Extrapulmonary silicosis: a clinical, morphologic, and ultrastructural study

Silicosis as an unusual cause of symptomatic cervical adenopathy

A case of symptomatic cervical adenopathy is reported as a presentation of silicosis. Silicosis is one of the most important occupational health diseases worldwide caused by the inhalation of airborne silica particles. The presence of thoracic adenopathies is a common clinical feature of silicosis, cervical silicotic adenopathies on the other hand are rare and unknown to most clinicians and can therefore lead to a differential diagnostic problem. Awareness of the clinical, radiological, and histological features is key for the diagnosis.

Asymptomatic Renal Function Abnormalities in Patients having Silicosis

BACKGROUND

A number of occupational exposures are associated with various types of renal dysfunction. Several studies for many years have drawn attention to renal dysfunction and nephrotoxicity among workers exposed to silica. This study was conducted to evaluate renal dysfunction, if any, among Indian patients having silicosis and its correlation with the duration of exposure to silica dust.

MATERIALS AND METHODS

This study includes 52 eligible patients with a history of silica dust exposure and silicosis confirm on radiological examination by the pneumoconiosis board. Investigations like serum creatinine, urinary albumin creatinine ratio, etc. were done. The "modification of diet in renal disease" (MDRD) formula was used to calculate the glomerular filtration rate (GFR).

RESULTS

This study showed 53.84% of patients (n = 28) having albuminuria and a mean "urinary albumin to creatinine ratio" (UACR) of 101.88 ± 128.99 mg/gm. Isolated macroalbuminuria was detected in 11.5% of patients (n = 6) while 42.3% of patients (n = 22) presented with microalbuminuria. The mean GFR was 81.94 ± 22.09 mL/min/1.73 m2 among study patients of which four (7.7%) patients had GFR value <60 mL/min/1.73 m2 . We could also identify a significant association between the duration of exposure to silica dust and UACR and GFR (p < 0.01).

CONCLUSION

Albuminuria and reduced estimated GFR in patients with silica dust exposure is not uncommon and reflect early underlying renal dysfunctions. Our study suggests a simple and cost-effective screening strategy for early detection of renal dysfunction among silicosis patients that may be considered as a tool to prevent further renal damage in such patients.

Segment-Long-Spacing (SLS) and the Polymorphic Structures of Fibrillar Collagen

The diverse and complex functions of collagen during the development of an organism are closely related to the polymorphism of its supramolecular structures in the extracellular matrix. SLS (segment-long-spacing) is one of the best understood alternative structures of collagen. SLS played an instrumental role in the original studies of collagen more than half a century ago that laid the foundation of nearly everything we know about collagen today. Despite being used mostly under in vitro conditions, the natural occurrence of SLS in tissues has also been reported. Here we will provide a brief overview of the major findings of the SLS and other structures of collagen based on a wealth of work published starting from the 1940s. We will discuss the factors that determine the stability and the structural specificity of the different molecular assemblies of collagen in light of the new studies using designed fibril forming collagen peptides. At the end of the chapter, we will summarize some recent discoveries of the alternative structures of collagen in tissues, especially those involved in pathogenic states. A revisit of SLS will likely inspire new understandings concerning the range of critical roles of fibrillar collagen in terms of its organizational diversity in the extracellular matrix.

Splenic Silicosis: A Rare Cause of Splenic Calcifications

Silicosis, an occupational menace is an irreversible lung disease caused by inhalation of tiny particles of crystalline silica. It is an occupational hazard both in industrialized as well as developing nations. Thoracic involvement is commonly described following exposure to silica, but extrathoracic involvement is a rare occurrence and often an incidental finding. It can manifest as calcifications in the liver, spleen, abdominal, axillary and cervical lymph nodes in addition to intrathoracic involvement. Silicosis as a cause of splenic calcifications often gets buried under the common differentials like tuberculosis, acquired immunodeficiency syndromes, amyloidosis, and Gamna-Gandy bodies. We herein describe a case of chronic complicated silicosis with splenic calcifications which appear similar to intrathoracic calcifications.

Characterization and toxicity evaluation of air-borne particles released by grinding from two dental resin composites in vitro

OBJECTIVE

The project aims to evaluate whether inhalation of particles released upon grinding of dental composites may pose a health hazard to dentists. The main objective of the study was to characterize the dust from polymer-based dental composites ground with different grain sized burs and investigate particle uptake and the potential cytotoxic effects in human bronchial cells.

METHODS

Polymerized blocks of two dental composites, Filtek™ Z250 and Filtek™ Z500 from 3M™ ESPE, were ground with super coarse (black) and fine (red) burs inside a glass chamber. Ultrafine airborne dust concentration and particle size distribution was measured real-time during grinding with a scanning mobility particle sizer (SMPS). Filter-collected airborne particles were characterized with dynamic light scattering (DLS) and scanning electron microscopy (SEM). Human bronchial epithelial cells (HBEC-3KT) were exposed to the dusts in dose-effect experiments. Toxicity was measured with lactate dehydrogenase (LDH) assay and cell counting kit-8 (CCK8). Cellular uptake was observed with transmission electron microscopy (TEM).

RESULTS

Airborne ultrafine particles showed that most particles were in the size range 15-35 nm (SMPS). SEM analysis proved that more than 80% of the particles have a minimum Feret diameter less than 1 μm. In solution (DLS), the particles have larger diameters and tend to agglomerate. Cell toxicity (LDH, CCK8) is shown after 48 h and 72 h exposure times and at the highest doses. TEM showed presence of the particles within the cell cytoplasm.

SIGNIFICANCE

Prolonged and frequent exposure through inhalation may have negative health implications for dentists.

