Stereological and Immunohistochemical Study of the Spleen in Hypothyroid Juvenile Rats

The purpose of this work was to investigate the influence of hypothyroidism on spleen tissue morphology and immune cell density in fourteen-day-old juvenile rats. Hypothyroidism in pups (n=10) was induced by administration of propylthiouracil (PTU) in drinking water (1.5 mg/L) to their mothers during pregnancy and period of lactation. Fourteen-day-old pups were sacrificed and the thyroid-stimulating hormone (TSH) serum concentration and thyroid activation index (Ia) were determined. Increased serum level of TSH and increased Ia showed that pups from PTU treated mothers were hypothyroid. White and red spleen pulp, marginal zone and connective tissue volume density has been assessed by using the stereological method. Using immunohistochemistry, the present CD3+ T lymphocytes, CD45RA+ B lymphocytes and CD68+ macrophages were quantified. A significant reduction of volume density of the periarteriolar lymphocyte sheath (VvPALS) and lymphatic follicles (Vvf) due to depletion of T and B lymphocytes respectively, was observed in the spleens of hypothyroid pups compared to controls. The volume density of the red pulp (Vvrp), marginal zone (Vvmz) and connective tissue (Vvct) was increased, as well as the number of CD68+ macrophages in the spleens of hypothyroid pups compared to controls. These results indicate that thyroid hormones might be important for normal development of both, specific and innate immune cells in the spleen during prenatal and early postnatal period.