Apoptosis Induction of Mouse Splenic Cells by Exposure to High-Level 17.BETA.-Estradiol and Endocrine Disrupting Chemicals

Abstract

It is commonly known that the sex hormones play important roles not only in the sexual organs, but also in the nervous system and immune systems. 17β-Estradiol affects the differentiation and the maturation of T cells in the thymus and B cells in the bone marrow, which are concerned with the homeostasis of variable immune actions such as the weight of the spleen and thymus, the secretion of thymic hormones, the secretion of cytokines and the production of antibodies. A number of endocrine disrupting chemicals (EDCs) exist in the environment and have hormonal, mainly estrogenic, effects. Because endogenous 17βestradiol modulates the immune functions as mentioned above, EDCs may be also assumed to affect the immune system as well. However, little is known about their modification of immune responses because EDCs have usually been studied in respect to developmental toxicity, teratogenicity or influence on sexual organs. The lymphocyte mitogenesis test is one of the in vitro immunotoxicity tests used to evaluate the safety of drugs. In this test, lymphocytes are stimulated by a polyclonal mitogen specific for either B cells or T cells as an indication of humoral immunity or cell-mediated immunity, respectively. We preliminarily evaluated the effect of 17β-estradiol on the immune function using this lymphocyte mitogenesis test and found that this chemical suppressed the lymphocyte proliferation. We further investigated the immunosuppressive activity of estrogenic compounds focused on cell death. Apoptosis, which refers to programmed death, is supposed to be triggered by cellular functional mechanisms, and necrosis is supposed to result from extrinsic damage. Apoptosis is achieved through several steps. A Fas ligand binds to the Fas protein on the surface of the cell, then several kinases and proteases including caspase are activated, and finally endonucleases cut the DNA between nucleosomes to make fragments in lengths of some integer times 180 base pairs. Then, the electrophoresed genomic DNA will show a ladder-like pattern. At apoptosis, cell membrane structure also changes. Phosphatidyl serine, which usually exists on the inner side of the *To whom correspondence should be addressed: Division of Environmental Health, Faculty of Pharmaceutical Sciences, Setsunan University, 45–1 Nagaotoge-cho, Hirakata, Osaka 573– 0101, Japan. Tel.: +81-72-866-3122; Fax: +81-72-866-3123; Email: nakamuro@pharm.setsunan.ac.jp Apoptosis Induction of Mouse Splenic Cells by Exposure to High-Level 17 -Estradiol and Endocrine Disrupting Chemicals