Autoimmunity and Risk Assessment Michael 1. Luster, Petia P. Simeonova, Randy Gallucci, and Joanna Matheson Toxicology and Molecular Biology Branch, Health Effects Laboratory Division, National Institute for Occupational Safety and Health, Morgantown, West Virginia USA

Among the issues dealing with identifying potential adverse immunologic effects (i.e., suppression, defect in T cells, assays designed to detect a hypersensitivity, or autoimmunity) associated with xenobiotic exposure, general agreement exists defect in B cells would provide a false nega- among the regulatory and pharmaceutical communities that predictive tests for autoimmunity are in tive. At the molecular level, depending upon most need of development in order to improve risk assessment. The estimation of risk (i.e., the the xenobiotic, an autoimmune disease can probability of a deleterious effect resulting from exposure) involves both the qualitative evaluation of develop from the expression (unmasking) of whether a hazard exists and the quantitative evaluation for determining an acceptable level of cryptic determinants, altered immunoregula- exposure in humans. Unless adequate human data are available, which is uncommon, this is based tion such as defects in the expression of inter- on animal studies. Although animal models exist to study autoimmune processes, these models do leukin 4 or interferon-y, or defects in the not readily lend themselves to interpretation in the risk assessment process due, for the most part, establishment of tolerance, which often to the complexity of autoimmune disease(s), as they are multifactorial and exhibit genetic involve missed deletion or activation of heterogeneity in humans. To improve the risk assessment process, researchers must develop and T validate animal models that not only incorporate mechanistic information into the assessment autoreactive cells. Finally, when using ani- process but also allow for consideration of potent genetic, physiologic, and environmental mal models, there is some uncertainty regard- influences. Key words: autoimmunity tests, immunotoxicology evaluation, immunotoxicology ing what actually constitutes autoimmunity. methods, risk assessment, xenobiotic-induced autoimmunity. - Environ Health Perspect 1 07(suppl This is reflected in humans by a lack of well- 5):679-680 (1999). defined diagnostic tests for identifying http.//ehpnetl.niehs.nih.gov/docs/1999/suppl-5/679-680luster/abstract.html autoimmune disease and is discussed in detail in other articles in this monograph. Despite these challenges, attempts to develop predictive screening assays for Overview large number ofexperimental models are used detecting xenobiotic-induced autoimmunity A study recently conducted by the successfully to study organ-specific and sys- have proceeded in several institutions includ- Environmental Defense Fund (1) indicates temic autoimmunity (Table 1). Furthermore, ing Virginia Commonwealth University that although the number of chemicals tested although many questions still remain on the (Richmond, Virginia) under the National for immunotoxicity is somewhat less than that etiology and biology of autoimmune diseases, Toxicology Program, the University of for other organ systems, such as the reproduc- scientists have provided a good road map of Utrecht (Utrecht, The Netherlands) funded tive, developmental, or nervous systems, disease development, allowing for successful by the Dutch Organization for Scientific almost 20% ofchemicals present at significant application of novel biotech therapies such as Research, and the University of Dusseldorf levels in the environment have been examined cytokine antagonists. The primary reason for (Dusseldorf, Germany). Models proposed to at some level for immunologic effects. A the lack ofvalidated screening assays probably evaluate the potential of xenobiotics to review of the literature, however, indicated the stems from the complexity of the disease. induce autoimmunity are majority of those chemicals studied were First, autoimmune disease is not one disease * Popliteal lymph node assay with reporter examined for their ability to cause either but a group of over 30 diseases affecting dif- antigens hypersensitivity or immunosuppression, and ferent organs, often through different mecha- * Increased titers of autoantibodies only a relatively few were tested for their nisms. Unless a common early process is * Examination of immunoglobulin potential to produce autoimmunity (2). identified, a single test would be unlikely to complexes/deposits (immunohistology) These observations appear at odds with results provide an adequate degree ofconcordance to * Spontaneous animal models. from a recent survey of the pharmaceutical be useful for predictive risk assessment. These models are clearly different from industry (3). This survey, in which 12 compa- Second, although most diseases are governed those described in Table 1, as the latter are nies responded, suggested that hematologic or by genetics, the degree of genetic and epige- designed to investigate the mechanisms of dermatologic problems consistent with auto- netic influences in autoimmune diseases is a specific autoimmune disease. Of the four immunity (or systemic allergy) were the most such that it could drastically alter the out- assays listed, immunohistology, in which common preclinical or postlaunch immuno- come of a test. For example, the relative risk immunoglobulin deposits or complexes are logic observations. Furthermore, the survey for developing autoimmunity from gold salt evaluated either on suspect organs or in the respondents indicated the most immediate increases 32-fold in individuals who possess periphery, has been evaluated the least, whereas need in the area of immunotoxicology evalua- the HL-A DR3 allele (7). Experimental the popliteal lymph node assay with reporter tion was the development of predictive tests studies of mercury-induced autoimmunity in antigens has been studied the most (8). Details for autoimmunity. Epidemiologic data sup- the Brown-Norway rat and B.10 mouse sug- port the survey results; approximately 5% of gest the same genetic influences apply in ani- the U.S. population suffers from some form of mal models (7). Third, development of This article is based on a presentation at the Workshop autoimmune disease (4), and 5-20% of autoimmune disease may occur through one on Linking Environmental Agents and Autoimmune the Diseases held 1-3 September 1998 in Research patients receiving certain drugs such as pro- of several mechanisms, thus increasing Triangle Park, North Carolina. cainamide or hydralazine develop drug-induced need to conduct multiple tests in risk assess- Address correspondence to M.l. Luster, Toxicology autoimmune diseases (5). ment. For example, at the cellular level, and Molecular Biology Branch, Health Effects a disease can occur from either Laboratory Division, NIOSH, 1095 Willowdale Rd., The question then arises, Why is there autoimmune Morgantown, WV 26505. Telephone: (304) 285-6060. lack ofvalidated autoimmune models suitable aberrant B-cell or T-cell responses. Thus, if a Fax: (304) 285-5708. E-mail: [email protected] for drug or chemical screening? Certainly a specific autoimmune disease results from a Received 1 1 January 1999; accepted 19 April 1999.

