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Int J Clin Exp Pathol 2010;3(6):587-592

Original Article
Characterization of T cell maturity in thymic epithelial cell tumors from BUF/Mna
spontaneous thymoma rats and BUF/Mna-Rnu/+ rats showing delayed thymomagenesis

Masayoshi Inoue, Mutsushi Matsuyama, Hiroyuki Shiono, Osamu Honda, Hiromitsu Sumikawa, Noriyuki Tomiyama, Meinoshin Okumura

Department of General Thoracic Surgery (L5), Department of Diagnostic and Interventional Radiology (D1), Osaka University Graduate School
of Medicine, Osaka, Department of Surgical Pathology, Fujita Health University Medical School, Japan

Received June 23, 2010, accepted June, 2010, available online July, 2010

Abstract: BUF/Mna rats develop thymomas spontaneously, which histologically mimic human thymomas. Although neoplasms in this rat strain
contain a large number of immature lymphocytes, the phenotype has not been sufficiently assessed. We characterized T cell phenotypes in
tumors from BUF/Mna rats in the present study. We also analyzed BUF/Mna-Rnu/+ rats, a heterozygous strain with suppressive
thymomagenesis, and compared the histology and T cell maturation with those from the BUF/Mna rats. A total of 11 BUF/Mna and 10
BUF/Mna-Rnu/+ rats were used. Three-color flow cytometry was performed with anti-CD3, CD4, and CD8 antibodies to identify infiltrated
lymphocytes, while tumor histology was evaluated with hematoxylin-eosin staining. The weight ratios of the entire thymic tissue including
thymoma as compared to the BUF/Mna and BUF/Mna-Rnu/+ rat bodies were 0.8±0.8% and 1.2±1.8%, respectively. Histological findings for
both rat congenic strains showed abundant lymphocytes surrounding large polygonal neoplastic thymic epithelia, which was compatible with
the type B1 classification of the World Health Organization for human thymoma. CD4+CD8+ T cells accounted for 73.7±8.0% of the cells in
tumors from BUF/Mna and 67.2±9.4% in those from BUF/Mna-Rnu/+ rats. Further, CD3-CD4-CD8+ T cells, intermediate between CD4-CD8-
and CD4+CD8+ cells, accounted for 47.7±17.5% and 38.0±14.0% of the cells in tumors from the BUF/Mna and BUF/Mna-Rnu/+ strains,
respectively. Thus, the proportion of developing thymic lymphocytes in and histology of thymomas from BUF/Mna and BUF/Mna-Rnu/+ rats were
similar. These results suggest that both BUF/Mna and BUF/Mna-Rnu/+ strains are suitable animal models for human thymoma to understand
the development of immature thymic lymphocytes. (IJCEP1006007).

Key words: Thymus, Thymoma, Animal model, Rat, T cells

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Address all correspondence to:
Masayoshi Inoue, MD, PhD
Department of General Thoracic Surgery
(L5) 2-2 Yamadaoka, Suita-City, Osaka 565-0871, Japan
Tel: +81-6-6879-3152, Fax: +81-6-6879-3164