Imaging flow cytometry methods for quantitative analysis of label-free crystalline silica particle interactions with immune cells

Exposure to respirable fractions of crystalline silica quartz dust particles is associated with silicosis, cancer and the development of autoimmune conditions. Early cellular interactions are not well understood, partly due to a lack of suitable technological methods. Improved techniques are needed to better quantify and study high-level respirable crystalline silica exposure in human populations. Techniques that can be applied to complex biological matrices are pivotal to understanding particle-cell interactions and the impact of particles within real, biologically complex environments. In this study, we investigated whether imaging flow cytometry could be used to assess the interactions between cells and crystalline silica when present within complex biological matrices. Using the respirable-size fine quartz crystalline silica dust Min-u-sil® 5, we first validated previous reports that, whilst associating with cells, crystalline silica particles can be detected solely through their differential light scattering profile using conventional flow cytometry. This same property reliably identified crystalline silica in association with primary monocytic cells in vitro using an imaging flow cytometry assay, where darkfield intensity measurements were able to detect crystalline silica concentrations as low as 2.5 μg/mL. Finally, we ultilised fresh whole blood as an exemplary complex biological matrix to test the technique. Even after the increased sample processing required to analyse cells within whole blood, imaging flow cytometry was capable of detecting and assessing silica-association to cells. As expected, in fresh whole blood exposed to crystalline silica, neutrophils and cells of the monocyte/macrophage lineage phagocytosed the particles. In addition to the use of this technique in in vitro exposure models, this method has the potential to be applied directly to ex vivo diagnostic studies and research models, where the identification of crystalline silica association with cells in complex biological matrices such as bronchial lavage fluids, alongside additional functional and phenotypic cellular readouts, is required.

Accelerated silicosis with bone marrow, hepatic and splenic involvement in a patient with lung transplantation

Chronic silicosis is an entity widely described in literature. However, other types such as accelerated, acute, complicated and extrapulmonary silicosis are little documented. We present a case of accelerated extrapulmonary silicosis in a lung transplant patient in whom the diagnosis of systemic silicosis was made incidental to non-respiratory complications that occurred during follow-up. The appearance of cytopenia and liver failure led to diagnostic tests that documented the presence of silicotic granulomas in those locations. Taking into account the intensity, time of exposure, onset and development of the disease, we found a highly atypical case of accelerated extrapulmonary silicosis in which inorganic particles (presumably silica) were documented inside granulomas and macrophages of the bone marrow. With these findings, we reflect on the lack of consideration of these entities within clinical practice, their probable under diagnosis and the need to study other pathophysiological mechanisms of acquisition and dissemination of silicosis.

Lupus Pleuritis with Silicotic Nodules in the Parietal Pleura

A 63-year-old man with occupational exposure to silica presented with cutaneous ulcer, pleuritic pain, and a fever. Laboratory data showed lymphopenia and positive serum antinuclear and anti-DNA antibodies. Computed tomography of the chest showed egg shell-like calcification of the hilar and mediastinal lymph nodes without pulmonary parenchymal involvement of silicosis. A surgical biopsy showed silicotic nodules with surrounding infiltration of lymphocytes and plasma cells in the parietal pleura. With a diagnosis of systemic lupus erythematosus (SLE), systemic corticosteroid therapy was given, which led to the resolution of symptoms and laboratory abnormalities. We discuss the relationship between silica exposure and the development of SLE.

Silicosis decreases bone mineral density in rats

Silicosis is the most common occupational lung disease in China, and is associated with a variety of complications, many of which are poorly understood. For example, recent data indicate that silicosis associates with the development of osteopenia, and in some cases this bone loss is severe, meeting criteria for osteoporosis. Although many factors are likely to contribute to this relationship, including a sedentary lifestyle in patients with advanced silicotic lung disease, we hypothesized that silica might directly reduce bone mineral density. In the present study, six Wistar rats were exposed to silica for 24 weeks in order to induce pulmonary silicosis and examine the relationship to bone mineral density. As expected, all rats exposed to silica developed severe pulmonary fibrosis, as manifested by the formation of innumerable silicotic nodules and the deposition of large amounts of interstitial collagen. Moreover, micro-CT results showed that bone mineral density (BMD) was also significantly reduced in rats exposed to silica when compared control animals and this associated with a modest reduction in serum calcium and 25-hydroxyvitamin D levels. In addition, we found that decreased BMD was also linked to increased osteoclast activity as well as fibrosis-like changes, and to the deposition of silica within bone marrow. In summary, our findings support the hypothesis that silicosis reduces bone mineral density and provide support for ongoing investigations into the mechanisms causing osteopenia in silicosis patients.

Environmental dust inhalation in the European badger (Meles meles): Systemic distribution of silica-laden macrophages, pathological changes, and association with Mycobacterium bovis infection status

Chronic inhalation of crystalline silica and silicates may lead to severe lung disease in humans, termed silicosis. The disease is an occupational health concern in miners and related professions worldwide. Silicosis is also a strong risk factor for tuberculosis in humans. Due to its subterranean lifestyle, the European badger (Meles meles) is continuously exposed to environmental dust, while this species is also susceptible to tuberculosis, caused by Mycobacterium bovis. To date, a thorough investigation of mineral dust retention and its possible implication as a risk factor for mycobacterial infection in badgers has not been performed. The aims of this retrospective histological study were (1) to describe the systemic tissue distribution of silica-laden macrophages (SLMs) in badgers; (2) to compare the amount of SLMs in tissues of badgers of differing M. bovis infection status, pulmonary SLM burden and age; and (3) to assess whether inflammation was associated with SLMs. We assessed lung, lymph nodes, liver and spleen of 60 wild-caught badgers of known M. bovis infection status for the presence of SLMs using polarizing light microscopy. SLMs were consistently present within the lungs and were widely distributed throughout the lymphatic system. No inflammatory reaction to SLMs, as occurs in human silicosis, was observed in any tissue. Distribution and amount of SLMs were similar between M. bovis positive and negative badgers, and we were not able to show an association between the amount of SLMs and M. bovis infection status. The amount of SLMs within intra- and extrathoracic lymph nodes was positively associated with the amount of pulmonary SLMs, and with age. This is the first report of substantial and systemic tissue retention of mineral dust particles in a mammalian species lacking associated chronic inflammation (i.e. silicosis). We further highlight different pathogenetic mechanisms underlying silicosis and benign SLM accumulations following siliceous dust inhalation.

