A study of CD^4＋ T lymphocyte infiltration level in the thyroid of experimental autoimmune thyroiditis rat

Abstract

Objective To establish a experimental autoimmune thyroiditis（EAT） rat model and to observe pathological change levels of CD4 ＋ T lymphocyte infiltration in thyroid tissues under different iodine nutrient conditions. Methods One hundred and thirty-five four weeks old female Lewis rats（body weight about 80 g） were divided into control （NC）, model （TG）, high iodine- Ⅰ （HⅠ ）, high iodine and model- Ⅰ（HⅠ ＋ TG）, high iodine-Ⅱ （HⅡ ）, high iodine and model-Ⅱ （HⅡ ＋ TG） groups according to body weight by random number table. There were 20 rats in NC, HⅠ and HⅡ groups, and 25 rats in TG, HⅠ ＋ TG and H Ⅱ ＋ TG groups. The rats of HⅠ and HⅠ ＋ TG groups drank deionized water containing iodine 25.7 mg/L; rats of HⅡ and HⅡ ＋ TG groups drank deionized water containing iodine 423.3 mg/L; rats of NC and TG groups drank distilled water. Rats of TG, HⅠ ＋ TG and HⅡ ＋ TG groups were immunized with 0.1 ml thyroglobulin（Tg, 8.0 g/L） in incomplete Freunds adjuvant（IFA）, once two weeks for three times. Urine samples were collected after immunization for 8 weeks; after immunization for 15 weeks, rats were killed, blood samples and thyroid tissues were taken. Urinary iodine was determined by arsenic-cerium catalytic spectrophotometry; pathological changes in thyroid tissue were observed by Hematoxylin-Eosin （HE） method ; immunohistochemical method was used to identify the infiltration of inflammatory cells in thyroid tissue. Results The difference of rat thyroid relative quality between groups was statistically significant （F = 44.428, P 〈 0.05）. Compared with NC group（0.085 25 mg/g）, thyroid relative qualities were increased in experimental groups （TG, HⅠ , HⅠ ＋ TG, H H, HⅡ ＋ TG groups： 0.095 22, 0.092 85, 0.097 48, 0.096 55, 0.095 33 mg/g, all P 〈 0.05）. The difference of urinary iodine between groups was statistically significant（χ2 = 106.4, P 〈 0.05）. Compared with NC group（456.45 μg/L）, urinary iodine levels in TG, HⅠ , HⅠ ＋ TG, HⅡ, HⅡ ＋ TG groups（800.08, 18 633.20, 13 869.00, 87 889.97, 61 661.51 μg/L） were increased（all P 〈 0.05 ）. The pathological changes of rats in each group were increased with increasing of iodine intake. Rats in NC group had normal thyroid structure ; in TG, HⅠ groups, a small amount of lymphocytes were found between thyroid follicular; the lymphocytes infiltrated into the follicular in HⅠ ＋ TG group; rats in HⅡ , HⅡ ＋ TG groups had follicular fusion, and diffused inflammatory cell infiltration. There was a tendency of increased CD4＋ T lymphocyte infiltration in rat thyroid with increasing of iodine intake. There was no CD4＋ T lymphocyte positive staining in NC group; TG group had a small amount of positive cells; HⅠ group had scattered yellowish-brown positive cells. HⅠ ＋ TG group had a focal lymphocyte infiltration; HⅡ group had follicular expansion obviously; follicular structure damage in H H ＋ TG group was serious, and showed a diffused yellow dye. Conclusion Excessive iodine intake and Tg immunization can induce and aggravate the incidence of autoimmune thyroiditis in rats, and pathological change situation has exacerbated with increasing of iodine intake; excessive iodine intake may also lead to an increased tendency of CD4＋ T lymphocytes infiltration in thyroid tissue of EAT rat. Key words: Iodine; Experimental autoimmunity thyroidits ; CD4＋ T lymphocyte