBT-8 cells. In contrast, the percentage of perforin+ cells decreased at both doses of CH exposure. CH exposure at 30 µg/ml did not suppress degranulation following stimulation with antibodies to CD3. Secreted production of IFN-γ stimulated via CD3 decreased by CH exposure at 30 µg/ml, although the percentage of IFN-γ + cells induced by PMA/ionomycin did not decrease. These results indicate that long-term exposure to asbestos can potentially suppress perforin levels and the production of IFN-γ in human CD8+ T cells.