Silica-Triggered Autoimmunity in Lupus-Prone Mice Blocked by Docosahexaenoic Acid Consumption

Occupational exposure to respirable crystalline silica (cSiO2, quartz) is etiologically linked to systemic lupus erythematosus (lupus) and other human autoimmune diseases (ADs). In the female NZBWF1 mouse, a widely used animal model that is genetically prone to lupus, short-term repeated intranasal exposure to cSiO2 triggers premature initiation of autoimmune responses in the lungs and kidneys. In contrast to cSiO2's triggering action, consumption of the ω-3 polyunsaturated fatty acid docosahexaenoic acid (DHA) prevents spontaneous onset of autoimmunity in this mouse strain. The aim of this study was to test the hypothesis that consumption of DHA will prevent cSiO2-triggered autoimmunity in the female NZBWF1 mouse. Mice (6 wk old) were fed isocaloric AIN-93G diets containing 0.0, 0.4, 1.2 or 2.4% DHA. Two wk after initiating feeding, mice were intranasally instilled with 1 mg cSiO2 once per wk for 4 wk and maintained on experimental diets for an additional 12 wk. Mice were then sacrificed and the lung, blood and kidney assessed for markers of inflammation and autoimmunity. DHA was incorporated into lung, red blood cells and kidney from diet in a concentration-dependent fashion. Dietary DHA dose-dependently suppressed cSiO2-triggered perivascular leukocyte infiltration and ectopic lymphoid tissue neogenesis in the lung. DHA consumption concurrently inhibited cSiO2-driven elevation of proinflammatory cytokines, B-cell proliferation factors, IgG and anti-dsDNA Ig in both bronchoalveolar lavage fluid and plasma. DHA's prophylactic effects were further mirrored in reduced proteinuria and glomerulonephritis in cSiO2-treated mice. Taken together, these results reveal that DHA consumption suppresses cSiO2 triggering of autoimmunity in female NZBWF1 mice as manifested in the lung, blood and kidney. Our findings provide novel insight into how dietary modulation of the lipidome might be used to prevent or delay triggering of AD by cSiO2. Such knowledge opens the possibility of developing practical, low-cost preventative strategies to reduce the risk of initiating AD and subsequent flaring in cSiO2-exposed individuals. Additional research in this model is required to establish the mechanisms by which DHA suppresses cSiO2-induced autoimmunity and to ascertain unique lipidome signatures predictive of susceptibility to cSiO2-triggered AD.

Overlap syndrome with Sjögren's syndrome and systemic sclerosis in a steel rolling mill worker: a case report

BACKGROUND

There are few reports about work-related factors associated with Sjögren's syndrome. We report a case of overlap syndrome with Sjögren's syndrome and systemic sclerosis.

CASE PRESENTATION

A 54-year-old man was admitted due to dyspnea on exertion. The results of physical examination and laboratory findings were compatible with Sjögren's syndrome with systemic sclerosis. The patient had no pre-existing autoimmune disease, and denied family history of autoimmune disease. The patient worked in the large-scale rolling department of a steel manufacturing company for 25 years. Hot rolling is a rolling process performed at between 1100 °C and 1200 °C, generating a high temperature and a large amount of fumes, involving jet-spraying of water throughout the process to remove the instantaneously generated oxide film and prevent the high generation of fumes. In this process, workers could be exposed to silica produced by thermal oxidation. Other potential toxic substances including nickel and manganese seemed to be less likely associated with the patient's clinical manifestations.

CONCLUSIONS

Occupational exposure to silica seemed to be associated with the patient's clinical manifestations of overlap syndrome with Sjögren's syndrome and systemic sclerosis. Although the underlying mechanism is still unclear, autoimmune disease including Sjögren's syndrome affects women more often than men and there was no family history of autoimmune disease. These suggested that there was an association between occupational silica exposure and the disease of the patient. Future research about the association between long-term low dose exposure to silica and the development of autoimmune diseases should be encouraged.

A case of complicated silicosis with a complex clinical course in a glass manufacturing worker

We reported a case of complicated silicosis that occurred in a glass manufacturing plant worker who had presumably been exposed to low-concentration free silica for almost 20 years. To the best of our knowledge this report is the first in the Republic of Korea. The physician’s first impression was cancer since the enlargement of neck and supraclavicuar lymph nodes had clearly progressed and metastasis was suspected in ultrasonography. However, it turned out to be reactive hyperplasia and anthracosis. Although lung cancer was suspected and tests were performed in 2 hospitals due to repetitive cough and dyspnea, along with weight loss of approximately 10% over the course of 7 months, the patient was eventually diagnosed with complicated silicosis and pneumothorax occurred after 1 year. Herein, we report this case with a literature review.

Liver functions in silica-exposed workers in Egypt: possible role of matrix remodeling and immunological factors

BACKGROUND

Brick manufacturing constitutes an important industrial sector in Egypt with considerable exposure to silica.

OBJECTIVES

We aimed for evaluating hepatic functions in silica-exposed workers in the clay brick industry, and the possible role of matrix remodeling and immunological factors.

METHODS

A case-control study, 87 workers as exposed and 45 as control subjects. Questionnaire, clinical examination, and laboratory investigations: liver functions, matrix metalloproteinase-9, immunoglobulins G and E, and anti-liver kidney microsomal antibody.

RESULTS

In the exposed workers, mean levels of liver functions, matrix metalloproteinase-9 (MMP-9), and IgG and IgE were significantly higher. In the silicotic subgroup the mean level of GGT was almost twice the level in the non-silicotic subjects. Logistic regression showed that abnormal GGT and ALT were associated with production workers.

CONCLUSION

Workers in the clay brick industry showed evidence of liver disease that could be related to matrix remodeling.