Environmental Health Perspectives * Vol 107, Supplement 5 * October 1999 679 LUSTER ET AL.

Table 1. Examples of experimental models used to Table 2. Structure-activity relationships of study autoimmune potential the autoimmune response. With regard to the diseases.a interest. association with myeloperoxidase substrates, Organ-specific autoimmunity Activity Chemical example it has been suggested that many of the chemi- Induced by immunization (EAE, AA) cals require metabolism in Spontaneous mice (NOD,b transgenics) Estrogenic Diethylstilbestrol proximity to Toxicant-induced (streptozotocin, Thymolytic Cyclosporin A, immune cells in order to be antigenic; Cd) immune cells such as Systemic autoimmunity cyclophosphamide monocytes contain high Allogeneic reactions Formation of protein adducts Halothane levels ofmyeloperoxidase (14). Neonatal thymectomy Altered immune regulation Mercury, interferon-y In any case, based upon the need to Spontaneous mice (New Zealand mixed)c Myeloperoxidase substrates Procainamide develop predictive screening models to iden- Altered methylation Hydralazine Abbreviations: AA, autoimmune arthritis; EAE, experimental tify the potential of xenobiotics to induce or autoimmune encephalitis; NOD, nonobese diabetic. 'Adapted exacerbate autoimmunity, combined with our from Pelletier et al. 16). bDevelop immune diabetes. CProne to increased understanding of immune and develop systemic lupus erythematosus. respect to the size of the population and the pharmacologic mechanisms and the rapidly length of treatment and could only be increasing array of available animal disease ofthese methods and the results so far obtained conducted with pharmaceuticals. models, suitable tests should be forthcoming. have been discussed by Pieters and Albers (9). Despite the challenges in developing However, none of these models have under- appropriate tests for autoimmunity that can REFERENCES AND NOTES gone a vigorous validation process to provide be used in risk assessment, the considerable sufficient confidence for use in risk assessment. amount of data generated by immunologists 1. Environmental Defense Fund. Toxic Ignorance. Washington, Such a validation process would involve, at the and DC:(1 997). pharmacologists pertaining to basic mech- 2. Dean JH, Cornacoff JB, Rosenthal GJ, Luster Ml. Immune sys- minimum, establishing an acceptable level of anisms of chemical-induced autoimmune dis- tem: evaluation of injury. In: Principles and Methods in concordance and an inter/intralaboratory vali- eases have provided a conceptual framework Toxicology, 3rd ed (Hayes AW, ed). New York:Raven Press, dation exercise. The former would involve that allows the 1994;1065-1090. establishment of potential 3. Dean JH. 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