Autoantibodies detectable in the sera of silicosis patients. The relationship between the anti-topoisomerase I antibody response and HLA-DQB1*0402 allele in Japanese silicosis patients

Clinical evaluation of CENP-B and Scl-70 autoantibodies in silicosis patients

Silicosis patients (SIL) suffer from respiratory disorders and dysregulation of autoimmunity. Frequent complications such as rheumatoid arthritis, systemic sclerosis (SSc) and vasculitis are known in SIL. Furthermore, we reported previously that some SIL exhibited better respiratory conditions in association with a worse immunological status. In this study, the clinical roles of anti-CENP-B and Scl-70 autoantibodies in SIL were analyzed. The titer index (Log10) of anti-CENP-B autoantibody in SIL was higher than that of healthy volunteers (HV), and that of SSc was higher than those of HV and SIL. This titer index was positively correlated with an assumed immune status of 1 for HV, 2 for SIL, and 3 for SSc. Moreover, although factor analysis revealed that the titer index of the anti-CENP-B autoantibody formed the same factor with the anti-Scl-70 autoantibody, IgG value and age in SIL cases, another extracted factor indicated that the IgA value and anti-Scl-70 antibody were positively related, but anti-CENP-B showed an opposite pattern in the results of the factor analysis. These findings indicated that the titer index of anti-CENP-B autoantibody may be a biomarker for dysregulation in SIL cases. Future clinical follow-up of SIL may therefore require both respiratory and immunological assessment.

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.

Silicon, a Possible Link between Environmental Exposure and Autoimmune Diseases: The Case of Rheumatoid Arthritis

Silicon is one of the most common chemicals on earth. Several compounds such as silica, asbestos, silicone or, nanoparticles are built from tetrahedral units with silicon as the central atom. Despite these, structural similarities, they have rarely been analyzed as a group. These compounds generate significant biological alterations that include immune hyperactivation, production of the reactive species of oxygen and tissue injury. These pathological processes may trigger autoimmune responses and lead to the development of rheumatoid arthritis. Populations at risk include those that constantly work in industrial process, mining, and agriculture as well as those that undergo silicone implants. Herein a review on the main features of these compounds and how they may induce autoimmune responses is presented.

Reductive alteration of the regulatory function of the CD4(+)CD25(+) T cell fraction in silicosis patients

Causal links have been documented between silica and rheumatoid arthritis, lupus erythematosus, systemic sclerosis and glomerulonephritis. Two different effects of silica have been suggested, an enhanced inflammatory response in the pulmonary region (e.g. activation of alveolar macrophages) and dysregulation of autoimmunity. Based on our previous reports showing in vitro activation of peripheral T cells by silica and reduced regulatory function of the peripheral CD4(+)CD25(+) fraction in which FoxP(3)+ regulatory T cells (Treg) are located, reconstitution of the CD4(+)CD25(+) fraction in silicosis patients (SILs) was investigated. Since T cells in peripheral CD4(+)CD25(+) and CD4(+)CD25(-) (effector T cells; Teff) fractions from SILs showed higher expression of pd-1 (a marker gene for T cell activation) in comparison to that of healthy donors (HDs), chronic T cell activation was considered to have occurred in SILs. In this study, a higher expression of the CD95/Fas molecule in Treg was recorded from silicosis patients (SILs) compared to healthy donors (HDs), and excess loss of FoxP3(+) Treg in freshly isolated peripheral blood mononuclear cells (PBMCs) from SILs relative to HDs was demonstrated when these cells were cultured with silica ex vivo, whereas CD25(+) cells were not reduced due to contamination of activated Teff in the CD4(+)CD25(+) fraction. The activation of both Teff and Treg results in reconstitution of the peripheral CD4(+)CD25(+) fraction, loss of Treg and contamination of activated Teff, resulting in reduction of the number and function of Treg. These results contribute to our understanding of the development of autoimmune diseases found in SILs.

Antinuclear antibody and rheumatoid factor in silica-exposed workers

A lot of workers in industries such as foundry, stonecutting, and sandblasting are exposed to higher than permissible levels of crystalline silica. Various alterations in humoral immune function have been reported in silicosis patients and workers exposed to silica dust. The aim of this study was to measure antinuclear antibody (ANA) and rheumatoid factor (RF) levels in foundry workers exposed to silica and to compare them with a control group without such exposure. ANA and RF were measured in 78 exposed and 73 non-exposed workers, and standard statistical methods were used to compare them. The two groups did not significantly differ in age and smoking. Mean work duration of the exposed and non-exposed workers was (14.9+/-4.72) years and (12.41+/-6.3) years, respectively. Ten exposed workers had silicosis. ANA was negative in all workers in either group. Its mean titer did not differ significantly between the exposed and control workers [(0.39+/-0.15) IU mL(-1) vs. (0.36+/-0.17) IU mL(-1), respectively]. RF was positive in two workers of each group. Other studies have reported an increase in ANA and RF associated with exposure to silica dust and silicosis.In contrast, our study suggests that exposure to silica dust does not increase the level of ANA and RF in exposed workers.