Consideration of Occupational Lung Disease and Pneumoconiosis in Forensic Pathology

Reports of workers stricken with lung disease sustained during the course of their employment date to antiquity. Despite stringent regulations to mitigate all manners of work place hazards, and the emergence of agencies and physicians engaged in the advancement of occupational health, occupational lung disease remains a significant problem within modern society. Inhalation of dusts and fumes sustained in the course of one's occupation may lead to significant morbidity and mortality, and lead to a huge cost to society in terms of lost productivity, medical care for the worker, and litigation. In certain circumstances, the identification of an underlying occupational lung disease may constitute a significant finding in medicolegal death investigation. This article will present an overview of common occupational diseases likely to be encountered in the practice of forensic pathology, based on the particular etiologic agent and occupational means of exposure.

Lymphocyte activation in silica-exposed workers

Exposure to silica dust has been examined as a possible risk factor for autoimmune diseases, including systemic sclerosis, rheumatoid arthritis, systemic lupus erythematosus and ANCA-associated vasculitis. However, the underlying cellular and molecular mechanisms resulting in the increased prevalence of autoimmunity remain elusive. To clarify these mechanisms, we studied various markers of immune activation in individuals occupationally exposed to silica dust, i.e., serum levels of soluble IL-2 receptor (sIL-2R), levels of IL-2, other pro- and anti-inflammatory cytokines and lymphoproliferation. Our results demonstrate that silica-exposed individuals present important alterations in their immune response when compared to controls, as shown by increased serum sIL-2R levels, decreased production of IL-2 and increased levels of the pro-inflammatory (IFN-γ, IL-1α, TNF-α, IL-6) as well as anti-inflammatory (IL-10 and TGF-β) cytokines. Furthermore, silica-exposed individuals presented enhanced lymphoproliferative responses. Our findings provide evidence that the maintenance of immune homeostasis may be disturbed in silica-exposed individuals, possibly resulting in autoimmune disorders.

Genetic polymorphisms and surface expression of CTLA-4 and PD-1 on T cells of silica-exposed workers

Exposure to silica dust has been examined as a possible risk factor for autoimmune diseases, including scleroderma, rheumatoid arthritis and systemic lupus erythematosus. Since CTLA-4 [CD152] and PD-1 [CD279] are important for the maintenance of peripheral tolerance by regulating T cell responsiveness, we evaluated the expression of these molecules on the surface of CD4 and CD8 T cells, as well as single nucleotide polymorphisms (SNP) in CTLA-4 and PDCD1 genes, of 70 silica-exposed workers and 30 non-exposed, age-, ethnically- and sex-matched controls. Expression of CTLA-4 was significantly (P<0.05) reduced in CD4 T cells of exposed individuals [median=0.1% and interquartile range, IQR 0.0-0.1% (exposed), median=0.20%, IQR 0.0-0.4% (control)]. Also the expression of PD-1 was significantly (P<0.0001) reduced in both CD4 [median=0.9%, IQR 0.4-2.3% (exposed), median=5.7%, IQR 1.4-13.3% (control)] and CD8 T cells [median=0.9%, IQR 0.3-1.9% (exposed), median=5.0%, IQR 3.4-8.9% (control)]. The study of polymorphisms demonstrated a lower frequency of the A allele in the analysis of the PD1.3 SNP in the exposed group, which might be associated with the lower expression of PD-1 on the surface of CD4 T cells. Our findings provide evidence for the association of silica exposure and the maintenance of self-tolerance, i.e., the susceptibility to autoimmune disorders.

Osteoporosis associated with pulmonary silicosis in an equine bone fragility syndrome

California horses incur a bone fragility syndrome manifested by pathologic fractures. This study investigated gross, radiographic, and histologic features of the disorder as well as relationships with silicosis and levels of heavy metals and trace minerals through a postmortem study of 9 affected and 3 unaffected horses. Bones and soft tissues were evaluated grossly and histologically. Bones, lymph nodes, and lung tissue were evaluated radiographically. Tissues were evaluated for silicon levels, intracytoplasmic crystals, heavy metals, and trace minerals. All 9 affected horses had osteoporosis and clinical or subclinical pulmonary disease due to silicosis (8/9) or pneumoconiosis (1/9). All affected horses had radiographic findings consistent with osteopenia and histologic evidence of osteoporosis characterized by osteopenia, numerous resorption cavities, cement lines, and a mosaic lamellar pattern indicative of multiple remodeling events. Silicosis was characterized by widespread pulmonary granuloma formation with fibrosis; variable tracheobronchiolar and mediastinal granulomatous lymphadenitis; intracellular crystals within lung and lymph node macrophages; and pronounced lymph node fibrosis, focal necrosis, and dystrophic calcification. Crystals in lung (6/9) and lymph node (8/9) tissues were identified as cytotoxic silica dioxide polymorphs. Lung and liver tissue from affected horses had elevated levels of elemental silicon. Osteoporosis was highly correlated (r = 0.8, P < .01) with silicosis. No abnormalities in heavy metal or trace minerals were detected. This evaluation indicated that horses with bone fragility disorder have systemic osteoporosis associated with fibrosing pulmonary silicosis. The etiopathogenesis of the bone fragility syndrome is unknown; however, this study provides circumstantial evidence for a silicate associated osteoporosis.

Goodpasture's Syndrome and Silica: A Case Report and Literature Review

We report a case of Goodpasture's syndrome following chronic low level and an acute, high level of exposure to crystalline silica. A 38-year-old male tilesetter was admitted to the emergency room with dyspnea and respiratory failure. He reported that his symptoms had developed over the previous week after inhaling a large amount of dust while dry-sanding and sweeping a silica-based product used to fill cracks in a cement floor. Over the following days, his pulmonary function declined and he developed acute renal failure. Tests of antiglomerular basement membrane antibody were positive and renal biopsy revealed global glomerulonephritis. He was diagnosed with Goodpasture's syndrome and treated with steroids, plasmapheresis, and hemodialysis. This man had a history of childhood asthma and a remote, one pack-year history of cigarette use. He used the flooring product for seven years prior to the inciting event, however, previous jobs had utilized significantly smaller amounts. Goodpasture's syndrome and other autoimmune diseases have been reported in association with silica exposure. The acute onset following high level silica exposure in this previously healthy man, suggest that clinicians should investigate silica exposure as a causal factor in cases of Goodpasture's syndrome.

