Environmental triggers of autoimmune thyroiditis

Environmental exposures and autoimmune thyroid disease

BACKGROUND

Environmental exposures, ranging from perchlorate in rocket fuel to polychlorinated biphenols, have been shown to influence thyroid function. Although most of these agents are associated with reduced thyroid hormone levels or impaired thyroid hormone action, a number of environmental exposures confer an increased risk of autoimmune thyroid disease.

SUMMARY

Factors that increase autoimmune thyroid disease risk include radiation exposure, both from nuclear fallout and medical radiation, increased iodine intake, as well as several contaminants in the environment that influence the thyroid. Although approximately 70% of the risk for developing autoimmune thyroid disease is attributable to genetic background, environmental triggers are thought to play a role in the development of autoimmune thyroid disease in susceptible individuals.

CONCLUSIONS

Understanding the association of environmental agents with thyroid dysfunction can be utilized to reduce the risk to populations. Knowledge of the specific factors that trigger autoimmune thyroid disease and their mode of action, however, may also inform risk reduction in the individual patient. These factors are especially relevant for those at increased risk of autoimmune thyroid disease based on family history.

Defining and analyzing geoepidemiology and human autoimmunity

Autoimmune diseases cumulatively affect 5-10% of the industrial world population and are a significant cause of morbidity and mortality. In recent decades rates are rising worldwide, and autoimmunity can no longer be associated solely with the more developed "Western" countries. Geoepidemiology of autoimmune diseases portrays the burden of these illnesses across various regions and ethnic populations. Furthermore, Geoepidemiology may yield important clues to the genetic and triggering environmental mechanisms of autoimmunity. In this review we compiled and discuss in depth abundant geoepidemiological data pertaining to four major autoimmune conditions, namely type-1 diabetes mellitus, multiple sclerosis, autoimmune thyroid disease, and inflammatory bowel disease. The following key results manifested in this review: 1) Ethno-geographic gradients in autoimmune disease risk are attributable to a complex interplay of genetic and environmental pressures. 2) Industrial regions, particularly Northern Europe and North America, still exhibit the highest rates for most autoimmune diseases. 3) Methods particularly useful in demonstrating the significant influence of genetic and environmental factors include comparative ethnic differences studies, migration studies, and recognition of 'hotspots'. 4) Key environmental determinants of geographical differences include diminished ultraviolet radiation exposure, Western or affluence-related lifestyle, infection exposure, environmental pollutants, nutritional factors and disease-specific precipitants (e.g., iodine exposure).

Drugs and autoimmunity--a contemporary review and mechanistic approach

Drug-induced autoimmunity is an idiosyncratic, non-IgE immune related drug reaction. Interestingly, although many drugs have been reported to induce autoantibodies, only a few have a definitive association with drug-induced autoimmune disease. The prototype disease is drug-induced lupus and the typical drug for drug-induced lupus is minocycline. The production of autoantibodies and the induction of symptoms in drug-induced lupus results from a variety of mechanisms, which can include suppression of central or peripheral tolerance, alteration of gene transcription in T and B cells, abnormal cytokine and/or cytokine receptor balance and function, chromatin structure modification and antigen modification. Multiple mechanisms may apply for different drugs, and understanding the pharmacological actions of these agents helps us decipher the etiology. For example, DNA hypomethylation may occur with hydralazine, which leads to increased transcription, increased LFA-1, the generation of autoreactive T cells and a breakdown in peripheral tolerance. Frequently, more than one pathway may be involved. Interestingly, most patients with newly formed autoantibodies resulting from drugs do not develop clinical disease. Nonetheless, the explosion in the use of biological modifiers has been associated with production of autoantibodies, an observation that illustrates the complex nature of these interactions, in that these agents are frequently used to treat autoimmunity, yet may produce autoimmune diseases themselves.

The immune effects of naturally occurring and synthetic nanoparticles

Ultrafine particles and engineered nanoparticles have unique aerodynamic and biochemical properties that affect the immune system and human health in ways that are different from or exceed those seen with gases or larger particulates. These effects result from a unique set of physical characteristics and surface moieties, which generate an ability of UFPs to enter tissues and cells, interact with proteins and DNA at a molecular level and directly and indirectly modulate the immune system by novel mechanisms. In recent years, a new field known as nanotechnology has impacted multiple industries by taking advantage of the special qualities of these small "atomic-sized" particles. Nanomedicine has already opened up a new avenue of research in cancer therapy, drug delivery and immune regulation. While the benefits of this new science to human civilization are seemingly immeasurable, it is also important to appreciate that these particles can also lead to harmful effects on human health. In vitro and animal studies are showing that nanoparticles and UFPs are capable of activating proinflammatory cytokines, chemokines and adhesion molecules, with recruitment of inflammatory cells including basophils, macrophages, dendritic cells, T cells, neutrophils and eosinophils. These changes may have an impact on immune defense, but also on the Th1/Th2 balance, and even on non-immunologic function. Resulting immune system derangement can lead to increases in incidence of autoimmune, allergic and even neoplastic diseases. Cardiorespiratory effects have been observed to occur in humans. Much further research is needed to establish safe exposure levels for this important new class of particulates.