An isologously transplantable mouse thyrotropic pituitary tumor (TtTb) that had been induced by radiothyroidectomy was found to form lobules composed of parenchymal glandular cell elements. The surfaces of these lobules were covered by stellate cells bearing long processes that gave a strong immunopositive reaction with a specific antiserum against glial fibrillary acidic protein (GFAP). GFAP was also positive in pituitary folliculo-stellate cells (FS cells). Since in the anterior pituitary gland, no other cellular component showing positive staining with anti-GFAP antibody was observed, it seems probable that the GFAP-positive cells in the thyrotropic tumor are related to the FS cells in the anterior pituitary. Upon cultivation of the thyrotropic tumor, cells with long processes appeared. These cells showed strong staining for GFAP and were dependent on basic fibroblast growth factor for cell growth. By repeated passage, the GFAP-positive cells became a stably growing immortal cell line, which was tentatively named TtT/GF. Since the characteristics of TtT/GF were similar to those of FS cells in the anterior pituitary, i.e. the presence of many lysosomes and numerous intermediate filaments in the cytoplasm, phagocytic activity, follicle formation, and GFAP and S-100 protein positivity, we suggest that TtT/GF cells are derived from pituitary FS cells.

MATERIALS AND METHODSA total of 30 male guinea-pigs weighing 400 to 600 g (at the time of sacrifice) were used. These had been exposed to laboratory conditions for at least 5 weeks prior to sacri fice. The animals were fed on a commercial solid diet (Oriental, Co., Japan) and water was allowed ad libitum.In experiment I, the animals were divided into 4 groups: a) actively sensitized animals, b) nonsensitized animals, control for group a, c) nonsensitized animals, where the small intestines were to be passively sensitized with serum of immunized rabbit and d) nonsensi tized animals, control for group c, where the small intestines were to be incubated with serum of nonimmunized rabbit. Experiment II, included 2 groups (e and f) of nonsensi tized animals, where the small intestines were to be passively sensitized with serum of im munized rabbit. There were five in each group.Active sensitization Thirty days after a subcutaneous injection of 5 mg of crystalline ovalbumin (Sigma Chemical Co., U.S.A.) together with 0.5 mg of Freund's complete adjuvant (Difco Labora tories, U.S.A.), guinea-pigs were given a single subcutaneous booster shot with 20 mg of the same antigen without the adjuvant. Five days after the last injection they were fasted overnight, sacrificed by a blow on the head and exsanguinated by decapitation. The total

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