Pericardial plaque: a unique complication of silicosis

The heart and the respiratory system are closely connected in such a way that disorders of one system would influence the function of the other. This unique case of silicosis complicated by corpulmonale associated with pericardial plaque formation in a young adult male is reported here due to an unknown complication of silicosis.

Hypotheses on the etiology of antineutrophil cytoplasmic autoantibody associated vasculitis: the cause is hidden, but the result is known

The first description of what is now known as antineutrophil cytoplasmic autoantibody-associated necrotizing vasculitis appeared more than 140 yr ago. Since then, many aspects of the pathogenic pathway have been elucidated, indicating the involvement of antineutrophil cytoplasmic autoantibodies, but why antineutrophil cytoplasmic autoantibodies are produced in the first place remains unknown. Over the years, many hypotheses have emerged addressing the etiology of antineutrophil cytoplasmic antibody production, but no exclusive factor or set of factors can so far be held responsible. Herein is reviewed the most influential hypotheses regarding the causes of antineutrophil cytoplasmic antibody-associated vasculitis with the aim of placing in an epidemiologic background the different hypotheses that are centered on environmental and genetic influences.

Association of silica exposure with anti-neutrophil cytoplasmic autoantibody small-vessel vasculitis: a population-based, case-control study

Anti-neutrophil cytoplasmic autoantibodies (ANCA) are associated with a category of small-vessel vasculitis (SVV) with frequent glomerulonephritis. The goal of this study was to evaluate the association of lifetime silica exposure with development of ANCA-SVV, with particular attention to exposure dosage, intensity, and time since last exposure. A southeastern United States, population-based, case-control study was conducted. Case patients had ANCA-SVV with pauci-immune crescentic glomerulonephritis. Population-based control subjects were frequency-matched to case patients by age, gender, and state. Jobs were assessed in a telephone interview. Silica exposure scores incorporated exposure duration, intensity, and probability for each job and then were categorized as none, low/medium, or high lifetime exposure. Logistic regression models were used to estimate adjusted odds ratios (OR) and 95% confidence intervals (CI). Silica exposure was found in 78 (60%) of 129 case patients and in 49 (45%) of 109 control subjects. There was no increased risk for disease from low/medium exposure relative to no exposure (OR 1.0; 95% CI 0.4 to 2.2) but increased risk with high exposure (OR 1.9; 95% CI 1.0 to 3.5; P = 0.05). Crop harvesting was associated with elevated risk (OR 2.5; 95% CI 1.1 to 5.4; P = 0.03). However, both agricultural and traditional occupational sources contributed to the cumulative silica exposure scores; therefore, the overall effect could not be attributed to agricultural exposures alone. There was no evidence of decreasing by duration of time since last exposure. High lifetime silica exposure was associated with ANCA-SVV. Exposure to silica from specific farming tasks related to harvesting may be of particular importance in the southeastern United States. Interval of time since last exposure did not influence development of ANCA-SVV.

Fibrous long spacing type collagen fibrils have a hierarchical internal structure

Nanodissection of single fibrous long spacing (FLS) type collagen fibrils by atomic force microscopy (AFM) reveals hierarchical internal structure: Fibrillar subcomponents with diameters of approximately 10 to 20 nm were observed to be running parallel to the long axis of the fibril in which they are found. The fibrillar subcomponent displayed protrusions with characteristic approximately 270 nm periodicity, such that protrusions on neighboring subfibrils were aligned in register. Hence, the banding pattern of mature FLS-type collagen fibrils arises from the in-register alignment of these fibrillar subcomponents. This hierarchical organization observed in FLS-type collagen fibrils is different from that previously reported for native-type collagen fibrils, displaying no supercoiling at the level of organization observed.

General aspects of immunotoxicology including validation issues

Histologic examination of lymphoid organs has revealed immunotoxic effects of a broad range of substances. The thymus has proven especially sensitive. The relative lack of sensitivity of mucosa-associated lymphoid cells and tissues may be due to shortcomings in the way they are examined. Validation of ways to examine mucosal lymphoid tissues and cells and development of histopathological tools to flag a compound as a potential inducer of autoimmune disease or allergy are challenges for the future.

Foreign body post-varicella granulomas due to talc

Foreign body granulomas in the skin have been described frequently and may have various causes. Diagnosis is relatively easy in most cases, as most are related to foreign material penetrating into the skin due to different kinds of traumas. We present the case of a boy with multiple facial granulomas, persisting more than 6 months and related to the use of topical anti-pruriginous talc powder applied to papuloexudative lesions caused by varicella. Data gathered in the anamnesis, examination with polarized light and images seen through the electron microscope enabled us to identify the causal agent talc as the inducer of the granulomatous lesions that the patient presented, discarding other types of foreign body granulomas of exogenous origin.

Collagen fibril form and function

The majority of collagen in the extracellular matrix is found in a fibrillar form, with long slender filaments each displaying a characteristic approximately 67?nm D-repeat. Here they provide the stiff resilient part of many tissues, where the inherent strength of the collagen triple helix is translated through a number of hierarchical levels to endow that tissue with its specific mechanical properties. A number of collagen types have important structural roles, either comprising the core of the fibril or decorating the fibril surface to give enhanced functionality. The architecture of subfibrillar and suprafibrillar structures (such as microfibrils), lateral crystalline and liquid crystal ordering, interfibrillar interactions, and fibril bundles is described. The fibril surface is recognized as an area that contains a number of intimate interactions between different collagen types and other molecular species, especially the proteoglycans. The interplay between molecular forms at the fibril surface is discussed in terms of their contribution to the regulation of fibril diameter and their role in interfibrillar interactions.

