Induction of Experimental Autoimmune Thyroiditis (EAT) in Sprague-Dawley Rats and Measurements of Severity of EAT Using Scanning Electron Microscopy
Date of Award
Master of Science (MS)
College of Science and Mathematics
Thesis Sponsor/Dissertation Chair/Project Chair
As early as the 1950’s it was shown that animals as mice, rats, guinea pigs, and monkeys that received one injection of xenogeneic thyroglobulin emulsified in Complete Freund’s Adjuvant (CFA) developed Experimental Autoimmune Thyroiditis (EAT) (Voller et al., 1980). The damage reported was destruction of the thyroid follicles, and infiltration of the thyroid by macrophages, neutrophils, and lymphocytes. An injection of Bordetella pertussis proved to enhance the incidence and severity of EAT in animal models. Bordetella pertussis is no longer manufactured in large quantities, and it is extremely difficult to purchase. Therefore, a different procedure had to be developed that would induce EAT in Sprague-Dawley rats. The procedure that was successful in inducing EAT required intradermal injections of bovine thyroglobulin (BTg) emulsified in CFA at days 0 and 7. The effective dose was 5.5 mg BTg/ per 100 grams of body weight emulsified in a volume of 0.15 ml of CFA and saline, and injected into each rear footpad. Control animals were injected with 0.15 ml of an emulsion of CFA and saline in each rear footpad.
Groups 2, 3, and 4 weighed 450 grams (12-14 weeks old) at the first injection, and 9 of 10 experimental animals developed EAT. On day 21, exploratory surgeries were performed to determine if the experimental animals had developed an increase in vascularity or enlargement of the thyroid. This is an indicator that the disease has been induced. The animals were sacrificed at day 21, and their thyroids were removed to be processed for viewing under the SEM. The numbers of thyroid follicles were greatly reduced in the experimental group, and large amounts of connective tissue was seen between follicles. Infiltrating cells were observed in some animals.
Group 1 animals weighed 250 grams (7-8 weeks old) at the first injection. Experimental animals received 5.5 mg BTg/ per 100 grams of body weight in 0.15 ml emulsion of CFA and saline injected into each rear footpad. On day 21, when the thyroids of Group 1 animals were observed during exploratory surgeries, no increase of size or vascularity of the thyroid was seen. Weekly exploratory surgeries were performed until day 42, and no enlargement of thyroid or increase in vascularity was observed. Group 1 animals were re-injected on days 42 and 49, followed by exploratory surgeries at day 63. At day 42 the animals weighed 450 grams and were 12-14 weeks old. On day 63, all experimental animals displayed enlargement and increase of vascularity, and they were sacrificed. Severe thyroid lesions were observed in 3 of 4 experimental animals. These thyroid lesions were characterized by a decreased number of follicles, increase in connective tissue between follicles, and occasionally cellular infiltration.
Since weight correlates to age in Sprague-Dawley rats until they reach a weight of 500 grams, age may be a factor determining the successful induction of EAT. Young animals may have an immature immune system, and thus cannot respond to the BTg emulsified in CFA. Levels of hormones vary between immature and mature animals and this is another factor that needs to be investigated in future research.
The identification of the infiltrating cells was not possible using just the SEM. SEM proved to be an useful tool to assess the severity of EAT.
Fernandez, Claudio Miguel, "Induction of Experimental Autoimmune Thyroiditis (EAT) in Sprague-Dawley Rats and Measurements of Severity of EAT Using Scanning Electron Microscopy" (2006). Theses, Dissertations and Culminating Projects. 1154.