Autoantibodies in silicosis patients and in silica-exposed individuals

The aim of this study was to evaluate the prevalence of autoantibodies in silica-exposed patients with and without silicosis and without any known rheumatic disease. We studied 61 males exposed to silica for a mean time of 12.2 +/- 10.2 years of exposure. A total of 72.1% (44/61) of them presented with pulmonary silicosis. As control group we included 62 healthy males. In all samples we screened for rheumatoid factor (latex agglutination), antinuclear antibodies (indirect immunofluorescence), anti Scl-70 (ELISA) and ANCA (indirect immunofluorescence technique). One patient (1.6%) of the silica group had weakly positive ANA (titer 1:80, centromeric pattern); one (1.6%) had atypical ANCA and seven patients (11.4%) presented positive rheumatoid factor (values range from 8 to 32 UI/ml). One control patient had a positive RF and none of them had positive ANA or ANCA. All patients and controls were negative for anti-Scl-70. The finding of positive RF was higher in the silica-exposed patients (p = 0.032; Fisher). All patients with positive RF had pulmonary silicosis. In the silica-exposed group we could not find a relationship between the presence of RF and age (p = 0.21; Mann-Whitney), smoking habits (p = 0.25; Fisher) but a positive relationship was found with exposure time to silica dust (p = 0.005; Mann-Whitney). We conclude that there was 11.4% prevalence of low titer RF in the silica-exposed patients without known rheumatic disease. RF was more common in patients with longer exposure to silica dust and appeared only in those with silicosis. The presence of ANA, Scl-70 and ANCA was the same as in the control population.

Induction of CD69 antigen expression in peripheral blood mononuclear cells on exposure to silica, but not by asbestos/chrysotile-A

While cases of silicosis are often complicated by various autoimmune disorders, patients with asbestosis develop malignant tumors such as lung cancer and malignant mesothelioma. These differences may derive from different biological effects, particularly on immunological cells, of silica and asbestos. To find differences between silica and asbestos, the early activation antigen, CD69, on T cells was examined because dysregulated and continuous activation of T cells may promote the survival of self-recognizing T cells. After cultivation of peripheral blood mononuclear cells with or without silica or chrysotile-A, an asbestos, only silica induced CD69 expression on the lymphocytes. This induction of CD69 expression was mediated by protein kinase C activation. In addition, cell-cell contact mediated by HLA-DR was more important than soluble factors secreted from silica-phagocytosed cells such as IL-1beta, IL-6, and IL-8, even though IL-6 and IL-8 were produced during the culture of PBMCs with silica and chrysotile-A. It should be examined how these activated, CD69-expressing lymphocytes affect other immune systems as well as alter themselves in terms of cytokine production and cell-cell interaction, leading to autoimmune disorders in silicosis patients.

Estudo de imunoglobulinas, complementos e auto-anticorpos em 58 trabalhadores expostos à sílica

INTRODUÇÃO: A silicose é a doença pulmonar ocupacional de maior prevalência em nosso meio. O agente patogênico da silicose é a poeira de sílica-livre ou dióxido de silício (SiO2) na forma cristalina. O processo inflamatório envolvendo o sistema imunológico na silicose ainda não está bem esclarecido. OBJETIVO: Estudar o perfil de IgG, IgM, IgA, C3, C4 e alguns auto-anticorpos no soro de trabalhadores expostos à sílica, com ou sem silicose, através de avaliação laboratorial imunológica, abrangendo tanto a imunidade inespecífica quanto a específica. MÉTODO: Foi examinada uma amostra de 58 pacientes ambulatoriais, do sexo masculino, constituída por trabalhadores expostos à sílica. Foram realizadas avaliações imunológica, radiológica e funcional pulmonar. Foram dosadas as imunoglobulinas IgG, IgA e IgM, os componentes C3 e C4 do sistema complemento e determinados auto-anticorpos. RESULTADOS: Vinte trabalhadores apresentaram radiograma normal e 38 apresentaram-no alterado, compatível com silicose. As médias dos valores de IgG no grupo com silicose foi maior que no grupo com radiograma normal (p < 0,05). Para a IgA e IgM, assim como para o C3 e C4, não houve diferença estatisticamente significativa nas médias (p > 0.05). O percentual de positividade dos auto-anticorpos foi maior no grupo silicótico em relação ao grupo com radiograma normal. CONCLUSÃO: O aumento de IgG nos doentes com silicose constitui um achado importante pois pode indicar a continuidade da reação granulomatosa, mesmo com o trabalhador afastado da exposição. Entretanto, ainda são necessários estudos que possibilitem a compreensão do processo imunogênico na silicose.