Investigations into the polymorphism of rat tail tendon fibrils using atomic force microscopy

Collagen type I displays a typical banding periodicity of 67 nm when visualized by atomic force or transmission electron microscopy imaging. We have investigated collagen fibers extracted from rat tail tendons using atomic force microscopy, under different ionic and pH conditions. The majority of the fibers reproduce the typical wavy structure with 67 nm spacing and a height difference between the peak and the grooves of at least 5 nm. However, we were also able to individuate two other banding patterns with 23+/-2 nm and 210+/-15 nm periodicities. The small pattern showed height differences of about 2 nm, whereas the large pattern seems to be a superposition of the 67 nm periodicity showing height differences of about 20 nm. Furthermore, we could show that at pH values of 3 and below the fibril structure gets dissolved whereas high concentrations of NaCl and CaCl(2) could prevent this effect.

Silica accelerated systemic autoimmune disease in lupus-prone New Zealand mixed mice

The genetic backgrounds of lupus-prone murine models are a valuable resource for studying the influence of environmental exposure on autoimmune diseases in sensitive populations. Epidemiological studies have shown associations between silica exposure and several autoimmune diseases, including scleroderma and systemic lupus erythematosus. To determine whether silica exposure can exacerbate systemic autoimmunity in genetically predisposed animals, New Zealand mixed mice were intranasally instilled twice with saline or saline suspensions of 1 mg silica or 500 micro g TiO2, a dose equivalent in surface area, and were evaluated with respect to health and immune status. Survival in silica exposed NZM mice was decreased compared to saline and TiO2 exposed mice. Proteinuria levels were elevated in silica exposed mice. Levels of circulating immune complexes, autoantibodies to nuclear antigen (ANA), histone, and double stranded DNA were measured every two weeks by ELISA. Circulating immune complexes showed a trend towards an increased acceleration in levels in the silica exposed mice compared to saline and TiO2 exposed mice. ANA levels were significantly higher in silica exposed animals compared to saline and TiO2 exposed animals (0.237 +/- 0.03 versus 0.140 +/- 0.029 and 0.125 +/- 0.03, P < 0.05) 16 weeks postexposure. Autoantibodies to histone were also significantly elevated after 16 weeks in silica exposed animals compared to saline and TiO2 exposed animals (0.227 +/- 0.03 versus 0.073 +/- 0.015 and 0.05 +/- 0.03, P < 0.05). In contrast, serum IgG levels were decreased in silica exposed NZM mice compared to the saline controls, however, IgM levels were unaffected. Lungs of the silica-exposed mice had increased inflammatory infiltrates as well as fibrotic lesions characterized by excess collagen deposition. Therefore, although NZM mice are susceptible to SLE, silica exposure significantly exacerbated the course of disease.

Investigating the ultrastructure of fibrous long spacing collagen by parallel atomic force and transmission electron microscopy

The ultrastructure of fibrous long spacing (FLS) collagen fibrils has been investigated by performing both atomic force microscopy (AFM) and transmission electron microscopy (TEM) on exactly the same area of FLS collagen fibril samples. These FLS collagen fibrils were formed in vitro from type I collagen and alpha1-acid glycoprotein (AAG) solutions. On the basis of the correlated AFM and TEM images obtained before and after negative staining, the periodic dark bands observed in TEM images along the longitudinal axis of the FLS collagen fibril correspond directly to periodic protrusions seen by AFM. This observation is in agreement with the original surmise made by Gross, Highberger, and Schmitt (Gross J, Highberger JH, Schmitt FO, Proc Natl Acad Sci USA 1954;40:679-688) that the major repeating dark bands of FLS collagen fibrils observed under TEM are thick relative to the interband region. Although these results do not refute the idea of negative stain penetration into gap regions proposed by Hodge and Petruska (Petruska JA, Hodge AJ. Aspects of protein structure. Ramachandran GN, editor. New York: Academic Press; 1963. p. 289-300), there is no need to invoke the presence of gap regions to explain the periodic dark bands observed in TEM images of FLS collagen fibrils.

Occupational exposure to crystalline silica and risk of systemic lupus erythematosus: a population-based, case-control study in the southeastern United States

OBJECTIVE

Crystalline silica may act as an immune adjuvant to increase inflammation and antibody production, and findings of occupational cohort studies suggest that silica exposure may be a risk factor for systemic lupus erythematosus (SLE). We undertook this population-based study to examine the association between occupational silica exposure and SLE in the southeastern US.

METHODS

SLE patients (n = 265; diagnosed between January 1, 1995 and July 31, 1999) were recruited from 4 university rheumatology practices and 30 community-based rheumatologists in 60 contiguous counties. Controls (n = 355), frequency-matched to patients by age, sex, and state of residence, were randomly selected from driver's license registries. The mean age of the patients at diagnosis was 39 years; 91% were women and 60% were African American. Detailed occupational and farming histories were collected by in-person interviews. Silica exposure was determined through blinded assessment of job histories by 3 industrial hygienists, and potential medium- or high-level exposures were confirmed through followup telephone interviews. Odds ratios (ORs) and 95% confidence intervals (95% CIs) were estimated by logistic regression.

RESULTS

More patients (19%) than controls (8%) had a history of medium- or high-level silica exposure from farming or trades. We observed an association between silica and SLE (medium exposure OR 2.1 [95% CI 1.1-4.0], high exposure OR 4.6 [95% CI 1.4-15.4]) that was seen in separate analyses by sex, race, and at different levels of education.

CONCLUSION

These results suggest that crystalline silica exposure may promote the development of SLE in some individuals. Additional research is recommended in other populations, using study designs that minimize potential selection bias and maximize the quality of exposure assessment.

Occupational exposures and autoimmune diseases

Autoimmune diseases are pathologic conditions defined by abnormal autoimmune responses and characterized by immune system reactivity in the form of autoantibodies and T cell responses to self-structures. Here we review the limited but growing epidemiologic and experimental literature pertaining to the association between autoimmune diseases and occupational exposure to silica, solvents, pesticides, and ultraviolet radiation. The strongest associations (i.e., relative risks of 3.0 and higher) have been documented in investigations of silica dust and rheumatoid arthritis, lupus, scleroderma and glomerulonephritis. Weaker associations are seen, however, for solvent exposures (in scleroderma, undifferentiated connective tissue disease, and multiple sclerosis) and for farming or pesticide exposures (in rheumatoid arthritis). Experimental studies suggest two different effects of these exposures: an enhanced proinflammatory (TH1) response (e.g., TNF-alpha and IL-1 cytokine production with T cell activation), and increased apoptosis of lymphocytes leading to exposure to or modification of endogenous proteins and subsequent autoantibody formation. The former is a general mechanism that may be relevant across a spectrum of autoimmune diseases, whereas the latter may be a mechanism more specific to particular diseases (e.g., ultraviolet radiation, Ro autoantibodies, and lupus). Occupational exposures are important risk factors for some autoimmune diseases, but improved exposure assessment methods and better coordination between experimental/animal models and epidemiologic studies are needed to define these risks more precisely.

Lymphopenia in occupational pulmonary silicosis with or without autoimmune disease

An increased prevalence of autoimmune diseases such as rheumatoid arthritis has been demonstrated in silica-exposed patients. The aim of this study was to determine the peripheral blood lymphocyte phenotype in a population of silicotic workers employed in the slate mines of the district. Silicosis was assessed in 58 patients according to the International Labor Office's criteria. Clinical and biological data including flow cytometric evaluation of the lymphocyte subsets were compared with those from 41 healthy volunteers. The silicotic patients had a higher prevalence of autoimmune diseases (6/58 versus 0/41: P < 0.05) and of elevated antinuclear antibody titres compared to the control group. A very significant decrease of total lymphocyte count (P < 0.001) involving B, T and Natural Killer cells was found in silicotic patients as compared with matched healthy volunteers. A significant increase in the percentage of activated T cells (12.3%) was observed in the silicotic group as compared to 6.5% in the control group (P = 5 x 10(-5)). Our results show that in silicotic patients, the absolute number of circulating lymphocytes is diminished with an increased proportion of activated T cells. Whether these findings could predispose to the development of autoimmune disorders is discussed.

Liver and kidney foreign bodies granulomatosis in a patient with malocclusion, bruxism, and worn dental prostheses

Granulomatous reactions caused by foreign bodies have been described in drug abusers, in subjects exposed to occupational pollutants, and more rarely, in association with the use of prosthetic devices. We describe a 62-year-old patient with multiorgan parenchymal granulomatosis caused by inorganic debris of unknown origin. The patient presented with fever, hepatosplenomegaly, progressive cholestasis, and acute renal failure. Liver and kidney biopsies showed the presence of noncaseating epithelioid giant-cell granulomas containing scattered polarizable particles. Similar particles were also present in stools. Studies by innovative scanning electron microscopy and energy-dispersive microanalytical techniques showed that the particles isolated in liver, kidney, and stools were made by feldspars, the main component of porcelain. No occupational or environmental exposure to these materials could be identified in this patient and the only reliable source of the porcelain debris turned out to be constituted by 2 dental bridges evidently worn because of a possible inappropriate construction, malocclusion, and bruxism. The porcelain of the dental prostheses had the same elemental spectrum of the particles isolated from stool specimens and liver-kidney granuloma. After identification of the dental prostheses as the most likely source of ceramic debris, and after their removal, the particles from stool specimens disappeared. The patient was then treated with steroids leading to a remission of the clinical symptoms and a decrease in granulomatous inflammatory reaction in both liver and kidney. This is the first report suggesting that a foreign body systemic granulomatosis can be associated with worn dental prostheses.

Structural variations of collagen in normal and pathological tissues: role of electron microscopy

The spectrum of ultrastructural appearances assumed by collagen in normal and pathological tissues is illustrated using techniques of thin section transmission electron microscopy and computer-assisted analysis. The normal fibrillar collagen types are described in order to provide a basis for comparing other normal and abnormal forms. In normal tissues, the anchoring fibril and basal lamina (basement membrane) represent tissue structures largely containing collagen but differing significantly in organisation from normal types I to III fibrillar collagen. In pathological tissue, deviations from normal fine structure are reflected in abnormal aggregates of collagen fibrils (amianthoid and skeinoid fibres) and abnormalities in fibril diameter and cross-sectional profile. Fibrous and segment long-spacing collagen represent two further organisational variants of collagen, the former found widely in pathological tissues, the latter very rarely. Much remains to be discovered about these abnormal collagen variants-their mode of formation, the cells that produce them, and their roles. They also present a challenge for the collagen biologist formulating hypotheses of collagen fibril assembly and molecular organisation.

A study of fibrous long spacing collagen ultrastructure and assembly by atomic force microscopy

Fibrous long spacing collagen (FLS) fibrils are collagen fibrils that display a banding with periodicity greater than the 67nm periodicity of native collagen. FLS fibrils can be formed in vitro by addition of alpha(1)-acid glycoprotein to an acidified solution of monomeric collagen, followed by dialysis of the resulting mixture. We have investigated the ultrastructure of FLS fibrils formed in vitro using the atomic force microscope (AFM). The majority of the fibrils imaged showed typical diameters of approximately 150nm and had a distinct banding pattern with a approximately 250nm periodicity. However, we have also observed an additional type of FLS fibril, which is characterized by a secondary banding pattern surrounding the primary bands. These results are compared with those obtained in past investigations of FLS ultrastructure carried out using the transmission electron microscope (TEM). The importance of the fibril's surface topography in TEM staining patterns is discussed. Images of FLS fibrils in various stages of assembly have also been collected, and the implications of these images in determining the mechanism of assembly and the formation of the characteristic banding pattern of the fibrils is discussed.

Predictive testing for pathogenic autoimmunity: the morphological approach

The term autoimmunity refers to physiologically normal immune processes against self-antigens. In rare cases, the regulatory mechanisms become deflective and the uncontrolled production of autoantibodies or activation of autoreactive T-cells can subsequently cause disease. Substances may be capable of evoking autoimmune disease, and it is a challenge in routine toxicology to recognize such substances. In in vivo toxicity studies, uncommon inflammation in exposed animals should be discussed in terms of non-immune toxicity (e.g. irritation), infection, allergy and autoimmunity, taking into account that a response in even a few animals may be significant. Moreover, early morphological indicators of inflammation and lymphoid organ alterations can direct further investigation.

Fibrous long spacing collagen ultrastructure elucidated by atomic force microscopy

Fibrous long spacing collagen (FLS) fibrils are collagen fibrils in which the periodicity is clearly greater than the 67-nm periodicity of native collagen. FLS fibrils were formed in vitro by the addition of alpha1-acid glycoprotein to an acidified solution of monomeric collagen and were imaged with atomic force microscopy. The fibrils formed were typically approximately 150 nm in diameter and had a distinct banding pattern with a 250-nm periodicity. At higher resolution, the mature FLS fibrils showed ultrastructure, both on the bands and in the interband region, which appears as protofibrils aligned along the main fibril axis. The alignment of protofibrils produced grooves along the main fibril, which were 2 nm deep and 20 nm in width. Examination of the tips of FLS fibrils suggests that they grow via the merging of protofibrils to the tip, followed by the entanglement and, ultimately, the tight packing of protofibrils. A comparison is made with native collagen in terms of structure and mechanism of assembly.

Silica-induced pleural disease: an unusual case mimicking malignant mesothelioma

A 57-year-old man with a history of exposure to silica for 32 years presented with pleural thickening of the lower lobe of the left lung and a chronic right-sided pleural effusion without any radiographic evidence of parenchymal nodules in either lung. Light microscopic examination of a left visceral pleural biopsy specimen revealed markedly thickened pleura with fibrosis and macrophages containing birefringent silica and silicates. Occasional rounded intrapleural silicotic nodules were present. The underlying lung tissue did not show fibrosis or silicotic nodules. An energy-dispersive x-ray analysis confirmed the presence of silica. In the absence of lung involvement, this case represents a very unusual pathologic reaction caused by silica and silicates and adds to the clinical differential diagnosis of chronic pleuritis and malignant mesothelioma.

Does the human cornea contain silicon?

BACKGROUND

Our study investigated the presence, type and quantity of silicon in the human cornea. We report the results of silicon measurements in the corneas of silicotic individuals, bricklayers and apparently normal human individuals and offer a hypothesis for the mechanism of silicon deposition in the human cornea.

METHODS

We examined corneas from 13 decreased subjects who suffered from silicosis, 2 bricklayers and 6 apparently healthy subjects. Cornea samples were examined by energy-dispersive x-ray analysis (EDXA) under calibrated conditions in a scanning electron microscope (SEM). The EDXA detector was a silicon-free germanium crystal. Five distinct layers (epithelium, Bowman's membrane, central stroma. Descemet's membrane and endothelium) were analyzed in each cornea. The method allows simultaneous semiquantitative analysis of, among other elements, silicon, calcium and oxygen. We measured amorphous silicon and visible particles of silicon.

RESULTS

We found amorphous silicon in low concentrations in 38% of the silicotic corneas and in very low concentrations in 29% of the healthy corneas. Bricklayers showed high concentrations of amorphous silicon. These accumulations of silicon were predominantly located in Descemet's membrane. Silicotic corneas showed significantly more silicon-containing particles than corneas of healthy controls (chi 2-test, P < 0.01).

CONCLUSION

Normal corneas contain very low amounts of silicon. Longterm exposure to inhalative silicon dusts results in only very slightly increased levels of amorphous silicon in the cornea. However, silicon-containing particles accumulate in the cornea of silicotic individuals. Bricklayers incorporate more amorphous silicon into the cornea.

Silica-associated connective tissue disease. A study of 24 cases

We prospectively studied all patients hospitalized for connective tissue disease (CTD) in our French rheumatology clinic from January 1979 to December 1989. Our aims were 1) to determine if CTDs associated with occupational exposure to silica (Si) are currently observed in a rheumatology clinic, and, if so, 2) to describe the major features of Si-associated CTD, and 3) to specify which individuals are affected by Si-associated CTD. Patients were divided into 2 groups based on their responses to a questionnaire: those who had been exposed to Si, and those who had no occupational exposure to Si. Among the 764 patients with CTD studied, 24 (3%) were patients with Si-associated CTD and 740 (97%) were patients with non-Si-associated CTD. The sex ratio between the 2 groups was significantly different with a high frequency of men and of immigrants in the Si-associated CTD group. Two thirds of the patients exposed to Si were male miners or sandblasters, but the other third had more unusual exposures to Si, which may involve members of all socio-economics sectors and both sexes, such as sculpture or exposure to abrasive powders. Progressive systemic sclerosis (PSS) was significantly more prevalent in the Si-associated CTD group. This group also consisted of patients with rheumatoid arthritis (RA), systemic lupus erythematosus (SLE), dermatomyositis (DM), and other autoimmune diseases. Si-associated CTD was characterized by the frequency of radiologic lung fibrosis, impaired pulmonary function tests, secondary Sjögren syndrome, and antinuclear antibodies. The number of mineral particles and crystalline Si content were raised in all the bronchoalveolar lavage specimens of Si-exposed patients but in none of those of nonexposed patients. In some cases of Si-associated CTD, the disease was reversible after early cessation of Si exposure. Epidemiologic studies are required to confirm our hypothesis that not only PSS and RA but also SLE and DM are associated with occupational exposure to Si. Pending such results, exposure to Si should be sought in the history of any patient with CTD, especially in a male patient with pulmonary signs, and if present, exposure should be stopped. In the meantime, steps should be taken to ensure that workers exposed to Si in all environments have adequate protection.

Extrapulmonary silicosis in two water buffaloes

Two cases of extrathoracic silicosis in buffaloes raised near a quartz quarry and suffering from clinically severe silicosis are described. The extrapulmonary changes were characterized by silicoconiotic nodules in the tonsils, mesenteric lymph nodes and spleen. A combination of energy dispersive X-ray microanalysis and scanning electron microscopy revealed that the mineral component of these lesions consisted mainly of silicon, aluminium, iron, calcium, magnesium, zinc, sulphur and potassium. It is concluded that domestic animals raised in polluted environmental conditions represent an important biological source from which helpful data may be obtained for assessing risks to human health and gaining new insight into pathogenetic mechanisms.